The determiner of photosynthetic acclimation induced by biochemical limitation under elevated CO in japonica rice.

Photosynthetic acclimation to prolonged elevated CO could be attributed to the two limited biochemical capacity, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation and ribulose-1,5-bisphosphate (RuBP) regeneration, however, which one is the primary driver is unclear. To quantify photosynthetic acclimation induced by biochemical limitation, we investigated photosynthetic characteristics and leaf nitrogen allocation to photosynthetic apparatus (Rubisco, bioenergetics, and light-harvesting complex) in a japonica rice grown in open-top chambers at ambient CO and ambient CO+200 μmol mol (e [CO]). Results showed that photosynthesis was stimulated under e [CO], but concomitantly, photosynthetic acclimation obviously occurred across the whole growth stages. The content of leaf nitrogen allocation to Rubisco and biogenetics was reduced by e [CO], while not in light-harvesting complex. Unlike the content, there was little effects of CO enrichment on the percentage of nitrogen allocation to photosynthetic components. Additionally, leaf nitrogen did not reallocate within photosynthetic apparatus until the imbalance of sink-source under e [CO]. The contribution of biochemical limitations, including Rubisco carboxylation and RuBP regeneration, to photosynthetic acclimation averaged 36.2% and 63.8% over the growing seasons, respectively. This study suggests that acclimation of photosynthesis is mainly driven by RuBP regeneration limitation and highlights the importance of RuBP regeneration relative to Rubisco carboxylation in the future CO enrichment.