【摘要】 研究表明 ,0～ 30cm土层 7月氮 (N)总储量为 479.2g·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～ 1 1 .3g·m-2 之间 ,7月无机N储量为 7.3g·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 .48g·m-2 ·a-1 ,植物根系向地上每年输送的N量为 2 .97g·m-2 ·a-1 ,地上活体向地下转移的N量为 1 .54g·m-2 ·a-1 ,植物地上部分每年转为立枯凋落物的N量为 1 .43gm-2·a-1 ,由立枯凋落物转为土壤有机N的量大于 1 .0 8g·m-2 ·a-1 ,植物根系每年转为土壤有机N的量为 1 .51g·m-2 ·a-1 。更多还原

【Abstract】 Objectives of the research were to determine the extent of internal cycling of N itrogen （N） in Leymus chinensis grasslands using the compartment model method. The internal ecosystem was divided into five compartments: （i） Above_gro und 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 whi le the underground biomass was collected from 25 cm×25 cm sections at 30 cm so il depth. The soil samples were washed, and dead roots were separated from livin g roots. Soil N for total N and mineral N test was sampled at two depths （0₁5 c m a nd 15₃0 cm）. The above samples were collected at 4 weeks intervals between mid April to mid_September with five replications. Standing dead and litter were col lected from five 1 m×1 m quadrats in mid_October, 1994, each 100 g of the sampl es was put into one nylon net bags, total 30 bags of the samples were randomly s cattered on grassland soil surface, and 5 samples were collected every month fro m mid_April to mid_Sep, in 1995. The remaining samples were weighed and N conten t 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 r esult indicated that the soil_plant system contained 479.2 g·m -2 of N, ne arly all in the orga nic 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 wa s even higher than NH + 4 N, which is different from the other type grassland s, where the peak of NH + 4_N contents appeared earlier than that of NO - 3_N cont ents. Pla nt 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 biom ass that turned to litter N is 1.43 g·m -2 ·a -1 . Approximately 1.08 g·m -2 ·a -1 N in litter changed to soil organic N, and 1.51 g·m -2 ·a -1 of N from the root changed into soil organic N. Comparison between Canadian mixed prairie and Northeast China L. chinensis g rasslands indicates that the utilization efficiency of soil N for grasses is low er in L. chinensis grasslands than that in Canadian mixed prairie.更多还原