Browsing by Autor "Lars Markesteijn"

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Ecological differentiation in xylem cavitation resistance is associated with stem and leaf structural traits
(Wiley, 2010) Lars Markesteijn; Lourens Poorter; Horacio Paz; Lawren Sack; Frans Bongers
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.
Functional traits determine trade-offs and niches in a tropical forest community
(National Academy of Sciences, 2011) Frank J. Sterck; Lars Markesteijn; F. Schieving; Lourens Poorter
How numerous tree species can coexist in diverse forest communities is a key 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
(Wiley, 2011) Lars Markesteijn; Lourens Poorter; Frans Bongers; Horacio Paz; Lawren Sack
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 (K(s) ) and leaf (K(l) ) 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 K(l) with drought tolerance, we found a strong, negative correlation between K(l) and species' shade tolerance. Across species, K(s) and K(l) 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.
La disponibilidad hídrica estacional y topográfica en un bosque seco y húmedo tropical y la variación en la morfología de plántulas arbóreas.
(2008) Lars Markesteijn; Lourens Poorter; Estrella Yanguas-Fernández
Seasonal and topographical water availability in a tropical dry and moist forest and variation in tree seedling morphology La composicion y diversidad de especies arboreas en los bosques tropicales varia considerablemente a lo largo de gradientes de disponibilidad de agua. La presencia de especies depende en gran parte por su habilidad para soportar la sequia. En este estudio evaluamos cambios estacionales en la disponibilidad hidrica del suelo en un bosque seco y humedo tropical. Analizamos como varia la morfologia de las plantulas arboreas entre bosques y como estas caracteristicas determinan la supervivencia de las especies a la sequia. A lo largo del ano, el bosque seco tiene menor humedad y menores potenciales hidricos del suelo que el bosque humedo. Dentro de los bosques, la disponibilidad hidrica varia tambien con la topografia y en general crece desde las cimas a los valles. Las especies del bosque seco, estan bien adaptadas para asegurar la entrada y/o conservacion del agua, mediante mas biomasa invertida en las raices, enraizamientos profundos y una transpiracion reducida. Las especies del bosque humedo, estan mas adaptadas para incrementar la intercepcion de luz, mediante areas foliares grandes, una gran inversion de biomasa en el tejido foliar y altas area foliares especificas. Ademas aumentan la adquisicion de nutrientes y agua por debajo del suelo, gracias a la formacion de grandes sistemas radicales con elevada longitud especifica de la raiz. Las especies del bosque seco pueden sobrevivir graves sequias, al menos dos veces mas largas que las especies del bosque humedo. Tener una elevada area foliar especifica, tipicamente relacionada con las especies caducifolias que evitan a la sequia con la caida de su hoja, demostro ser el mejor indicador de la supervivencia de las plantulas. Palabras claves: Sequia, morfologia de plantulas, supervivencia a la sequia, bosques tropicales, Bolivia ABSTRACT Species composition and species diversity vary considerably along water availability gradients. The presence of a species depends to great extent on its ability to tolerate drought. In this study we evaluate seasonal changes in soil water availability in a tropical dry and moist forest. We analyse how the seedling morphology of tree species varies between forests and how these characteristics determine species drought survival. Throughout the year the dry forest has lower soil water contents and lower soil water potentials then the moist forest. Within forests soil water availability varies with topography and generally increases from hilltops to valley bottoms. The variation in water availability between forests is reflected in clear differences in seedling morphology. Dry forest species are well adapted to secure water capture and/or water conservation, with more biomass invested in the roots, deeper rooting and reduced transpiration. Moist forest species are better adapted to increase light interception, with large leaf areas, more biomass invested to the leaf tissue and higher specific leaf areas. Furthermore they increase water and nutrient acquisition below ground through the formation of large root systems with a high specific root length. Dry forest species can survive acute drought at least twice as long as moist forest species. A high specific leaf area, which is typical for deciduous species that avoid drought by shedding their leaves, turned out to be the best predictor of seedling drought survival. Keywords: Drought, seedling morphology, droughtsurvival, tropical forests, Bolivia
Light‐dependent leaf trait variation in 43 tropical dry forest tree species
(Wiley, 2007) Lars Markesteijn; Lourens Poorter; Frans Bongers
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 ontogenetic 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 N(area) and P(area) 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.
Sapling performance along resource gradients drives tree species distributions within and across tropical forests
(Wiley, 2014) Frank J. Sterck; Lars Markesteijn; Marisol Toledo; F. Schieving; Lourens Poorter
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 km 2 ) 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.
Seasonal variation in soil and plant water potentials in a Bolivian tropical moist and dry forest
(Cambridge University Press, 2010) Lars Markesteijn; José Iraipi; Frans Bongers; Lourens Poorter
Abstract: We determined seasonal variation in soil matric potentials (ψ 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 (ψ pd ) and drought response (midday leaf water potential at a standardized ψ pd of −0.98 MPa; ψ md ) of saplings of three tree species, varying in shade-tolerance and leaf phenology. ψ 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.
Seedling root morphology and biomass allocation of 62 tropical tree species in relation to drought‐ and shade‐tolerance
(Wiley, 2009) Lars Markesteijn; Lourens Poorter
Summary 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.
Seedling Traits Determine Drought Tolerance of Tropical Tree Species
(Wiley, 2008) Lourens Poorter; Lars Markesteijn
ABSTRACT 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.