Fertilizer-N Uptake and Distribution in Rice Plants Using 15N Tracer Technique Distribution and Fate of Anthropogenic Nitrogen in the Calamagrostis angustifolia Wetland Ecosystem of Sanjiang Plain, Northeast China Review of Nitrogen Cycle in Plant-soil System Based on Application of 15N Tracer Technique Nitrogen absorption/distribution and physiological characteristics of Salix matsudana seedlings grown in hydroponic solution Investigation on the economically-ecologically appropriate amount of nitrogen fertilizer applied in rice production in Fe-leaching-Stagnic Anthrosols of the Taihu Lake region