In recent years, excessive use of chemical nitrogen （N） fertilizers has resulted in the accumulation of excess ammonium （NH4＋） in many agricultural soils. Though rice is known as an NH4＋-tolerant species and can directly absorb soil intact amino acids, we still know considerably less about the role of high exogenous NH4＋ content on rice uptake of soil amino acids. This experiment examined the effects of the exogenous NH4＋ concentration on rice uptake of soil adsorbed glycine in two different soils under sterile culture. Our data showed that the sorption capacity of glycine was closely related to soils＇ physical and chemical properties, such as organic matter and cation exchange capacity. Rice biomass was significantly inhibited by the exogenous NH4＋ content at different glycine adsorption concentrations. A three-way analysis of variance demonstrated that rice glycine uptake and glycine nutritional contribution were not related to its sorption capacity, but significantly related to its glycine：NH4＋ concentration ratio. After 21-d sterile cultivation, the rice uptake of adsorbed glycine accounted for 8.8%-22.6% of rice total N uptake, which indicates that soil adsorbed amino acids theoretically can serve as an important N source for plant growth in spite of a high NH4＋ application rate. However, further studies are needed to investigate the extent to which this bioavailability is realized in the field using the 13C, 15N double labeling technology.
Xiao-chuang CAOQing-xu MALiang-huan WULian-feng ZHUQian-yu JIN
