Functional Traits and Water Transport Strategies in Lowland Tropical Rainforest Trees

Abstract

Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species’ hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios.

Rainforest trees respond to drought by modifying their hydraulic architecture

“…We observed in one species, Endiandra , that drought‐affected individuals had smaller mean and maximum vessel areas than control individuals, although the mean of these traits was not significant different. However, detecting significant change in vessel area is challenging because this trait can vary greatly within and between individual trees (Apgaua et al, ). Hence, the interpretation of this feature may benefit by visualizing vessel area class distributions rather than simply averaging a range of values (e.g., Apgaua et al, ), which corroborate that in Endiandra , control individuals had a wider range of vessel areas and a higher proportion of vessels in the larger area classes than drought‐affected individuals.…”

“…We demonstrate that tropical trees respond in their hydraulic architecture traits to short-term water deficit, representing diverse trait strategies across species (Apgaua et al, 2015). In both wood and leaf traits, species varied in their capacity to modify specific traits, as visualized in various trait trade-offs or co-ordinations when species were ordinated in trait space.…”

“…Instead, a rapidly growing branch of functional ecology, functional anatomy, emphasizes the utility of wood anatomical characters rather than simply morphological-based traits (Carlquist, 2001;Martínez-Cabrera, Jones, Espino, & Schenk, 2009;Zanne et al, 2010). Expressly, the vessel network in tree sapwood and associated tissues that facilitate water transport or storage thus represents the hydraulic architecture of trees (Tyree & Zimmermann, 2002) and these features can therefore provide a framework for understanding species-specific water-use strategies, in terms of unique trait combinations within species or trait tradeoffs across species (Apgaua et al, 2015(Apgaua et al, , 2017Worbes, Blanchart, & Fichtler, 2013).…”

Trait integration and functional differentiation among co‐existing plant species

“…Therefore, we chose NMDS because it does not assume linear relationships among variables (Minchin, ; McCune and Grace, ). While principal component analysis (PCA) is the most common approach, NMDS is increasingly applied to analyze species‐trait matrices (e.g., Cadotte et al., ; Apgaua et al., ; Miller et al., ). So that all traits were on the same scale, each trait was relativized to vary between zero and one.…”

Low Phosphorus Availability Decreases Susceptibility of Tropical Primary Productivity to Droughts

“…Tropical ecosystems are characterized by variable trait strategies related to water (Apgaua et al, 2015) and nutrient use (Turner et al, 2018), as well as by variability in forest height and age (canopy heterogeneity) (Giardina et al, 2018). Although functional diversity is being discussed as a relevant measure for ecosystem level gas exchange, there is still limited empirical evidence demonstrating the role of functional trait diversity (Reichstein et al, 2014).…”