Comparison of upper leaf and lower leaf of rice plants in response to supplemental nitrogen levels

A field study was conducted to study effects of four nitrogen (N) supplemental levels on biomass, protein-N, non-protein-N, and starch of an upper and a lower leaf in rice (Oryza sativa L.). The ranges of leaf protein-N, non-protein-N, total N, and starch concentrations were from 1.18% to 3.66%, from 0.13% to 0.67%, from 1.32% to 4.14%, and from 38.4 mg g(-1) to 108.6 mg g(-1) respectively. The upper leaf appeared to be more sensitive than the lower leaf in response to N levels on biomass, but larger differences of protein-N, total N, and starch contents were observed among nitrogen level treatments in the lower leaf than in the upper leaf Protein-N may be the best indicative of N status in rice. The lower leaf had a considerably higher ratio of protein-N to non-protein-N at panicle formation and heading growth stage. The lower leaf had higher starch contents, which decreased with increasing N level. The response differences between the upper leaf and the lower leaf with relation to light conditions, developmental extent and leaf function were discussed. The results suggested that the lower leaf could be more suitable as a test sample for N status diagnosis by leaf chemical analysis, especially during the reproductive growth stage.