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

BACKGROUND

Nitrogen (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) of rice leaves will be of great significance for further increasing leaf P, 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.

RESULTS

Compared with N0 (0 kg N ha) and K0 (0 kg KO ha) treatments, the P was increased by 17.1 and 12.2% with the supply of N and K. Compared with N0K0 (0 kg N and 0 kg KO ha), N0K120 (0 kg N and 120 kg KO ha) and N0K180 (0 kg N and 180 kg KO ha), N supply increased the absolute content of photosynthetic N (N) by 15.1, 15.5 and 10.5% on average, and the storage N (N) was increased by 32.7, 64.9 and 72.7% on average. The relative content of N was decreased by 5.6, 12.1 and 14.5%, while that of N was increased by 8.7, 27.8 and 33.8%. Supply of K promoted the transformation of N to N despite the leaf N content (N) was indeed decreased. Compared with N0K0, N180K0 (180 kg N and 0 kg KO ha) and N270K0 (270 kg N and 0 kg KO ha), K supply increased the relative content of N by 17.7, 8.8 and 7.3%, and decreased the relative content of N by 24.2, 11.4 and 8.7% respectively.

CONCLUSIONS

This study indicated the mechanism that K supply decreased the N but increased the N content and then increased leaf P and PNUE from a new viewpoint of leaf N allocation. The supply of K promoted the transformation of N to N and increased the PNUE. The decreased N 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 content and PNUE.