Leaf economics and plant hydraulics drive leaf : wood area ratios

Abstract

Biomass and area ratios between leaves, stems and roots regulate many physiological and ecological processes. The Huber value H v (sapwood area/leaf area ratio) is central to plant water balance and drought responses. However, its coordination with key plant functional traits is poorly understood, and prevents developing trait-based prediction models.Based on theoretical arguments, we hypothesise that global patterns in H v of terminal woody branches can be predicted from variables related to plant trait spectra, that is plant hydraulics and size and leaf economics.Using a global compilation of 1135 species-averaged H v , we show that H v varies over three orders of magnitude. Higher H v are seen in short small-leaved low-specific leaf area (SLA) shrubs with low K s in arid relative to tall large-leaved high-SLA trees with high K s in moist environments. All traits depend on climate but climatic correlations are stronger for explanatory traits than H v . Negative isometry is found between H v and K s , suggesting a compensation to maintain hydraulic supply to leaves across species.This work identifies the major global drivers of branch sapwood/leaf area ratios. Our approach based on widely available traits facilitates the development of accurate models of above-ground biomass allocation and helps predict vegetation responses to drought.

Stomatal optimization based on xylem hydraulics (SOX) improves land surface model simulation of vegetation responses to climate

“…Alternatively, the SOX structure (i.e. the K function in Eqn 2) would need to explicitly represent the variability between different hydraulic compartments along the soil–plant–atmosphere pathway, similar to SPA or other models (Eller et al ., ; Kennedy et al ., ; Mencuccini et al ., ).…”

“…Considering that the observations used in this study were not collected in the same FLUXNET sites used to evaluate SOX, some of the observed discrepancies between calibrated and measured parameters might reflect hydraulic differences between populations treated as the same PFT in this study. For example, the deciduous angiosperms species present in the XFT dataset used in this study contain mostly hydraulic data from cold‐deciduous temperate species (Mencuccini et al ., ), which might not be adequate to describe the hydraulic system of tropical and subtropical drought‐deciduous. Our hydraulic scheme opens up possibilities of improving the representation of different global vegetation types in JULES with different hydraulic and phenological strategies.…”

“…() dataset updated recently by Mencuccini et al . (). The shape parameter a of the xylem vulnerability function (Eqn 2) was estimated from the linear gradient between Ψ 50 and the Ψ when the plant loses 88% of its maximum hydraulic conductance.…”

“…All the data used for these calculations were obtained from the hydraulic dataset from Mencuccini et al . (). We note that scaling branch to whole tree r pmin requires several assumptions about tree hydraulic architecture (Notes S4).…”

Understanding the uncertainty in global forest carbon turnover

“…Norby et al, 2016) to determine whether a change in seedling assimilation rates is likely to lead to a vegetation composition shift, thus affecting τ via MP mechanisms. Second, recruitment of new tree cohorts is strongly affected by the light and moisture environment at the forest floor (Muscolo et al, 2014;Poorter et al, 2019).…”