Interactive effects of nitrogen and potassium on photosynthesis and photosynthetic nitrogen allocation of rice leaves

BackgroundNitrogen (N) and potassium (K) are two important mineral nutrients in regulating leaf photosynthesis. Studying the interactive effects of N and K on regulating N allocation and photosynthesis (P-n) of rice leaves will be of great significance for further increasing leaf P-n, photosynthetic N use efficiency (PNUE) and grain yield. We measured the gas exchange of rice leaves in a field experiment and tested different kinds of leaf N based on N morphology and function, and calculated the interactive effects of N and K on N allocation and the PNUE.ResultsCompared with N0 (0kgNha(-1)) and K0 (0kg K2O ha(-1)) treatments, the P-n was increased by 17.1 and 12.2% with the supply of N and K. Compared with N0K0 (0kgN and 0kg K2O ha(-1)), N0K120 (0kgN and 120kg K2O ha(-1)) and N0K180 (0kgN and 180kg K2O ha(-1)), N supply increased the absolute content of photosynthetic N (N-psn) by 15.1, 15.5 and 10.5% on average, and the storage N (N-store) was increased by 32.7, 64.9 and 72.7% on average. The relative content of N-psn was decreased by 5.6, 12.1 and 14.5%, while that of N-store was increased by 8.7, 27.8 and 33.8%. Supply of K promoted the transformation of N-store to N-psn despite the leaf N content (N-a) was indeed decreased. Compared with N0K0, N180K0 (180kgN and 0kg K2O ha(-1)) and N270K0 (270kgN and 0kg K2O ha(-1)), K supply increased the relative content of N-psn by 17.7, 8.8 and 7.3%, and decreased the relative content of N-store by 24.2, 11.4 and 8.7% respectively.ConclusionsThis study indicated the mechanism that K supply decreased the N-a but increased the N-psn content and then increased leaf P-n and PNUE from a new viewpoint of leaf N allocation. The supply of K promoted the transformation of N-store to N-psn and increased the PNUE. The decreased N-store mainly resulted from the decrease of non-protein N. Combined use of N and K could optimize leaf N allocation and maintain a high leaf N-psn content and PNUE.