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 kg N ha− 1) and K0 (0 kg K2O ha− 1) treatments, the Pn was increased by 17.1 and 12.2% with the supply of N and K. Compared with N0K0 (0 kg N and 0 kg K2O ha− 1), N0K120 (0 kg N and 120 kg K2O ha− 1) and N0K180 (0 kg N and 180 kg K2O ha− 1), 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 kg N and 0 kg K2O ha− 1) and N270K0 (270 kg N and 0 kg K2O ha− 1), 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.
Highlights
Nitrogen (N) and potassium (K) are two important mineral nutrients in regulating leaf photosynthesis
A research on the N allocation of Ageratina adenophora showed that the invasive plants allocated 13.0% more leaf N to photosynthesis and had 24.4% higher photosynthetic rate (Pn) and 20.2% higher photosynthetic N use efficiency (PNUE) that that of native plants, and there was no significant differences between leaf total N content [14]
Based on our original assumption that the supply of K could influence the leaf N allocation, what happened to the leaf N allocation? Compared with N0K0, N180K0 and N270K0, the supply of K increased the relative content of N consisted of photosynthetic N (Npsn) by 17.7, 8.8 and 7.3%, while the relative content of Nstore was decreased by 24.2, 11.4 and 8.7% on average, respectively
Summary
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 (Pn) of rice leaves will be of great significance for further increasing leaf Pn, photosynthetic N use efficiency (PNUE) and grain yield. Germinator leaves invested more N to cell wall to produce structurally tough leaves and maintain a long photosynthesis period, which was at the expense of lower allocation of N to Rubisco, lower Pn and lower PNUE. A research on the N allocation of Ageratina adenophora showed that the invasive plants allocated 13.0% more leaf N to photosynthesis and had 24.4% higher Pn and 20.2% higher PNUE that that of native plants, and there was no significant differences between leaf total N content [14]. Invasive plants allocated 45.2% lower cell wall protein content, 37.8% lower ratio of cell wall protein to leaf total protein, and 46.5% lower ratio of leaf N allocated to cell wall [14]
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