不同放牧强度下荒漠草原土壤氮矿化季节性动态研究

The Study on Seasonal Dynamics of Soil Nitrogen MinerAlization under Different Grazing Intensities in Desert Steppe

放牧是中国北方主要的草地利用方式。放牧强度通过影响群落结构和土壤的理化性状以及土壤微生物活性对草地生态系统的养分循环产生显著影响。以位于内蒙古四子王旗的荒漠草原长期放牧控制试验平台为研究对象,通过设置四个放牧强度,即对照(CK)、轻度放牧(LG)、中度放牧(MG)和重度放牧(HG),探讨了放牧强度对土壤无机氮库和氮矿化过程季节变化的影响。根据该地区气候特点和植物生长季节,将一年划分为3个时期,分别为生长季初期(5-6月)、生长季盛期(7-9月)和非生长季(10月至次年4月)。结果表明,(1)在生长季初期,放牧抑制了土壤氮矿化作用,土壤温度与土壤无机氮含量呈显著负相关。(2)在生长季盛期,放牧促进了土壤净氮矿化作用,其中LG区的净氮矿化速率和净硝化速率显著高于对照区均较高;土壤净氮矿化和净硝化速率与土壤温度和含水量均呈显著正相关关系。(3)在非生长季,放牧抑制了土壤氮矿化作用,对照区不放牧处理的土壤净氮矿化速率显著高于放牧区;土壤含水量与土壤无机氮含量呈显著正相关,而与净氮矿化速率和净硝化速率均呈显著负相关关系。综上,高强度放牧抑制了土壤氮矿化过程,可能会进一步加剧净初级生产力的氮素限制。同时,放牧对土壤氮素转换过程的影响存在显著的季节性差异。

Grazing is major utilization of grasslands in Northern China,and the grazing intensity can be a driving factor for nutrient cycling,especially for the soil nitrogen(N)transformation processes.This study tried to explore the seasonal variation of soil inorganic nitrogen pool and nitrogen mineralization process under different grazing intensities in a long-term grazing experimental site with four grazing intensity treatments including control(CK),light grazing(LG),moderate grazing(MG),and heavy grazing(HG).In this study,we divided a year into three periods which were regarded as early growing season(from May to June),peak growing season(from July to September),and non-growing season(from October to the following March),according to the characteristics of climate and vegetation growth.Our results showed that,(1)in early growing season,grazing restrained soil nitrogen mineralization.There was significant negative correlation between soil temperature and inorganic nitrogen content.(2)In peak growing season,grazing accelerated soil nitrogen mineralization,and the higher rates of net nitrogen mineralization and nitrification occurred in light grazing plots.There were significant positive correlations between soil net nitrogen mineralization,nitrification rate and soil temperature,humidity.And(3)in non-growing season,grazing decreased soil nitrogen mineralization,and the soil net nitrogen mineralization rate in CK plots was significantly higher than in grazing plots.Soil humidity showed significant positive correlation with the inorganic nitrogen pool while significant negative correlation with net nitrogen mineralization and nitrification rates.Our results reveal that the soil N mineralization may be inhibited by heavy grazing,and this will aggravate nitrogen limitation for net primary productivity in this desert steppe area.Besides,there is significant seasonality in the impacts of grazing on soil N storage and soil N transformation processes.