Optimal allocation of leaf‐level nitrogen: Implications for covariation of V_cmax and J_max and photosynthetic downregulation

Abstract

The maximum rate of carboxylation, Vcmax, and the maximum rate of electron transport, Jmax, describe leaf‐level capacities of the photosynthetic system and are critical in determining the net fluxes of carbon dioxide and water vapor in the terrestrial biosphere. Although both Vcmax and Jmax exhibit high spatial and temporal variability, most descriptions of photosynthesis in terrestrial biosphere models assume constant values for Vcmax and Jmax at a reference temperature ignoring intraseasonal, interannual, and water stress‐induced variations. Although general patterns of variation of Vcmax and Jmax have been correlated across groups of species, climates, and nitrogen concentrations, scant theoretical support has been provided to explain these variations. We present a new approach to determine Vcmax and Jmax based on the assumption that a limited amount of leaf nitrogen is allocated optimally among the various components of the photosynthetic system in such a way that expected carbon assimilation is maximized. The optimal allocation is constrained by available nitrogen and responds dynamically to the near‐term environmental conditions of light and water supply and to their variability. The resulting optimal allocations of a finite supply of nitrogen replicate observed relationships in nature, including the ratio of Jmax/Vcmax, the relationship of leaf nitrogen to Vcmax, and the changes in nitrogen allocation under varying water availability and light environments. This optimal allocation approach provides a mechanism to describe the response of leaf‐level photosynthetic capacity to varying environmental and resource supply conditions that can be incorporated into terrestrial biosphere models providing improved estimates of carbon and water fluxes in the soil‐plant‐atmosphere continuum.

Acclimation of leaf respiration consistent with optimal photosynthetic capacity

“…This is the ‘strong form’ of the co‐ordination hypothesis (Chen et al, ; Haxeltine & Prentice, ; Maire et al, ), contrasting with a ‘weak form’ that assumes that the total metabolic N content of the leaf is prescribed so that only the allocation of N to carboxylation versus electron transport capacities is optimized (e.g. Quebbeman & Ramirez, ). In response to environmental variations, the co‐ordination hypothesis predicts vertical variation of V cmax,tg within the canopy, geographic variation among sites and temporal variations with atmospheric CO 2 concentration and climate (Haxeltine & Prentice, ; Smith et al, ; Terrer et al, ).…”

Estimation of Leaf Photosynthetic Capacity From Leaf Chlorophyll Content and Leaf Age in a Subtropical Evergreen Coniferous Plantation

“…Previous studies have found a significant correlation between leaf V cmax and leaf N content in different ecosystems (Crous et al, 2008;Kattge et al, 2009;Quebbeman & Ramirez, 2016;Ripullone et al, 2003), due to a large amount of total leaf N (15-35%) that is allocated to Rubisco protein in C 3 plants (Evans, 1989b;Feng & Dietze, 2013). Consequently, many TBMs adopted fixed relationships between V cmax and leaf nitrogen content to constrain photosynthetic capacity (Dietze, 2014).…”

Triose phosphate limitation in photosynthesis models reduces leaf photosynthesis and global terrestrial carbon storage

“…Additionally, recent work using the coordination theory of photosynthesis (e.g. Wang et al 2017, Quebbeman andRamirez 2016) suggests that plants adjust carboxylation-and electron transport-limited photosynthetic processes such that neither is strongly limiting at current growth conditions. It is possible that similar acclimation of export-limited photosynthesis occurs, though more measurements are needed to fully assess this response.…”