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.

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    On the importance of root traits in seedlings of tropical tree species
    Boonman, Coline C.F. ; Langevelde, Frank van; Oliveras, Imma ; Couédon, Jeremy ; Luijken, Natascha ; Martini, David ; Veenendaal, Elmar M. - \ 2019
    New Phytologist 227 (2019)1. - ISSN 0028-646X - p. 156 - 167.
    biomass allocation - root morphology - rooting depth - savanna - specific root length - tropical forest - vertical root distribution

    Plant biomass allocation may be optimized to acquire and conserve resources. How trade-offs in the allocation of tropical tree seedlings depend on different stressors remains poorly understood. Here we test whether above- and below-ground traits of tropical tree seedlings could explain observed occurrence along gradients of resources (light, water) and defoliation (fire, herbivory). We grew 24 tree species occurring in five African vegetation types, varying from dry savanna to moist forest, in a glasshouse for 6 months, and measured traits associated with biomass allocation. Classification based on above-ground traits resulted in clusters representing savanna and forest species, with low and high shoot investment, respectively. Classification based on root traits resulted in four clusters representing dry savanna, humid savanna, dry forest and moist forest, characterized by a deep mean rooting depth, root starch investment, high specific root length in deeper soil layers, and high specific root length in the top soil layer, respectively. In conclusion, tree seedlings in this study show root trait syndromes, which vary along gradients of resources and defoliation: seedlings from dry areas invest in deep roots, seedlings from shaded environments optimize shoot investment, and seedlings experiencing frequent defoliation store resources in the roots.

    BAAD: a Biomass And Allometry Database for woody plants
    Falster, D.S. ; Markesteijn, L. ; Poorter, Lourens ; Sterck, Frank ; Anten, Niels - \ 2016
    Macquarie University
    allometric equations - biomass allocation - global carbon cycle - biomass partitioning - plant allometry - plant traits
    Understanding how plants are constructed—i.e., how key size dimensions and the amount of mass invested in different tissues varies among individuals—is essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The BAAD contains 259 634 measurements collected in 176 different studies, from 21 084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01–100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric equations (except in very large trees where biomass was estimated from detailed sub-sampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem cross-section including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area, wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the world's vegetation.
    Sapwood allocation in tropical trees: a test of hypotheses
    Schippers, P. ; Vlam, M. ; Zuidema, P.A. ; Sterck, F.J. - \ 2015
    Functional Plant Biology 42 (2015)7. - ISSN 1445-4408 - p. 697 - 709.
    temperate forest trees - global vegetation models - carbon allocation - shade-tolerance - rain-forest - biomass allocation - seasonal dynamics - use efficiency - climate-change - growth habits
    Carbon allocation to sapwood in tropical canopy trees is a key process determining forest carbon sequestration, and is at the heart of tree growth and dynamic global vegetation models (DGVM). Several allocation hypotheses exist including those applying assumptions on fixed allocation, pipe model, and hierarchical allocation between plant organs. We use a tree growth model (IBTREE) to evaluate these hypotheses by comparing simulated sapwood growth with 30 year tree ring records of the tropical long-lived tree Toona ciliata M. Roem. in Thailand. Simulated annual variation in wood production varied among hypotheses. Observed and simulated growth patterns matched most closely (r2 = 0.70) when hierarchical allocation was implemented, with low priority for sapwood. This allocation method showed realistic results with respect to reserve dynamics, partitioning and productivity and was the only one able to capture the large annual variation in tree ring width. Consequently, this method might also explain the large temporal variation in diameter growth and the occurrence of missing rings often encountered in other tropical tree species. Overall, our results show that sapwood growth is highly sensitive to allocation principles, and that allocation assumptions may greatly influence estimated carbon sequestration of tropical forests under climatic change.
    Enemies lost: parallel evolution in structural defense and tolerance to herbivory of invasive Jacobaea vulgaris
    Lin, T. ; Doorduin, L. ; Temme, A. ; Pons, T.L. ; Lamers, G.E.M. ; Anten, N.P.R. ; Vrieling, K. - \ 2015
    Biological Invasions 17 (2015)8. - ISSN 1387-3547 - p. 2339 - 2355.
    nitrogen-use efficiency - increased competitive ability - leaf construction cost - pyrrolizidine alkaloids - senecio-jacobaea - united-states - generalist herbivores - biomass allocation - biological-control - sapium-sebiferum
    According to the Shifting Defense Hypothesis, invasive plants should trade-off their costly quantitative defense to cheaper qualitative defense and growth due to the lack of natural specialist enemies and the presence of generalist enemies in the introduced areas. Several studies showed that plant genotypes from the invasive areas had a better qualitative defense than genotypes from the native area but only a few studies have focused on the quantitative defenses and tolerance ability. We compared structural defenses, tolerance and growth between invasive and native plant populations from different continents using the model plant Jacobaea vulgaris. We examined several microscopical structure traits, toughness, amount of cell wall proteins, growth and root-shoot ratio, which is a proxy for tolerance. The results show that invasive Jacobaea vulgaris have thinner leaves, lower leaf mass area, lower leaf cell wall protein contents and a lower root-shoot ratio than native genotypes. It indicates that invasive genotypes have poorer structural defense and tolerance to herbivory but potentially higher growth compared to native genotypes. These findings are in line with the Evolution of Increased Competitive Ability hypothesis and Shifting Defense Hypothesis. We also show that the invasiveness of this species in three geographically separated regions is consistently associated with the loss of parts of its quantitative defense and tolerance ability. The simultaneous change in quantitative defense and tolerance of the same magnitude and direction in the three nvasive regions can be explained by parallel evolution. We argue that such parallel evolution might be attributed to the absence of natural enemies rather than adaptation to local abiotic factors, since climate conditions among these three regions were different. Understanding such evolutionary changes helps to understand why plant species become invasive and might be important for biological control.
    European Mixed Forests: Definition and research perspectives
    Bravo-Oviedo, A. ; Pretzsch, H. ; Ammer, C. ; Andenmatten, E. ; Barbati, A. ; Barreiro, S. ; Brang, P. ; Bravo, F. ; Coll, L. ; Corona, P. ; Ouden, J. den - \ 2014
    Forest Systems 23 (2014)3. - ISSN 2171-5068 - p. 518 - 533.
    stand-density index - fagus-sylvatica l. - species stands - norway spruce - picea-abies - pure stands - biomass allocation - climate-change - biodiversity - productivity
    Aim of study: We aim at (i) developing a reference definition of mixed forests in order to harmonize comparative research in mixed forests and (ii) briefly review the research perspectives in mixed forests. Area of study: The definition is developed in Europe but can be tested worldwide. Material and methods: Review of existent definitions of mixed forests based and literature review encompassing dynamics, management and economic valuation of mixed forests. Main results: A mixed forest is defined as a forest unit, excluding linear formations, where at least two tree species coexist at any developmental stage, sharing common resources (light, water, and/or soil nutrients). The presence of each of the component species is normally quantified as a proportion of the number of stems or of basal area, although volume, biomass or canopy cover as well as proportions by occupied stand area may be used for specific objectives. A variety of structures and patterns of mixtures can occur, and the interactions between the component species and their relative proportions may change over time. The research perspectives identified are (i) species interactions and responses to hazards, (ii) the concept of maximum density in mixed forests, (iii) conversion of monocultures to mixed-species forest and (iv) economic valuation of ecosystem services provided by mixed forests. Research highlights: The definition is considered a high-level one which encompasses previous attempts to define mixed forests. Current fields of research indicate that gradient studies, experimental design approaches, and model simulations are key topics providing new research opportunities.
    East African highland bananas (Musa spp. AAA-EA) 'worry' more about potassium deficiency than drought stress
    Taulya, G. - \ 2013
    Field Crops Research 151 (2013). - ISSN 0378-4290 - p. 45 - 55.
    foliar nutrient status - biomass allocation - osmotic adjustment - plant-growth - root ratio - soil-water - nitrogen - shoot - fertilizer - weevil
    Drought stress, potassium (K) and nitrogen (N) deficiencies are major constraints to rain-fed East African highland banana (EAHB) production in Uganda. It was hypothesised that the reduction in fresh bunch mass and increase in dry matter (DM) allocation to corms with drought stress, K and N deficiency is additive. Individual plant measurements at harvest from two field trials in central and south western Uganda were analyzed to evaluate effects of cumulative rainfall (CRF) received 365 days from sucker emergence, mineral K and N inputs on EAHB bunch yields. Dry matter content in aerial shoot (leaves and pseudostems) relative to that in the subterranean corm was also analyzed to evaluate DM allocation plasticity due to drought stress, K and N deficiency. This was verified with allometric analysis using pre-harvest stage plants from farms of known K and N nutritional status and plants from a screen house drought stress pot trial in Uganda. Dry matter production and yields were mainly driven by K interacting with CRF. Within 12 months, K input (250-600 kg K ha(-1) yr(-1)) increased bunch yield from 8 to 15 Mg ha(-1) yr(-1) irrespective of whether dry (CRF <1100 mm) or wet (CRF >= 1100 mm) conditions prevailed, possibly due to K-mediated osmotic adjustment under dry conditions. Without K input, wet conditions increased bunch yield from 6 to 8 Mg ha(-1) yr(-1) while dry conditions decreased it from 6 to 4 Mg ha(-1) yr(-1) within 12 months. Total DM and its distribution between the biomass structures followed similar trends. Nitrogen input (150-400 kg N ha(-1) yr(-1)) neither affected bunch yield nor DM allocation at harvest stage. At pre-harvest stage, reduction in DM allocation to the corm per unit increase in total DM was 14-22% significantly lower with N and/or K deficiency compared with that under sufficient K and N. Drought stress per se had no effect on DM allocation but enhanced DM allocation shifts due to K deficiency. Drought-stressed EAHB thus increase DM allocation to subterranean structures only if K-deficient, unlike responses reported for other plant species. Potassium nutrition is perhaps a more viable entry point for mitigation of drought stress in EAHB cropping systems than irrigation but this requires further agronomic and economic evaluation. It may be important to account for carbon allocated to osmotic adjustment for realistic simulation of water- and K-limited growth in EAHB. (c) 2013 Elsevier B.V. All rights reserved.
    Molecular mechanisms of plant competition: neighbour detection and response strategies
    Pierik, R. ; Mommer, L. ; Voesenek, L.A.C.J. - \ 2013
    Functional Ecology 27 (2013)4. - ISSN 0269-8463 - p. 841 - 853.
    shade-avoidance responses - ethylene-insensitive tobacco - root-system architecture - blue-light - arabidopsis-thaliana - phytochrome b - auxin biosynthesis - biomass allocation - cryptochrome 1 - wild tobacco
    Plant competition determines the diversity and species abundance of natural communities as well as potential yields in agricultural systems. Understanding the mechanisms of plant competition is instrumental to understanding plant performance in true vegetations. In this review, we will address various components of competition between plant individuals with a specific focus on molecular aspects. As plant–plant interactions during competition are multiple and complex, we will focus here on a restricted set of examples of plant traits that are thought to enhance their performance during competition. To respond to competition by neighbours, plants first need to detect these competitors in a reliable way. We discuss the various ways of molecular detection of competition through light-quality signals, nutrient levels, soluble root exudates and volatile organic compounds emitted by neighbouring plants. Once perceived, these signals are translated into responses such as shade avoidance, root foraging and allelopathy. We integrate the various molecular patterns of signal detection and subsequent plant responses, both above- and below-ground and including their interaction. We outline research strategies towards creating a general, mechanistic understanding of how plants increase their performance during competition.
    Interactive effects of mechanical stress, sand burial and defoliation on growth and mechanical properties in Cynanchum komarovii
    Xu, L. ; Yu, F.H. ; Werger, M. ; Dong, M. ; Anten, N.P.R. - \ 2013
    Plant Biology 15 (2013)1. - ISSN 1435-8603 - p. 126 - 134.
    biomass allocation - resource-allocation - plant-response - lateral shade - gas-exchange - wind speeds - stem - thigmomorphogenesis - stimulation - tolerance
    In drylands, wind, sand burial and grazing are three important factors affecting growth and mechanical properties of plants, but their interactive effects have not yet been investigated. Plants of the semi-shrub Cynanchum komarovii, common in semi-arid parts of NE Asia, were subjected to brushing, burial and defoliation. We measured biomass allocation and relative increment rates of dry mass (RGRm), height (RGRh) and basal diameter (RGRd). We also measured the stem mechanical properties, Young’s modulus (E), second moment of area (I), flexural stiffness (EI) and breaking stress (sb), and scaled these traits to the whole-plant level to determine the maximum lateral force (Flateral) and the buckling safety factor (BSF). Brushing increased RGRm; neither burial nor defoliation independently affected RGRm, but together they reduced it. Among buried plants, brushing positively affected stem rigidity and strength through increasing RGRd, E, I and EI, and at whole plant level this resulted in a larger BSF and Flateral. However, among unburied plants this pattern was not observed. Our results thus show that effects of mechanical stress and grazing on plants can be strongly modified by burial, and these interactions should be taken into account when considering adaptive significance of plant mechanical traits in drylands.
    Non-linear effects of drought under shade: reconciling physiological and ecological models in plant communities
    Holmgren, M. ; Gomez-Aparicio, L. ; Quero, J.L. ; Valladares, F. - \ 2012
    Oecologia 169 (2012)2. - ISSN 0029-8549 - p. 293 - 305.
    stress-gradient hypothesis - oak quercus-suber - seedling establishment - positive interactions - biomass allocation - semiarid woodland - woody seedlings - water relations - summer drought - abiotic stress
    The combined effects of shade and drought on plant performance and the implications for species interactions are highly debated in plant ecology. Empirical evidence for positive and negative effects of shade on the performance of plants under dry conditions supports two contrasting theoretical models about the role of shade under dry conditions: the trade-off and the facilitation hypotheses. We performed a meta-analysis of field and greenhouse studies evaluating the effects of drought at two or more irradiance levels on nine response variables describing plant physiological condition, growth, and survival. We explored differences in plant response across plant functional types, ecosystem types and methodological approaches. The data were best fit using quadratic models indicating a humped-back shape response to drought along an irradiance gradient for survival, whole plant biomass, maximum photosynthetic capacity, stomatal conductance and maximal photochemical efficiency. Drought effects were ameliorated at intermediate irradiance, becoming more severe at higher or lower light levels. This general pattern was maintained when controlling for potential variations in the strength of the drought treatment among light levels. Our quantitative meta-analysis indicates that dense shade ameliorates drought especially among drought-intolerant and shade-tolerant species. Wet tropical species showed larger negative effects of drought with increasing irradiance than semiarid and cold temperate species. Non-linear responses to irradiance were stronger under field conditions than under controlled greenhouse conditions. Non-linear responses to drought along the irradiance gradient reconciliate opposing views in plant ecology, indicating that facilitation is more likely within certain range of environmental conditions, fading under deep shade, especially for drought-tolerant species.
    The relative importance of above- versus belowground competition for tree growth and survival during early succession of a tropical moist forest
    Breugel, M. van; Breugel, P. van; Jansen, P.A. ; Martinez-Ramos, M. ; Bongers, F. - \ 2012
    Plant Ecology 213 (2012)1. - ISSN 1385-0237 - p. 25 - 34.
    plant-populations - rain-forests - asymmetric competition - secondary succession - local interference - biomass allocation - light interception - size asymmetry - life-history - dry forest
    Competition between neighboring plants plays a major role in the population dynamics of tree species in the early phases of humid tropical forest succession. We evaluated the relative importance of above- versus below-ground competition during the first years of old-field succession on soil with low fertility in Southern Mexico, using the premise that competition for light is size-asymmetric, unlike competition for nutrients. Plant growth is thus expected to be disproportionally impeded by larger neighbors. We studied how growth and survival of 3.5–5.5 m tall saplings of Cecropia peltata and Trichospermum mexicanum, two pioneer species that dominate the secondary forests in the study region, varied with the abundance and size of neighboring trees in 1–2 year old secondary vegetation. We found that local neighborhood basal area varied 10-fold (3 to 30 cm2 m-2) and explained most of the variation in diameter and height growth of the target saplings. Most growth variables were strongly affected by the neighbors bigger than the focal trees with no significant additive effect of the smaller neighbors, indicating asymmetric competition. Smaller neighbors did have a small but significant additive effect on the diameter growth of Cecropia saplings and stem slenderness of Trichospermum saplings. We conclude that competition for light was more important than belowground competition in this initial phase of moist tropical forest successional, despite the low soil fertility
    Quantifying the effects of nitrogen on fruit growth and yield of cucumber crop in greenhouses
    Dai, J. ; Liu, S. ; Zhang, W. ; Xu, R. ; Luo, W. ; Yin, X. ; Han, L. ; Chen, S. - \ 2011
    Scientia Horticulturae 130 (2011)3. - ISSN 0304-4238 - p. 551 - 561.
    dynamic simulation-model - capsicum-annuum-l - dry-matter - biomass allocation - prediction - wheat - water - temperature - lettuce - quality
    Nitrogen supply can improve crop growth and yield. An over-use of nitrogen fertilizer in greenhouse crop productions, however, causes many environmental problems. The aim of this study was to quantify the effects of nitrogen on fruit growth and yield so as to facilitate the optimization of nitrogen management for cucumber (Cucumis sativus) crop in greenhouses. Four experiments with different levels of nitrogen treatments, substrates and planting dates on cucumber (cv. Deltastar) were conducted in greenhouses located at Shanghai during 2005 and 2007. Using data of one experiment, seasonal time courses of leaf nitrogen content (NL), leaf area per plant (LA), and the number of fruits growing per plant (nFG), as well as time course of the length of individual fruit growing on the plant (LF(i)) under different levels of nitrogen supply conditions were, respectively, determined as functions of a photo-thermal index (PTI). The impact of NL on LA was determined by curve fitting to the experimental data. The source/sink ratio (LA/nFG), an indicative of the source size per fruit, was then derived from the seasonal time courses of LA and nFG. The impact of NL on LF(i) was indirectly quantified by the relationship between source/sink ratio (LA/nFG) and the elongation rate of individual fruit (RFL(i)). Both the harvest date and fresh weight (WF(i)) of individual fruit growing at different node, and number of harvested fruits (nFH) were then calculated as functions of the fruit length. These quantitative relationships were assembled to form a model for predicting the effects of nitrogen on fruit growth and yield (fruit fresh weight per plant). Independent data from other experiments were used to validate the model. Our model gives satisfactory predictions of cucumber fruit growth and yield under different levels of nitrogen supply and growing season conditions. The coefficient of determination (r2) and the relative root mean squared error (rRMSE) between the predicted and measured values are, respectively, 0.92 and 0.22 (r2, rRMSE) for leaf area per plant, 0.90 and 0.24 for the number of fruits growing on the plant, 0.91 and 0.22, 0.90 and 0.23, and 0.92 and 0.21, respectively, for the length, harvest date and fresh weight of individual fruit growing on the plant, 0.94 and 0.20 for yield. The model may be used for the optimization of nitrogen management for cucumber production in greenhouses. Further model calibration and test would be needed when applying this model to a wider range of conditions
    Hydraulics and life history of tropical dry forest tree species: coordination of species' drought and shade tolerance
    Markesteijn, L. ; Poorter, L. ; Bongers, F. ; Paz, H. ; Sack, L. - \ 2011
    New Phytologist 191 (2011)2. - ISSN 0028-646X - p. 480 - 495.
    woody-plants - cavitation resistance - xylem cavitation - desiccation-tolerance - leaf traits - trade-off - photosynthetic traits - regeneration niche - biomass allocation - water potentials
    Plant hydraulic architecture has been studied extensively, yet we know little about how hydraulic properties relate to species’ life history strategies, such as drought and shade tolerance. The prevailing theories seem contradictory. We measured the sapwood (Ks) and leaf (Kl) hydraulic conductivities of 40 coexisting tree species in a Bolivian dry forest, and examined associations with functional stem and leaf traits and indices of species’ drought (dry-season leaf water potential) and shade (juvenile crown exposure) tolerance. Hydraulic properties varied across species and between life-history groups (pioneers vs shade-tolerant, and deciduous vs evergreen species). In addition to the expected negative correlation of Kl with drought tolerance, we found a strong, negative correlation between Kl and species’ shade tolerance. Across species, Ks and Kl were negatively correlated with wood density and positively with maximum vessel length. Consequently, drought and shade tolerance scaled similarly with hydraulic properties, wood density and leaf dry matter content. We found that deciduous species also had traits conferring efficient water transport relative to evergreen species. Hydraulic properties varied across species, corresponding to the classical trade-off between hydraulic efficiency and safety, which for these dry forest trees resulted in coordinated drought and shade tolerance across species rather than the frequently hypothesized trade-off.
    Plant functional traits and the distribution of West African rain forest trees along the rainfall gradient
    Maharjan, S.K. ; Poorter, L. ; Holmgren, M. ; Bongers, F. ; Wieringa, J.J. ; Hawthorne, W.D. - \ 2011
    Biotropica 43 (2011)5. - ISSN 0006-3606 - p. 552 - 561.
    life-history variation - relative growth-rate - tropical forest - species distributions - shade-tolerance - biomass allocation - soil fertility - canopy trees - woody-plants - seed size
    Plant morphological and physiological traits affect the way plants tolerate environmental stresses and therefore play an important role in shaping species distribution patterns in relation to environmental gradients. Despite our growing knowledge on the role of functional traits in structuring plant communities, few studies have tested their importance at large scales in the wet tropics. Here, we describe the distribution patterns of the most important West African rain forest timber species along the regional rainfall gradient and relate them to their functional traits. We found that the distribution patterns of 25 out of the 31 studied species (80%) were significantly related to mean annual rainfall. Shade tolerance and drought resistance were identified as the main strategy axes of variation. Wood density and leaf deciduousness emerged as the best predictor traits of species position along the rainfall gradient, explaining respectively 32 and 15 percent of the variation. Species traits tended to show stronger relationships with estimated optimum annual rainfall for each species than to the extreme rainfall conditions where they occur. The significant role of rainfall in shaping timber species distribution and the strong relationships between species traits and rainfall indicate that changes in climate, especially declining rainfall, could have strong effects on species composition and abundance in these tropical forests
    Effects of soil compaction and light on growth of Quercus pyrenaica Willd. (Fagaceae) seedlings
    Bejarano, M.D. ; Villar, R. ; Murillo, A.M. ; Quero Pérez, J.L. - \ 2010
    Soil & Tillage Research 110 (2010)1. - ISSN 0167-1987 - p. 108 - 114.
    biomass allocation - mediterranean oak - seed-mass - niche differentiation - natural regeneration - woody seedlings - root morphology - plant-growth - trade-offs - drought
    Soil compaction and light availability influence plant growth via different mechanisms. In general, soil compaction has a direct effect on roots, whereas light affects leaves and stems. Although plants in nature are exposed to variable levels of soil compaction and light, no study on the potential mutual interactions of these limiting factors in woody plants has to the authors' knowledge been reported to date. The aim of this work was therefore to elucidate the effects of soil compaction and light availability on growth and biomass allocation in the deciduous oak Quercus pyrenaica. To this end, a study was conducted at two light levels (viz. 3% and 100% of incident light, designated as low-light and high-light, respectively) under a wide range of soil compaction (0.02-3 MPa as penetration resistance) in a greenhouse. Total biomass was found to be positively affected by both light and soil compaction. There was marginally significant interaction between the effects of the two factors on total biomass, which was positively affected by soil compaction only under high-light conditions. Soil compaction had a strong, negative effect on the length of the main root; thus, at maximum soil compaction, such a length was roughly one-half that observed at lower compaction levels. Also, the specific root length of main root (root length to root mass ratio) was reduced by roughly one-half in highly compacted soils. These results suggest that an unfavourable combination of soil compaction and light availability may have severely adverse effects on woody plant performance in drought periods since plants with short roots can hardly access water at deep soil levels. The strength of this effect may be modulated by light availability.
    Effects of competition on root-shoot allocation in Plantago lanceolata L.: adaptive plasticity or ontogenetic drift?
    Berendse, F. ; Möller, F. - \ 2009
    Plant Ecology 201 (2009)2. - ISSN 1385-0237 - p. 567 - 573.
    below-ground competition - biomass allocation - nutrients - intensity - grassland - gradient
    We investigated how shoot and root allocation in plants responds to increasing levels of competitive stress at different levels of soil fertility. In addition, we analyzed whether different responses were due to adaptive plasticity or should be attributed to ontogenetic drift. Plantago lanceolata plants were grown during 18 weeks at five plant densities and four nutrient supply levels in pots in the greenhouse. Thereafter root and shoot biomass was measured. There were clear negative effects of increasing plant densities on plant weights revealing strong intraspecific competition. At the lower N-treatments, the proportional allocation to root mass increased with increasing competitive stress, indicating the important role of belowground competition. At the higher N-supply rate, the relationship between competitive stress and shoot to root ratio was neutral. These responses could not be attributed to ontogenetic drift, but could only be explained by assuming adaptive plasticity. It was concluded that at lower N-supplies belowground competition dominates and leads to increased allocation to roots, while at the higher N-supply competition for soil resources and light had balanced impacts on shoot and root allocation. An alternative hypothesis explaining the observed pattern is that light competition has far less pronounced impacts on root¿shoot allocation than nutrient deprival.
    Above- and below-ground competition in high and low irradiance: tree seedling responses to a competing liana Byttneria grandifolia
    Chen, J.Y. ; Bongers, F. ; Cao, K.F. ; Cai, Z.Q. - \ 2008
    Journal of Tropical Ecology 24 (2008)5. - ISSN 0266-4674 - p. 517 - 524.
    tropical wet forest - rain-forest - biomass allocation - liquidambar-styraciflua - plant competition - root biomass - canopy gaps - growth - regeneration - architecture
    Abstract: In tropical forests, trees compete not only with other trees, but also with lianas, which may limit tree growth and regeneration. Liana effects may depend on the availability of above- and below-ground resources and differ between tree species. We conducted a shade house experiment to test the effect of light (4% and 35% full sun, using neutral-density screen) on the competitive interactions between seedlings of one liana (Byttneria grandifolia) and three tree species (two shade-tolerant trees, Litsea dilleniifolia and Pometia tomentosa, and one light-demanding tree, Bauhinia variegata) and to evaluate the contribution of both above- and below-ground competition. Trees were grown in four competition treatments with the liana: no competition, root competition, shoot competition and root and shoot competition. Light strongly affected leaf photosynthetic capacity (light-saturated photosynthetic rate, Pn), growth and most morphological traits of the tree species. Liana-induced competition resulted in reduced Pn, total leaf areas and relative growth rates (RGR) of the three tree species. The relative importance of above- and below-ground competition differed between the two light levels. In low light, RGR of the three tree species was reduced more strongly by shoot competition (23.1¿28.7% reduction) than by root competition (5.3¿26.4%). In high light, in contrast, root competition rather than shoot competition greatly reduced RGR. Liana competition affected most morphological traits (except for specific leaf area and leaf area ratio of Litsea and Pometia), and differentially altered patterns of biomass allocation in the tree seedlings. These findings suggest that competition from liana seedlings can greatly suppress growth in tree seedlings of both light-demanding and shade-tolerant species and those effects differ with competition type (below- and above-ground) and with irradiance
    Relating leaf photosynthetic rate to whole-plant growth: drought and shade effects on seedlings of four Quercus species
    Quero Perez, J.L. ; Villar, R. ; Marañón, T. ; Zamora, R. ; Vega, D. ; Sack, L. - \ 2008
    Functional Plant Biology 35 (2008)8. - ISSN 1445-4408 - p. 725 - 737.
    net assimilation rate - light-dependent changes - biomass allocation - seed-mass - rain-forest - woody seedlings - tree seedlings - gas-exchange - trade-offs - niche differentiation
    Understanding the impacts of combined resource supplies on seedlings is critical to enable prediction of establishment growth, and forest dynamics. We investigated the effects of irradiance and water treatments on absolute growth, and relative growth rate (RGR) and its components, for seedlings of four Quercus species differing in leaf habit and with a wide variation in seed mass. Plants were grown for 6.5 months at three levels of irradiance (100, 27, and 3% daylight), and treated during the last 2.5 months with two watering treatments (frequent watering v. suspended watering). Both shade and drought reduced seedling growth rates, with a significant interaction: under full irradiance the drought treatment had a stronger impact on RGR and final biomass than under deep shade. For three species, seed mass was positively related to absolute growth, with stronger correlations at lower irradiance. The evergreen species grew faster than the deciduous species, though leaf habit accounted for a minor part of the interspecific variation in absolute growth. Seedling biomass was determined positively either byRGRor seed mass;RGRwas positively linked with net assimilation rate (NAR) and leaf mass fraction (LMF), and seed mass was negatively linked with RGR and LMF, but positively linked with NAR. Seedling RGR was not correlated with light-saturated net photosynthetic rate, but was strongly correlated with the net carbon balance estimated, from photosynthetic light-response curves, considering daily variation in irradiance. These findings suggest an approach to applying short-term physiological measurements to predict the RGR and absolute growth rate of seedlings in a wide range of combinations of irradiance and water supplies. Additional keywords: biomass allocation, carbon balance, growth analysis, leaf habit, Mediterranean oak, relative growth rate, seed mass, specific leaf area.
    Seedling growth strategies in Bauhinia species: comparing lianas and trees
    Cai, Z.Q. ; Poorter, L. ; Cao, K.F. ; Bongers, F.J.J.M. - \ 2007
    Annals of Botany 100 (2007)4. - ISSN 0305-7364 - p. 831 - 838.
    life-history diversity - rain-forest - tropical forest - allocation patterns - relative importance - biomass allocation - leaf-area - plant - light - traits
    Background and Aims: Lianas are expected to differ from trees in their growth strategies. As a result these two groups of woody species will have different spatial distributions: lianas are more common in high light environments. This study determines the differences in growth patterns, biomass allocation and leaf traits in five closely related liana and tree species of the genus Bauhinia. Methods: Seedlings of two light-demanding lianas (Bauhinia tenuiflora and B. claviflora), one shade-tolerant liana (B. aurea), and two light-demanding trees (B. purpurea and B. monandra) were grown in a shadehouse at 25 % of full sunlight. A range of physiological, morphological and biomass parameters at the leaf and whole plant level were compared among these five species. Key Results: The two light-demanding liana species had higher relative growth rate (RGR), allocated more biomass to leaf production [higher leaf mass fraction (LMF) and higher leaf area ratio (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. The two light-demanding lianas had lower photosynthetic rates per unit area (Aarea) and similar photosynthetic rates per unit mass (Amass) than the trees. Across species, RGR was positively related to SLA, but not to LAR and Aarea. Conclusions: It is concluded that the faster growth of light-demanding lianas compared with 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 slow-growth strategy, compared with the light-demanding species
    Ethylene sensitivity affects changes in growth patterns, but not stem properties, in response to mechanical stress in tobacco
    Anten, N.P.R. ; Casado-Garcia, R. ; Pierik, R. ; Pons, T.L. - \ 2006
    Physiologia Plantarum 128 (2006)2. - ISSN 0031-9317 - p. 274 - 282.
    bryonia-dioica - biomass allocation - lateral shade - thigmomorphogenesis - arabidopsis - plants - stimulation - elongation - expression - roots
    Plant responses to mechanical stress (e.g. wind or touch) involve a suite of physiologic and developmental changes, collectively known as thigmomorphogenesis, including reductions in height increment, Young's modulus of stems, shoot growth, and seed production, and increased stem girth and root growth. A role of the phytohormone ethylene in thigmomorphogenesis has been proposed but the extent of this involvement is not entirely clear. To address this issue, wild-type (WT) and ethylene-insensitive transgenic (Tetr) tobacco (Nicotianum tabacum) plants were subjected to three levels of mechanical stress: 0, 25 and 75 daily flexures. Flexed plants produced shorter, thicker stems with a lower Young's modulus than non-flexed ones, and these responses occurred independently of genotype. This suggests that ethylene does not play a role in thigmomorphogenesis-related changes in stem characteristics in tobacco. The effect of mechanical stress on dry mass increment (growth), on the other hand, differed between the genotypes: in the WT plants, shoot growth but not root growth was reduced under mechanical stress, resulting in reduced total growth and increased root mass fractions. In the Tetr plants, neither shoot nor root growth were affected. This suggests that ethylene is involved in the inhibition of tobacco shoot growth under mechanical stress
    Mechanical branch constraints contribute to life-history variation across tree species in a Bolivian forest.
    Sterck, F.J. ; Gelder, H.A. van; Poorter, L. - \ 2006
    Journal of Ecology 94 (2006)6. - ISSN 0022-0477 - p. 1192 - 1200.
    rain-forest - crown architecture - biomass allocation - understory plants - tropical trees - support costs - light capture - leaf traits - trade-offs - growth
    1 Trade-offs among plant traits may contribute to specialization for different environments and coexistence of plant species. This may be the first study that shows how trade-offs among branch traits contribute to variation in crown size, light requirements and maximum height across multiple sympatric tree species in a tropical rain forest. 2 Ten saplings were selected for each of 30 tree species in a Bolivian rain forest. Sapling height and crown dimensions were measured and branch and stem samples were harvested. Fresh density, dry density, modulus of rupture, centre of mass, biomass and diameters were determined for those samples. For each species, cantilever theory predicted the mass needed to produce a stable 1-m long horizontal branch. 3 Generally, shade-tolerant species had denser and stronger branches, and produced a stable horizontal branch at lower resource costs. These species had branches with a higher resistance against mechanical failure, and a wide crown that favours effective light acquisition. Less shade-tolerant species had low density and weak branches, short branches, high resource costs per unit branch length, and low resource costs per unit stem length. These traits seem advantageous under conditions of prolonged exposure to direct sunlight, where such species grow rapidly to reproductive size, while mechanical risks are low and light levels are favourable. 4 Branch (wood and bark) traits are good predictors for performance differences across tree species in heterogeneous forest light environments. Physical trade-offs among branch traits contribute to the specialization of tree species for different light habitats and to tree species coexistence in tropical rain forests, even within classical functional groups such as pioneers and shade tolerants
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