不同氮效率水稻品种增硝营养下根系生长的响应特征

Response of root growth of rice genotypes with different N use efficiency to enhanced nitrate nutrition

试验采用两室分根盒和溶液培养方法,研究了在增硝营养下不同氮效率水稻品种根系生长的响应特征。结果表明,在本试验条件下,与全铵培养下的根系相比,氮高效水稻品种南光在铵硝混合培养下的根系干重和氮积累量显著增加,增幅达33%和41%;同时其根系表面积、根系体积和侧根数增幅均达到显著水平,但根系长度却无明显增加。氮低效水稻品种Elio在铵硝混合培养下的根系生长差异均不显著。这表明氮高效水稻品种南光的根系生长对增硝营养的响应度强,进而促进了根系对氮素的吸收利用。从本试验的结果可推论,水稻对增硝营养的强响应度可能是水稻氮素高效吸收利用的生理机制之一。

Rice roots can excrete O2 to surrounding soil and this can convert ammonium （NH4^＋ ） to nitrate （NO3^-） in the process of nitrification at root surface or in rhizosphere and rice roots are actually always exposed to a mixture of NH4^＋ and NO3^- , although the predominant species of mineral nitrogen （N） in the soil collected from the lowland rice field is NH4^＋ . Therefore, NO3^- nutrition on the surface of rice roots is an important part of N nutrition of rice plants. Two experiments, including whole plant root culture and root-split culture in NH4^＋ and NH4^＋/NO3^- （75/25） solutions, were conducted to study the effect of enhanced NO3^- nutrition on root growth of rice cultivars with different N use efficiency （NUE） during whole growth stage. Two rice cultivars, namely Nangnang （a high NUE rice cultivar） and Elio （a low NUE rice cultivar） selected from 2003 and 2004 field experiments were used in the two experiments. Whole plant root culture indicated that differences existed in the root biomass accumulation between the two rice cultivars when rice roots were exposed to a mixture of NH4^＋ and NO3^- . Compared to NH4^＋ solution, enhanced NO3^- nutrition increased root biomass accumulation of Nangnang during different growth stages while no difference occurred in Elio. Root-split culture showed that the growth of rice roots was stimulated by localized NO3^- supply. For example, localized NO3- nutrition increased root biomass accumulation and N accumulation of localized roots in Nangnang cultivar by about 33% and 41%. Moreover, the number of laberal root, surface area and volume of localized roots were also significantly increased in Nangnang cultivar. It is coneluded that high N use efficiency rice cultivar was more responsive to NO3^- nutrition than low NUE cultivar, implying that enhanced growth of rice roots by NO3^- may be one of physiological mechanisms of high nitrogen use efficiency in rice plants.