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 (NO3-) 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 NO3- deficiency. The effects of NO3- 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 NO3- sufficient condition, suggesting that the nitrogen requirement for rice normal growth could be satisfied with only half of roots supplied with NO3-. In the root split treatment, N uptake was positively correlated with the average of lateral root length (ALRL) in NO3- 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.
硝态氮（No3- ）对水稻侧根生长及其氮吸收的影响
王小兵 吴平* 胡 彬 陈青爽
（浙江大学生命科学院，杭州310029）
摘要: 侧根是植物吸收利用土壤养分的重要器官，其生长发育受内部遗传因子和外部环境矿质养分的影响。通过琼脂分层发现：局部供应No3- 可以诱导水稻（Oryza sativa L.)主根或不定根上侧根的生长。为研究旱种条件下No3- 对水稻侧根发育及其N吸收的影响，设置了3个蛭石培养实验：分根处理，全株缺N，全株供N处理。分根处理（一半根系供应3mmol/L,KON 3，另一半根系供应3mmol/L KCl)结果表明：局部供应NO3^-能够促进水稻侧根生长。而在全株处理下，N饥饿衣导了侧根的伸长。水稻根系对No3- 的这两种反应都存在着显著的基因型差异。同时对地上部N浓度，可溶性总糖含量及N含量分析表明，这些生理指标在分根处理与全株加N处理中的差异均不显著，表明分根处理也能基本满足植株正常生长对N的需求。在分根处理中，水稻的N含量与分根处理中供N一侧的平均侧根长度存在显著正相关，这表明在养分不均一的介质中，侧根长度对水稻N素吸收具有十分重要的作用。而在N素充足的条件下，两者之间的相关性并不显著，这暗示在养分充足的环境下，侧根长度可能并不是决定根系吸收N素的主要因素。
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