冻融作用下模拟氮沉降对土壤酶活性与土壤无机氮含量的影响

采用野外模拟实验方法研究了冻融作用下氮沉降对东北松嫩羊草草地土壤酶活性和无机氮含量的影响。结果表明:氮沉降对土壤脲酶和蛋白酶活性具有一定的影响,而且随着氮沉降量的升高,两种酶活性均呈先升高后降低的趋势;土壤脲酶和蛋白酶活性在T1取样时间(秋冬冻融循环时期)和T2取样时间(冬春冻融循环时期)差异显著。土壤铵态氮含量随氮沉降量的增加呈上升趋势,且T1与T2取样时间差异显著;土壤硝态氮含量在T1取样时间随氮沉降量的增加而增加,在T2取样时间随施氮量的增加呈先升高后降低的趋势,且在温度较低的T1取样时间含量明显高于T2取样时间。刈割处理对T1取样时间土壤硝态氮含量影响显著,对T2取样时间土壤脲酶活性及土壤铵态氮含量影响显著。

Effects of Simulated Nitrogen Deposition on Enzymatic Activities and Inorganic Nitrogen Contents in Soil During Freeze - Thaw Cycles

Atmospheric nitrogen deposition and freeze-thaw cycles impact soil nitrogen transformation. In this study, a field simulation experiment was conducted to investigate the effects of nitrogen deposition on enzymatic activities and inorganic nitrogen contents in soil during freeze-thaw cycles in Songnen grassland of Northeastern China. Nitrogen deposition exerted some impacts on soil urease and protease activities. The activities of both enzymes increased with nitrogen rates, but decreased at higher nitrogen, which may relate to N saturation. Urease and protease activities were significantly higher in the sampling time 2(T2)(freeze-thaw cycles during winter/ spring seasons) than in the sampling time 1(T1)(freeze-thaw cycles during fall/ winter seasons), due to more freeze-thaw cycles occurred in T2 resulted from higher temperature. The contents of soil ammonium nitrogen increased with nitrogen deposition, and was significantly higher in T2 than in T1. With nitrogen addition, nitrate nitrogen contents in soil increased in T1, while it increased initially but decreased then in T2. Soil nitrate nitrogen contents were significantly higher in T1 than in T2, which might be due to nitrate leaching by water from the melting process in the early spring. Compared with non-clipping, clipping significantly reduced soil nitrate nitrogen contents in T1, but increased soil urease activity and soil ammonium nitrogen contents in T2. The changes in soil surface temperature and grass residues caused by clipping may also influence soil enzyme activities and inorganic nitrogen contents.