PHOTOSYNTHETICA

Photosynthetica 2016, 54(4):484-490 | DOI: 10.1007/s11099-016-0215-9

Light dependence of carboxylation capacity for C₃ photosynthesis models

J. A. Bunce^1,*

¹ USDA-ARS, Crop Systems and Global Change Laboratory, BARC-West, Beltsville, USA

C₃ photosynthesis at high light is often modeled by assuming limitation by the maximum capacity of Rubisco carboxylation (V_Cmax) at low CO₂ concentrations, by electron transport capacity (J_max) at higher CO₂ concentrations, and sometimes by triose-phosphate utilization rate at the highest CO₂ concentrations. Net photosynthetic rate (P _N) at lower light is often modeled simply by assuming that it becomes limited by electron transport (J). However, it is known that Rubisco can become deactivated at less than saturating light, and it is possible that P _N at low light could be limited by the rate of Rubisco carboxylation (V _C) rather than J. This could have important consequences for responses of P _N to CO₂ and temperature at low light. In this work, P _N responses to CO₂ concentration of common bean, quinoa, and soybean leaves measured over a wide range of temperatures and PPFDs were compared with rates modeled assuming either VC or J limitation at limiting light. In all cases, observed rates of P _N were better predicted by assuming limitation by VC rather than J at limiting light both below and above the current ambient CO₂. One manifestation of this plant response was that the relative stimulation of P _N with increasing the ambient CO₂ concentration from 380 to 570 µmol mol^-1 did not decrease at less than saturating PPFDs. The ratio of VC to V_Cmax at each lower PPFD varied linearly with the ratio of P _N at low PPFD to P _N at high PPFD measured at 380 µmol(CO₂) mol^-1 in all cases. This modification of the standard C₃ biochemical model was much better at reproducing observed responses of light-limited P _N to CO₂ concentrations from pre-industrial to projected future atmospheric concentrations.

Keywords: carbon dioxide; climate change; modeling; temperature

Received: December 1, 2015; Accepted: February 26, 2016; Published: December 1, 2016Show citation