Dry‐season decline in tree sapflux is correlated with leaf turgor loss point in a tropical rainforest

Abstract

Water availability is a key determinant of forest ecosystem function and tree species distributions. While droughts are increasing in frequency in many ecosystems, including in the tropics, plant responses to water supply vary with species and drought intensity and are therefore difficult to model. Based on physiological first principles, we hypothesized that trees with a lower turgor loss point (πtlp), that is, a more negative leaf water potential at wilting, would maintain water transport for longer into a dry season. We measured sapflux density of 22 mature trees of 10 species during a dry season in an Amazonian rainforest, quantified sapflux decline as soil water content decreased and tested its relationship to tree πtlp, size and leaf predawn and midday water potentials measured after the onset of the dry season. The measured trees varied strongly in the response of water use to the seasonal drought, with sapflux at the end of the dry season ranging from 37 to 117% (on average 83 ± 5 %) of that at the beginning of the dry season. The decline of water transport as soil dried was correlated with tree πtlp (Spearman’s ρ ≥ 0.63), but not with tree size or predawn and midday water potentials. Thus, trees with more drought‐tolerant leaves better maintained water transport during the seasonal drought. Our study provides an explicit correlation between a trait, measurable at the leaf level, and whole‐plant performance under drying conditions. Physiological traits such as πtlp can be used to assess and model higher scale processes in response to drying conditions. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13188/suppinfo is available for this article.

Functional diversity improves tropical forest resilience: Insights from a long‐term virtual experiment

“…Here, we used traits identified as key predictors of ecological functions in Neotropical forests (Baraloto et al, ), but other traits, e.g. hydraulic traits such as vulnerability to cavitation or leaf water potential at turgor loss point, play an important role in resilience to specific disturbances such as drought (Maréchaux et al, ; Santiago et al, ). We hope to include these other facets of functional diversity in future contributions, as more data are becoming available for these physiological traits.…”

Disentangling the effects of environment and ontogeny on tree functional dimensions for congeneric species in tropical forests

“…Our work suggests that using a ‘mean field’ approach (here, using mean trait values to represent species physiology) would fail to capture important seasonal patterns in species functioning. This further emphasizes the need to incorporate seasonally measured physiological traits along with leaf phenology information in experiments and models to gain a more mechanistic understanding of how tropical tree species will respond to spatiotemporal variation in water availability (Bartlett et al , ; Anderegg et al , ; Weng et al , ; Maréchaux et al , ).…”

“…Tropical tree distribution is strongly shaped by spatiotemporal variation in water availability (Engelbrecht et al , ; Bartlett et al , ; Esquivel‐Muelbert et al , ), but we are still lacking detailed information on the physiological response to drought for the vast majority of tropical tree species because of time and resource constraints (Anderegg et al , ). A pressing challenge for ecologists is to evaluate the potential for relatively easy‐to‐measure traits to capture essential features of tropical tree physiology (O'Brien et al , ; Santiago et al , ; Maréchaux et al , ; Barros et al , ).…”

Leaf drought tolerance cannot be inferred from classic leaf traits in a tropical rainforest

“…(−) More negative π tlp is related to increasing anisohydry and greater leaf turgor, allowing sustained greater g w under drying conditions (Maréchaux et al, ; Meinzer et al, ) and overall (Meinzer et al, )…”