Quantifying Light Response of Leaf-Scale Water-Use Efficiency and Its Interrelationships With Photosynthesis and Stomatal Conductance in C3 and C4 Species

Abstract

Light intensity (I) is the most dynamic and significant environmental variable affecting photosynthesis (A n), stomatal conductance (g s), transpiration (T r), and water-use efficiency (WUE). Currently, studies characterizing leaf-scale WUE-I responses are rare and key questions have not been answered. In particular, (1) What shape does the response function take? (2) Are there maximum intrinsic (WUE i ; WUE i−max) and instantaneous WUE (WUE inst ; WUE inst−max) at the corresponding saturation irradiances (I i−sat and I inst−sat)? This study developed WUE i-I and WUE inst-I models sharing the same non-asymptotic function with previously published A n-I and g s-I models. Observation-modeling intercomparison was conducted for field-grown plants of soybean (C 3) and grain amaranth (C 4) to assess the robustness of our models versus the non-rectangular hyperbola models (NH models). Both types of models can reproduce WUE-I curves well over light-limited range. However, at light-saturated range, NH models overestimated WUE i−max and WUE inst−max and cannot return I i−sat and I inst−sat due to its asymptotic function. Moreover, NH models cannot describe the downregulation of WUE induced by high light, on which our models described well. The results showed that WUE i and WUE inst increased rapidly within low range of I, driven by uncoupled photosynthesis and stomatal responsiveness. Initial response rapidity of WUE i was higher than WUE inst because the greatest increase of A n and T r occurred at low g s. C 4 species showed higher WUE i−max and WUE inst−max than C 3 species-at similar I i−sat and I inst−sat. Our intercomparison highlighted larger discrepancy between WUE i-I and WUE inst-I responses in C 3 than C 4 species, quantitatively characterizing an

Modeling Light Response of Electron Transport Rate and Its Allocation for Ribulose Biphosphate Carboxylation and Oxygenation

“…The overestimation of A nmax by NH model found in this study is consistent with the previous reports (e.g., Calama et al., 2013 ; dos Santos et al., 2013 ; Lobo et al., 2014 ; Ježilová et al., 2015 ; Mayoral et al., 2015 ; Ogawa, 2015 ; Park et al., 2016 ; Quiroz et al., 2017 ; Poirier-Pocovi et al., 2018 ; Ye et al., 2020 ). The accurate returning of A nmax by Ye model found in this study is consistent with previous studies using Ye model for various species under different environmental conditions (e.g., Wargent et al., 2011 ; Zu et al., 2011 ; Xu et al., 2012a ; Xu et al., 2012b ; Lobo et al., 2014 ; Xu et al., 2014 ; Song et al., 2015 ; Chen et al., 2016 ; Ye et al., 2019 ; Yang et al., 2020 ; Ye et al., 2020 ). The robustness of Ye model has also been validated for microalgae observations, including four freshwater and three marine microalgae species ( Yang et al., 2020 ).…”

“…For the first time, our study discloses the previously widely reported overestimation of J max (and A nmax ) by the NH model is linked to its overestimation of J C-max but not J O-max . The overestimation of A nmax by NH model found in this study is consistent with the previous reports (e.g., Calama et al, 2013;dos Santos et al, 2013;Lobo et al, 2014;Jezǐlováet al, 2015;Mayoral et al, 2015;Ogawa, 2015;Park et al, 2016;Quiroz et al, 2017;Poirier-Pocovi et al, 2018;Ye et al, 2020). The accurate returning of A nmax by Ye model found in this study is consistent with previous studies using Ye model for various species under different environmental conditions (e.g., Wargent et al, 2011;Zu et al, 2011;Xu et al, 2012a;Xu et al, 2012b;Lobo et al, 2014;Xu et al, 2014;Song et al, 2015;Chen et al, 2016;Ye et al, 2019;Yang et al, 2020;Ye et al, 2020).…”

“…The findings, and the approach of bridging experiment and modeling, in the present study remain to be tested for (1) species of different plant function types and/or climatic origin, which could exhibit different response patterns (Ye et al, 2020) and (2) plant response to interaction of multiple environmental factors (e.g., temperature, rainfall pattern, soil type) involving fluctuating light. The explicit and consistent modeling framework and parameter definitions on light responses (i.e.…”

“…The detailed descriptions about soil and meteorological conditions in this experiment station were referred to Ye et al. (2019 ; 2020) . Winter wheat was planted on October 4 th , 2011 and the measurements were conducted on April 23 th , 2012.…”

“…By simulating light-response curves of photosynthesis ( A n –I curve), NH model has been widely used to obtain key photosynthetic characteristics (e.g., the maximum net photosynthetic rate, A nmax ; light compensation point when A n = 0, I c ; dark respiration rate, R d ) for various species under different environmental conditions (e.g., Ögren & Evans, 1993 ; Thornley, 1998 ; Ye, 2007 ; Aspinwall et al., 2011 ; dos Santos et al., 2013 ; Mayoral et al., 2015 ; Sun et al., 2015 ; Park et al., 2016 ; Quiroz et al., 2017 ; Yao et al., 2017 ; Xu et al., 2019 ; Yang et al., 2020 ; Ye et al., 2020 ). Significant difference between observed A nmax values and that estimated by NH model for various species has been widely reported (e.g., Chen et al., 2011 ; dos Santos et al., 2013 ; Lobo et al., 2014 ; Ogawa, 2015 ; Sun et al., 2015 ; Quiroz et al., 2017 ; Poirier-Pocovi et al., 2018 ; Ye et al., 2020 ). This long-standing challenge has been resolved by an A n – I model, which adopts a nonasymptotic function and can accurately reproduce A n – I curve over light-limited, light-saturated and photoinhibitory I levels ( Ye et al., 2013 ) (hereafter, Ye model).…”