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

How do Mediterranean shrub species cope with shade? Ecophysiological response to different light intensities

Under natural conditions, light exposure for Mediterranean shrubs can be highly variable, especially during cloudy days or under a canopy, and can interfere with other environmental factors such as temperature and water availability. With the aim of decoupling the effect of radiation and temperature from water availability, we conducted an experiment where two perennial and three summer semi-deciduous shrub species were subjected to different levels of irradiation. In order to follow plant responses to light exposure, we measured gas exchange, photosystem II photochemical efficiency, photosynthetic pigments and leaf mass area in spring and summer. Results showed that all study species presented a plastic response to different light conditions, and that light-related traits varied in a coordinated manner. Summer semi-deciduous species exhibited a more opportunistic response, with higher photosynthesis rates in full sun, but under shade conditions, the two strategies presented similar assimilation rates. Stomatal conductance did not show such a drastic response as photosynthetsis, being related to changes in WUE. Daily cycles of Fv/Fm revealed a slight photoinhibitory response during summer, mainly in perennial species. In all cases photosynthetic pigments adjusted to the radiation level; leaves had lower chlorophyll content, higher pool of xanthophylls and higher proportion of the de-epoxydaded state of xanthophylls under sun conditions. Lutein content increased in relation to the xanthophyll pool under shade conditions. Our results evidenced that radiation is an important driving factor controlling morphological and physiological status of Mediterranean shrub species, independently of water availability. Summer semi-deciduous species exhibit a set of traits with higher response variability, maximising their photosynthetic assimilation under different sun conditions

Gender dimorphism in Corema album across its biogeographical area and implications under a scenario of extreme drought events

In dioecious species, traits may have evolved because of significantly different resource demands associated with male versus female sexual reproduction. It is generally assumed that females have higher reproductive costs, thereafter in long-lived species, males often exceed females in vigour and suffer lower physiological limitations under stress. However, large-scale studies of gender dimorphism and the link between survival and physiological responses and compensation mechanisms are still lacking. In this study, we compared canopy performance, photochemical efficiency, leaf water potential, Δ13C, leaf nitrogen content and δ15N in both genders of the dioecious species Corema album (Ericaceae) across all the species’ biogeographical distribution. This area corresponds to a wide climatic gradient, from temperate and humid to Mediterranean, across the Atlantic coast of the Iberian Peninsula. Our results evidenced that the species responds to the bioclimatic gradient, and most variables were significantly correlated with annual rainfall and bioclimatic indices, although gender dimorphism was only manifested in Δ13C and in leaf water potential at the peak of the drought season. Female plants have significantly higher values of Δ13C, which could be attributed to lower water use efficiency; however, male plants presented more negative leaf water potentials than females, especially in the populations with the warmest and most arid climate. We concluded that C. album populations adjust to the climatic gradient at different hierarchical scales, from physiological instantaneous to time-integrated traits, with gender dimorphism only occurring in sub-optimal environments The absence of morphological differences between genders and the maintenance of a less negative water potential in females in the dry period in southern more arid populations, suggests the existence of compensatory mechanisms at underground level.Fundação para a Ciência e a Tecnologia (FCT) UID/BIA/00329/201

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