Polygonum sachalinense alters the balance between capacities of regeneration and carboxylation of ribulose-1,5-bisphosphate in response to growth CO2 increment but not the nitrogen allocation within the photosynthetic apparatus

The limiting step of photosynthesis changes depending on CO2 concentration and, in theory, photosynthetic nitrogen use efficiency at a respective CO2 concentration is maximized if nitrogen is redistributed from non-limiting to limiting processes. It has been shown that some plants increase the capacity of ribulose-1,5-bisphoshate (RuBP) regeneration (evaluated as Jmax) relative to the RuBP carboxylation capacity (evaluated as Vcmax) at elevated CO2, which is in accord with the theory. However, there is no study that tests whether this change is accompanied by redistribution of nitrogen in the photosynthetic apparatus. We raised a perennial plant, Polygonum sachalinense, at two nutrient availabilities under two CO2 concentrations. The Jmax to Vcmax ratio significantly changed with CO2 increment but the nitrogen allocation among the photosynthetic apparatus did not respond to growth CO2. Enzymes involved in RuBP regeneration might be more activated at elevated CO2, leading to the higher Jmax to Vcmax ratio. Our result suggests that nitrogen partitioning is not responsive to elevated CO2 even in species that alters the balance between RuBP regeneration and carboxylation. Nitrogen partitioning seems to be conservative against changes in growth CO2 concentration.