Intra‐Specific Variability in Plant Hydraulic Parameters Inferred From Model Inversion of Sap Flux Data

Abstract

Understanding plant hydraulic regulation is critical for predicting plant and ecosystem responses to projected increases in drought stress. Plant hydraulic regulation is controlled by observable, diverse plant hydraulic traits that can vary as much across individuals of the same species as they do across different species. Direct measurements of plant hydraulic traits from a range of ecosystems remain limited in comparison to other, more readily measured traits (e.g., specific leaf area). Furthermore, plant hydraulic trait measurements, often made at leaf or branch levels, are not easily scaled to whole‐plant values that are typically used to predict plant and ecosystem fluxes. In this study, multiple whole‐plant hydraulic parameters are inferred from observations of plant water use (i.e., sap flow), soil properties, and meteorological data. We use a Markov Chain Monte Carlo model inversion approach to obtain the best estimates and uncertainty of plant hydraulic parameters that capture whole‐plant effective embolism resistance and stomatal sensitivity to decreasing plant water potential. We then use the inferred values in the model to estimate whole‐tree water use and isohydricity. This approach reliably infers whole‐plant parameter values with enough specificity to resolve inter‐ and intra‐specific differences, and thus supplements time‐ and labor‐intensive direct measurements of traits.

The Role of the Intraspecific Variability of Hydraulic Traits for Modeling the Plant Water Use in Different European Forest Ecosystems

“…In CLM5, the default parameterization of the plant hydraulic traits is the same for the PFTs under analysis at the four experimental sites. This parameterization does not agree with the current evidence showing a high degree of variability for parameters such as Ψ p50 (e.g., Eller et al., 2020; Lu et al., 2022; Xie et al., 2023). Nonetheless, this homogeneity in the parameterization of the plant hydraulic traits of CLM5 provided the opportunity to evaluate the effect of the environmental conditions, namely the dynamics of atmospheric water demand and soil water availability, on the simulated plant hydraulic response.…”

“…These results illustrate the effective role of k max in constraining the water use at sites with seasonal water limitations (i.e., FR‐Pue and ES‐Alt). The maximum hydraulic conductance is a parameter highly influenced by plant segment age (Weithmann et al., 2022) and local environmental conditions rather than genetics (Hochberg et al., 2018; Lu et al., 2022). However, the complex interactions between environmental conditions and individual species made it difficult to identify individual environmental drivers for temperate tree species such as Acer platanoides L., Carpinus betulus L., and Tilia cordata Mill (Fuchs et al., 2021).…”

A Theory of Maximum Entropy Production and Its Application to Microwave Remote Sensing—Simultaneous Retrieval of Soil Moisture and Vegetation Water Content

“…Canopy transmissivity $$\gamma $$ is expressed in terms of the VOD τ , $$$\gamma =\mathrm{exp}\left(-\frac{\tau }{\cos \,{\theta }_{0}}\right),$$$ where θ 0 is the surface incident angle of the radiometer and τ is related to VWC and dry vegetation (e.g., Jackson, 1993; Njoku, 2014; Njoku & Entekhabi, 1996), $$$\tau =\left(\frac{VWC}{{\rho }_{w}}\frac{1}{{\delta }_{w}}+\frac{{M}_{v}}{{\rho }_{v}}\frac{1}{{\delta }_{v}}\right)\approx \frac{VWC}{{\rho }_{w}{\delta }_{w}},$$$ where M v is dry vegetation mass content (kg m −2 ). Since δ v ≫ δ w (Table 1), VWC / ρ w and M v / ρ v are comparable (e.g., Aviabile et al., 2016; Lu et al., 2022), VWC is obtained from Equations and , $$$VWC={\rho }_{w}{\delta }_{w}\,\cos \,{\theta }_{0}\,\mathrm{ln}\frac{1}{\gamma }$$$ where γ is the MEP solution in Equation , referred to as the MEP VWC retrieval algorithm.…”

“…M v is dry vegetation mass content (kg m 2 ). Since δ v ≫ δ w (Table1), VWC/ρ w and M v /ρ v are comparable (e.g.,Aviabile et al, 2016;Lu et al, 2022), VWC is obtained from Equations 11 and 12,…”

The role of the intraspecific variability of hydraulic traits for modelling the plant water use in different European forest ecosystems

“…The presented results illustrate the effective role of k max in constraining the water use at sites with seasonal water limitations (i.e., FR-Pue and ES-Alt). The maximum specific hydraulic conductance is a parameter highly influenced by local environmental conditions rather than genetics (Hochberg et al, 2018;Lu et al, 2022). This characteristic is represented by the range of k max values observed for the same species (Figure S5).…”