不同湿度条件下模拟增温对科尔沁沙质草地土壤氮矿化的影响

Effects of Warming on Soil Nitrogen Mineralization under Different Soil Moisture Conditions in the Horqin Sandy Grassland

氮矿化作用是影响沙质草地植物群落物种组成和初级生产力的重要因素之一。温度和水分被认为是影响土壤氮矿化/硝化作用的两个关键环境因子,认识沙质草地土壤氮矿化作用对温度和水分的响应,对于预测全球变化对沙质草地生态系统结构和功能的影响具有重要作用。本文通过测定开顶式生长室(OTC)内不同湿度条件下增温时沙质草地净氨化速率、净硝化速率和净矿化速率的变化,分析增温和湿度变化对土壤氮矿化作用的影响。结果表明:不论增温与否,沙质草地土壤净氨化速率、净硝化速率和净矿化速率随着土壤湿度增加而明显提高。土壤净氨化速率在土壤湿度为15.2%时最大,但是净硝化速率和净矿化速率在土壤湿度为11.8%时最大,土壤湿度达到时15.2%表现下降趋势。增温使沙质草地土壤氮矿化作用发生显著变化,但增温的效应与土壤湿度存在一定的关联。土壤湿度为3.4%、5.1%、8.5%时,增温处理使土壤净氨化速率较对照明显提高;但是土壤湿度为11.8%、15.2%时,增温处理时土壤净氨化速率较对照显著降低;土壤湿度为8.5%和11.8%时,增温使土壤净硝化速率和净矿化速率显著升高(p<0.05),在湿度为1.7%、3.4%、5.1%以及15.2%时,增温处理和对照之间的净硝化速率、净矿化速率无显著差异。这说明只有在适宜的土壤湿度条件下,增温才显著影响沙质草地土壤矿化作用,当土壤湿度处于相对干旱或过度湿润的状态下,增温对沙质草地土壤矿化作用没有显著影响。

Temperature and moisture are the key factors determining soil nitrogen mineralization rate which affect species composition and primary productivity of sandy grassland. Our objective was to examine the re sponse of soil nitrogen mineralization in the Horqin sandy grassland to temperature increase under different soil moisture conditions, which is essential to predict the effects of global warming and precipitation varia tion on sandy grassland ecosystem structure and function. Our results showed that net ammonification rates, net nitrification rates and net mineralization rates of soil N increased significantly with soil moisture rising under condition of warming or not. Net ammonification rate of soil N reached the maximum at the moisture of 15.2%. Net nitrification rates and net mineralization rates of soil N, however, reached their maximums at the moisture of 11.8% and decreased at the moisture of 15.2 %. Warming by OTC significantly acceler ated net ammonification rate, net nitrification rates and net mineralization rates of soil N. But the effects of warming were related to soil moisture. Net ammonification rates under warming condition were significantly higher than those without warming at the moisture of 3.4 %, 5.1%, 8.5 %, but significantly lower than those without warming at the moisture of 11.8 % and 15.2 %. Net nitrification rates and net mineralization rates of soil N under warming condition were significantly higher than those of control at the moisture of 8.5 % and 11.8 %. At the moisture of 1.7 % ,3.4 %, 5.1% and 15.2 %, however, there were no significant differences of net nitrification rates and net mineralization rates of soil N between warming and control. This implies that effect of warming on soil N mineralization is significant only at the appropriate moisture conditions in the Kerqin sandy grassland.