Changes in Leaf Internal Structure of Rice Plants to Application of Varied Rates of Nitrogen Fertilizer

Abstract

Experiments were conducted to examine changes in leaf internal structure of field-grown rice plants (Oryza sativa L. cv. TNG 67) to varied rates of nitrogen (N) fertilizer, from 0 to 180kg N ha^(-1) with 60kg N ha^(-1) intervals, applied to the experimental plots during the first and the second cropping seasons of 2001. Results showed that aboveground N content of rice plants measured in the panicle initiation stage was related to the increase of N rates applied to the paddy and a linear fashion was displayed in the range of N application rates. A diversity of leaf anatomical characteristics was observed in leaves from tagged plants of varied N status grown in both crops, especially between plants treated with 0 and 180kg N ha^(-1). The packing and arrangement of starch granules within parenchyma cells changed in leaves treated with varied N rates. Starch granules were loosely distributed and packed in plants of higher N content (180kg N ha^(-1)) relative to those of lower N one (0kg N ha^(-1)). Leaf thickness increased progressively with increasing aboveground N content and leaf water content (LWC) changed in a curvilinear trend. Under normal growth conditions leaves may roll to a certain extent owing to water loss through transpiration even with sufficient water supply, while this phenomenon was relieved in plants applied with heavy rate of N fertilizer. A higher value of leaf rolling index (LRI) was computed in high N-treated plants, showing in a linear trend. Changes in the ratio of bulliform/mesophyll to aboveground N content were a quadratic function. Results imply that rice plants have the ability and plasticity to regulate their leaf internal structure and thus may enable them adapting to soils varying in N supply in both cropping seasons.