Estimation of intrinsic water-use efficiency from δ13C signature of C3 leaves: Assumptions and uncertainty

Abstract

Carbon isotope composition (δ13C) has been widely used to estimate the intrinsic water-use efficiency (iWUE) of plants in ecosystems around the world, providing an ultimate record of the functional response of plants to climate change. This approach relies on established relationships between leaf gas exchange and isotopic discrimination, which are reflected in different formulations of 13C-based iWUE models. In the current literature, most studies have utilized the simple, linear equation of photosynthetic discrimination to estimate iWUE. However, recent studies demonstrated that using this linear model for quantitative studies of iWUE could be problematic. Despite these advances, there is a scarcity of review papers that have comprehensively reviewed the theoretical basis, assumptions, and uncertainty of 13C-based iWUE models. Here, we 1) present the theoretical basis of 13C-based iWUE models: the classical model (iWUEsim), the comprehensive model (iWUEcom), and the model incorporating mesophyll conductance (iWUEmes); 2) discuss the limitations of the widely used iWUEsim model; 3) and make suggestions on the application of the iWUEmes model. Finally, we suggest that a mechanistic understanding of mesophyll conductance associated effects and post-photosynthetic fractionation are the bottlenecks for improving the 13C-based estimation of iWUE.

Climate gradient and leaf carbon investment influence the effects of climate change on water use efficiency of forests: A meta‐analysis

“…Similar results have been reported in young olive trees exposed to long-term eT (+4°C) (Miserere et al, 2021), suggesting an inevitable water loss in trees under eT. Moreover, uncertainty regarding the estimation of WUEi from δ 13 C existed due to the potential interferences with mesophyll conductance to CO 2 and postphotosynthetic fractionation (Ma et al, 2023). A study with Eucalyptus tereticornis also reported the difference in mesophyll conductance between the whole-tree and leaf scales as well as the necessity of incorporating mesophyll conductance to 13 C-based WUEi model (Gimeno et al, 2021).…”

Shining a New Light on the Classical Concepts of Carbon-Isotope Dendrochronology

“…iWUE is regarded as an important functional property of plant ecosystems and a key determinant in the response of regional and global carbon, water, and energy cycles to climate change (19,20). Retrospective assessment of iWUE across large spatiotemporal scales relies on Δtrc analysis (1-5) which, in turn, relies on the assumption that DR discrimination governs Δtrc variability (6,11,21). However, DR discrimination accounts for merely ≈17.6% of the total variance of Δglu during the late period while PR discrimination accounts for ≈45.4% (Fig.…”

Linking functional composition moments of the sub-Mediterranean ecotone with environmental drivers

“…From this material, five aboveground and three belowground functional traits related to water and nutrient acquisition were measured (see functional roles in Table 1): Leaf Dry Matter Content (LDMC; leaf dry mass per unit of water-saturated fresh mass; mg g -1 ), Specific Leaf Area (SLA; leaf area per unit of leaf dry mass; m 2 kg -1 ), leaf carbon isotopic composition (d 13 C; ‰), leaf carbon to nitrogen ratio (leaf C:N), Stem Dry Matter Content (SDMC; stem dry mass per unit of watersaturated fresh mass; mg g -1 ), Huber value (Hv; sapwood crosssectional branch area to supported leaf area ratio; cm 2 cm -2 ), Specific Root Area (SRA; root area per unit of root dry mass; m 2 kg -1 ), average root diameter (Rdi; mm), and root C:N ratio (root C:N). Leaf d 13 C is a proxy of intrinsic water use efficiency (iWUE, Prieto et al, 2018;Ma et al, 2023). The Huber value reflects the mass investment in xylem area with respect to leaf area (Mencuccini et al, 2019); it is thus a measure of how species adjust their leaf and sapwood areas to water supply (Carter and White, 2009;Zhang et al, 2019) and is related to groundwater depth extraction (Carter and White, 2009).…”