Contrasting stomatal sensitivity to temperature and soil drought in mature alpine conifers

Abstract

Conifers growing at high elevations need to optimize their stomatal conductance (g s ) for maximizing photosynthetic yield while minimizing water loss under less favourable thermal conditions. Yet the ability of high-elevation conifers to adjust their g s sensitivity to environmental drivers remains largely unexplored.We used 4 years of sap flow measurements to elucidate intraspecific and interspecific variability of g s in Larix decidua Mill. and Picea abies (L.) Karst along an elevational gradient and contrasting soil moisture conditions. Site-and species-specific g s response to main environmental drivers were examined, including vapour pressure deficit, air temperature, solar irradiance, and soil water potential.Our results indicate that maximum g s of L. decidua is >2 times higher, shows a more plastic response to temperature, and down-regulates g s stronger during atmospheric drought compared to P. abies. These differences allow L. decidua to exert more efficient water use, adjust to site-specific thermal conditions, and reduce water loss during drought episodes.The stronger plasticity of g s sensitivity to temperature and higher conductance of L. decidua compared to P. abies provide new insights into species-specific water use strategies, which affect species' performance and should be considered when predicting terrestrial water dynamics under future climatic change.Abbreviations: A L , leaf area; A S , sapwood area; C p , heat capacity of air; D, vapour pressure deficit; DBH, stem diameter at breast height (1.3 m); E, transpiration; F d , sap flux density; g s , stomatal conductance (standardized to A L ); g s /g s.max , stomatal conductance relative to the maximum (99th quantile); g sap , crown conductance (standardized to A S ); g sap.int , intercept of the linear relationship between ψ soil and g sap /g sap.max ; g sap /g sap.max , crown conductance relative to the maximum (99th quantile); g sap.ref , reference conductance when D = 1 kPa; K, ΔT standardized for ΔT max ; R g , solar irradiance; RH, relative humidity; T a , air temperature; T s , soil temperature; W u , whole-tree water flux; γ, psychrometric constant; ΔT, temperature difference between heated and unheated sap flow probe; ΔT max , temperature difference during zero-flow conditions; −δ, slope coefficient of the power function between T a and g sap ; θ, volumetric soil water content; Λ, slope coefficient of the linear relationship between ψ soil and g sap /g sap.max ; λ, latent heat of vaporization; ρ, air density; ψ soil , soil water potential

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