Non-structural carbohydrates mediate seasonal water stress across Amazon forests

Abstract

Non-structural carbohydrates (NSC) are major substrates for plant metabolism and have been implicated in mediating drought-induced tree mortality. Despite their significance, NSC dynamics in tropical forests remain little studied. We present leaf and branch NSC data for 82 Amazon canopy tree species in six sites spanning a broad precipitation gradient. During the wet season, total NSC (NSCT) concentrations in both organs were remarkably similar across communities. However, NSCT and its soluble sugar (SS) and starch components varied much more across sites during the dry season. Notably, the proportion of leaf NSCT in the form of SS (SS:NSCT) increased greatly in the dry season in almost all species in the driest sites, implying an important role of SS in mediating water stress in these sites. This adjustment of leaf NSC balance was not observed in tree species less-adapted to water deficit, even under exceptionally dry conditions. Thus, leaf carbon metabolism may help to explain floristic sorting across water availability gradients in Amazonia and enable better prediction of forest responses to future climate change.

Surface temperatures reveal the patterns of vegetation water stress and their environmental drivers across the tropical Americas

“…Within the rainforest, the regions with the strongest sensitivity to VPD lie at lower elevations (Figure 5i,j), which have greater soil moisture and greater access to groundwater (e.g., from partial inundation). In these low-lying environments, we explain the vegetation sensitivity to VPD by the fact that plants acclimated to plentiful soil water supplies have developed lower resistance to xylem embolism (Oliveira et al, 2019;Signori-Müller et al, 2021), and are thus sensitive to VPD increases, since (partial) stomatal closure occurs at high VPD, causing a rise of LST/T air .…”

Elastic and collapsible: current understanding of cell walls in succulent plants

“…tolerating low Ψ) among non-succulent plants ( Lenz et al , 2006 ; Blackman et al , 2010 ). Many arid-adapted non-succulents respond to drought by lowering their already low TLP Ψ through physiological adjustments, primarily osmotic adjustments ( Bartlett et al , 2012 ; Turner, 2018 ; Signori-Müller et al , 2021 ). On the other hand, measurements of TLP Ψ and the closely related Ψ S (see formula in Bartlett et al , 2012 ) in drought-avoiding succulents have shown that they exhibit relatively high TLP Ψ values ( Walter and Stadelmann, 1974 ; Smith and Lüttge, 1985 ; von Willert et al , 1992 ; Donatz and Eller, 1993 ; Gotsch et al , 2021 , Preprint; Leverett et al , 2021 ); their ability to maintain high Ψ seems to relax the need for a low TLP Ψ .…”

Wood Nutrient-Water-Density Linkages Are Influenced by Both Species and Environment

“…The structural mechanisms responsible for enhancing the water storage capacity in trees are underpinned by the anatomical configuration of the woody tissues with both capillary storage compartments (i.e., open vessels, tracheids, fibers, intercellular spaces, and cracks) and elastic storage compartments (i.e., living parenchyma cells) likely to be relevant ( Borchert and Pockman, 2005 ; Scholz et al, 2008 ; Jupa et al, 2016 ; Kawai et al, 2021 ). Not only the anatomic features define plant water storing capacity but also the chemical compounds with osmotic activity play an essential role in plant osmotic adjustment ( Turner and Jones, 1980 ; Turner, 2018 ; Signori-Müller et al, 2021 ). The accumulation of osmotically active elements in the tissues decreases the water potential, thus enabling the maintenance of high cellular turgor potential and water retention ( Blum, 2017 ; Traversari et al, 2020 ; da Silva et al, 2021 ).…”