短花针茅荒漠草原土壤氮素矿化对载畜率的响应

摘要

Nitrogen mineralization is a key process affecting nitrogen availability and nitrogen cycling in soils.The desert steppe is a grassland ecosystem with poor resources,a harsh climate,and a relatively simple vegetation structure.Therefore,it is important to study nitrogen availability on the desert steppe to maintain the stable development of these grasslands.In this study,the net nitrogen mineralization rate was monitored over the whole growing season by using the top-buried tube culture method.We monitored the net nitrogen mineralization rate under four grazing treatments [0 (CK),0.91 (light grazing),1.82 (moderate grazing),2.71 (heavy grazing) sheep/(hm2 · a)],and analyzed the relationships between environmental factors (soil temperature and humidity) and soil nitrogen content and mineralization.The aim of these analyses was to provide reference data to develop strategies for the sustainable utilization of nitrogen in the desert grassland ecosystem.The soil net nitrogen mineralization rate first increased and then decreased during the growing season,and the effect of stocking rate was higher in July and August in the peak growth period.The net nitrogen mineralization rate was highest in the moderate grazing treatment [l.82 sheep/(hm2 · a)] and lowest in the heavy grazing treatment [2.71 sheep/(hm2 · a)].Pearson's correlation analyses showed that the nitrification rate was positively correlated with net nitrogen mineralization rate,and the net nitrogen mineralization rate was greatly affected by nitrification during the whole growing season.There was a significant negative correlation between soil water content and net nitrogen mineralization rate,but not between soil temperature and net nitrogen mineralization rate.In summary,the moderate grazing treatment [1.82 sheep/(hm2 · a)] represents the ideal stocking rate to maintain a stable nitrogen mineralization rate in desert steppe grasslands.%氮矿化是决定土壤提供可利用性氮的关键生态环节,同时也是当今国内外土壤氮素循环的研究热点,荒漠草原作为草地生态系统中极特殊的一种草地类型,其资源贫乏,气候严酷,植被结构相对简单,因此研究荒漠草原氮素的可利用性对维持荒漠草原稳定发展十分必要.鉴于此,本研究以内蒙古四子王旗短花针茅荒漠草原为对象,采用顶盖埋管培养法,通过在整个生长季的跟踪调查,主要探讨了净氮矿化速率对4个载畜率梯度[0(对照)、0.91(轻度放牧)、1.82(中度放牧)、2.71(重度放牧)羊/(hm2·a)]的响应,并结合土壤温湿度,分析其与土壤氮矿化的关系,旨在为荒漠草原生态系统氮素可持续利用的研究提供基础数据及管理参考.结果显示,土壤的净氮矿化速率在整个生长季呈现出先降后增的趋势,并且在生长高峰期7月及8月受载畜率的影响较大.4种载畜率梯度下中度放牧处理[1.82羊/(hm2· a)]具有最高的净氮矿化速率,重度放牧处理中[2.71羊/(hm2· a)]净氮矿化速率最低.皮尔森相关分析表明硝化速率与净氮矿化速率显著正相关,在整个生长季中净氮矿化速率受硝化作用影响较大.不同载畜率梯度下,土壤水分与净氮矿化速率极显著负相关,而土壤温度则与净氮矿化速率无显著相关性.综上所述中度载畜率水平[1.82羊/(hm2·a)]是维持荒漠草原稳定矿化速率的理想载畜率.