On the ratio of intercellular to ambient CO2 (c i/c a) derived from ecosystem flux

Abstract

The ratio of intercellular to ambient CO concentrations (c /c) plays a key role in ecophysiology, micrometeorology, and global climatic change. However, systematic investigation on c /c variation and its determinants are rare. Here, the c /c was derived from measuring ecosystem fluxes in an even-aged monoculture of rubber trees (Hevea brasiliensis). We tested whether c /c is constant across environmental gradients and if not, which dominant factors control c /c variations. Evidence indicates that c /c is not a constant. The c /c exhibits a clear "V"-shaped diurnal pattern and varies across the environmental gradient. Water vapor pressure deficit (D) is the dominant factor controls over the c /c variations. c /c consistently decreases with increasing D. c /c decreases with square root of D as predicted by the optimal stomatal model. The D-driving single-variable model could simulate c /c as well as that of sophisticated model. Many variables function on longer timescales than a daily cycle, such as soil water content, could improve c /c model prediction ability. Ecosystem flux can be effectively used to calculate c /c and use it to better understand various natural cycles.

Partitioning Eddy Covariance Water Flux Components Using Physiological and Micrometeorological Approaches

“…This effective χ o is to be interpreted here within the context of a big leaf representation and considered as the basis to solve for the canopy stomatal conductance ( g c ) control of the exchange rates of P h and T (equation (1)–(7) in Figure ). The computed χ o accommodates short‐term kinetic adjustments (i.e., hours and seasons; equation (2) in Figure ). There is some evidence that canopy‐scale χ derived from ecosystem fluxes might exhibit diel patterns in response to variations in ambient vapor pressure deficit (Tan et al, ), which also agree with leaf‐level observations (Fites & Teskey, ; James & Gifford, ; Jones, ; Katul et al, ). Different mathematical forms describing the dependence of χ with vapor pressure deficit can be found elsewhere (Katul et al, ; Leuning, ; Medlyn et al, ; Prentice et al, ). Short‐term χ variations can be considered as part of the plant optimization problem and without the need of ignoring the boundary layer conductance influence. Environmental dependencies of g c , represented by a Jarvis type formulation, are constrained in accordance with the inferred EC P h pattern (equation (1)–(5)).…”

“…The overlined characters ( and ) are used to denote growing season average daytime values, and C is a coefficient fixed to 1.189 for C 3 plants according to Wang et al (). Given that equation predicts a long‐term optimal value ( χ o ), which might mask short‐term responses, here we further hypothesize that χ decays over the course of a day with increasing D (Mortazavi et al, ; Tan et al, ). For example, a simplified leaf‐level optimality approach (for Rubisco‐limited photosynthesis of C3 plants) predicts short‐term variations in , provided the marginal water use efficiency λ varies with atmospheric CO 2 over long timescales (Katul et al, ).…”

Alternative Crassulacean Acid Metabolism Modes Provide Environment-Specific Water-Saving Benefits in a Leaf Metabolic Model

“…The uptake rate for CO2 was limited to a value of 15 μmol m -2 s -1 based on values for different C3 and CAM species (Nobel, 2012). We assumed an average ci:c, ratio of 0.7 (Tan et al, 2017;Kumarathunge et al, 2019;Cai et al, 2020;Busch, 2020) (see Supplemental Methods, Section 1.2.5 and Supplemental Results, Section 2.5 for more information and a sensitivity analysis of the predicted water loss in dependence of the internal CO2 concentration). All other fluxes were unconstrained.…”

Sensitivity and Uncertainty Analyses of Flux-based Ecosystem Model towards Improvement of Forest GPP Simulation

“…So, future research of the comparison of the SIs of parameters, especially V 25 m , would be in demand. f Ci was also important, and the most sensitive parameter overall for the GPP and NEE output, and a recent study indicates that f Ci was not a constant and varies along with environmental gradients [61], which was coincided with the parameter SA experiment. According to the above, the SA and other studies need to discover some parameters vary with the environment, the initial setting of the parameters as a constant was thus a crucial source of uncertainty [1,62].…”