Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 19 / 19

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    Ecophysiology and environmental distribution of organohalide-respiring bacteria
    Lu, Y. - \ 2016
    Wageningen University. Promotor(en): Hauke Smidt, co-promotor(en): Siavash Atashgahi. - Wageningen : Wageningen University - ISBN 9789462578418 - 239
    bacteria - halides - ecophysiology - phylogenetics - genomics - lakes - halogens - pollutants - bacteriën - haliden - ecofysiologie - fylogenetica - genomica - meren - halogenen - verontreinigende stoffen

    Organohalide-respiring bacteria (OHRB) are able to breathe natural and anthropogenically produced organohalides persistent in a broad range of oxygen-depleted environments. Therefore, these microorganisms are of high interest for organohalide-contaminated site bioremediation and natural halogen and carbon cycle. Nevertheless, to assess and adjust in situ bioremediation strategies and to enhance current understanding about the role of OHRB in natural habitats, thorough understanding of their ecophysiology and interaction with surrounding biotic and abiotic forces is necessary. To this end, this thesis focused on exploring ecophysiology and environmental distribution of OHRB in pristine and contaminated sites and unraveling their interactions with the co-existing microbial guilds in the community and geochemical parameters by application of a suite of physiological, molecular and geochemical analyses.

    Based on a comprehensive overview of currently known organohalide-respiring isolates and their environmental distribution, the presence of yet unknown OHRB in extreme environments was proposed as the known organohalide-respiring isolates survive/thrive at a moderate range of pH and salinity in laboratory culture. Therefore, the OHRB were surveyed in alkaline and hypersaline sediments collected from Lake Strawbridge, Western Australia, that was known to emit organohalides. As a result, for the first time, the dechlorination of chloroform and perchloroethene (PCE) to dichloromethane and trichloroethene, respectively, was documented from an alkaline hypersaline pristine environment.

    Corrinoids are essential cofactors for the activity of reductive dehalogenase enzymes. Ironically, some OHRB are reported to be corrinoid auxotrophs. Using transcriptional analysis and shotgun proteomics, here we show corrinoid auxotrophy in Dehalobacter restrictus PER-K23T. This detrimental deficiency seems to be compensated by up-regulation of relevant cobalamin salvaging and transport pathways to ensure sufficient corrinoid supply under partial corrinoid starvation. Hence, such OHRB incapable of de novo corrinoid synthesis will be dependent on non-dechlorinating community members to fulfill their nutritional needs indicating paramount importance of syntrophic interactions in supporting robust growth and activity of OHRB.

    Bacterial community analysis of chlorinated benzene dechlorinating consortia derived from contaminated harbour sludge suggested members of the Bacteroidetes phylum and Clostridiales order as well as sulfate-reducing Deltaproteobacteria as putative stimulating guilds that provide electron donor and/or organic cofactors to OHRB i.e. D. mccartyi and Dehalobacter. However, despite well-controlled lab condition, syntrophic interactions could be influenced by geochemical parameters under field settings. Accordingly, analysis of geochemical and microbial determinants of OHR at a site biostimulated by glycerol injection further verified supportive role of fermenters and sulfate reducers under highly reduced condition following biostimulation. However, towards the end of field experiment, reducing condition faded and sulfate increased concurrent with the appearance of Epsilonproteobacteria and Deferribacteres as putative oxidizers of reduced sulfur compounds. The latter guilds might serve as detoxifiers of sulfide and thereby stimulate D. mccartyi, but could also be inhibitory as successors of the more important syntrophic fermenting and sulfate reducing bacteria.

    In conclusion, this thesis expands our understanding of ecophysiology and environmental distribution of OHRB, addressing their presence in pristine environments as well as providing further evidence for their dependencies on other microbial community members in order to meet their nutritional requirements. Hence, research described here strengthens the scientific foundation for evaluating and optimizing strategies for the bioremediation of organohalide-contaminated sites and expands the natural niche of OHRB to extreme pristine environments.

    Imaging spectroscopy for ecological analysis in forest and grassland ecosystems
    Homolova, L. - \ 2014
    Wageningen University. Promotor(en): Michael Schaepman, co-promotor(en): Jan Clevers. - Wageningen : Wageningen University - ISBN 9789461738240 - 177
    remote sensing - naaldbossen - alpenweiden - picea abies - bladoppervlakte - ecofysiologie - ecosysteemdiensten - vegetatie - chlorofyl - cartografie - beeldvormende spectroscopie - remote sensing - coniferous forests - alpine grasslands - picea abies - leaf area - ecophysiology - ecosystem services - vegetation - chlorophyll - mapping - imaging spectroscopy

    Terrestrial vegetation is an important component of the Earth’s biosphere and therefore playing an essential role in climate regulation, carbon sequestration, and it provides large variety of services to humans. For a sustainable management of terrestrial ecosystems it is essential to understand vegetation responses to various pressures, to monitor and to predict the spatial extent and the rate of ecosystem changes. Remote sensing (RS) therefore offers a unique opportunity for spatially continuous, and for some type of RS data, also frequent monitoring of terrestrial ecosystems.

    RS of vegetation is a broad research field, where a lot of progress has been made in the last three decades. However, the complexity of interactions between vegetation and solar radiation, constantly modulated by environmental factors, offers room for deeper investigation. Rather than solving one big research problem, this thesis built a few bridges on a way leading towards better understanding of using airborne imaging spectroscopy for ecological analysis in temperate coniferous forests and subalpine grasslands. The research was divided into a theoretical and an applied part. The theoretical part contributed to a critical evaluation of research achievements and challenges in optical RS of plant traits (Chapter 2). The applied part addressed three research topics: i) investigating variability of total to projected leaf area ratio in spruce canopies and its implications on RS of chlorophyll content (Chapter 3), ii) testing chlorophyll retrieval methods based on continuum removal in spruce canopies (Chapter 4), and iii) exploring potentials of imaging spectroscopy to map ecosystem properties and the capacity of subalpine grasslands in providing ecosystem services in comparison with a plant trait-based modelling approach (Chapter 5).

    In Chapter 2, we reviewed achievements and challenges in RS estimation of key plant traits and we concentrated our discussion on eight traits with the strongest potential to be mapped using RS (plant growth and life forms, flammability properties, photosynthetic pathways and photosynthesis activity, plant height, leaf lifespan and phenology, specific leaf area, leaf nitrogen and phosphorous). The review indicated that imaging spectroscopy facilitates better retrievals of plant traits related to leaf biochemistry, photosynthesis and phenology rather than traits related to vegetations structure. Estimation of the canopy structure related traits (e.g. plant height) can certainly benefit from increasing synergies between imaging spectroscopy and active RS (radar or laser scanning). One of major challenges in RS of plant traits is to effectively suppress the negative influences of water absorption and canopy structure, which would facilitate more accurate retrievals of biochemical and photosynthesis-related traits. Secondly, a successful integration of RS and plant ecology concepts would require careful matching of spatial scales of in-situ trait data with RS observations.

    In Chapter 3, measurement methods and variability of total to projected leaf area within spruce crowns were investigated. Comparison of six laboratory methods revealed that methods using an elliptic approximation of a needle shape underestimated total leaf area compared to methods using a parallelepiped approximation. The variability in total to projected leaf area was primarily driven by the vertical sampling position and less by needle age or forest stand age. We found that total leaf area estimation has an important implication on RS of leaf chlorophyll content. An error associated with biased estimates of total leaf area can reach up to 30% of the expected chlorophyll range commonly found in forest canopies and therefore negatively influences the validation of RS-based chlorophyll maps. In Chapter 4, potentials of the continuum removal transformation for mapping of chlorophyll content in spruce canopies were investigated. We tested two methods based on continuum removal: artificial neural networks and an optical index. The optical index was newly designed here and it was based on the spectral continuum between 650 and 720 nm. Both continuum removal based methods exhibited superior accuracy in chlorophyll retrieval compared to commonly used narrow-band vegetation indices (e.g. NDVI, TCARI/OSAVI). The newly designed index was equally accurate, but certainly provided a more operational approach as compared to the neural network.

    In Chapter 5, mapping of ecosystem properties that underline ecosystem services provided by subalpine grasslands using RS methods was tested and further compared with a statistical plant trait-based modelling approach. Imaging spectroscopy in combination with empirical retrieval methods was partly successful to map ecosystem properties. The prediction accuracy at the calibration phase was comparable to the trait-based modelling approach. Spatial comparison between the two approaches revealed rather small agreement. The average fuzzy similarity between the approaches was around 20% for ecosystem properties, but in case of the total ecosystem service supply it decreased below 10%. However, the RS approach detected more variability in ecosystem properties and thereby in services, which was driven by local topography and microclimatic conditions, which could not be detected by the plant trait-based approach. Especially Chapters 2 and 5 indicated that one of the future RS research directions may be in spatial ecology, i.e. spatially explicit mapping of plant traits, ecosystem properties and ecosystem services. High quality RS data are certainly essential building elements for spatial ecology. But in order to address the effects of climate and land use changes on biodiversity and ecosystems, their properties and services, the integration of in-situ and RS data will be ultimately required. Therefore, more coherent experiments, where in-situ and RS data are measured simultaneously at different spatial scales, are needed in the future.

    Growth and nutrient budgets (C-N-P) of the manila clam Venerupsis philippinarum in a commercial pond system
    Brinke, N. ten; Jansen, H.M. ; Verdegem, M.C.J. - \ 2012
    Yerseke : IMARES (Report / IMARES Wageningen UR 12.017) - 25
    venerupis philippinarum - clams - growth - nutrients - ecophysiology - ponds - zeeland - venerupis philippinarum - kokkels - groei - voedingsstoffen - ecofysiologie - plassen - zeeland
    To study potential mechanism(s) causing the reduced growth of the clam Venerupis philippinarum at the end of the production cycle, observed in the culture ponds at Zeeland Aquaculture in 2011, specific studies on eco-physiology and nutrient dynamics of individual clams were performed in the culture ponds during the production period in 2012. The study was divided in two sub-projects: Sub-project I: which focused on the uptake of the clam in terms of clearance rates and absorption efficiencies, Sub-Project II: focused on the internal nutrient fluxes of carbon, nitrogen and phosphorus, of the clams in the culture ponds in relation to food availability and environmental conditions, described in this report.
    Ecophysiology of microorganisms in microbial elctrolysis cells
    Croese, E. - \ 2012
    Wageningen University. Promotor(en): Fons Stams; G.J.W. Euverink, co-promotor(en): J.S. Geelhoed. - S.l. : s.n. - ISBN 9789461733047 - 149
    microbiële fysiologie - ecofysiologie - elektrolyse - microbiële brandstofcellen - microbial physiology - ecophysiology - electrolysis - microbial fuel cells

    One of the main challenges for improvement of the microbial electrolysis cell (MEC) has been the reduction of the cost of the cathode catalyst. As catalyst at the cathode, microorganisms offer great possibilities. Previous research has shown the principle possibilities for the biocathode for H2 production with mixed microbial communities. In this thesis we analyzed the microbial communities from several biocathodes for H2 production. The microbial population of the very first MEC biocathode for H2 production (Chapter 2) showed a dominant population of Desulfovibrio spp.. A member of those dominant species, Desulfovibrio strain G11 was reinoculated in a biocathode and produced current and H2. On basis of previous knowledge of known Desulfovibrio spp., the molecular mechanism of electron uptake from a cathode with H2 production was proposed to have similarities to mechanisms that have been proposed for syntrophic growth.
    In Chapter 3 the microbial population of 5 more MEC biocathodes was analyzed. Those MECs were fed with either acetate or bicarbonate and consisted of two different designs. The results showed that the microbial communities from the same setup design are more similar than fed with the same carbon source. Furthermore, ribotypes from the phyla, Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria were found to be dominant. To understand more on the mechanisms of H2 production in the MEC, a hydrogenase gene microarray was used to analyze the hydrogenase genes present in 3 of the cathode samples. Those results showed that genes coding for bidirection NAD(P) dependent hydrogenases were mostly present in the MEC biocathode. Those results suggest a mechanisms involving cytoplasmatic NAD(P) dependent hydrogenases rather than energy converting hydrogenases as proposed before.
    To understand the molecular mechanisms it is important to obtain pure cultures from the MEC biocathode and test them for biocathode activity. In chapter 4 we describe a Citrobacter species strain PS2 which was isolated from the MEC biocathode. PS2 was very similar to other Citrobacter spp. able to produce fermentative H2 from a diversity of carbon sources. When inoculated in the MEC biocathode fed with pyruvate, current increased and H2 was produced with comparable efficiencies and production rates as mixed cultures biocathodes. Addition of membrane potential uncouplers nigericin and monensin showed no change in current and H2 production rates, suggesting that the molecular mechanism does not involve membrane potential driven processes.
    Finally, in chapter 5, we explored the usefulness of statistical methods to pinpoint which species are most important for MEC performance. We analyzed DGGE profiles from 5 different MEC anodes using two distinct statistical techniques, Radundacy analysis (RDA) and QR factorization (QRE), and tried to link those profiles to experimental data current, resistance, potential and overpotential. The results showed that current was mostly related to species composition and we were able to pinpoint a few band from DGGE that were influencing changes in experimental parameters most. The results showed that both RDA and QRE are useful methods, of which RDA takes all bands into account, but is therefore less precise; QRE is numerical precise but by eliminating bands that explain least of the variation and therefore using QRE might neglect effect of those bands. Altogether, RDA with additional QRE is useful to give an indication of which species from a mixed community are most likely important for MEC performance and can be used to find a focus in mixed community analysis.
    From our results we conclude that a large diversity of bacteria is able to catalyze the biocathodes reaction for H2 production. The species that develop at a cathode might be largely influenced by the design of the used setup, which has to be considered when comparing different experiments. In addition, our results suggest that a general mechanism, present in many different bacterial species, is involved in MEC H2 production. We propose a molecular mechanism involving a series of cytochromes and cytoplasmatic H2 production by NAD(P)+ dependent bidirectional hydrogenases that use energy from electrons derived from the cathode. The biocathode is a promising technology for application in the MEC, although to date the chemical cathodes still outcompete the biocathode, the biocathode offers great possibilities for future applications including production of other products such as ethanol, methane, succinate or acetate.

    Analysis of growth dynamics of Mediterranean bioenergy crops
    Archontoulis, S.V. - \ 2011
    Wageningen University. Promotor(en): Paul Struik, co-promotor(en): N.G. Danalatos; Xinyou Yin. - [S.l.] : S.n. - ISBN 9789461730091 - 235
    agro-ecologie - ecofysiologie - bio-energie - biobrandstoffen - brandstofgewassen - helianthus annuus - hibiscus cannabinus - cynara cardunculus - gewasproductie - griekenland - middellandse-zeegebied - biobased economy - agroecology - ecophysiology - bioenergy - biofuels - fuel crops - helianthus annuus - hibiscus cannabinus - cynara cardunculus - crop production - greece - mediterranean region - biobased economy

    In spite of the rapidly growing bioenergy production worldwide, there is lack of field experience and experimental data on the cultivation of bioenergy crops. This study aims to advance crop management operations and modelling studies by providing essential information on phenology, agronomy and crop physiology of three Mediterranean bioenergy crops: Helianthus annuus (sunflower), Hibiscus cannabinus (kenaf) and Cynara cardunculus (cynara). These crops cover a wide range of bio-industrial applications and fit into different cropping strategies. For these crops, we identified the most important knowledge gaps and performed a series of field experiments to fill some of those, particularly for cynara.

    Information on phenology and seed yield potential for cynara was missing mainly due to its complex inflorescence structure. This thesis codifies and describes cynara’s phenological growth stages according to the universal BBCH coding system. This scale can be used by everyone involved in the production of this crop under all circumstances. In addition, we present a robust allometric model for estimating seed yield under diverse management and environmental conditions. Inputs to the model are two easily quantifiable inflorescence traits: total weight and number of seed-bearing heads per unit area.

    Additionally, this thesis investigates factors at leaf, canopy and crop level that determine biomass production for all tested crops and provides key parameters for crop growth modelling. Leaf photosynthesis and respiration rates in response to light, temperature and leaf nitrogen were quantified. Based on such data, a biochemical model for C3 leaf photosynthesis and an empirical model for respiration were parameterized and validated. Then, to upscale these rates from the leaf to the canopy level, light- and nitrogen extinction coefficients over time and in response to water availability were determined in detail. It was shown that the light extinction coefficient changes under water stress conditions and time of year, while leaf nitrogen only shows a strong vertical distribution within crop canopy during the mid-season. Relevant agronomic data, such as biomass production over time and leaf area index in response to management practices, are also presented for the three crops.

    This thesis contributes to the general objective of gaining more insight into bioenergy production from crop species. The findings can help farmers, researchers and modellers to better evaluate agricultural land uses and to improve biomass quantity and quality. Among the studied species, the perennial cynara shows the greatest potential for energy production in the Mediterranean region because a significant part of the production is achieved in the winter–spring period relying on natural rainfall.

    Key words: cynara, kenaf, sunflower, phenology, agronomy, crop physiology, modelling, biomass production, crop growth, growth stages, BBCH code, seed yield, oil/seed ratio, leaf area index, leaf nitrogen, light and nitrogen extinction coefficients, photosynthesis, respiration, respiration acclimation, bioenergy, Greece, Mediterranean region.

    Growth and development of true sago palm (Metroxylon sagu Rottbøll) : with special reference to accumulation of starch in the trunk : a study on morphology, genetic variation and ecophysiology, and their implications for cultivation
    Schuiling, D.L. - \ 2009
    Wageningen University. Promotor(en): Paul Struik. - [S.l.] : S.n. - ISBN 9789085858546 - 259
    metroxylon sagu - sago - arecaceae - starch crops - plant development - growth analysis - plant morphology - agronomy - maluku - indonesia - ecophysiology - economic botany - metroxylon sagu - sago - arecaceae - zetmeelgewassen - plantenontwikkeling - groeianalyse - plantenmorfologie - agronomie - molukken - indonesië - ecofysiologie - economische botanie
    Keywords: Metroxylon sagu, Arecaceae, starch crops, plant growth and development, plant morphology, inflorescence structure, electron microscopy, phenological scale, genetic variation, plant taxonomy, folk taxonomy, ethnobotany, leaf area, leaf area index, starch accumulation, starch distribution, plant ecophysiology, tropical lowlands, wetlands, traditional processing, estate cultivation, agronomy, Moluccas, Maluku.

    True sago palm (Metroxylon sagu Rottbøll) is a stout, clustering palm adapted to swampy tropical lowland conditions. Each axis in a sago palm clump flowers once at the end of its life after having amassed a large amount of starch in its trunk. Man can harvest this starch by felling the trunk, pulverizing the pith and leaching the starch out with water, and use it like other starches for food or non-food purposes. It is a staple food mainly in eastern Indonesia and in Papua New Guinea where it is harvested mostly from semi-managed stands. For establishing sago palm as a full-fledged plantation crop, desirable because of its envisaged large yield potential as a perennial, its niche habitat, and its potential as a raw material provider for bio-ethanol production, the scientific base for establishing the right felling time to harvest the starch needed strengthening.

    Between October 1988 and November 1990, 27 sago trunks in the Adult Vegetative (AV) or Generative (G) phase belonging to six varieties were selected from semi wild sago stands in the Moluccas, eastern Indonesia: 23 trunks (4 varieties) on the alluvial coastal plain near Hatusua village, Seram Island, and 4 trunks (2 varieties) on hilly terrain near Siri Sori Serani village, Saparua Island. These trunks were felled, dissected, morphologically described and sampled for the amount and distribution of starch they contained. The leafless parts of the trunks were 4.45 to 19.65 m long, had a mean starch density of 4.6 to 254 kg/m3 and contained five to 777 kg of starch (maximum found in a whole trunk: 819 kg).

    To link starch content to age, the ages of the sampled trunks had to be estimated. To enable age estimation by counting leaf scars on the trunk, the leaf unfolding rate of 36 AV-phase palms around Hatusua (31 palms) and Siri-Sori Serani (5 palms) was monitored for varying periods between 1989 and 1992. Probably due to large variation in habitat and genetic make up, this rate varied from 2 to 14 leaves per year (mean 7.85), rendering number of leaf scars unfit as accurate age estimator. Also trunk height proved unfit for this purpose. From monitoring 5 G-phase palms, the G-phase could be subdivided into 3 sub-phases (G1, G2, G3), recognizable from the ground by the phased development of the successive orders of inflorescence branches. By combining gathered morphological and monitoring data, a phenological scale of a model palm was composed consisting of two parallel timelines of hidden and outwardly visible events: two years after the start of the Establishment (E) phase, the first AV-phase leaf is initiated in the apical growing point, to unfold only 2.5 years later; the initiation of the first AV-phase tissues is followed 12.5 to 14.5 years later by the initiation of the first G-phase tissues, followed 4 to 5.5 years later by the shedding of fruits, and finally by a 2- to 5-year Recycling phase (name proposed here) in which the axis decays and collapses. This scale, which accounts for the large time gap between initiation of trunk parts and their becoming visible, may help to correctly time cultural measures. The 27 sampled trunks could tentatively be ranked according to physiological age into 4 AV phase classes and 9 G phase classes.

    Since the examined palms belonged to 6 different local varieties, their relative rareness or commonness had to be established to assess the validity of the findings. Based on literature and on interviews with informants, an overview of locally recognised sago palm varieties is presented. The number of unique variety names in 32 localities in Indonesia and Papua New Guinea totalled 325, ranging from 2 (spined vs unspined only) to 34 per locality. On the basis of this survey, the Hatusua varieties were considered average. The nomenclatural category folk variety (fovar, fv.) is proposed to unambiguously name local varieties by adding to the variety name an indication of the location where, and (if known) the ethnic/linguistic group by which that name is used.

    Leaf area estimation methods were devised to enable investigation of the relationship between leaf area and starch content. In the AV-phase the Total leaf area (TLA) of a sago palm axis ranged from 200 m2 to 325 m2, one axis having an exceptional TLA of 388 m2. The TLA in the G-phase before fruiting mostly remained within the same range, possibly exceeding it for a short period early in that stage. The Leaf area index (LAI) of an individual axis showed an upward trend from 1 - 1.5 in the E-phase to 1.25 - 1.75 in the AV-phase, to more than 2 in the early G-phase, followed by a decrease to about 1.5 again in the late G-phase before fruiting. No fruiting palms were available for analysis. The TLA and LAI of a single trunk could not be linked to the mean starch density of its pith, nor to the total amount of starch the pith contained.
    Generally, starch density in the trunk first increased with height above ground level, reached a maximum about half-way to two-thirds up the leafless part of the trunk, and then sharply dropped towards the top of the trunk. From the late AV phase onward the maximum starch density ranged from 238 to 284 kg/m3. The four trunks with the highest maximum starch densities, all closely around 280 kg/m3, belonged to three different varieties, suggesting that 280 kg/m3 may be considered the maximum starch storage capacity in the pith of any variety.
    The starch distribution pattern in the leafless part of the trunk showed a tendency to evolve with age from two tailed (density gradually increasing from base, gradually decreasing towards top) to one tailed (density gradually increasing from base, sharply decreasing towards top). The differences in distribution pattern found strongly suggested that there must be other factors besides age and development phase affecting starch accumulation. Attempts to determine the effect of palm variety and of the environment mostly failed.

    Potential yield of a model palm based on the maximum starch density of 280 kg/m3 was estimated at 840 kg of dry starch. That this amount is much higher than generally found may partly be due to poor recovery ratios, as the results of a traditionally processed trunk demonstrated: only 47% of the starch in the processed trunk part was recovered, and if the unharvested starch present in the traditionally discarded basal and top part of the trunk is taken into account, recovery drops to 44%.

    In an attempt to establish the point in time at which a sago palm starts to be a nett consumer of its own starch, the course of the energy producing and consuming capacity of an axis during its life time was modelled based on the assumption that by the end of the AV-phase the existing TLA of the axis produces just the amount of energy needed to maintain existing biomass, to keep up the normal regular growth, and to fill new trunk with starch. Using this model, assimilate requirements for building and maintaining the inflorescence and the fruits could not be met by the production capacity of the leaves plus the starch reserves in the trunk. For this modelling approach to succeed in predicting the turning point from nett production to nett consumption of starch by a sago palm axis, additional data on chemical composition of its parts and on assimilation rate are needed.

    Lack of precise data on the age of the sampled trunks and lack of uniformity of their genetic make up and growing conditions made it impossible to arrive at the sought-after detailed timetable of the evolution of trunk starch accumulation and depletion to base the right felling time of a sago palm on. The high starch density found in the trunk of a palm with half-grown fruits indicated that depletion of starch reserves by the palm itself may set in much later than generally assumed.
    Once the course of starch accumulation in time in a single axis is unravelled, the next research question should be how this adds up in a clump - the actual production unit in a plantation - with axes of different age. Timing felling in such a situation should be aimed at maintaining a maximum starch accumulation rate for the plantation as a whole rather than at harvesting a maximum amount of starch per trunk.

    Data sheets of each palm examined containing all primary and some secondary data, and including photographs, are appended in digital form.

    Partitioning European grassland net ecosystem CO2 exchange into grass primary productivity and ecosystem respiration using response function analysis
    Gilmanov, T.G. ; Soussana, J.F. ; Aires, A. ; Allard, V. ; Ammann, C. ; Balzarolo, M. ; Barcza, C. ; Bernhofer, C. ; Campbell, C.L. ; Cernusca, A. ; Cescatti, A. ; Clifton-Brown, J.C. ; Dirks, B.O.M. ; Dore, S. ; Eugster, W. ; Fuhrer, J. ; Gimeno, C. ; Gruenwald, T. ; Haszpra, L. ; Hensen, A. ; Ibrom, A. ; Jacobs, A.F.G. ; Jones, M.B. ; Lanigan, G. ; Laurila, T. ; Lohila, A. ; Manca, G. ; Nagy, Z. ; Pilegaard, K. ; Pinter, K. ; Pio, C. ; Raschi, A. ; Rogiers, N. ; Sanz, M.J. ; Stefani, P. ; Sutton, M. ; Tuba, Z. ; Valentini, R. ; Williams, M.L. ; Wohlfahrt, G. - \ 2007
    Agriculture, Ecosystems and Environment 121 (2007)1-2. - ISSN 0167-8809 - p. 93 - 120.
    graslanden - ecofysiologie - kooldioxide - productiviteit - lichtrelaties - grasslands - ecophysiology - carbon dioxide - productivity - light relations - intercepted solar-radiation - carbon-dioxide exchange - water-vapor exchange - flux measurements - soil respiration - eddy covariance - use efficiency - climate-change - temperate grassland - tallgrass prairie
    Tower CO2 flux measurements from 20 European grasslands in the EUROGRASSFLUX data set covering a wide range of environmental and management conditions were analyzed with respect to their ecophysiological characteristics and CO2 exchange (gross primary production, P g, and ecosystem respiration, R e) using light-response function analysis. Photosynthetically active radiation (Q ) and top-soil temperature (T s) were identified as key factors controlling CO2 exchange between grasslands and the atmosphere at the 30-min scale. A nonrectangular hyperbolic light-response model P (Q ) and modified nonrectangular hyperbolic light–temperature-response model P (Q , T s) proved to be flexible tools for modeling CO2 exchange in the light. At night, it was not possible to establish robust instantaneous relationships between CO2 evolution rate r n and environmental drivers, though under certain conditions, a significant relationship rn=r0 ekTTsrn=r0 ekTTs was found using observation windows 7–14 days wide. Principal light-response parameters—apparent quantum yield, saturated gross photosynthesis, daytime ecosystem respiration, and gross ecological light-use efficiency, ɛ = Pg/Q, display patterns of seasonal dynamics which can be formalized and used for modeling. Maximums of these parameters were found in intensively managed grasslands of Atlantic climate. Extensively used semi-natural grasslands of southern and central Europe have much lower production, respiration, and light-use efficiency, while temperate and mountain grasslands of central Europe ranged between these two extremes. Parameters from light–temperature-response analysis of tower data are in agreement with values obtained using closed chambers and free-air CO2 enrichment. Correlations between light-response and productivity parameters provides the possibility to use the easier to measure parameters to estimate the parameters that are more difficult to measure. Gross primary production (Pg) of European grasslands ranges from 1700 g CO2 m−2 year−1 in dry semi-natural pastures to 6900 g CO2 m−2 year−1 in intensively managed Atlantic grasslands. Ecosystem respiration (Re) is in the range 1800 2400 g CO2 m−2 year−1) to significant release (
    Tower CO2 flux measurements from 20 European grasslands in the EUROGRASSFLUX data set covering a wide range of environmental and management conditions were analyzed with respect to their ecophysiological characteristics and CO2 exchange (gross primary production, P-g, and ecosystem respiration, R-e) using light-response function analysis. Photosynthetically active radiation (Q) and top-soil temperature (T-s) were identified as key factors controlling CO2 exchange between grasslands and the atmosphere at the 30-min scale. A nonrectangular hyperbolic light-response model P(Q) and modified nonrectangular hyperbolic light-temperature-response model P(Q, T-s) proved to be flexible tools for modeling CO2 exchange in the light. At night, it was not possible to establish robust instantaneous relationships between CO2 evolution rate r(n) and environmental drivers, though under certain conditions, a significant relationship r(n) = r(0) e(kTTs) was found using observation windows 7-14 days wide. Principal light-response parameters-apparent quantum yield, saturated gross photosynthesis, daytime ecosystem respiration, and gross ecological light-use efficiency, epsilon = P-g/Q, display patterns of seasonal dynamics which can be formalized and used for modeling. Maximums of these parameters were found in intensively managed grasslands of Atlantic climate. Extensively used semi-natural grasslands of southern and central Europe have much lower production, respiration, and light-use efficiency, while temperate and mountain grasslands of central Europe ranged between these two extremes. Parameters from light-temperature-response analysis of tower data are in agreement with values obtained using closed chambers and free-air CO, enrichment. Correlations between light-response and productivity parameters provides the possibility to use the easier to measure parameters to estimate the parameters that are more difficult to measure. Gross primary production (P,) of European grasslands ranges from 1700 g CO2 m(-2) year(-1) in dry semi-natural pastures to 6900 g CO2 m(-2) year(-1) in intensively managed Atlantic grasslands. Ecosystem respiration (R-e) is in the range 1800 2400 g CO2 m(-2) year(-1)) to significant release (<-600 g CO2 m(-2) year(-1)), though in 15 out of 19 cases grasslands performed as net CO2 sinks. The carbon source was associated with organic rich soils, grazing, and heat stress. Comparison of P-g, R-e, and NEE for tower sites with the same characteristics from previously published papers obtained with other methods did not reveal significant discrepancies. Preliminary results indicate relationships of grassland P-g and R-e to macroclimatic factors (precipitation and temperature), but these relationships cannot be reduced to simple monofactorial models. (c) 2006 Elsevier B.V. All rights reserved.
    Lianas and trees in tropical forests in south China
    Cai, Z.Q. - \ 2007
    Wageningen University. Promotor(en): Frans Bongers, co-promotor(en): K.F. Cao. - [S.l.] : S.n. - ISBN 9789085046530 - 162
    klimplanten - bosbomen - bomen - tropische bossen - biodiversiteit - plantenecologie - plantenmorfologie - china - ecofysiologie - climbing plants - forest trees - trees - tropical forests - biodiversity - plant ecology - plant morphology - china - ecophysiology
    Lianas (woody climbers) and trees are the most important life-forms in most tropical forests. In many of these forests lianas are abundant and diverse and their presence is often a key physiognomic feature. Lianas contribute substantially to the floristic, structural and functional diversity of tropical forests, and have both positive (providing valuable food resources, habitat, and connections among tree canopies that are used as pathways by arboreal animals) and negative (reducing tree growth, fecundity and survivorship) effects on forests.

    Lianas are increasingly well studied in many areas around the world, but in southeast Asia they are relatively unknown. This PhD dissertation describes liana communities in selected but well distributed tropical forests in Xhishuangbanna, southwest China. In addition the question what makes lianas functionally different from trees is addressed. A number of structural-functional characteristics of lianas are analysed, comparative to trees. Special attention is put to growth performance and ecophysiological leaf and plant characters in a framework of adaptive ecology. The last part of the dissertation addresses adaptive behavior, both within one liana species as across a number of species differing in adult stature.

    Liana communities in different forests

    The liana communities of three common forest types are analysed: seasonally wet. montane forest and evergreen broad-leaved forest. In each forest five 0.1 ha (20 x 50 m) plots were established. The density of lianas varied significantly among the three forests, with on average 445, 276 and 301 individuals per plot in the seasonally wet, montane, and evergreen forests,respectively. All three forests combined consisted of a total of 147 liana species, representing 48 families and 75 genera. A plot had on average 40, 26, and 21 species in the seasonally wet, montane, and evergreen forest, respectively. The forests were rather different as similarity between their liana assemblages was low. In all three forests, most lianas were stem twiners and scramblers, with relatively few hook, tendril and root climbers. Liana species were mostly wind dispersed in the evergreen forest, but animal and gravity dispersed in the other two forests.

    The higher liana abundance in the seasonal forest is consistent with the documented pattern that lianas peak in abundance with increasing seasonality. Compared to other tropical Asian tropical forests, the diversity and abundance of lianas is relatively high in Xishuangbanna, which may be due to the relatively warm climate, as well as its high seasonal rainfall and its high rates of disturbance and forest fragmentation.

    How different are lianas from trees?

    In two studies a large number of liana and tree species were compared for selected leaf structural and physiological characteritics. Chapter 3 focusses on differences in adaptation to climate seasonality. Most organisms decrease in abundance with decreasing annual precipitation and increasing seasonality. However, lianas are an exception to this general rule: they increase in abundance with increasing seasonality (Schnitzer 2005). In this chapter the hypothesis is tested that lianas are physiologically more robust than trees during the dry season, thus contributing to an explanation of their relatively high abundance in seasonal forests. We compared a range of leaf-level physiological attributes of 18 co-occurring liana and 16 tree species during the wet and dry seasons in a tropical seasonal rainforest in Xishuangbanna. During the wet season, lianas (liana leaves) had significantly higher nitrogen concentrations ( Nmass ), δ13 Cvalues, and lower leaf mass per area (LMA) than trees, indicating that lianas have higher water-use efficiency (WUE) and lower structural investments. However, liana and tree species did not differ significantly in photosynthesis ( Aarea ), dark respiration (R darea ), chlorophyll content (Chl mass ), carotenoid to chlorophyll ratio (Car/Chl), phosphorus concentration ( Pmass ), N:P ratios, and photosynthetic nitrogen- and phosphorus- use effeciency (PNUE, PPUE). During the dry season, the decrease in Aarea and Nmass was far lower in lianas than in trees, suggesting that lianas fix more carbon and suffer less from water stress during this season. From the wet to the dry season, average Aarea decreased by 30.1% in tree species, compared with only 12.8 % in liana species. Nmass , Pmass and PNUE changed little for lianas, while these factors decreased strongly for tree species. The δ13 C, LMA and Car/Chl values for both lianas and trees did not vary significantly with the season.

    These results show that lianas are less negatively effected by a dry season than trees, providing eco-physiological evidences as to why lianas are abundant in the seasonally rainforest. The leaf-level physiological characteristics show that lianas tend to fix more carbon, have a higher resource capture efficiency (water and nitrogen) in the dry season, and have lower cost of resource capture, compared to trees, thus confirming the hypothesis that differences in photosynthetic attributes may contribute to the competitive advantage of lianas over trees in seasonal forests.

    Chapter 4 addresses the question whether lianas are more efficient than trees in nutrient resorption during leaf senescence. This would give an additional advantage in nutrient poor environments as many tropical forests are. The chapter presents changes in leaf size, leaf mass and foliar nutrient concentrations during leaf senescence in 12 liana and 14 tree species in a tropical strongly phosporus-limited montane rain forest in Xishuangbanna. The relative leaf shrinkage and mass loss during senescence did not differ significantly between lianas and trees. Nutrient concentrations in mature leaves and nitrogen resorption efficiency of liana species were similar to those of tree species, but the phosphorus concentrations of liana litter were higher, and liana's phosphorus resorption efficiencies were lower. These results therefore provide clear evidence in favour of a novel mechanism whereby lianas may influence the ecosystems in which they occur. Through the production of nutrient-rich litter, they have the potential to greatly enhance the availability of nutrients in areas where they are abundant, and thus they may have significant effects on small-scale biodiversity.

    Another important difference between lianas and trees is the larger growth rate of lianas, as has been often postulated. To examine this hypothesis more closely, a range of physiological, morphological, and biomass parameters at the leaf and whole plant level were compared in seedlingsof five Bauhinia species of different life form and light demand: two light-demanding lianas, one shade-tolerant liana, and two light-demanding trees. Seedlings of these five species were grown in a shadehouse with 25% of full sunlight. Compared to trees, the two light-demanding lianas had lower photosynthetic rates per unit area (Aarea ) and similar photosynthetic rates per unit mass (Amass ). High specific leaf area (SLA) and leaf mass fraction (leaf mass/plant mass, LMF) in the two light-demanding lianas were reflected in a higher leaf area ratio (LAR). The two light-demanding liana species had higher relative growth rate (RGR), allocated more biomass to leaf production (higher LMF and LAR) and stem mass fraction (SMF), and less biomass to the roots (root mass fraction, RMF) than the two tree species. The shade-tolerant liana had the lowest RGR of all five species, and had a higher RMF, lower SMF, and similar LMF than the two light-demanding liana species. Across species, RGR was positively related toSLA, but not to LAR and Aarea. The faster growth of light-demanding lianas compared to light-demanding trees is based on morphological parameters (SLA, LMF, and LAR), and cannot be attributed to higher photosynthetic rates at the leaf level. The shade-tolerant liana exhibited a different growth strategy from the light-demanding species. Our study shows that, even within a genus (in this case Bauhinia), plant growth is rather variable, and that this variation is related to life form (lianas vs trees) and to light demand (light-demanding vs shade tolerant).

    Seasonal acclimation of a liana

    Under natural conditions, photosynthesis is biochemically regulated to maintain a balance between the rates of its component processes and the concentrations of metabolites, and is affected by continuously changing environmental variables, such as light, water availability, and temperature. Xishuangbanna, biogeographically located in the transitional zone between tropical Southeast Asia and subtropical East Asia, has a rich tropical flora and typical tropical rain forests in the lowland area. It has been hypothesized that the vegetation there is likely to be affected by the seasonal drought and chilling because it is far from the Equator and at a relatively high altitude. To test this hypothesis, Chapter 6 addresses the photosynthetic adaptation and growth responses in seedlings of a local liana species (Zizyphus attopensis Pierre) in three contrasting natural microhabitats: understory, a small gap and a large gap. Photosynthetic capacity(light-saturated photosynthetic rate, Amax ), maximum rate of carboxylation (Vcmax ) and electron transport ( Jmax ), and partitioning of leaf nitrogen into carboxylation ( Pc ) and electron light transport ( Pb ) differed significantly between seasons and microhabitats. Specific leaf area (SLA) did not change seasonally, but was different between plants grown in each of the three microhabitats and was negatively linear related to the daily integrated photon flux density (PPFD i ). In contrast, nitrogen content per unit area (Na ) changed seasonally but did not differ among microhabitats. Measurements of maximum photosystem II (PSII) photochemical efficiency showed that no chronic photoinhibition occurred for all microhabitats throughout the experimental period. Photosynthetic capacity was greatest in the wet season and lowest in the cool season. During the cool and dry seasons, the reduction in Amax was greater in seedlings grown in the large gap than in those grown in understory and small gap. Close logarithmic relationships were detected between PPFD, leaf Na and photosynthetic capacity. Stem mass ratio decreased and root mass ratio increased in the dry season. These results show that seasonal acclimation in growth and photosynthesis of the seedlings was due to changes in biochemical features (particularly Na and partitioning of total leaf nitrogen between the different photosynthetic pools) and biomass allocation, rather than to changes in leaf morphological features (such asSLA). The local light level is the main factor driving seasonal variations in growth and photosynthesis in the study area due to the presence of heavy fog during the cool and dry seasons which reduces irradiance and supplies water to the soil surface layers.

    Light acclimation, adult stature and shade tolerance

    Finally, Chapter 7 addresses light acclimation of seedlings of six late-successional common woody species differing in adult stature and shade tolerance. Especially morphological and physiological leaf and whole-plant features are analysed. After 1 year of growth in low light (4.5% full sun), seedlings were transferred to high light (24.5% full sun) to investigate acclimation responses of existing leaves to forest gap opening and to determine whether seedling capacity for acclimation is a limiting factor in its natural regeneration. Leaves of the small shrub species are shade-adapted, as indicated by their low photosynthetic capacity, efficiency in using sunflecks, low stomatal density, low Chl a/b ratio and high spongy/palisade mesophyll ratio. The shrub species utilized sunflecks efficiently because of a short photosynthetic induction time and low induction loss. In all species, transfer of seedlings to high light resulted in a substantial initial reduction in the dark-adapted quantum yield of photosystem II ( Fv / Fm ) atmidday. Predawn Fv / Fm of the taller species did not change greatly, but predawn Fv / Fm of the short species (shrubs) decreased significantly without complete recovery within 25 days of transfer to high light, indicating chronic photoinhibition and damage to the previously shade-adapted leaves. Maximum net photosynthetic rate and dark respiration of the four taller species increased considerably after transfer to high light, but not in the shrub species. Similar trends were observed for the number of newly formed leaves and relative height growth rate. We conclude that the short species have limited potential for developmental and physiological acclimation to high light, which explains their absence from forest gaps. Compared with shrub species, the taller tree species, which are more likely to experience high light during their life span, showed a greater potential for light acclimation. Physiological differences among the four tree species were not consistent with differences in adult stature.

    Lianas versus trees: are differences adaptive?

    Phenotypic changes that we see over evolutionary time, across diverse environments and among taxa, often reflect adaptive evolution. In the broad sense adaptations are phenotypic traits that have been favored by natural selection, and can be identified by being variable, heritable and responsible for variation in fitness. The evolution of growth forms since the early terrestrial radiations is a complex history of innovation, complexification, simplification, conservatism, radiation and extinction (Rowe and Speck 2003, 2005). Trees and lianas have different ecological preferences and different attributes, but we are far from being able to link this directly to evolutionary differences. In more general terms we are confronted with questions like: are certain types of growth form highly constrained and immovable in evolutionary terms? Are some plant groups more 'flexible' in their capacity to evolve widely differing growth forms and is this capacity related to the evolutionary age or complexity of the group? What are the ecological factors that coerce to either canalise or facilitate growth form variation and evolution? Much more work is needed to be able to answer these questions. It is clear that lianas have growth strategies different from trees, as shown for some aspects in this thesis, but lianas do not always follow expected patterns. Additionally, for some characteristics lianas are far less different from trees than expected, as has been showed by a number of recent studies (Gilbert et al. 2006, Santiago and Wright 2007, Selaya 2007, this thesis). These new results shed new light on patterns of adaptive ecology of lianas versus trees in tropical forests. Together, these results force us to re-evaluate the broad generalizations that we sometimes use. This warrants further studies on the ecological differences between lianas and trees, including variations therein among forest types in different climates.
    The influence of time and severity of Striga infection on the Sorghum bicolor - Striga hermonthica association
    Ast, A. van - \ 2006
    Wageningen University. Promotor(en): Martin Kropff, co-promotor(en): Lammert Bastiaans. - Wageningen : s.n. - ISBN 9789085043997 - 154
    striga hermonthica - striga - parasitaire planten - onkruiden - sorghum bicolor - sorghum - infectie - aantasting - onkruidbestrijding - plantenecologie - ecofysiologie - striga hermonthica - striga - parasitic plants - weeds - sorghum bicolor - sorghum - infection - infestation - weed control - plant ecology - ecophysiology
    Keywords: Striga hermonthica , Sorghum bicolor , infection time, infection level, tolerance.

    This thesis presents the results of a study on the interaction between the parasitic weed Strigahermonthica (Del.) Benth. and sorghum ( Sorghum bicolor [L.] Moench). The main objective of the study was to investigate the effects of time and level of Striga infection on the interaction between host plant and parasite. Consequences for sorghum performance and the growth and development of the parasite were examined. A comparison between two sorghum cultivars differing in level of Striga tolerance, revealed that the absence of a negative effect of Striga infection on photosynthetic rate and a delayed time of first Striga infection both contributed to the lower extent of yield reduction of the tolerant cultivar. Likewise, in an experiment with a wide range of Striga seed infestation levels, it was observed that higher soil infestations levels did not only result in a higher Striga infection level, but also in an advanced time of first Striga infection.The importance of time of infection was further investigated in a pot experiment in which the time of infection was artificially delayed.Striga parasitism and reproduction, and the detrimental effects of Striga on crop performance could be strongly reduced by delaying the time of first infection. Prospects of reducing Striga parasitism by means of cultural control methods that are based on the principle of a delayed onset of Striga attachment were assessed. In a pot experiment, the combination ofshallow soil tillage, deep planting and the use of transplantsresulted in a four-week delay in first emergence of the parasite, a strongly reduced infection level of the sorghum host and highly improved sorghum yields. Evaluation of these methods under field conditions resulted in a 85% reduction in Striga -infection level, but as no delay in time of parasite infection was established, no beneficial effect on crop yield was obtained. Potential causes of the absence of a delay in Striga infection time under field conditions were discussed and alternative options for establishing a delayed infection in the field were proposed.
    The influence of time and severity of Striga infection on the Sorghum bicolor - Striga hermonthica association
    Ast, A. van - \ 2006
    Wageningen : Wageningen University and Research Centre (Tropical resource management papers no. 77) - ISBN 9789085850588 - 154
    striga hermonthica - striga - parasitaire planten - onkruiden - sorghum bicolor - sorghum - infectie - aantasting - onkruidbestrijding - plantenecologie - ecofysiologie - striga hermonthica - striga - parasitic plants - weeds - sorghum bicolor - sorghum - infection - infestation - weed control - plant ecology - ecophysiology
    A growth model of the cockle (Cerastoderma edule L.) tested in the Ooosterschelde estuary (The Netherlands)
    Rueda, J. ; Smaal, A.C. ; Scholten, H. - \ 2005
    Journal of Sea Research 54 (2005)4. - ISSN 1385-1101 - p. 276 - 298.
    bivalvia - groei - hydrobiologie - voortplanting - simulatiemodellen - nederland - oosterschelde - ecofysiologie - aquatische ecosystemen - bivalvia - growth - hydrobiology - reproduction - simulation models - netherlands - eastern scheldt - ecophysiology - aquatic ecosystems - mussel mytilus-edulis - gut-passage time - marennes-oleron - seasonal-variation - preingestive selection - ecophysiological model - seston concentration - variable conditions - particle selection - crassostrea-gigas
    The authors present an ecophysiological model of the bivalve Cerastoderma edule that simulates individual growth and reproduction under ambient conditions in temperature and food availability in the Oosterschelde estuary, SW Netherlands. The model contains feedback loops in the uptake and metabolism of food and in the partitioning of carbon to the internal state variables: somatic tissue, storage, organic shell matrix and gametes. The model was calibrated for 24 parameters, based on random distributions of parameter values. This procedure includes an estimate of confidence intervals of the output variables. The simulated growth of shell length and animal wet and dry weight reflected the observed values of growth in the field for the period 1993–1997. The model is a tool for the integration of ecophysiological knowledge of this species and also for carrying-capacity studies of shellfish culture and for environmental management of populations in estuarine and coastal areas
    We present an ecophysiological model of the bivalve Cerastoderma edule that Simulates individual growth and reproduction under ambient conditions in temperature and food availability in the Oosterschelde estuary, SW Netherlands. The model contains feedback loops in the uptake and metabolism of food and in the partitioning of carbon to the internal state variables: somatic tissue, storage, organic shell matrix and gametes. The model was calibrated for 24 parameters, based on random distributions of parameter values. This procedure includes an estimate of confidence intervals of the output variables. The simulated growth of shell length and animal wet and dry weight reflected the observed values of growth in the field for the period 1993-1997, The model is a tool for the integration of ecophysiological knowledge of this species and also for carrying-capacity studies of shellfish Culture and for environmental management of populations in estuarine and coastal areas. (c) 2005 Elsevier B.V. All rights reserved.
    Crop Systems Dynamics: an ecophysiological simulation model for genotype-by-environment interactions
    Yin, X. ; Laar, H.H. van - \ 2005
    Wageningen : Wageningen Academic Publishers - ISBN 9789076998558 - 155
    gewasproductie - gewasopbrengst - simulatiemodellen - wiskundige modellen - plantenfysiologie - plant-water relaties - stikstofbalans - source-sink relaties - wortel spruit ratio - groeianalyse - agro-ecologie - ecofysiologie - crop production - crop yield - simulation models - mathematical models - plant physiology - plant water relations - nitrogen balance - source sink relations - root shoot ratio - growth analysis - agroecology - ecophysiology
    This book presents a generic process-based crop growth model, GECROS (Genotype-by-Environment interaction on CROp growth Simulator), developed in Wageningen. The model uses robust yet simple algorithms to summarize the current knowledge of individual physiological processes and their interactions and feedback mechanisms. It was structured from the basics of whole-crop systems dynamics to embody the physiological causes rather than descriptive algorithms of the emergent consequences. It also attempts to model each process at a consistent level of detail, so that no area is overemphasized and similarly no area is treated in a trivial manner. Main attention has been paid to interactive aspects in crop growth such as photosynthesis-transpiration coupling via stomatal conductance, carbon-nitrogen interaction on leaf area index, functional balance between shoot and root activities, and interplay between source supply and sink demand on reserve formation and remobilization. GECROS is presented here in an open style, rather than as a ‘black-box’. Model theories are described in individual chapters, and their supporting texts (notably model derivations) are given in Appendices. The model source code, written in the simulation language FST (FORTRAN Simulation Translator), and the definition of variables are provided.
    A physiological production model for cacao: model description and technical program manual of CASE2 version 2.2
    Zuidema, P.A. ; Gerritsma, W. ; Mommer, L. ; Leffelaar, P.A. - \ 2003
    Wageningen : S.n. - 145
    theobroma cacao - cacao - simulatiemodellen - naslagwerken - groei - gewasproductie - plantenfysiologie - agro-ecologie - ecofysiologie - theobroma cacao - cocoa - simulation models - reference works - growth - crop production - plant physiology - agroecology - ecophysiology
    Process Simulation and Application of Cropping System Models
    Donatelli, M. ; Bindi, M. ; Porter, J.R. ; Ittersum, M.K. van - \ 2002
    Amsterdam [etc.] : Elsevier - 185
    teeltsystemen - simulatiemodellen - ecofysiologie - agro-ecologie - cropping systems - simulation models - ecophysiology - agroecology
    Les principes de la théorie de l'écologie de la production
    Lövenstein, H.M. ; Lantinga, E.A. ; Rabbinge, R. ; Keulen, H. van - \ 1995
    Wageningen : AB-DLO (Rapports PSS 13) - 181
    plantenfysiologie - plantenecologie - ecosystemen - plantenontwikkeling - groei - wiskundige modellen - systeemanalyse - agro-ecologie - ecofysiologie - agro-ecosystemen - plant physiology - plant ecology - ecosystems - plant development - growth - mathematical models - systems analysis - agroecology - ecophysiology - agroecosystems
    Econatuurkunde oftewel De entropie van het gazon.
    Lyklema, J. - \ 1995
    Wageningen : Landbouwuniversiteit Wageningen - 33
    ecologie - colleges (hoorcolleges) - fysische chemie - fysiologie - ecofysiologie - ecology - lectures - physical chemistry - physiology - ecophysiology
    ORYZA 1 : an ecophysiological model for irrigated rice production
    Kropff, M.J. ; Laar, H.H. van; Matthews, R.B. - \ 1994
    Wageningen [etc.] : DLO-Research Institute for Agrobiology and Soil Fertility (SARP research proceedings ) - ISBN 9789073384231 - 110
    computer simulation - crops - ecology - growth - mathematical models - oryza sativa - physiology - plant development - research - rice - simulation - simulation models - yield increases - yield losses - yields - ecophysiology - computersimulatie - gewassen - ecologie - groei - wiskundige modellen - oryza sativa - fysiologie - plantenontwikkeling - onderzoek - rijst - simulatie - simulatiemodellen - oogsttoename - oogstverliezen - opbrengsten - ecofysiologie
    Sulfur and carbon cycling in a stratifying freshwater lake
    Hordijk, C.A. - \ 1993
    Agricultural University. Promotor(en): N. van Breemen; T.E. Cappenberg. - S.l. : Hordijk - ISBN 9789054851554 - 177
    biocenose - ecosystemen - kringlopen - biogeochemie - koolstof - zwavel - meren - reservoirs - plassen - chemische eigenschappen - waterverontreiniging - waterkwaliteit - eutrofiëring - ecofysiologie - waterbodems - biocoenosis - ecosystems - cycling - biogeochemistry - carbon - sulfur - lakes - reservoirs - ponds - chemical properties - water pollution - water quality - eutrophication - ecophysiology - water bottoms

    This thesis is a synopsis of a ten-years research on the anaerobic breakdown of organic matter in the stratifying Lake Vechten. Special attention has been paid to the sulfur cycle and how this cycle interacts with carbon mineralization. The sediment plays an important role in the breakdown of organic matter in freshwater ecosystems. Until a few years ago, there was no insight in how mineralization processes were spatial organized in the sediment. New analytical developments have enabled to measure the steep concentration profiles in flocculent sediment layers of a few cm. These techniques are discussed in the second chapter of this thesis. Chapter 3 is more focused on field data collection and evaluation and Chapter 4 is discussing perspectives for future research.

    The study in Lake Vechten demonstrated that the penetration depth of O 2 , NO 3-, and SO 42-into the sediment can be limited to a few mm till a few cm in freshwaters. This is a crucial difference with marine systems where SO 42-usually penetrates much deeper.
    This difference makes it also expectable that microbial kinetics in freshwaters differ from those in marine sediments.
    The ability to measure concentration profiles across narrow depth intervals has open new ways to estimate electron acceptor consumptions by mathematical modeling. To support modeling, diffusion coefficients, adsorption effects, and kinetics were determined independently. The uptake of sulfate and nitrate in sediment in batches collected form the respiring horizon followed a first order kinetics. This indicates that electron limitation occurs in the top layer of the sediment. Assuming first order kinetics and using the measured concentration profiles, sulfate and nitrate consumption rates were estimated by the model of Berner. The estimated rates for sulfate reduction were twice lower that the values obtained from the batch experiments.

    A notable result of the batch experiments was the fast uptake rate of nitrate and sulfate in the batches collected from the methanogenic horizon (3-7 cm). Under in situ conditions, nitrate and sulfate will not penetrate till this horizon. The absence of a 'lag time' indicated the presence of a vital sulfate and nitrate reducing community in sediment of approximately 6-14 years old.

    In the second stage in this study we examined if the accumulated total sulfur in the sediment could give an indication on sulfate reduction rates integrated over a longer period. By comparison sulfate reduction rates and total sulfur sedimentation rates with the actual amount of sulfur present in the sediment, it appears that only about 15% of the annual sulfur input is permanently buried in the sediment. Thus, more than 80% of the sulfur is released again into the lake water column. This idea was supported by the concentration profiles of sulfur species seen in the lake-water column. The lake-water measurements also revealed that substantial more sulfur bearing species were present in the lake water column as could be explained by the sulfate, FeS, and ΣH 2 S pool only.

    In the last stage of the study we have related the sulfur and carbon cycle by comparing the kinetics of the 'key metabolites' acetate and sulfate. This comparison indicated that the role of sulfate as electron acceptor in the oxidation of acetate in freshwaters is dubious. Accumulation of acetate after addition of molybdate has several times been used as evidence that sulfidogens uses mainly acetate as electron donor in marine systems. Comparable experiments in Lake Vechten indicated however that molybdate also affected other acetate consuming processes besides sulfate reduction, making conclusions from this type of inhibition experiments tentative. In conclusion, sulfate reduction does not play an important role in acetate consumption in freshwater like it does in marine systems.

    Acetate uptake rates are relative high if compared with sulfate reduction rates and methane production rates. This indicated the existence of other quantitative important acetate consuming processes in the anaerobic part of the sediment. The acetate uptake rates did however not exceed total carbon sedimentation rates as in marine systems.

    Dependence of elongation on wavelength of supplementary irradiation
    Lint, P.J.A.L. de - \ 1961
    Wageningen : [s.n.] (Mededelingen van de Landbouwhogeschool te Wageningen 61(1961)16) - 16
    ecologie - fysiologie - licht - fotoperiode - fotoperiodiciteit - schaduw - ecofysiologie - ecology - physiology - light - photoperiod - photoperiodism - shade - ecophysiology
    Check title to add to marked list

    Show 20 50 100 records per page

    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.