High/low nitrogen adapted hybrid of rice cultivars and their physiological responses
Seventy (70) selective bred hybrid of rice combinations were treated with three levels of pure nitrogen (N1/2, 20.0mg/l; N1, 40.0mg/l; N2, 80.0mg/l) for two weeks for indentifying the adaptation of nitrogen. They were divided into six types with the cluster analysis as flowers: Type 1 with good adaptability of different concentrations of nitrogen, their ratio of root and stem (R/S ratio) was significantly increased under N1/2 and N2 treatment; but type 6 with sensitivity to those environments, the R/S ratio was significantly decreased under corresponding treatments. Other four types were lying in the middle with moderate adaptability of nitrogen. Furthermore, five varieties were selected from each of the mentioned six types and then grew in N-free conditions to investigate their performance on lack of N. The results showed that type 1, the dry weight of the materials originally growing in N2 and N1/2 conditions were both decreased, which had the lowest adaptability to N-free conditions; type 3, those of the materials growing similar conditions were both increased, which had better adaptability to N-free conditions. On the whole physiologically, the rice materials with good adaption of N were due to higher nitrate reductase activity (NRA) at low nitrogen conditions, more chlorophyll content and soluble protein in high nitrogen conditions, and the Rubisco mobilized in N-free conditions as well.
Key words: Rice, ratio of root and stem, SPAD, nitrogen, adaptation.