牧压梯度下海北高寒草甸土壤速效氮变化特征及其影响因素分析

在青海海北高寒矮嵩草草甸设置封育禁牧(CK)、轻牧(LG)、中牧(MG)和重牧(HG)放牧梯度试验样地, 进行了土壤速效氮变化特征及影响因素的分析. 结果表明: 植物生长期的5-9月, 土壤NH₄⁺-N、NO₃^--N和速效氮(NH₄⁺-N和NO₃^--N之和)含量季节变化明显, 基本表现为植物生长初期高, 末期低. CK、LG、MG和HG条件下, 5-9月0~40 cm土壤NH₄⁺-N平均含量分别为17.62 mg·kg^-1、17.84 mg·kg^-1、18.63 mg·kg^-1和16.67 mg·kg^-1, NO₃^--N平均含量为8.91 mg·kg^-1、8.23 mg·kg^-1、7.99 mg·kg^-1和7.94 mg·kg^-1, 速效氮平均含量为26.53 mg·kg^-1、26.07 mg·kg^-1、26.62 mg·kg^-1和24.61 mg·kg^-1, 基本表现出随放牧强度增大而降低. 土壤速效氮月际变化与地上绿体生物量具有一定的负相关关系, 表明地上生物量越大, 消耗土壤速效氮越趋明显; 与枯落物有一定的正相关关系, 与地下生物量关系不甚明显, 与湿沉降呈现负的相关性. 土壤NH₄⁺-N含量与土壤有机碳有负相关关系, 而NO₃^--N含量与有机碳相关性差, 表明土壤有机碳越高, 土壤NH₄⁺-N消耗越明显.

Analysis of the variation characteristics and controlling factors of soil rapidly available nitrogen in Haibei alpine meadow under grazing pressure gradient

Variation of soil available nitrogen and its controlling factors in different grazing intensities,including banning grazing (CK),light grazing (LG),moderate grazing (MG)and heavy grazing (HG),were studied in Haibei alpine Kobresia humilis meadow area of Qinghai Province.The following results were obtained:1 )The content of ammonia nitrogen,nitrate nitrogen and soil available nitrogen have obvious variation from May to September.They are higher at the beginning of growing season and decline towards the end.2 )The average ammonia nitrogen content of CK,LG,MG and HG in the upper 40cm soil is 17.62 mg·kg -1 ,17.84 mg· kg -1,18.63 mg·kg -1 and 16.67 mg·kg -1,respectively;the average nitrate nitrogen content is 8.91 mg· kg -1 ,8.23 mg·kg -1 ,7.99 mg·kg -1 and 7.94 mg·kg -1 ,respectively;the soil available nitrogen content is 26.53 mg·kg -1,26.07 mg·kg -1,26.62 mg·kg -1 and 24.61 mg·kg -1,respectively.Grazing could reduce the ammonia nitrogen and soil available nitrogen content to some extent,especially in the heavy grazing, but not evidently affect the nitrate nitrogen content.3 )Statistical analysis found that soil ammonia nitrogen, nitrate nitrogen and available nitrogen have some negative correlation with the aboveground green biomass:the more the aboveground biomass,the more soil rapidly available nitrogen consumed.This is obvious in banning grazing (CK)and light grazing (LG)and has some positive correlation with the litters.This means that litter decomposition and surface mini environment could influence the nitrogen replenishment to the soil.They have no obvious correlation with underground biomass and have negative correlation with wet deposition of nitrogen. Though wet subsidence has evident nitrogen supplies,the nitrogen consumption is still greater than supplies. Ammonia nitrogen and available nitrogen have significant negative correlation with soil organic carbon,but the correlation between nitrate nitrogen and organic carbon is not obvious.It is revealed that the more soil organic carbon,the more consumption of soil ammonia nitrogen and available nitrogen.