Three photosynthetic patterns characterized by cluster analysis of gas exchange data in two rice populations

Plant photosynthetic rate is affected by stomatal status and internal CO₂ carboxylation. Understanding which process determines photosynthetic rate is essential for developing strategies for breeding crops with high photosynthetic efficiency. In this study, we identified different physiological patterns of photosynthetic rate in two different rice populations. Photosynthetic gas exchange parameters were measured during the flowering stage in two rice populations. Clustering and correlation analyses were performed on the resulting data. Five or six groups were defined by K-means clustering according to differences in net photosynthetic rates (P_n). According to differences in stomatal conductance (g_s) and carboxylation efficiency (CE), each group was clustered into three subgroups characterized by physiological patterns stomatal pattern, carboxylation pattern, and intermediate pattern. P_n was significantly correlated with g_s (r=0.810) and CE (r=0.531). P_n was also significantly correlated with g_s and CE in the three physiological patterns. The correlation coefficients were highest in the stomatal pattern (0.905 and 0.957) and lowest in the carboxylation pattern (0.825 and 0.859). Higher correlation coefficients between P_n and g_s or CE in the three physiological patterns indicate that clustering is very important for understanding factors limiting rice photosynthesis.