Representation of Plant Hydraulics in the Noah‐MP Land Surface Model: Model Development and Multiscale Evaluation. (16th April 2021)

• Record Type: Journal Article
• Authors: Li, Lingcheng; Yang, Zong‐Liang; Matheny, Ashley M.; Zheng, Hui; Swenson, Sean C.; Lawrence, David M.; Barlage, Michael; Yan, Binyan; McDowell, Nate G.; Leung, L. Ruby
• Is Part Of: Journal of advances in modeling earth systems. Volume 13:Number 4(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-04-16
• Subjects: land surface model -- plant hydraulics -- water and carbon cycles; Geological modeling -- Periodicals; Climatology -- Periodicals; Geochemical modeling -- Periodicals; 551.5011
• DOI: 10.1029/2020MS002214
• Languages: English
• ISSNs: 1942-2466

Abstract

Abstract: Plants are expected to face increasing water stress under future climate change. Most land surface models, including Noah‐MP, employ an idealized "big‐leaf" concept to regulate water and carbon fluxes in response to soil moisture stress through empirical soil hydraulics schemes (SHSs). However, such schemes have been shown to cause significant uncertainties in carbon and water simulations. In this paper, we present a novel plant hydraulics scheme (PHS) for Noah‐MP (hereafter, Noah‐MP‐PHS), which employs a big‐tree rather than big‐leaf concept, wherein the whole‐plant hydraulic strategy is considered, including root‐level soil water acquisition, stem‐level hydraulic conductance and capacitance, and leaf‐level anisohydricity and hydraulic capacitance. Evaluated against plot‐level observations from a mature, mixed hardwood forest at the University of Michigan Biological Station and compared with the default Noah‐MP, Noah‐MP‐PHS better represents plant water stress and improves water and carbon simulations, especially during periods of dry soil conditions. Noah‐MP‐PHS also improves the asymmetrical diel simulation of gross primary production under low soil moisture conditions. Noah‐MP‐PHS is able to reproduce different patterns of transpiration, stem water storage and root water uptake during a 2‐week dry‐down period for two species with contrasting plant hydraulic behaviors, i.e., the "cavitation risk‐averse" red maple and the "cavitation risk‐prone" red oak. Sensitivity experiments with plant hydraulic capacitance show that the stem water storage enables nocturnal plant water recharge, affects plant water use efficiency, and provides an important buffer to relieve xylem hydraulic stress during dry soil conditions. Plain Language Summary: Plants regulate transpiration dynamically through the stomatal aperture, which, in many cases, is governed by plant water status and hydraulic properties. Plant hydraulics describes the mechanics of water movement through plant vascular systems, which is the culmination of emergent phenotypical hydraulic functional traits at the leaf, stem, and root levels. Such physiological mechanisms are excluded in most land surface models, which typically represent plant water stress through empirical soil hydraulics schemes (SHSs) based on either soil water content or soil water potential. In this study, we present a novel plant hydraulics scheme (PHS) to represent plant water stress and the regulation of stomatal conductance for use in the Noah‐MP land surface model. Our results show Noah‐MP‐PHS performs better in its water and carbon simulations than the default Noah‐MP with traditional SHSs, especially under dry soil conditions. Noah‐MP‐PHS also successfully captures the different plant hydraulic behaviors between the "cavitation risk‐averse" red maple and the "cavitation risk‐prone" red oak. Sensitivity experiments also highlight the vital role played by plant water storage in water and carbon simulations in terms of buffering xylem hydraulic stress during soil moisture dry‐down periods. The incorporation of a holistic, whole‐plant hydraulic strategy, along with hydraulic trait‐based vegetation representation, can serve to improve simulations of carbon and water fluxes, particularly in cases of drought and other related disturbances. Key Points: Noah‐MP‐PHS improves the water and carbon simulations over the default soil hydraulics schemes, especially under dry soil conditions Noah‐MP‐PHS captures different plant hydraulic behaviors between the "cavitation risk‐averse" maple and the "cavitation risk‐prone" oak Plant water storage plays a vital role in water and carbon fluxes and relieves xylem hydraulic stress during soil moisture dry‐down periods