Effects of Nitrate on the Growth of Lateral Root and Nitrogen Absorption in Rice

Lateral root is primary organ for plant to explore and utilize soil nutrient efficiently. The development of lateral roots (LR) is controlled by both genetic factors and nutrient status in environment. To investigate the effects of nitrate (NO - 3) on rice lateral root growth and nitrogen (N) uptake efficiency under upland condition, three treatments, including root_split culture and whole plant culture in N sufficient and deficient conditions, were used in a vermiculite culture experiment. Root_split treatment showed that the growth of lateral roots was stimulated by localized nitrate supply. However, in whole plant culture, elongation of lateral roots was induced by NO - 3 deficiency. The effects of NO - 3 on rice lateral root growth were genotype_dependent. Similar N concentration, soluble sugar concentration and N content in shoot were observed in both root_split treatment and whole plant culture under NO - 3 sufficient condition, suggesting that the nitrogen requirement for rice normal growth could be satisfied with only half of roots supplied with NO - 3. In the root_split treatment, N uptake was positively correlated with the average of lateral root length (ALRL) in NO - 3_supplied side, suggesting that the ALRL is important for rice root N uptake in the environment where the nitrogen nutrient is limiting factor. No significant correlation was observed between N uptake and ALRL in whole plant culture under N sufficient condition, which implies that the length of lateral roots may not be the main factor to determine the rice root N uptake in nutrient_rich zone. Morphological and metabolic evidence in this study provided some prospects for genetic improvement of root system characters to improve the efficiency of nutrient absorption in rice.