研究表明， 0～30 cm土层7月氮（N）总储量为479.2 g·m－2,其中主要为有机N，占总N量的98.5%,土壤中的无机N年度变化很大，在2.55～11.3 g·m－2之间，7月无机N储量为7.3 g·m－2，与其它类型草地不同，该类型草地土壤铵态N与硝态N含量有些季节相差不大，有些季节硝态N的含量超过铵态N的含量，铵态N的峰值出现的时间早于硝态N。植物根系吸收利用的无机N约为3.48 g·m－2·a－1,植物根系向地上每年输送的N量为2.97 g·m－2·a－1, 地上活体向地下转移的N量为1.54 g·m－2·a－1,植物地上部分每年转为立枯凋落物的N量为1.43 g m－2·a－1, 由立枯凋落物转为土壤有机N的量大于1.08 g·m－2·a－1,植物根系每年转为土壤有机N的量为1.51 g·m－2·a－1。
Objectives of the research were to determine the extent of internal cycling of Nitrogen (N) in Leymus chinensis grasslands using the compartment model method. The internal ecosystem was divided into five compartments: (i) Above_ground N, (ii) Standing dead and litter N, (iii) Living root N, (iv) Soil organic N, and (v) Soil mineral N. Above_ground biomass was harvested from five 1 m ×1 m quadrats in each plot while the underground biomass was collected from 25 cm×25 cm sections at 30 cm soil depth. The soil samples were washed, and dead roots were separated from living roots. Soil N for total N and mineral N test was sampled at two depths (0_15 cm and 15_30 cm). The above samples were collected at 4 weeks intervals between mid_April to mid_September with five replications. Standing dead and litter were collected from five 1 m×1 m quadrats in mid_October, 1994, each 100 g of the samples was put into one nylon net bags, total 30 bags of the samples were randomly scattered on grassland soil surface, and 5 samples were collected every month from mid_April to mid_Sep, in 1995. The remaining samples were weighed and N content was tested for each sample. The total N of plant and soil was measured using Kjeldahl digestion method. The amounts of NH+4-N and NO－ 3-N measured by distillation method. The result indicated that the soil_plant system contained 479.2 g·m-2 of N, nearly all in the organic form. The plant available N, about 1.5% of total N in the forms of NH+4 and NO－3,the seasonal changes of the two forms were great, the storage of soil mineral compartment was between 2.55-11.3 g·m-2，and the content of NO－3 -N was even higher than NH+4N, which is different from the other type grasslands, where the peak of NH+4-N contents appeared earlier than that of NO－3 -N contents. Plant root uptook N 3.48 g·m-2·a-1, the above_ground took up N 2.97 g·m-2·a-1, the N re_translocation was about 1.54 g·m-2·a-1 from above_ground to root. The N of above_ground biomass that turned to litter N is 1.43 g·m m-2·a-1. Approximately 1.08 g·m m-2·a-1 N in litter changed to soil organic N, and 1.51 g·m m-2·a-1 of N from the root changed into soil organic N. Comparison between Canadian mixed prairie and Northeast China L. chinensis grasslands indicates that the utilization efficiency of soil N for grasses is lower in L. chinensis grasslands than that in Canadian mixed prairie.