Light dependence of carboxylation capacity for C₃ photosynthesis models

Abstract

C 3 photosynthesis at high light is often modeled by assuming limitation by the maximum capacity of Rubisco carboxylation (V Cmax ) at low CO 2 concentrations, by electron transport capacity (J max ) at higher CO 2 concentrations, and sometimes by triose-phosphate utilization rate at the highest CO 2 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 CO 2 and temperature at low light. In this work, P N responses to CO 2 concentration of common bean, quinoa, and soybean leaves measured over a wide range of temperatures and PPFDs were compared with rates modeled assuming either V C or J limitation at limiting light. In all cases, observed rates of P N were better predicted by assuming limitation by V C rather than J at limiting light both below and above the current ambient CO 2 . One manifestation of this plant response was that the relative stimulation of P N with increasing the ambient CO 2 concentration from 380 to 570 mol mol -1 did not decrease at less than saturating PPFDs. The ratio of V C 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 mol mol -1 CO 2 in all cases. This modification of the standard C 3 biochemical model was much better at reproducing observed responses of light-limited P N to CO 2 concentrations from pre-industrial to projected future atmospheric concentrations.

Diffusive and Metabolic Constraints to Photosynthesis in Quinoa during Drought and Salt Stress

“…The uppermost fully expanded leaf on five replicate plants for each treatment was analyzed. The P N - C i response of quinoa is sensitive to light intensity [ 70 ]; therefore, a saturating PPFD of 2000 μmol m −2 s −1 was used. The concentration of [CO 2 ] within the leaf cuvette was lowered to 50 μmol mol −1 for 60 min to fully open stomata and remove any diffusive limitations to P N before [CO 2 ] was increased in stages every 3 to 4 min when P N had stabilized ([CO 2 ] steps: 50, 100, 200, 300, 400, 600, 800, 1000, 1200, 1400, 1600, 1800, 2000 μmol mol −1 ) [ 39 ].…”

Soybean Architecture Plants: From Solar Radiation Interception to Crop Protection

“…and internal CO 2 concentrations above 800 µmol CO 2 mol -1 [ 43]. Historically, with genetic improvement in soybean crop, there have been considerable modifications in plant architecture components with the goal of improving mechanization efficiency principally on the height of insertion of pods.…”

Carboxylation Capacity Can Limit C3 Photosynthesis at Elevated CO2 throughout Diurnal Cycles

“…Bunce [8] found that the initial slope of A vs. Ci curves, an in situ measure of Rubisco carboxylation capacity, decreased as PPFD decreased in the steady-state, in a range of C3 species measured, over a range of temperatures. The result was that the relative stimulation of A at elevated vs. ambient CO2 did not decrease as PPFD decreased, at any temperature [8]. At lower PPFD, it is often assumed that carboxylation capacity remains constant while electron transport rate decreases.…”

“…This primarily lowers A at higher C i (Figure 2) and would result in a smaller relative stimulation of A between a C i of 250 and 375 µmol mol −1 , for example [7]. However, the assumption of constant carboxylation capacity at lower PPFD is incorrect, in the steady-state [8]. Bunce [8] found that the initial slope of A vs. C i curves, an in situ measure of Rubisco carboxylation capacity, decreased as PPFD decreased in the steady-state, in a range of C 3 species measured, over a range of temperatures.…”