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

Abstract

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 (Pn) of rice leaves will be of great significance for further increasing leaf Pn, 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 (0\u2009kg\u2009N\u2009ha−\u20091) and K0 (0\u2009kg K2O ha−\u20091) treatments, the Pn was increased by 17.1 and 12.2% with the supply of N and K. Compared with N0K0 (0\u2009kg\u2009N and 0\u2009kg K2O ha−\u20091), N0K120 (0\u2009kg\u2009N and 120\u2009kg K2O ha−\u20091) and N0K180 (0\u2009kg\u2009N and 180\u2009kg K2O ha−\u20091), N supply increased the absolute content of photosynthetic N (Npsn) by 15.1, 15.5 and 10.5% on average, and the storage N (Nstore) was increased by 32.7, 64.9 and 72.7% on average. The relative content of Npsn was decreased by 5.6, 12.1 and 14.5%, while that of Nstore was increased by 8.7, 27.8 and 33.8%. Supply of K promoted the transformation of Nstore to Npsn despite the leaf N content (Na) was indeed decreased. Compared with N0K0, N180K0 (180\u2009kg\u2009N and 0\u2009kg K2O ha−\u20091) and N270K0 (270\u2009kg\u2009N and 0\u2009kg K2O ha−\u20091), K supply increased the relative content of Npsn by 17.7, 8.8 and 7.3%, and decreased the relative content of Nstore by 24.2, 11.4 and 8.7% respectively.ConclusionsThis study indicated the mechanism that K supply decreased the Na but increased the Npsn content and then increased leaf Pn and PNUE from a new viewpoint of leaf N allocation. The supply of K promoted the transformation of Nstore to Npsn and increased the PNUE. The decreased Nstore 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 Npsn content and PNUE.