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 180 kg N ha-1 with 60 kg 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 180 kg 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 (180 kg N ha-1) relative to those of lower N one (0 kg 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. 本項研究利用生育期間施予不等量氮肥方式(於0-180 kg N ha-1範圍每隔60 kg N ha-1 劃分四不同等級)，探討不同含氮狀態之田間生長稻株(Oryza sativa L. cv. TNG 67)葉片內部構造之變化。根據試驗結果，穗形成啟始期之稻株地上部含氮狀態與氮肥施用量之間呈現顯著直線正相關，無論2001年一、二期稻作皆出現類似關係。不同含氮狀態之稻株顯示出不等葉片解剖特徵差異，尤以0 kg N ha-1及180 kg N ha-1兩處理差異最為明顯。諸如葉肉細胞內澱粉顆粒排列及分佈，即隨著氮肥施用量而異。相較於含氮狀態較低之葉肉細胞(如0 kg N ha-1處理)，高含氮狀態之葉肉細胞(如180 kg N ha-1處理)其澱粉顆粒排列及分佈較為鬆散。葉片厚度伴隨稻株地上部含氮狀態之升高而增加，葉片水分含量則呈現二次曲線改變。儘管水分不虞匱乏，常態環境下葉片因蒸散之水分損耗可能出現不等捲曲現象，惟施用較高氮肥稻株之葉片其捲曲情形較為緩和。進一步計算葉片捲曲指數(leaf rolling index, LRI)，發現含氮較高者之LRI 值較大( 即葉片捲曲程度較小)，為一線性關係，而泡狀細胞面積與葉肉層面積比值(bulliform/mesophyll ratio)與地上部氮素含量之間則呈現二次曲線關係。綜合本試驗之研究結果，顯示稻株具有調節葉片內部構造之能力與可塑性，使其能夠自我調適存活於不等土壤氮素供應環境。