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The hydraulic efficiency-safety trade-off differs between lianas and trees
Sande, Masha T. van der; Poorter, Lourens ; Schnitzer, Stefan A. ; Engelbrecht, Bettina M.J. ; Markesteijn, Lars - \ 2019
Ecology 100 (2019)5. - ISSN 0012-9658
Hydraulic traits are important for woody plant functioning and distribution. Associations among hydraulic traits, other leaf and stem traits, and species’ performance are relatively well understood for trees, but remain poorly studied for lianas. We evaluated the coordination among hydraulic efficiency (i.e. maximum hydraulic conductivity), hydraulic safety (i.e. cavitation resistance), a suite of 8 morphological and physiological traits, and species’ abundances for saplings of 24 liana species and 27 tree species in wet tropical forests in Panama. Trees showed a strong trade‐off between hydraulic efficiency and hydraulic safety, whereas efficiency and safety were decoupled in lianas. Hydraulic efficiency was strongly and similarly correlated with acquisitive traits for lianas and trees (e.g. positively with gas exchange rates and negatively with wood density). Hydraulic safety, however, showed no correlations with other traits in lianas, but with several in trees (e.g. positively with leaf dry matter content and wood density and negatively with gas exchange rates), indicating that in lianas hydraulic efficiency is an anchor trait because it is correlated with many other traits, while in trees both efficiency and safety are anchor traits. Traits related to shade‐tolerance (e.g. low specific leaf area and high wood density) were associated with high local tree sapling abundance, but not with liana abundance. Our results suggest that different, yet unknown mechanisms determine hydraulic safety and local‐scale abundance for lianas compared to trees. For trees, the trade‐off between efficiency and safety will provide less possibilities for ecological strategies. For lianas, however, the uncoupling of efficiency and safety could allow them to have high hydraulic efficiency, and hence high growth rates, without compromising resistance to cavitation under drought, thus allowing them to thrive and outperform trees under drier conditions.
Data from: The hydraulic efficiency–safety trade-off differs between lianas and trees
Sande, M.T. van der; Poorter, L. ; Schnitzer, S.A. ; Engelbrecht, B.M.J. ; Markesteijn, L. - \ 2019
drought tolerance - functional traits - hydraulic conductivity - hydraulic architecture - plant-water relations - lianas - Panama - P50 - specia abundance - tropical forest
Hydraulic traits are important for woody plant functioning and distribution. Associations among hydraulic traits, other leaf and stem traits, and species’ performance are relatively well understood for trees, but remain poorly studied for lianas. We evaluated the coordination among hydraulic efficiency (i.e. maximum hydraulic conductivity), hydraulic safety (i.e. cavitation resistance), a suite of 8 morphological and physiological traits, and species’ abundances for saplings of 24 liana species and 27 tree species in wet tropical forests in Panama.
BAAD: a Biomass And Allometry Database for woody plants
Falster, D.S. ; Markesteijn, L. ; Poorter, L. ; Sterck, F.J. ; Anten, N.P.R. - \ 2015
Ecology 96 (2015)5. - ISSN 0012-9658 - p. 1445 - 1445.
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. Read More: http://www.esajournals.org/doi/10.1890/14-1889.1
Sapling performance along resource gradients drives tree species distributions within and across tropical forests
Sterck, F.J. ; Markesteijn, L. ; Toledo, M. ; Schieving, F. ; Poorter, L. - \ 2014
Ecology 95 (2014)9. - ISSN 0012-9658 - p. 2514 - 2525.
dry forest - shade-tolerance - functional traits - distribution patterns - light requirements - global convergence - community ecology - xylem cavitation - woody-plants - life-history
Niche differentiation is a major hypothesized determinant of species distributions, but its practical importance is heavily debated and its underlying mechanisms are poorly understood. Trait-based approaches have been used to infer niche differentiation and predict species distributions. For understanding underlying mechanisms, individual traits should be scaled up to whole-plant performance, which has rarely been done. We measured seven key traits that are important for carbon and water balance for 37 tropical tree species. We used a process-based plant physiological model to simulate the carbon budget of saplings along gradients of light and water availability, and quantified the performance of the species in terms of their light compensation points (a proxy for shade tolerance), water compensation points (proxy for drought tolerance), and maximum carbon gain rates (proxy for potential growth rate). We linked species performances to their observed distributions (the realized niches) at two spatial scales in Bolivian lowland forests: along a canopy openness gradient at local scale (~1 km2) and along a rainfall gradient (1100–2200 mm/yr) at regional (~1000 km) scale. We show that the water compensation point was the best predictor of species distributions along water and light resource gradients within and across tropical forests. A sensitivity analysis suggests that the stomatal regulation of minimum leaf water potentials, rather than stem hydraulic traits (sapwood area and specific conductivity), contributed to the species differences in the water compensation point of saplings. The light compensation point and maximum carbon gain, both driven by leaf area index and leaf nitrogen concentration, also contributed to differential species distributions at the local scale, but not or only marginally at the regional scale. Trait-and-physiology-based simulations of whole-plant performance thus help to evaluate the possible roles of individual traits in physiological processes underlying species performance along environmental gradients. The development of such whole-plant concepts will improve our ability to understand responses of plant communities to shifts in resource availability and stress under global change.
Leaf vein length per unit area is not intrinsically dependent on image magnification: avoiding measurement artifacts for accuracy and precision.
Sack, L. ; Caringella, M. ; Scoffoni, C. ; Rawls, M. ; Markesteijn, L. ; Poorter, L. - \ 2014
Plant Physiology 166 (2014)2. - ISSN 0032-0889 - p. 829 - 838.
Leaf vein length per unit leaf area (VLA; also known as vein density) is an important determinant of water and sugar transport, photosynthetic function, and biomechanical support. A range of software methods are in use to visualize and measure vein systems in cleared leaf images; typically, users locate veins by digital tracing, but recent articles introduced software by which users can locate veins using thresholding (i.e. based on the contrasting of veins in the image). Based on the use of this method, a recent study argued against the existence of a fixed VLA value for a given leaf, proposing instead that VLA increases with the magnification of the image due to intrinsic properties of the vein system, and recommended that future measurements use a common, low image magnification for measurements. We tested these claims with new measurements using the software LEAFGUI in comparison with digital tracing using ImageJ software. We found that the apparent increase of VLA with magnification was an artifact of (1) using low-quality and low-magnification images and (2) errors in the algorithms of LEAFGUI. Given the use of images of sufficient magnification and quality, and analysis with error-free software, the VLA can be measured precisely and accurately. These findings point to important principles for improving the quantity and quality of important information gathered from leaf vein systems.
Are lianas more drought-tolerant than trees? A test for the role of hydraulic architecture and other stem and leaf traits
Sande, M.T. van der; Poorter, L. ; Schnitzer, S.A. ; Markesteijn, L. - \ 2013
Oecologia 172 (2013)4. - ISSN 0029-8549 - p. 961 - 972.
dry forest canopy - tropical forest - xylem cavitation - functional traits - lowland forest - woody-plants - trade-offs - growth - vulnerability - strategies
Lianas are an important component of Neotropical forests, where evidence suggests that they are increasing in abundance and biomass. Lianas are especially abundant in seasonally dry tropical forests, and as such it has been hypothesized that they are better adapted to drought, or that they are at an advantage under the higher light conditions in these forests. However, the physiological and morphological characteristics that allow lianas to capitalize more on seasonal forest conditions compared to trees are poorly understood. Here, we evaluate how saplings of 21 tree and liana species from a seasonal tropical forest in Panama differ in cavitation resistance (P50) and maximum hydraulic conductivity (Kh), and how saplings of 24 tree and liana species differ in four photosynthetic leaf traits (e.g., maximum assimilation and stomatal conductance) and six morphological leaf and stem traits (e.g., wood density, maximum vessel length, and specific leaf area). At the sapling stage, lianas had a lower cavitation resistance than trees, implying lower drought tolerance, and they tended to have a higher potential hydraulic conductivity. In contrast to studies focusing on adult trees and lianas, we found no clear differences in morphological and photosynthetic traits between the life forms. Possibly, lianas and trees are functionally different at later ontogenetic stages, with lianas having deeper root systems than trees, or experience their main growth advantage during wet periods, when they are less vulnerable to cavitation and can achieve high conductivity. This study shows, however, that the hydraulic characteristics and functional traits that we examined do not explain differences in liana and tree distributions in seasonal forests
Functional traits determine trade-offs and niches in a tropical forest community
Sterck, F.J. ; Markesteijn, L. ; Schieving, F. ; Poorter, L. - \ 2011
Proceedings of the National Academy of Sciences of the United States of America 108 (2011)51. - ISSN 0027-8424 - p. 20627 - 20632.
rain-forest - dry forest - habitat associations - species coexistence - plant-communities - amazonian forest - shade tolerance - neutral theory - leaf - light
question in community ecology. Whereas neutral theory assumes that species are adapted to common field conditions and coexist by chance, niche theory predicts that species are functionally different and coexist because they are specialized for different niches. We integrated biophysical principles into a mathematical plant model to determine whether and how functional plant traits and trade-offs may cause functional divergence and niche separation of tree species. We used this model to compare the carbon budget of saplings across 13 co-occurring dry-forest tree species along gradients of light and water availability. We found that species ranged in strategy, from acquisitive species with high carbon budgets at highest resource levels to more conservative species with high tolerances for both shade and drought. The crown leaf area index and nitrogen mass per leaf area drove the functional divergence along the simulated light gradient, which was consistent with observed species distributions along light gradients in the forest. Stomatal coordination to avoid low water potentials or hydraulic failure caused functional divergence along the simulated water gradient, but was not correlated to observed species distributions along the water gradient in the forest. The trait-based biophysical model thus explains how functional traits cause functional divergence across species and whether such divergence contributes to niche separation along resource gradients.
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.
Global patterns of leaf mechanical properties
Onoda, Y. ; Westoby, M. ; Adler, N.E. ; Choong, A.M.L. ; Clissold, F.J. ; Cornelissen, J.H.C. ; Diaz, S. ; Dominy, N.J. ; Elgart, A. ; Markesteijn, L. ; Poorter, L. ; Kitajima, K. - \ 2011
Ecology Letters 14 (2011)3. - ISSN 1461-023X - p. 301 - 312.
fracture-toughness - life-span - latitudinal variation - economics spectrum - leaves - plants - traits - shade - photosynthesis - biomechanics
Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500-800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughness per density was associated with long leaf lifespan especially in forest understory. Seldom appreciated in the past, toughness per density is a key factor in leaf mechanical resistance, which itself influences plant-animal interactions and ecosystem functions across the globe
Ecological differentiation in xylem cavitation resistance is associated with stem and leaf structural traits
Markesteijn, L. ; Poorter, L. ; Paz, H. ; Sack, L. ; Bongers, F. - \ 2011
Plant, Cell & Environment 34 (2011)1. - ISSN 0140-7791 - p. 137 - 148.
tropical dry forest - soil-nutrient gradients - life-history variation - hydraulic traits - woody-plants - shade-tolerance - water-stress - photosynthetic traits - drought performance - chaparral shrubs
Cavitation resistance is a critical determinant of drought tolerance in tropical tree species, but little is known of its association with life history strategies, particularly for seasonal dry forests, a system critically driven by variation in water availability. We analysed vulnerability curves for saplings of 13 tropical dry forest tree species differing in life history and leaf phenology. We examined how vulnerability to cavitation (P50) related to dry season leaf water potentials and stem and leaf traits. P50-values ranged from -0.8 to -6.2 MPa, with pioneers on average 38% more vulnerable to cavitation than shade-tolerants. Vulnerability to cavitation was related to structural traits conferring tissue stress vulnerability, being negatively correlated with wood density, and surprisingly maximum vessel length. Vulnerability to cavitation was negatively related to the Huber-value and leaf dry matter content, and positively with leaf size. It was not related to SLA. We found a strong trade-off between cavitation resistance and hydraulic efficiency. Most species in the field were operating at leaf water potentials well above their P50, but pioneers and deciduous species had smaller hydraulic safety margins than shade-tolerants and evergreens. A trade-off between hydraulic safety and efficiency underlies ecological differentiation across these tropical dry forest tree species
Juniperus procera (Cupressaceae) in Afromontane Forests in Ethiopia: From Tree Growth and Population Dynamics to Sustainable Forest Use
Sterck, F.J. ; Couralet, C. ; Nangendo, G. ; Wassie Eshete, Alemayehu ; Sahle, Y. ; Sass-Klaassen, U. ; Markesteijn, L. ; Bekele, T. ; Bongers, F. - \ 2010
In: Degraded Forests in Eastern Africa: management and resoration / Bongers, F, Tennigkeit, T, London : The Earthscan Forest Library - ISBN 9781844077670 - p. 291 - 303.
Seasonal variation in soil and plant water potentials in a Bolivian tropical moist and dry forest
Markesteijn, L. ; Iraipi, J. ; Bongers, F. ; Poorter, L. - \ 2010
Journal of Tropical Ecology 26 (2010). - ISSN 0266-4674 - p. 497 - 508.
tree species distributions - lowland rain-forest - silvicultural treatments - distribution patterns - topographic position - habitat associations - xylem cavitation - woody-plants - growth-rates - drought
We determined seasonal variation in soil matric potentials (¿soil) along a topographical gradient and with soil depth in a Bolivian tropical dry (1160 mm y-1 rain) and moist forest (1580 mm y-1). In each forest we analysed the effect of drought on predawn leaf water potentials (¿pd) and drought response (midday leaf water potential at a standardized ¿pd of -0.98 MPa; ¿md) of saplings of three tree species, varying in shade-tolerance and leaf phenology. ¿soil changed during the dry season and most extreme in the dry forest. Crests were drier than slopes and valleys. Dry-forest top soil was drier than deep soil in the dry season, the inverse was found in the wet season. In the moist forest the drought-deciduous species, Sweetia fruticosa, occupied dry sites. In the dry forest the short-lived pioneer, Solanum riparium, occupied wet sites and the shade-tolerant species, Acosmium cardenasii drier sites. Moist-forest species had similar drought response. The dry-forest pioneer showed a larger drought response than the other two species. Heterogeneity in soil water availability and interspecific differences in moisture requirements and drought response suggest great potential for niche differentiation. Species may coexist at different topographical locations, by extracting water from different soil layers and/or by doing so at different moments in time
Drought tolerance of tropical tree species : functional traits, trade-offs and species distribution
Markesteijn, L. - \ 2010
Wageningen University. Promotor(en): Frans Bongers, co-promotor(en): Lourens Poorter. - [S.l. : S.n. - ISBN 9789085855347 - 189
bomen - droogteresistentie - tropische bossen - soortendiversiteit - soorten - waterbeschikbaarheid - bosecologie - bodemwater - regen - trees - drought resistance - tropical forests - species diversity - species - water availability - forest ecology - soil water - rain
Bolivia, drought tolerance, shade tolerance, functional traits, trade-offs, ecophysiology, species distribution
Tropical forests occur under rainfall regimes that vary greatly in the rainfall pattern and frequency and intensity of drought. Consequently water availability is one of the most important environmental factors influencing community structure, species composition, and plant functioning across large-scale rainfall gradients and small-scale topographic gradients within forests. The relative success of tree species to establish along these gradients of water availability and their success in dealing with future changes in water availability will depend on how they are adapted to tolerate drought.
In this dissertation I applied a multi-species, multi-trait approach in field studies and a controlled experiment to give detailed information on the mechanisms of drought-tolerance of a large set of tropical dry and moist forest tree species. The following research questions were addressed; 1) How do dry and moist forests differ in soil water availability? 2) How are dry and moist forest species adapted to drought and what different drought-strategies can be distinguished? 3) Is there a trade-off between drought- and shade-tolerance? and 4) How do drought- and shade-tolerance determine local and regional tree species distribution?
Dry season soil water availability is clearly lower in the dry forest than in the moist forest. Especially in the dry forest there is a lot of temporal and spatial variation in soil water availability. Temporal variation depends on the annual cycle of precipitation. Spatial heterogeneity is two-dimensional; 1) water availability varies with topography of the landscape; elevated crests are dry in comparison to slopes and low valleys, and 2) soil water is vertically redistributed with soil depth; in the dry season more water is available in deep soil layers while in the wet season most water is found in the top soil. When combining temporal and spatial dimensions, a complex mosaic of soil water availability emerges that shows great potential for niche partitioning among species at various levels, if species are adapted to exploit this variation.
Seedlings of dry forest species have evolved mechanisms that enhance their access to water in deep soil layers, increase drought-induced cavitation resistance and increase water conservation. Seedlings of moist forest species show adaptations that improve their light foraging capacity and increase nutrient and water acquisition. Associations among functional traits show that there are three major drought strategies among tropical tree species, 1) physiological drought-tolerance, 2) drought-intolerance and 3) drought-avoidance.
No conclusive evidence for a direct trade-off between species drought- and shade-tolerance was found, and the association between drought- and shade-tolerance is mainly subject to the scale of observation. On small scales, within the dry forest, drought- and shade-tolerance are positively related, as species hydraulic properties are integrally linked with niche differentiation for both light and water. This implies that in their distribution, light-demanding species will be restricted to habitats that combine high light and high moisture availability, while shade-tolerant species will be the better competitors in drier and shadier habitats. On larger scales a strong trade-off between above and belowground biomass allocation was found, which should in theory have resulted in a trade-off between drought- and shade-tolerance, but in practice it did not. Plants can compensate for a low root mass fraction by producing relatively cheap roots with a large specific root length and compensate for a low leaf mass fraction by making cheap leaves with a large specific leaf area. Drought- and shade-tolerance thus depend largely on different suites of morphological traits and can be uncoupled.
Species distribution along the rainfall gradient was not directly explained by species drought survival, mainly because deciduousness was the most important factor contributing to survival and deciduous species are well represented in both dry and moist forests. The occurrence of evergreen species at the dry end of the rainfall gradient largely depends on drought related traits as a high wood density and a large biomass allocation to deep roots. Species occurrence at the moist end of the rainfall gradient was mainly determined by traits related to light-demand, as a high leaf mass fraction and long, branched root systems. In conclusion, I propose that at small scales, within forests, species distribution along water gradients depends on the interaction between species drought- and shade-tolerance while at larger scales distribution of (evergreen) species is mainly determined by their drought-tolerance.
Seedling root morphology and biomass allocation of 62 tropical tree species in relation to drought- and shade-tolerance
Markesteijn, L. ; Poorter, L. - \ 2009
Journal of Ecology 97 (2009)2. - ISSN 0022-0477 - p. 311 - 325.
dry forest - rain-forest - wood density - moist forest - growth-rate - physiological processes - niche differentiation - plant-communities - climate-change - water-stress
Water availability is the main determinant of species' distribution in lowland tropical forests. Species' occurrence along water availability gradients depends on their ability to tolerate drought. To identify species' traits underlying drought-tolerance we excavated first year seedlings of 62 dry and moist forest tree species at the onset of the dry season. We evaluate how morphological seedling traits differ between forests, and whether functional groups of species can be identified based on trait relations. We also compare seedling traits along independent axes of drought and shade-tolerance to assess a hypothesized trade-off. Seedlings of dry forest species improve water foraging capacity in deep soil layers by an increased below-ground biomass allocation and by having deep roots. They minimize the risk of cavitation by making dense stems, and reduce transpiration by producing less leaf tissue. Moist forest seedlings have large leaf areas and a greater above-ground biomass, to maximize light interception, and long, cheap, branched root systems, to increase water and nutrient capture. Associations among seedling traits reveal three major drought strategies: (i) evergreen drought-tolerant species have high biomass investment in enduring organs, minimize cavitation and minimize transpiration to persist under dry conditions; (ii) drought-avoiding species maximize resource capture during a limited growing season and then avoid stress with a deciduous leaf habit in the dry season; (iii) drought-intolerant species maximize both below- and above-ground resource capture to increase competitiveness for light, but are consequently precluded from dry habitats. We found no direct trade-off between drought- and shade-tolerance, because they depend largely on different morphological adaptations. Drought-tolerance is supported by a high biomass investment to the root system, whereas shade-tolerance is mainly promoted by a low growth rate and low SLA. Synthesis. We conclude that there are three general adaptation strategies of drought-tolerance, which seemingly hold true across biomes and for different life forms. Drought- and shade-tolerance are largely independent from one another, suggesting a high potential for niche differentiation, as species' specialization can occur at different combinations of water and light availability
|La disponibilidad hídrica estacional y topográfica en un bosque seco y húmedo tropical y la variación en la morfología de plántulas arbóreas.
Markesteijn, L. ; Poorter, L. ; Yanguas-Fernandez, E. - \ 2008
Revista Boliviana de Ecología y Conservación Ambiental 24 (2008). - ISSN 1997-1192 - p. 27 - 42.
Seedling traits determine drought tolerance of tropical tree species
Poorter, L. ; Markesteijn, L. - \ 2008
Biotropica 40 (2008)3. - ISSN 0006-3606 - p. 321 - 331.
phylogenetically independent contrasts - woody-plants - moist forest - dry forest - water-stress - responses - patterns - growth - shade - root
Water availability is the most important factor determining tree species distribution in the tropics, but the underlying mechanisms are still not clear. In this study, we compared functional traits of 38 tropical tree species from dry and moist forest, and quantified their ability to survive drought in a dry-down experiment in which wilting and survival were monitored. We evaluated how seedling traits affect drought survival, and how drought survival determines species distribution along the rainfall gradient. Dry forest species tended to have compound leaves, high stem dry matter content (stem dry mass/fresh mass), and low leaf area ratio, suggesting that reduction of transpiration and avoidance of xylem cavitation are important for their success. Three functional groups were identified based on the seedling traits: (1) drought avoiders with a deciduous leaf habitat and taproots; (2) drought resisters with tough tissues (i.e., a high dry matter content); and (3) light-demanding moist forest species with a large belowground foraging capacity. Dry forest species had a longer drought survival time (62 d) than moist forest species (25 d). Deciduousness explained 69 percent of interspecific variation in drought survival. Among evergreen species, stem density explained 20 percent of the drought survival. Drought survival was not related to species distribution along the rainfall gradient, because it was mainly determined by deciduousness, and species with deciduous seedlings are found in both dry and moist forests. Among evergreen species, drought survival explained 28 percent of the variation in species position along the rainfall gradient. This suggests that, apart from drought tolerance, other factors such as history, dispersal limitation, shade tolerance, and fire shape species distribution patterns along the rainfall gradient.
Light-dependent leaf trait variation in 43 tropical dry forest tree species
Markesteijn, L. ; Poorter, L. ; Bongers, F.J.J.M. - \ 2007
American Journal of Botany 94 (2007)4. - ISSN 0002-9122 - p. 515 - 525.
rain-forest - relative importance - alocasia-macrorrhiza - trade-offs - life-span - shade - acclimation - irradiance - anatomy - plants
Our understanding of leaf acclimation in relation to irradiance of fully grown or juvenile trees is mainly based on research involving tropical wet forest species. We studied sun¿shade plasticity of 24 leaf traits of 43 tree species in a Bolivian dry deciduous forest. Sampling was confined to small trees. For each species, leaves were taken from five of the most and five of the least illuminated crowns. Trees were selected based on the percentage of the hemisphere uncovered by other crowns. We examined leaf trait variation and the relation between trait plasticity and light demand, maximum adult stature, and ntogenetic changes in crown exposure of the species. Leaf trait variation was mainly related to differences among species and to a minor extent to differences in light availability. Traits related to the palisade layer, thickness of the outer cell wall, and Narea and Parea had the greatest plasticity, suggesting their importance for leaf function in different light environments. Short-lived pioneers had the highest trait plasticity. Overall plasticity was modest and rarely associated with juvenile light requirements, adult stature, or ontogenetic changes in crown exposure. Dry forest tree species had a lower light-related plasticity than wet forest species, probably because wet forests cast deeper shade. In dry forests light availability may be less limiting, and low water availability may constrain leaf trait plasticity in response to irradiance. Key words: Bolivia; crown exposure; leaf traits; light acclimation; plasticity; tropical dry deciduous forest.