Trade-offs Between Water Transport Capacity and Drought Resistance in Neotropical Canopy Liana and Tree Species

In tropical forest canopies, it is critical for upper shoots to efficiently provide water to leaves for physiological function while safely preventing loss of hydraulic conductivity due to cavitation during periods of soil water deficit or high evaporative demand. We compared hydraulic physiology of upper canopy trees and lianas in a seasonally dry tropical forest to test whether trade-offs between safety and efficiency of water transport shape differences in hydraulic function between these two major tropical woody growth forms. We found that lianas showed greater maximum stem-specific hydraulic conductivity than trees, but lost hydraulic conductivity at less negative water potentials than trees, resulting in a negative correlation and trade-off between safety and efficiency of water transport. Lianas also exhibited greater diurnal changes in leaf water potential than trees. The magnitude of diurnal water potential change was negatively correlated with sapwood capacitance, indicating that lianas are highly reliant on conducting capability to maintain leaf water status, whereas trees relied more on stored water in stems to maintain leaf water status. Leaf nitrogen concentration was related to maximum leaf-specific hydraulic conductivity only for lianas suggesting that greater water transport capacity is more tied to leaf processes in lianas compared to trees. Our results are consistent with a trade-off between safety and efficiency of water transport and may have implications for increasing liana abundance in neotropical forests

Liana Competition with Tropical Trees Varies Seasonally but not with Tree Species Identity

Lianas in tropical forests compete intensely with trees for above‐ and belowground resources and limit tree growth and regeneration. Liana competition with adult canopy trees may be particularly strong, and, if lianas compete more intensely with some tree species than others, they may influence tree species composition. We performed the first systematic, large‐scale liana removal experiment to assess the competitive effects of lianas on multiple tropical tree species by measuring sap velocity and growth in a lowland tropical forest in Panama. Tree sap velocity increased 60% soon after liana removal compared to control trees, and tree diameter growth increased 25% after one year. Although tree species varied in their response to lianas, this variation was not significant, suggesting that lianas competed similarly with all tree species examined. The effect of lianas on tree sap velocity was particularly strong during the dry season, when soil moisture was low, suggesting that lianas compete intensely with trees for water. Under the predicted global change scenario of increased temperature and drought intensity, competition from lianas may become more prevalent in seasonal tropical forests, which, according to our data, should have a negative effect on most tropical tree species

Evaluating grazing response strategies in winter annuals : A multi-trait approach

Plants minimize fitness losses through grazing by three fundamental strategies: tolerance, avoidance and escape. Annual species have been traditionally assumed to escape grazing through their short life cycle and seed dormancy; however, their grazing response strategies remain almost unexplored. How traits and their coordination affect species' grazing responses, and whether the generalized grazing model, which posits convergent filtering by grazing and drought, is applicable to this ecologically and economically important species group thus remain unclear. We used a trait-based approach to evaluate grazing response strategies of winter annuals from the Middle East. Across 23 species, we examined the coordination of 16 traits hypothesized to be relevant for grazing responses, and linked them to species' fecundity responses, as proxy for fitness responses, to simulated grazing in controlled conditions, to species' abundance responses to grazing in the field and to species' distribution along a large-scale rainfall gradient. Winter annuals exhibited both grazing escape and to a lesser extent tolerance indicated by (a) independent coordination of escape and tolerance traits, and (b) maintenance of higher fecundity in species with more pronounced escape or tolerance traits under simulated grazing. In the natural habitat, species with a more pronounced escape but not tolerance strategy maintained higher abundance under grazing in dry habitats, indicating convergent favouring of escape by both grazing and drought. However, this finding at the local scale was not mirrored by a strategy shift along a large-scale rainfall gradient. Synthesis. The convergent favouring of escape traits by grazing and drought in annuals is consistent with the generalized grazing model. This model, which has been developed for perennials based on the avoidance strategy, can thus be extended to annuals based on escape, a finding that should facilitate projecting consequences of global change in drylands dominated by annuals. © 2021 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Societ

Evaluating grazing response strategies in winter annuals : A multi-trait approach

Plants minimize fitness losses through grazing by three fundamental strategies: tolerance, avoidance and escape. Annual species have been traditionally assumed to escape grazing through their short life cycle and seed dormancy; however, their grazing response strategies remain almost unexplored. How traits and their coordination affect species' grazing responses, and whether the generalized grazing model, which posits convergent filtering by grazing and drought, is applicable to this ecologically and economically important species group thus remain unclear. We used a trait-based approach to evaluate grazing response strategies of winter annuals from the Middle East. Across 23 species, we examined the coordination of 16 traits hypothesized to be relevant for grazing responses, and linked them to species' fecundity responses, as proxy for fitness responses, to simulated grazing in controlled conditions, to species' abundance responses to grazing in the field and to species' distribution along a large-scale rainfall gradient. Winter annuals exhibited both grazing escape and to a lesser extent tolerance indicated by (a) independent coordination of escape and tolerance traits, and (b) maintenance of higher fecundity in species with more pronounced escape or tolerance traits under simulated grazing. In the natural habitat, species with a more pronounced escape but not tolerance strategy maintained higher abundance under grazing in dry habitats, indicating convergent favouring of escape by both grazing and drought. However, this finding at the local scale was not mirrored by a strategy shift along a large-scale rainfall gradient. Synthesis. The convergent favouring of escape traits by grazing and drought in annuals is consistent with the generalized grazing model. This model, which has been developed for perennials based on the avoidance strategy, can thus be extended to annuals based on escape, a finding that should facilitate projecting consequences of global change in drylands dominated by annuals. © 2021 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Societ

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 (πtlp) is a recently emerged trait that has been linked to species distributions across gradients of water availability. However, a direct relationship between πtlp and species ability to survive drought has yet to be established for woody species. Using a manipulative field experiment to quantify species drought resistance (i.e., their survival response to drought), combined with measurements of πtlp for 16 tree species, we show a negative relationship between πtlp and seedling drought resistance. Using long-term forest plot data, we also show that πtlp predicts seedling survival responses to a severe El Niño-related drought, although additional factors are clearly also important. Our study demonstrates that species with lower πtlp exhibit higher survival under both experimental and natural drought. These results provide a missing cornerstone in the assessment of the traits underlying drought resistance in woody species and strengthen πtlp as a proxy for evaluating which species will lose or win under projections of exacerbating drought regimes.National Science Foundation DEB-1464866, DEB-1623775, DEB-184540

Influencias del paisaje, climatología y manejo agrícola sobre la biodiversidad asociada a viña: efectos sobre servicios ecosistémicos y sostenibilidad frente a cambio global (Proyecto BA C O)

Dentro de un contexto dominado por el cambio rápido y frecuente, es básico analizar sus efectos sobre la biodiversidad y los servicios ecosistémicos que ésta provee. El cultivo de la viña es uno de los sistemas agrícolas más antiguos de la región Mediterránea, con una interacción muy estrecha entre el manejo humano y el ambiente natural circundante. El proyecto BA C O pretende, desde un enfoque multidisciplinar, evaluar el papel del clima, paisaje y manejo sobre la biodiversidad y los servicios ecosistémicos asociados a viñedos. Se proponen los siguientes objetivos: i) caracterizar el paisaje, ambiente, clima y tipo de manejo de las principales explotaciones de vid; ii) evaluar la influencia del paisaje, ambiente y manejo en la biodiversidad de los viñedos y iii) estimar los servicios ecosistémicos que esta diversidad aporta. Se usarán tres escalas espaciales de resolución: a) Regional, considerando todos los viñedos y sistemas de manejo (convencional/ ecológico; variedades de uva) presentes en Andalucía; b) F inca, situadas en un gradiente altitudinal (proxi de Tª) y de paisaje, en las que se realizarán medidas de biodiversidad, servicios ecosistémicos, productividad, funcionalidad y sostenibilidad del viñedo frente a cambio global y c) Cepa, en las que se tomarán muestras de suelo, sarmientos, hojas, raíces, estado fisiológico, afectación por plagas, productividad y calidad. Los resultados esperamos que sirvan para: 1) mejorar predicciones y tomas de decisiones de gestión; 2) generar documentos de transferencia identificando las prácticas de manejo y uso agrícola más sostenibles que optimicen la conservación de los recursos naturales y los beneficios socioeconómicos y 3) el desarrollo de herramientas que permitan predecir efectos futuros derivados de cambio climático y de usos de suelo, así como su interacción y sus efectos sobre la biodiversidad, servicios ecosistémicos asociados y su capacidad de resiliencia.Dentro de un contexto dominado por el cambio rápido y frecuente, es básico analizar sus efectos sobre la biodiversidad y los servicios ecosistémicos que ésta provee. El cultivo de la viña es uno de los sistemas agrícolas más antiguos de la región Mediterránea, con una interacción muy estrecha entre el manejo humano y el ambiente natural circundante. El proyecto BA C O pretende, desde un enfoque multidisciplinar, evaluar el papel del clima, paisaje y manejo sobre la biodiversidad y los servicios ecosistémicos asociados a viñedos. Se proponen los siguientes objetivos: i) caracterizar el paisaje, ambiente, clima y tipo de manejo de las principales explotaciones de vid; ii) evaluar la influencia del paisaje, ambiente y manejo en la biodiversidad de los viñedos y iii) estimar los servicios ecosistémicos que esta diversidad aporta. Se usarán tres escalas espaciales de resolución: a) Regional, considerando todos los viñedos y sistemas de manejo (convencional/ ecológico; variedades de uva) presentes en Andalucía; b) F inca, situadas en un gradiente altitudinal (proxi de Tª) y de paisaje, en las que se realizarán medidas de biodiversidad, servicios ecosistémicos, productividad, funcionalidad y sostenibilidad del viñedo frente a cambio global y c) Cepa, en las que se tomarán muestras de suelo, sarmientos, hojas, raíces, estado fisiológico, afectación por plagas, productividad y calidad. Los resultados esperamos que sirvan para: 1) mejorar predicciones y tomas de decisiones de gestión; 2) generar documentos de transferencia identificando las prácticas de manejo y uso agrícola más sostenibles que optimicen la conservación de los recursos naturales y los beneficios socioeconómicos y 3) el desarrollo de herramientas que permitan predecir efectos futuros derivados de cambio climático y de usos de suelo, así como su interacción y sus efectos sobre la biodiversidad, servicios ecosistémicos asociados y su capacidad de resiliencia

Lianas Suppress Seedling Growth and Survival of 14 Tree Species in a Panamanian Tropical Forest

Lianas are a common plant growth form in tropical forests, where they compete intensely with trees, decreasing tree recruitment, growth, and survival. If the detrimental effects of lianas vary significantly with tree species identity, as is often assumed, then lianas may influence tree species diversity and community composition. Furthermore, recent studies have shown that liana abundance and biomass are increasing relative to trees in neotropical forests, which will likely magnify the detrimental effects of lianas and may ultimately alter tree species diversity, relative abundances, and community composition. Few studies, however, have tested the responses of multiple tree species to the presence of lianas in robust, well‐replicated experiments. We tested the hypotheses that lianas reduce tree seedling growth and survival, and that the effect of lianas varies with tree species identity. We used a large‐scale liana removal experiment in Central Panama in which we planted 14 replicate seedlings of 14 different tree species that varied in shade tolerance in each of 16 80 × 80 m plots (eight liana‐removal and eight unmanipulated controls; 3136 total seedlings). Over a nearly two‐yr period, we found that tree seedlings survived 75% more, grew 300% taller, and had twice the aboveground biomass in liana‐removal plots than seedlings in control plots, consistent with strong competition between lianas and tree seedlings. There were no significant differences in the response of tree species to liana competition (i.e., there was no species by treatment interaction), indicating that lianas had a similar negative effect on all 14 tree species. Furthermore, the effect of lianas did not vary with tree species shade tolerance classification, suggesting that the liana effect was not solely based on light. Based on these findings, recently observed increases in liana abundance in neotropical forests will substantially reduce tree regeneration, but will not significantly alter tropical tree species diversity, relative abundance, or community composition

Pervasive and strong effects of plants on soil chemistry: a meta-analysis of individual plant ‘Zinke’ effects

Plant species leave a chemical signature in the soils below them, generating fine-scale spatial variation that drives ecological processes. Since the publication of a seminal paper on plant-mediated soil heterogeneity by Paul Zinke in 1962, a robust literature has developed examining effects of individual plants on their local environments (individual plant effects). Here, we synthesize this work using meta-analysis to show that plant effects are strong and pervasive across ecosystems on six continents. Overall, soil properties beneath individual plants differ from those of neighbours by an average of 41%. Although the magnitudes of individual plant effects exhibit weak relationships with climate and latitude, they are significantly stronger in deserts and tundra than forests, and weaker in intensively managed ecosystems. The ubiquitous effects of plant individuals and species on local soil properties imply that individual plant effects have a role in plant–soil feedbacks, linking individual plants with biogeochemical processes at the ecosystem scale