Limited intraspecific variation in drought resistance along a pronounced tropical rainfall gradient.

Assessing within-species variation in response to drought is crucial for predicting species' responses to climate change and informing restoration and conservation efforts, yet experimental data are lacking for the vast majority of tropical tree species. We assessed intraspecific variation in response to water availability across a strong rainfall gradient for 16 tropical tree species using reciprocal transplant and common garden field experiments, along with measurements of gene flow and key functional traits linked to drought resistance. Although drought resistance varies widely among species in these forests, we found little evidence for within-species variation in drought resistance.

Effects of leaf silicon on drought performance of tropical tree seedlings.

Elevated leaf silicon (Si) concentrations improve drought resistance in cultivated plants, suggesting Si might also improve drought performance of wild species. Tropical tree species, for instance, take up substantial amounts of Si, and leaf Si varies markedly at local and regional scales, suggesting consequences for seedling drought resistance. Yet, whether elevated leaf Si improves seedling drought performance in tropical forests is unknown.

Silicon-based anti-herbivore defense in tropical tree seedlings.

Silicon-based defenses deter insect herbivores in many cultivated and wild grass species. Furthermore, in some of these species, silicon (Si) uptake and defense can be induced by herbivory. Tropical trees also take up Si and leaf Si concentrations vary greatly across and within species.

Nutrient effects on drought responses vary across common temperate grassland species.

Drought and nutrient input are two main global change drivers that threaten ecosystem function and services. Resolving the interactive effects of human-induced stressors on individual species is necessary to improve our understanding of community and ecosystem responses. This study comparatively assessed how different nutrient conditions affect whole-plant drought responses across 13 common temperate grassland species.

Turgor loss point predicts survival responses to experimental and natural drought in tropical tree seedlings.

Identifying key traits that can serve as proxies for species drought resistance is crucial for predicting and mitigating the effects of climate change in diverse plant communities. Turgor loss point (π ) is a recently emerged trait that has been linked to species distributions across gradients of water availability. However, a direct relationship between π and species ability to survive drought has yet to be established for woody species.

Increased mortality of tropical tree seedlings during the extreme 2015-16 El Niño.

As extreme climate events are predicted to become more frequent because of global climate change, understanding their impacts on natural systems is crucial. Tropical forests are vulnerable to droughts associated with extreme El Niño events. However, little is known about how tropical seedling communities respond to El Niño-related droughts, even though patterns of seedling survival shape future forest structure and diversity.

Variation of foliar silicon concentrations in temperate forbs: effects of soil silicon, phylogeny and habitat.

Silicon (Si) accumulation is known to alleviate various biotic and abiotic stressors in plants with potential ecological consequences. However, for dicotyledonous plants our understanding of Si variation remains limited. We conducted a comparative experimental study to investigate (1) interspecific variation of foliar Si concentrations across 37 dicotyledonous forbs of temperate grasslands, (2) intraspecific variation in foliar Si concentration in response to soil Si availability, the influence of (3) phylogenetic relatedness, and (4) habitat association to moisture.

Rethinking the Plant Economics Spectrum for Annuals: A Multi-Species Study.

The plant economics spectrum hypothesizes a correlation among resource-use related traits along one single axis, which determines species' growth rates and their ecological filtering along resource gradients. This concept has been mostly investigated and shown in perennial species, but has rarely been tested in annual species. Annuals evade unfavorable seasons as seeds and thus may underlie different constraints, with consequences for interspecific trait-trait, trait-growth, and trait-environment relations.

Local adaptation to herbivory within tropical tree species along a rainfall gradient.

In tropical forests, insect herbivores exert significant pressure on plant populations. Adaptation to such pressure is hypothesized to be a driver of high tropical diversity, but direct evidence for local adaptation to herbivory in tropical forests is sparse. At the same time, herbivore pressure has been hypothesized to increase with rainfall in the tropics, which could lead to differences among sites in the degree of local adaptation.

Comparative drought resistance of temperate grassland species: testing performance trade-offs and the relation to distribution.

To improve projections of consequences of increasing intensity and frequency of drought events for grasslands, we need a thorough understanding of species performance responses to drought, of performance trade-offs and how drought resistance is related to species distributions. However, comparative and quantitative assessments of whole-plant drought resistance that allow to rigorously address these aspects are lacking for temperate grassland species. We conducted a common garden experiment with 40 common temperate grassland species to compare species survival and growth under intense drought and well-irrigated conditions.

Performance of tropical forest seedlings under shade and drought: an interspecific trade-off in demographic responses.

Seedlings in moist tropical forests must cope with deep shade and seasonal drought. However, the interspecific relationship between seedling performance in shade and drought remains unsettled. We quantified spatiotemporal variation in shade and drought in the seasonal moist tropical forest on Barro Colorado Island (BCI), Panama, and estimated responses of naturally regenerating seedlings as the slope of the relationship between performance and shade or drought intensity.

Dry season soil water potential maps of a 50 hectare tropical forest plot on Barro Colorado Island, Panama.

Fine scale spatial variation in soil moisture influences plant performance, species distributions and diversity. However, detailed information on local soil moisture variation is scarce, particularly in species-rich tropical forests. We measured soil water potential and soil water content in the 50-ha Forest Dynamics Plot on Barro Colorado Island (BCI), Panama, one of the best-studied tropical forests in the world.

The hydraulic efficiency-safety trade-off differs between lianas and trees.

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.

Effects of Drought, Pest Pressure and Light Availability on Seedling Establishment and Growth: Their Role for Distribution of Tree Species across a Tropical Rainfall Gradient.

Tree species distributions associated with rainfall are among the most prominent patterns in tropical forests. Understanding the mechanisms shaping these patterns is important to project impacts of global climate change on tree distributions and diversity in the tropics. Beside direct effects of water availability, additional factors co-varying with rainfall have been hypothesized to play an important role, including pest pressure and light availability.

Species distributions in response to individual soil nutrients and seasonal drought across a community of tropical trees.

Tropical forest vegetation is shaped by climate and by soil, but understanding how the distributions of individual tree species respond to specific resources has been hindered by high diversity and consequent rarity. To study species over an entire community, we surveyed trees and measured soil chemistry across climatic and geological gradients in central Panama and then used a unique hierarchical model of species occurrence as a function of rainfall and soil chemistry to circumvent analytical difficulties posed by rare species. The results are a quantitative assessment of the responses of 550 tree species to eight environmental factors, providing a measure of the importance of each factor across the entire tree community.

Resource limitation, tolerance, and the future of ecological plant classification.

Throughout the evolutionary history of plants, drought, shade, and scarcity of nutrients have structured ecosystems and communities globally. Humans have begun to drastically alter the prevalence of these environmental factors with untold consequences for plant communities and ecosystems worldwide. Given limitations in using organ-level traits to predict ecological performance of species, recent advances using tolerances of low resource availability as plant functional traits are revealing the often hidden roles these factors have in structuring communities and are becoming central to classifying plants ecologically.

Geological substrates shape tree species and trait distributions in African moist forests.

Background: Understanding the factors that shape the distribution of tropical tree species at large scales is a central issue in ecology, conservation and forest management. The aims of this study were to (i) assess the importance of environmental factors relative to historical factors for tree species distributions in the semi-evergreen forests of the northern Congo basin; and to (ii) identify potential mechanisms explaining distribution patterns through a trait-based approach.

Methodology/principal Findings: We analyzed the distribution patterns of 31 common tree species in an area of more than 700,000 km(2) spanning the borders of Cameroon, the Central African Republic, and the Republic of Congo using forest inventory data from 56,445 0.

Functional traits and the growth-mortality trade-off in tropical trees.

A trade-off between growth and mortality rates characterizes tree species in closed canopy forests. This trade-off is maintained by inherent differences among species and spatial variation in light availability caused by canopy-opening disturbances. We evaluated conditions under which the trade-off is expressed and relationships with four key functional traits for 103 tree species from Barro Colorado Island, Panama.

Seasonal and spatial variation in water availability drive habitat associations in a tropical forest.

Associations with topographic units or soil types that vary in water availability are widespread in plant communities and are one of the main structuring aspects for local species distribution patterns, yet the underlying mechanisms are poorly understood. We hypothesized that differential seedling performance across habitats, particularly during the dry season, leads to habitat associations in seasonal tropical forests. We expected this pattern to be most pronounced in particularly dry years, such as those associated with El Niño Southern Oscillation (ENSO) events.

When sex is not enough: ecological correlates of resprouting capacity in congeneric tropical forest shrubs.

In moist tropical forests resprouting may be an important component of life history, contributing to asexual reproduction through the clonal spread of individuals derived from shoot fragments. However, in contrast to other ecosystems where resprouting is common, the ecological correlates of resprouting capacity in tropical forests remain largely unexplored. In this study we characterized shade tolerance, resprouting capacity and sexual reproductive success of eight co-occurring Piper species from lowland forests of Panama.

Drought sensitivity shapes species distribution patterns in tropical forests.

Although patterns of tree species distributions along environmental gradients have been amply documented in tropical forests, mechanisms causing these patterns are seldom known. Efforts to evaluate proposed mechanisms have been hampered by a lack of comparative data on species' reactions to relevant axes of environmental variation. Here we show that differential drought sensitivity shapes plant distributions in tropical forests at both regional and local scales.

Linking physiological processes with mangrove forest structure: phosphorus deficiency limits canopy development, hydraulic conductivity and photosynthetic carbon gain in dwarf Rhizophora mangle.

Spatial gradients in mangrove tree height in barrier islands of Belize are associated with nutrient deficiency and sustained flooding in the absence of a salinity gradient. While nutrient deficiency is likely to affect many parameters, here we show that addition of phosphorus (P) to dwarf mangroves stimulated increases in diameters of xylem vessels, area of conductive xylem tissue and leaf area index (LAI) of the canopy. These changes in structure were consistent with related changes in function, as addition of P also increased hydraulic conductivity (Ks), stomatal conductance and photosynthetic assimilation rates to the same levels measured in taller trees fringing the seaward margin of the mangrove.

Differences in plant function in phosphorus- and nitrogen-limited mangrove ecosystems.

Mangrove ecosystems can be either nitrogen (N) or phosphorus (P) limited and are therefore vulnerable to nutrient pollution. Nutrient enrichment with either N or P may have differing effects on ecosystems because of underlying differences in plant physiological responses to these nutrients in either N- or P-limited settings. Using a common mangrove species, Avicennia germinans, in sites where growth was either N or P limited, we investigated differing physiological responses to N and P limitation and fertilization.

Short dry spells in the wet season increase mortality of tropical pioneer seedlings.

Variation in plant species performance in response to water availability offers a potential axis for temporal and spatial habitat partitioning and may therefore affect community composition in tropical forests. We hypothesized that short dry spells during the wet season are a significant source of mortality for the newly emerging seedlings of pioneer species that recruit in treefall gaps in tropical forests. An analysis of a 49-year rainfall record for three forests across a rainfall gradient in central Panama confirmed that dry spells of > or = 10 days during the wet season occur on average once a year in a deciduous forest, and once every other year in a semi-deciduous moist and an evergreen wet forest.