Staff Publications

Staff Publications

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    '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.

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Phenotyping of field-grown wheat in the UK highlights contribution of light response of photosynthesis and flag leaf longevity to grain yield
Carmo-Silva, Elizabete ; Andralojc, P.J. ; Scales, Joanna C. ; Driever, Steven M. ; Mead, Andrew ; Lawson, Tracy ; Raines, Christine A. ; Parry, Martin A.J. - \ 2017
Journal of Experimental Botany 68 (2017)13. - ISSN 0022-0957 - p. 3473 - 3486.
CO2 assimilation - crop yield - light response - post-anthesis - pre-anthesis - productivity - Rubisco
Improving photosynthesis is a major target for increasing crop yields and ensuring food security. Phenotyping of photosynthesis in the field is critical to understand the limits to crop performance in agricultural settings. Yet, detailed phenotyping of photosynthetic traits is relatively scarce in field-grown wheat, with previous studies focusing on narrow germplasm selections. Flag leaf photosynthetic traits, crop development, and yield traits were compared in 64 field-grown wheat cultivars in the UK. Pre-anthesis and post-anthesis photosynthetic traits correlated significantly and positively with grain yield and harvest index (HI). These traits included net CO2 assimilation measured at ambient CO2 concentrations and a range of photosynthetic photon flux densities, and traits associated with the light response of photosynthesis. In most cultivars, photosynthesis decreased post-anthesis compared with pre-anthesis, and this was associated with decreased Rubisco activity and abundance. Heritability of photosynthetic traits suggests that phenotypic variation can be used to inform breeding programmes. Specific cultivars were identified with traits relevant to breeding for increased crop yields in the UK: pre-anthesis photosynthesis, post-anthesis photosynthesis, light response of photosynthesis, and Rubisco amounts. The results indicate that flag leaf longevity and operating photosynthetic activity in the canopy can be further exploited to maximize grain filling in UK bread wheat.
Biodiversity and climate determine the functioning of Neotropical forests
Poorter, L. ; Sande, M.T. van der; Arets, E.J.M.M. ; Ascarrunz, N. ; Enquist, B.J. ; Finegan, B. ; Licona, J.C. ; Martinez-Ramos, M. ; Mazzei, L. ; Meave, J. ; Munoz, R. ; Nytch, C.J. ; Oliveira, A.A. de; Perez-Garcia, E.A. ; Prado-Junior, J.A. ; Rodriguez-Velazquez, J. ; Ruschel, A.R. ; Salgado Negret, B. ; Schiavini, I. ; Swenson, N.G. ; Tenorio, E.A. ; Thompson, J. ; Toledo, M. ; Uriarte, M. ; Hout, P. van der; Zimmerman, J.K. ; Pena Claros, M. - \ 2017
biodiversity - biomass - carbon - ecosystem functioning - forest dynamics - productivity - soil fertility - tropical forest - water
Tropical forests account for a quarter of the global carbon storage and a third of the terrestrial productivity. Few studies have teased apart the relative importance of environmental factors and forest attributes for ecosystem functioning, especially for the tropics. This study aims to relate aboveground biomass (AGB), biomass dynamics (i.e., net biomass productivity and its underlying demographic drivers: biomass recruitment, growth and mortality) to forest attributes (tree diversity, community-mean traits, and stand basal area) and environmental conditions (water availability, soil fertility and disturbance). We used data from 26 sites, 201 one-ha plots and >92,000 trees distributed across the Neotropics. We quantified for each site water availability and soil total exchangeable bases and for each plot three key community-weighted mean functional traits that are important for biomass stocks and productivity. We used structural equation models to test the hypothesis that all drivers have independent, positive effects on biomass stocks and dynamics. Of the relationships analysed, vegetation attributes were more frequently significantly associated with biomass stocks and dynamics than environmental conditions (in 67% versus 33% of the relationships). High climatic water availability increased biomass growth and stocks, light disturbance increased biomass growth, and soil bases had no effect. Rarefied tree species richness had consistent positive relationships with biomass stocks and dynamics, probably because of niche complementarity, but was not related to net biomass productivity. Community-mean traits were good predictors of biomass stocks and dynamics. Water availability has a strong positive effect on biomass stocks and growth, and a future predicted increase in (atmospheric) drought might, therefore, potentially reduce carbon storage. Forest attributes – including species diversity and community-weighted mean traits – have independent and important relationships with AGB stocks, dynamics, and ecosystem functioning, not only in relatively simple temperate systems, but also in structurally complex hyper-diverse tropical forests.
A comprehensive assessment of agriculture in lowlands of south Brazil: characterization and comparison of current and alternative concepts
Theisen, Giovani - \ 2017
University. Promotor(en): Niels Anten, co-promotor(en): Lammert Bastiaans. - Wageningen : Wageningen University - ISBN 9789463436380 - 234
cropping systems - farming systems - crop management - lowland areas - wetlands - pampas - brazil - intensification - sustainability - productivity - indicators - soil management - rice - flooded rice - oryza sativa - maize - zea mays - glycine max - cover crops - livestock - rotation - mixed farming - seedbed preparation - farm machinery - teeltsystemen - bedrijfssystemen - gewasteelt - laaglandgebieden - pampa's - brazilië - intensivering - duurzaamheid (sustainability) - productiviteit - indicatoren - bodembeheer - rijst - natte rijst - maïs - dekgewassen - vee - rotatie - gemengde landbouw - zaaibedbereiding - landbouwwerktuigen

Agriculture in the lowlands of south Brazil is of strategic importance at the national level, since it supplies around 80% of the rice consumed by the Brazilian population. In Rio Grande do Sul, the southernmost state in Brazil, three million hectares of lowlands are ready for grain-based agriculture. Of this area, about half is fallow, partly used for cattle grazing, and irrigated rice is the predominant crop, cultivated annually on 1.1 million ha. The remaining area is used for soybean and other crops. The predominant cropping system is a combination of irrigated rice and cattle. Over the last decades, rice yields have steadily increased, but this rise in yield level has to a large extent been obtained at the expense of a continuously higher use of external inputs. The recent introduction of soybean in rotation with rice has partially improved the system, but in most areas the situation is becoming incompatible with the modern demands for sustainability. This thesis presents a long-term study (2006-2015) of five cropping systems for lowlands. Next to monocrop rice and two rice-soybean rotations conducted in either conventional or minimum tillage, the experiment contained two novel systems based on large ridges, on which soybean and maize were combined with either cover crops or crop-livestock integration in winter. In these last systems, 8-m-wide ridges were built to avoid flooding, thus allowing for diversification of cash crops and the cultivation of cover crops or pastures in winter time, as well as the use of no-tillage. All systems were evaluated at process-level, including soil preparation, seeding, plant nutrition, pest management, irrigation, harvesting, transport and cattle management, as well as regarding their performance for the different dimensions of sustainability, particularly environment, land productivity, economics, energy-use and labour. Next to system assessment, two additional experiments were conducted for the evaluation of two specific technologies for soil management in these areas. Crop livestock integration on the ridge-based system offered the best balance between food production, environmental impact and economics. This system is well suited to be used in fields that are kept fallow, thereby enlarging the agricultural productivity of the lowlands. The additional experiments revealed that a knife-roller can successfully substitute plough-and-harrow for soil preparation after rice harvest, and that germination of weed seeds can be reduced if crop seeding is conducted at a lower speed or using a no-tillage seeder equipped with an improved cutting mechanism. Overall the results show that by using alternative cropping systems that allow for diversification and new methods of field management it is possible to simultaneously attain a larger agricultural production and improved sustainability in the lowlands.

Agronomic and socioeconomic sustainability of farming systems : A case in Chencha, South Ethiopia
Dersseh, Waga Mazengia - \ 2017
University. Promotor(en): Paul Struik, co-promotor(en): Rogier Schulte. - Wageningen : Wageningen University - ISBN 9789463436830 - 157
potatoes - solanum tuberosum - ethiopia - food security - farming systems - mixed farming - sustainability - optimization - efficiency - farm surveys - household surveys - socioeconomics - self sufficiency - profits - training - agronomic characteristics - productivity - soil fertility - rotation - animal feeding - improved varieties - inorganic fertilizers - aardappelen - ethiopië - voedselzekerheid - bedrijfssystemen - gemengde landbouw - duurzaamheid (sustainability) - optimalisatie - efficiëntie - bedrijfsonderzoeken - huishoudonderzoeken - sociale economie - zelfvoorziening - winsten - opleiding - agronomische kenmerken - productiviteit - bodemvruchtbaarheid - rotatie - diervoedering - veredelde rassen - anorganische meststoffen

Potato has multiple benefits and thus can play a vital role in ensuring food security in Ethiopia. However, for diverse reasons, its productivity is low. The farming systems in Ethiopia in which potato is grown, are predominantly mixed farming systems.

Most of the research in Ethiopia is focused on crop-specific constraints and thus there is limited research in which the interrelations between crop and livestock management practices are investigated. There is also not enough research focused on combined analysis of soil nutrient and animal feed balances and agronomic and socioeconomic efficiencies at farm level.

This study assessed production constraints and agronomic and socioeconomic sustainability of the farming systems in South Ethiopia and explored the possible synergetic options to alleviate major constraints. More specifically, the study intended to quantify the variation in input and output among farms, to identify constraints hindering expansion of potato production, to evaluate the sustainability of the farming systems at farm level, to identify constraints of sustainable intensification, and to explore synergetic solutions for the major constraints. Different research approaches were used ranging from lab analysis, household surveys, group discussions, to farm surveys.

Results showed that constraints related to input and product use in potato production vary across households indicating a need for a pluriform advisory model recognizing (and building upon alleviation of) the diversity of constraints identified in this analysis. The sustainability of the farming system is constrained by low agricultural productivity, low soil fertility, poor labour efficiency and limited economic return associated with improper crop rotation, inappropriate soil fertility management practices, shortage of animal feed, labour- and economically inefficient farm practices and labour shortage. However, there is ample scope to overcome the major constraints and simultaneously to optimize farm management.

The core messages of the study can be summarized as follows:

1) the current potato production is characterized by low productivity and economic returns due to various socioeconomic, agronomic and biological factors;

2) the soil fertility is low and there is uneven distribution of nutrients over plots with relatively high fertility levels in the homestead areas;

3) the current labour shortage can be attributed to mainly inefficiency of agricultural management practices and labour migration to towns for economic reasons indicating that the farming system is not sustainable in terms of labour;

4) considering the direct return from animal production, most of the farms had very low gross margin with the current management system and this reduced the overall operating profit of farms. The low return from animal rearing was offset by the relatively high profit from crop production indicating the benefit of mixed farming system in sustaining agricultural production; and

5) each farm can have a wide range of optimized solutions mainly through introduction of improved technologies and subsequent redesigning of the farm managements.

In general, the findings of the current study indicate that it is worthwhile to assess the sustainability of agricultural production in different farming systems and agro-ecologies of Ethiopia. In addition, the combined effect of introducing improved agricultural technologies and subsequent reconfiguring the farm management is very crucial to increase and sustain agricultural production.

Fire and plant diversity at the global scale
Pausas, Juli G. ; Carvalho Ribeiro, Eloi - \ 2017
Global Ecology and Biogeography 26 (2017)8. - ISSN 1466-822X - p. 889 - 897.
diversity - fire regime - plant richness - productivity - pyrogeography

Aim: Understanding the drivers of global diversity has challenged ecologists for decades. Drivers related to the environment, productivity and heterogeneity are considered primary factors, whereas disturbance has received less attention. Given that fire is a global factor that has been affecting many regions around the world over geological time scales, we hypothesize that the fire regime should explain a significant proportion of global coarse-scale plant diversity. Location: All terrestrial ecosystems, excluding Antarctica. Time period: Data collected throughout the late 20th and early 21st century. Taxa: Seed plants (= spermatophytes = phanerogamae). Methods: We used available global plant diversity information at the ecoregion scale and compiled productivity, heterogeneity and fire information for each ecoregion using 15 years of remotely sensed data. We regressed plant diversity against environmental variables; thereafter, we tested whether fire activity still explained a significant proportion of the variance. Results: Ecoregional plant diversity was positively related to both productivity (R2 =.30) and fire activity (R2 =.38). Once productivity and other environmental variables were in the model (R2 =.50), fire regime still explained a significant proportion of the variability in plant diversity (overall model, R2 =.71). The results suggest that fire drives temporal and spatial variability in many ecosystems, providing opportunities for a diversity of plants. Main conclusions: Fire regime is a primary factor explaining plant diversity around the globe, even after accounting for productivity. Fires delay competitive exclusion, increase landscape heterogeneity and generate new niches; thus, they provide opportunities for a large variety of species. Consequently, fire regime should be considered in order to understand global ecosystem distribution and diversity.

Abiotic and biotic drivers of biomass change in a Neotropical forest
Sande, M.T. van der; Peña-Claros, M. ; Ascarrunz, N. ; Arets, E.J.M.M. ; Licona, J.C. ; Toledo, M. ; Poorter, L. - \ 2017
biomass growth - disturbance - ecosystem functioning - functional diversity - mortality - productivity - recruitment - soil conditions - species diversity
Abiotic and biotic variables and growth, recruitment and mortality for 48 1-ha plots in a moist tropical forest in Bolivia
Data from: The evolutionary legacy of diversification predicts ecosystem function
Yguel, Benjamin ; Jactel, H. ; Pearse, Ian S. ; Moen, Daniel ; Winter, M. de; Hortal, J. ; Helmus, Matthew R. ; Kühn, I. ; Pavoine, S. ; Purschke, Oliver ; Weiher, Evan ; Violle, C. ; Ozinga, W.A. ; Brändle, Martin ; Bartish, I. ; Prinzing, Andreas - \ 2016
community ecology - evolutionary history - lineage-through-time plots - phylogenetic diversity - productivity - species coexistence
The Rdata files are simulated phylogenies and lineage through time plot of these simulated phylogenies, used in Yguel et al. 2016 AmNat. The code to extract the LTT plot from the phylogenies is given in the Appendices of the article as well as the method used to make these simulations.The name of the Rdata file indicates which simulation the file is refering to. The Excel files contain measures of phylogenetic structure of these simulated phylogenies (Measure phylogenetic structure parameters on simulated phylogenies.xlsx) and phylogenies of the experimental communities used in the article (Measure phylogenetic structure parameters on Cadotte Zanne phylog.xlsx). The code to calculate a1, a2, a3, and to measure S1 and S2 are given in the method of the article. In all excel files, a1 a2 a3 are the polynomial parameters fitted on the LTT plots. S1 and S2 are respectively ES1 and ES2, the "elderness surface" presented in the article. MPD, MNTD, gamma, and Colless are the common phylogenetic structure measurement (see also method), and invNRI and invNTI the standardized version of MPD and MNTD. RichSpe or Sps correspond to the species richness. PlotID corresponds to the identification of the plot. Mean19962007 corresponds to the mean productivity from 1996 to 2007.
Batch and repeated-batch oil production by microalgae
Benvenuti, G. - \ 2016
University. Promotor(en): Rene Wijffels, co-promotor(en): Rouke Bosma; Maria Barbosa. - Wageningen : Wageningen University - ISBN 9789462576582 - 149 p.
algae - chlorella - arthrospira - dunaliella - nostoc - triacylglycerols - light - lipogenesis - photosynthesis - oil products - productivity - biomass conversion - economic analysis - algen - triacylglycerolen - licht - lipogenese - fotosynthese - olieproducten - productiviteit - biomassaconversie - economische analyse

Microalgal triglycerides (TAGs) are promising feedstocks for the commodity markets (i.e. food, chemical and biofuel). Nevertheless, microalgal TAGs are not yet economically feasible due to the high production costs. To reduce these costs, TAG productivity needs to be maximized.

The aim of this thesis was to increase microalgal TAG productivity by investigating the effects of biological and engineering parameters (i.e. production strain and operational strategy).

We first screened seven marine species on their TAG productivity under nitrogen (N) starvation. Nannochloropsis sp. was identified as the most suitable species as it retained its photosynthetic activity while accumulating large amounts of TAGs ensuring the highest TAG productivity. Therefore, Nannochloropsis sp. was used in all following studies.

Next, we aimed at optimizing TAG productivity by investigating the effect of initial-biomass-specific (IBS) light availability (i.e. ratio of light impinging on reactor ground area divided by initial biomass concentration per ground area) in batch outdoor cultivations carried out in horizontal and vertically stacked tubular reactors at different initial biomass concentrations at the start of the TAG accumulation phase, over different seasons. Based on the observed trends of TAG productivity for the Dutch climate, optimal initial biomass concentrations were suggested to achieve high areal TAG productivities for each reactor configuration and season.

Subsequently, repeated-batch processes were investigated to further increase TAG productivity compared to batch processes. For this, repeated-batch cultivations were tested and compared to batch cultivations both at lab-scale under day/night cycles and in two identical, simultaneously operated, outdoor vertically stacked tubular reactors over different seasons. Although at lab-scale, batch and repeated-batch cultivations led to similar TAG productivities, outdoor repeated-batch processes were always outcompeted by the batch. It was concluded that repeated-batch processes require further optimization.

For this, the physiological responses of Nannochloropsis sp. to N-starvation and N-replenishment were determined under continuous light in lab-scale batch and repeated-batch cultivations and condensed into a mechanistic model describing both cultivation strategies. Scenarios for improved TAG yields on light were simulated and, based on the optimized yields, a comparison of the two processes was performed. It was concluded that under continuous light, an optimized batch process will always result in higher TAG productivities than an optimized repeated-batch process.

Finally, a techno-economic analysis for a two-step-continuous TAG production process (i.e. growth reactors are operated in continuous mode such that multiple batch-operated stress reactors are inoculated and sequentially harvested) is performed for a hypothetical 100 ha-scale plant in southern Spain using vertically stacked tubular reactors. Photosynthetic efficiencies based on outdoor pilot data were used as model input. By optimizing both photosynthetic efficiency and process technology, the production cost could be decreased from 7.4 to 3.0 €·kg-1 of TAG-enriched biomass. We believe to be on the right track to achieve an economically feasible TAG production platform provided that photosynthetic efficiency is further improved, the whole biomass is valorized and cheaper reactors are designed.

Uitbreiden ondanks nieuwe wetgeving?
Berentsen, P.B.M. ; Klootwijk, C.W. ; Middelaar, C.E. van; Boer, I.J.M. de - \ 2015
Veeteelt 32 (2015)19. - ISSN 0168-7565 - p. 12 - 14.
fosfaat - melkveehouderij - landbouw en milieu - capaciteit - productiegroei - verkoopbaar - melkprijzen - productiviteit - phosphate - dairy farming - agriculture and environment - capacity - production growth - saleable - milk prices - productivity
Kunnen bedrijven nog wel ontwikkelen na de komst van de Melkveewet en fosfaatrechten? Onderzoekers in Wageningen brachten via een rekenmodel de gevolgen in kaart. Zij concluderen dat het interessant blijft om beschikbare stalcapaciteit te benutten en dat fosfaatrechten niet snel de limiterende factor zijn.
Strain improvement of oleaginous microalgae
Jaeger, L. de - \ 2015
University. Promotor(en): Gerrit Eggink; Rene Wijffels, co-promotor(en): Dirk Martens. - Wageningen : Wageningen University - ISBN 9789462574847 - 200
algen - biomassa - oliën - productiviteit - opbrengsten - transcriptomica - triacylglycerol lipase - bioreactoren - transformatie - mutanten - algenteelt - biomassa productie - algae - biomass - oils - productivity - yields - transcriptomics - bioreactors - transformation - mutants - algae culture - biomass production

The increasing world population and living standards have enlarged the demand for food, feed, and for chemicals. Traditional fossil fuel based commodities need to be replaced, not only because these resources are finite, but also to relieve the impact of carbon emission and pollution, resulting from fossil fuel derived processes. Much attention is on using plants to produce sustainable, renewable alternatives to petrochemical based processes. Palm oil is the crop with the highest lipid yield known today, but the production of palm oil causes deforestation on a large scale. Microalgae are a promising platform for the production of sustainable commodity products. A commodity product that can be produced in microalgae is triacylglycerol (TAG). The TAG molecules that are accumulated in microalgae are comparable to the TAG profiles of commonly used vegetable oils, and can directly be applied for edible oil as well as for biodiesel production. Currently, microalgae derived products have proven to be functional and a potential replacement for conventional crops. However, microalgae derived products, especially TAGs, are not economically feasible yet. In order to make microalgal derived products a reality we need to decrease the production costs by smart technological solutions, biological understanding and metabolic engineering.

To get more insight in the lipid accumulation mechanism of microalgae, and to define targets for future strain improvement strategies, transcriptome sequencing of the oleaginous microalgae Neochloris oleoabundans was done. This oleaginous microalga can be cultivated in fresh water as well as salt water. The possibility to use salt water gives opportunities for reducing production costs and fresh water footprint for large scale cultivation.

In chapter 2 the lipid accumulation pathway was studied to gain insight in the gene regulation 24 hours after nitrogen was depleted. Oil accumulation is increased under nitrogen depleted conditions in a comparable way in both fresh and salt water. The transcriptome sequencing revealed a number of genes, such as glycerol-3-phosphate acyltransferase and via glycerol-3-phosphate dehydrogenase, that are of special interest and can be targeted to increase TAG accumulation in microalgae. NMR spectroscopy revealed an increase in proline content in saline adapted cells, which was supported by up regulation of the genes involved in proline biosynthesis. In addition to proline, the ascorbate-glutathione cycle seems to be of importance for successful osmoregulation by removal of reactive oxygen species in N. oleoabundans, because multiple genes in this pathway were upregulated under salt conditions. The mechanism behind the biosynthesis of compatible osmolytes in N. oleoabundans can be used to improve salt resistance in other industrially relevant microalgal strains.

Another very promising candidate for TAG production is the oleaginous green microalga Scenedesmus obliquus.

In chapter 3, UV mutagenesis was used to create starchless mutants, since no transformation approach was available for this species, due to its rigid and robust cell wall. All five starchless mutants that were isolated from over 3500 screened mutants, showed an increased triacylglycerol productivity. All five starchless mutants showed a decreased or completely absent starch content. In parallel, an increased TAG accumulation rate was observed for the starchless mutants and no substantial decrease in biomass productivity was perceived. The most promising mutant (Slm1) showed an increase in TFA productivity of 41% at 4 days after nitrogen depletion and reached a TAG content of 49.4% (%CDW).

In chapter 4 the Slm1 strain was compared to the wild type strain using photobioreactors. In the wild type, TAG and starch accumulated simultaneously during initial nitrogen starvation, and starch was subsequently degraded and likely converted into TAG. The Slm1 did not produce starch and the carbon and energy acquired from photosynthesis was partitioned towards TAG synthesis. This resulted in an increase of the maximum TAG content in Slm1 to 57% (%CDW) compared to 45% (%CDW) in the wild type. Furthermore, it increased the maximum yield of TAG on light by 51%, from 0.144 in the wild type to 0.217 g TAG mol-1 photon-1 in the Slm1 mutant. No differences in photosynthetic efficiency between the Slm1 mutant and the wild type were observed, indicating that the mutation specifically improved carbon partitioning towards TAG and the photosynthetic capacity was not affected.

To identify the mutation that caused the starchless phenotype of Slm1 the transcriptome of both the wild type and the Slm1 mutant was sequenced as described in chapter 5. A single nucleotide polymorphism (SNP) was discovered in the small subunit of the starch biosynthesis rate-controlling enzyme ADP-glucose pyrophosphorylase, which resulted in the introduction of a STOP codon in the messenger RNA of the enzyme. The characterization of the mutation increases the understanding of carbon partitioning in oleaginous microalgae, leading to a promising target for future genetic engineering approaches to increase TAG accumulation in microalgae.

To use the insight that is gained in chapters 2-5 for metabolic engineering of TAG accumulation and carbon partitioning, a metabolic engineering toolbox is required. However, the development of transformation protocols for new and less well studied industrially relevant microalgae is challenging. In chapter 6, a simple and effective tool for the optimization of transformation protocols is proposed. Optimal voltage settings were determined for five microalgae: C. reinhardtii, Chlorella vulgaris, N. oleoabundans, S. obliquus, and Nannochloropsis sp. This method can be used to speed up the screening process for species that are susceptible for transformation and to successfully develop transformation strategies for industrially relevant microalgae, which lack an efficient transformation protocol.

In addition to the increase in productivity, improving the quality in terms of fatty acid composition of TAG molecules would be desired as well. For example, the accumulation of stearic acid rich TAG molecules is of special interest, because of the improved structural properties. The lipid accumulating starchless mutant of the model species C. reinhardtii BAFJ5 was used as model species in chapter 7, since genetic toolbox is well established for this species. In this chapter, stearoyl-ACP desaturase (SAD), is silenced by artificial microRNA. The mRNA levels for SAD were reduced after the silencing construct was induced. In one of the strains, the reduction in SAD mRNA resulted in a doubling of the stearic acid content in triacylglycerol molecules, which shows that increasing the fraction of stearic acid in TAG is possible. Furthermore, we hypothesize that in addition to direct conversion in the chloroplast, C. reinhardtii is able to redirect stearic acid from the chloroplast to the cytosol and convert it to oleic acid in the endoplasmic reticulum by stearoyl-CoA desaturase.

In chapter 8, an outlook is given on microalgal strain improvement strategies for the future, reflecting on the results obtained in this thesis. Also a roadmap is suggested to get genetically modified microalgal derived products on the market. The results presented in this thesis, provide a significant improvement in the understanding of TAG accumulation and carbon partitioning in oleaginous microalgae. Furthermore, improved microalgal strains with increased TAG accumulation or improved TAG fatty acid composition under nitrogen depleted conditions were generated. In addition, an outlook is presented in which the major bottlenecks are presented in future industrial applications of microalgae.

Environmental changes drive the temporal stability of semi-arid natural grasslands through altering species asynchrony
Xu, Z. ; Ren, H. ; Li, M.H. ; Ruijven, J. van; Han, X. ; Wan, S. ; Li, H. ; Yu, Q. ; Jiang, Y. ; Jiang, L. - \ 2015
Journal of Ecology 103 (2015)5. - ISSN 0022-0477 - p. 1308 - 1306.
nitrogen addition - statistical inevitability - competitive communities - ecosystem stability - water availability - plant diversity - inner-mongolia - biodiversity - productivity - precipitation
1.Stability is an important property of ecological systems, many of which are experiencing increasing levels of anthropogenic environmental changes. However, how these environmental changes influence ecosystem stability remains poorly understood. 2.We conducted an 8-year field experiment in a semi-arid natural grassland to explore the effects of two common environmental changes, precipitation and nitrogen enrichment, on the temporal stability of plant above-ground biomass. A split-plot design, with precipitation as the main plot factor and nitrogen as the subplot factor, was used. Temporal stability was related to potential explanatory abiotic and biotic variables using regressions and structural equation modelling. 3.Increase in growing season precipitation enhanced plant species richness and promoted temporal stability of plant above-ground biomass. Nitrogen fertilization, however, reduced both plant species richness and temporal stability of plant above-ground biomass. Contrary to expectations, species richness was not an important driver of stability. Instead, community temporal stability was mainly driven by water and nitrogen availability that modulated the degree of species asynchrony and, to a lesser extent, by the stability of dominant plant species. 4.Synthesis. Our results highlight the importance of limiting resources for regulating community biomass stability and suggest that the projected increase in growing season precipitation may potentially offset negative effects of increased atmospheric nitrogen deposition on species diversity and community stability in semi-arid grasslands.
A food web model of invertebrate subtidal soft-bottom communities Part A: model derivation and effects of productivity
Kooten, T. van; Schellekens, T. - \ 2015
IJmuiden : IMARES (Report / IMARES Wageningen UR C130/15) - 18
zee-invertebraten - voedselwebben - modellen - aquatische gemeenschappen - zeevisserij - productiviteit - visserijbiologie - vistuig - natura 2000 - noordzee - marine invertebrates - food webs - models - aquatic communities - marine fisheries - productivity - fishery biology - fishing gear - north sea
Om visserij in de Natura-2000 gebieden Noordzeekustzone en Vlakte van de Raan zodanig te reguleren, dat zij het behalen van de geformuleerde beleidsdoelen niet in de weg staat, is het VIBEG-akkoord gesloten. Kern van de afspraken vormt een ruimtelijke zonering waarmee wordt bepaald welke visserijtechnieken in welke gebieden wel of niet zijn toegestaan.
Delivery of crop pollination services is an insufficient argument for wild pollinator conservation
Kleijn, D. ; Winfree, R. ; Bartomeus, D. ; Carvalheiro, L.G. ; Bommarco, R. ; Scheper, J. ; Tscharntke, T. ; Verhulst, J. ; Potts, S.G. - \ 2015
Nature Communications 6 (2015). - ISSN 2041-1723 - 8 p.
ecosystem services - native bees - biodiversity conservation - european countries - plant diversity - fruit-set - abundance - productivity - decline - pollen
There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments.
Long-term decline in soil fertility and responsiveness to fertiliser as mitigated by short fallow periods in sub-Sahelian area of Togo
Kintché, K. ; Guibert, H. ; Bonfoh, B. ; Tittonell, P.A. - \ 2015
Nutrient Cycling in Agroecosystems 101 (2015)3. - ISSN 1385-1314 - p. 333 - 350.
organic-matter dynamics - nitrogen dynamics - burn agriculture - tropical fallows - no-tillage - carbon - management - biomass - productivity - yield
Using 40-year experiment data from a mono-modal rainfall area of northern Togo, we analyzed soil fertility dynamics when 2 and 3-year fallows were alternated with 3-year rotation of groundnut, cotton and sorghum. The control treatment consisted to continuous cultivate the soil in a rotation of groundnut/cotton/sorghum without fallow periods. For each rotation, two fertilisation rates were applied: no fertilisation and mineral fertiliser application during the cropping and/or the fallow periods. Yields of unfertilised crops, which averaged 1 t ha-1 during the first years of cultivation, were often nil in the long-term. In the long-term, yields of fertilised cotton and sorghum decreased by 32 and 50 %, respectively compared to the average of 2.4 and 1.6 t ha-1 obtained during the first decade of cultivation. The long-term decline in crop productivity was mitigated when fallow periods were alternated with cropping periods, and consequently there was partial compensation in terms of production for the unproductive fallowed plots. Long-term yields of fertilised cotton and sorghum in the periodically fallowed plots were 40 and 50 % higher than those in continuously cropped plots, respectively; they were 90 and 60 % higher than those in continuously cropped plots without fertilisation. Like for crop productivity, soil C, N and exchangeable Ca and Mg decreased less in periodically fallowed plots than in continuously cropped plots. The limited soil C decline when fallows were alternated with crops appears to be the consequence of no-tillage period rather than the effect of the highest C inputs to the soil.
Economic trade-offs of biomass use in crop-livestock systems: Exploring more sustainable options in semi-arid Zimbabwe
Homann Kee, S. ; Valbuena Vargas, D.F. ; Masikati, P. ; Descheemaeker, K.K.E. ; Nyamangara, J. ; Claessens, L.F.G. ; Erenstein, O. ; Rooyen, A.F. van; Nkomboni, D. - \ 2015
Agricultural Systems 134 (2015). - ISSN 0308-521X - p. 48 - 60.
conservation agriculture - smallholder farmers - intensification - productivity - challenges - strategies - countries - benefits - tropics - africa
In complex mixed crop-livestock systems with limited resources and biomass scarcity, crop residues play an important but increasingly contested role. This paper focuses on farming systems in the semi-arid areas of Zimbabwe, where biomass production is limited and farmers integrate crop and livestock activities. Conservation Agriculture (CA) is promoted to intensify crop production, emphasizing the retention of surface mulch with crop residues (CR). This paper quantifies the associated potential economic tradeoffs and profitability of using residues for soil amendment or as livestock feed, and explores alternative biomass production options. We draw on household surveys, stakeholder feedback, crop, livestock and economic modeling tools. We use the Trade-Off Analysis Model for Multi Dimensional Impact Assessment (TOA-MD) to compare different CR use scenarios at community level and for different farm types: particularly the current base system (cattle grazing of maize residues) and sustainable intensification alternatives based on a CA option (mulching using maize residues ± inorganic fertilizer) and a maize– mucuna (Mucuna pruriens) rotation. Our results indicate that a maize–mucuna rotation can reduce trade-offs between CR uses for feed and mulch, providing locally available organic soil enhancement, supplementary feed and a potential source of income. Conservation Agriculture without fertilizer application and at non-subsidized fertilizer prices is not financially viable; whereas with subsidized fertilizer it can benefit half the farm population. The poverty effects of all considered alternative biomass options are however limited; they do not raise income sufficiently to lift farmers out of poverty. Further research is needed to establish the competitiveness of alternative biomass enhancing technologies and the socio-economic processes that can facilitate sustainable intensification of mixed crop-livestock systems, particularly in semi-arid environments.
Rassenproef zwarte bessen 2011-2014
Heijerman-Peppelman, G. ; Dam, M.F.N. van - \ 2015
Randwijk : Praktijkonderzoek Plant en Omgeving, Bloembollen, Boomkwekerij & Fruit - 19
tuinbouw - fruitteelt - zwarte bessen - rassenproeven - classificatie van rassen - gewaskwaliteit - rassen (planten) - productiviteit - gewasbescherming - horticulture - fruit growing - black currants - variety trials - variety classification - crop quality - varieties - productivity - plant protection
Vanaf 2011 heeft het Praktijkonderzoek Plant & Omgeving (PPO) sector Fruit te Randwijk het rassenonderzoek met zwarte bessen gedurende vier jaren voortgezet. Het doel is (nieuwe) rassen te zoeken en te toetsen onder Nederlandse (Zeeuwse) teeltomstandigheden, die een verbetering kunnen zijn van de huidige rassen voor wat betreft de productiviteit, de beskwaliteit en de gevoeligheid voor ziekten en plagen. Dit rapport is het eindverslag van het project dat eind 2014 is afgelopen.
Hyperdominance in Amazonian forest carbon cycling
Fauset, S. ; Arets, E.J.M.M. ; Steege, H. ter; Pena Claros, M. ; Poorter, L. ; Levis, C. ; Toledo, M. - \ 2015
Nature Communications 6 (2015). - ISSN 2041-1723
tropical forests - rain-forest - experimental drought - species composition - economics spectrum - biomass - trees - allometry - productivity - mortality
While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few ‘hyperdominant’ species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only ˜1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region.
Loss of Plant Species Diversity Reduces Soil Erosion Resistance
Berendse, F. ; Ruijven, J. van; Jongejans, E. ; Keesstra, S.D. - \ 2015
Ecosystems 18 (2015)5. - ISSN 1432-9840 - p. 881 - 888.
biodiversity loss - productivity - ecology - stability - future - impact
In many estuarine areas around the world, the safety of human societies depends on the functioning of embankments (dikes) that provide protection against river floods and storm tides. Vegetation on land-side slopes protects these embankments from erosion by heavy rains or overtopping waves. We carried out a field experiment to investigate the effect of plant species diversity on soil loss through erosion on a simulated dike. The experiment included four diversity treatments (1, 2, 4, and 8 species). In the third year of the experiment, we measured net annual soil loss by measuring erosion losses every 2 weeks. We show that loss of plant species diversity reduces erosion resistance on these slopes: net annual soil loss increased twofold when diversity declines fourfold. The different plant species had strongly diverging effects on soil erosion, both in the single-species and in the multi-species plots. Analysis of the dynamics of the individual species revealed that the main mechanism explaining the strong effects of plant species diversity on soil erosion is the compensation or insurance effect, that is, the capacity of diverse communities to supply species to take over the functions of species that went extinct as a consequence of fluctuating environmental conditions. We conclude that the protection and restoration of diverse plant communities on embankments and other vegetated slopes are essential to minimize soil erosion, and can contribute to greater safety in the most densely populated areas of the world. Key words: plant species diversity; soil erosion; plant competition; insurance effect; compensation effect.
The contribution of phenotypic plasticity to complementary light capture in plant mixtures
Zhu, J. ; Werf, W. van der; Anten, N.P.R. ; Vos, J. ; Evers, J.B. - \ 2015
New Phytologist 207 (2015)4. - ISSN 0028-646X - p. 1213 - 1222.
functional diversity - current knowledge - biodiversity - productivity - photosynthesis - competition - model - communities - variability - environment
Interspecific differences in functional traits are a key factor for explaining the positive diversity– productivity relationship in plant communities. However, the role of intraspecific variation attributable to phenotypic plasticity in diversity–productivity relationships has largely been overlooked. By taking a wheat (Triticum aestivum)–maize (Zea mays) intercrop as an elementary example of mixed vegetation, we show that plasticity in plant traits is an important factor contributing to complementary light capture in species mixtures. We conceptually separated net biodiversity effect into the effect attributable to interspecific trait differences and species distribution (community structure effect), and the effect attributable to phenotypic plasticity. Using a novel plant architectural modelling approach, whole vegetation light capture was simulated for scenarios with and without plasticity based on empirical plant trait data. Light capture was 23% higher in the intercrop with plasticity than the expected value from monocultures, of which 36% was attributable to community structure and 64% was attributable to plasticity. For wheat, plasticity in tillering was the main reason for increased light capture, whereas for intercropped maize, plasticity induced a major reduction in light capture. The results illustrate the potential of plasticity for enhancing resource acquisition in mixed stands, and indicate the importance of plasticity in the performance of species-diverse plant communities.
Trade-offs around the use of biomass for livestock feed and soil cover in dairy farms in the Alaotra lake region of Madagascar. Special Issue: Biomass use trade-offs in cereal cropping systems: Lessons and implications from the developing world
Naudin, K. ; Bruelle, G. ; Salgado, P. ; Penot, E. ; Lubbers, M.T.M.H. ; Ridder, N. de; Giller, K.E. - \ 2015
Agricultural Systems 134 (2015). - ISSN 0308-521X - p. 36 - 47.
cropping systems - conservation agriculture - physical-properties - zero-tillage - south-asia - residue - africa - maize - rice - productivity
Conservation agriculture (CA) is promoted as a promising technology to stabilize or improve crop yields in Africa and Madagascar. However, small-scale farmers face difficulties to retain soil cover, mainly because of competing uses for the biomass produced, especially to feed cattle. To explore the relation between dairy production and CA we developed an optimisation model at farm level. Our aim was to explore trade-offs between CA practices and the size of dairy cow herds. Our model includes three main components: the farm, the crops and the cattle herd. The optimisation was made on the total net income for three years. Biomass produced by cropping activities can either serve as mulch or to feed cows. We applied a constraint on the minimum soil cover % to keep at the end of each year for CA fields: from 30% to 95%. We simulated two scenarios of milk market: a small milk market with low forage price and an open milk market scenario with higher price of forage. Three prototypes of farms were simulated with different proportion and size of four kinds of field. These three prototypes were: medium-sized farm with hillsides dominating, medium-sized farm with paddy fields dominating and small-sized farm with hillsides. Changing the degree of soil cover to be retained on CA plots did not significantly modify the total net farm income. It was more strongly influenced by the characteristics of the milk market. In case of a limited milk market it was not profitable to have more than seven cows because the expenses were not compensated by animal production. When setting minimum soil cover to 30% then all of the simulated results include biomass coming from CA cropping system even with 12 cows/farm. Conversely when setting this constraint to 95%, above 6/7 cows/farm forage come only from conventional fields. In all of the situations simulated even with 6 cows, with the current and twice the price for forage, it was possible to keep at least 50% of soil cover on 30–60% of the total farm area. CA was not feasible for farms with no irrigated paddy fields or when forage fetched a high price regardless of the constraint for % of soil cover to be kept on CA fields. Overall, CA systems can be beneficial for dairy cow farmers due to the forage produced, although the milk market and thus the value of biomass for forage, has a strong influence on CA practice at field level.
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