冻融交替下高山土壤微生物和矿质氮库对外源氮输入的响应

Response of Mineral Nitrogen Pool and Microorganism to External Nitrogen Input in Alpine Soil under Freeze-Thaw Alternation

【目的】研究外源氮输入和冻融交替对高山土壤生态的影响。【方法】采集青藏高原东缘高山土壤,在室内模拟不同水平外源氮输入(CK:不添加外源氮,N1:添加0.1mg·g^(-1)外源氮,N2:添加0.4mg·g^(-1)外源氮)和不同变温幅度冻融(剧烈冻融:温度变化范围为-20~2℃,温和冻融:温度变化范围为-2~2℃,持续冻结:温度保持为-2℃)处理,分析它们对土壤微生物和矿质氮库的影响。【结果】外源氮输入水平对土壤真菌数量无明显的影响,但明显增加了细菌数量和提高了过氧化氢酶和纤维素酶的活性。N2处理下过氧化氢酶和纤维素酶活性最高,分别为20,4mg·kg^(-1)·h^(-1)。不同变温幅度的冻融处理也对过氧化氢酶和纤维素酶的活性有明显的影响:剧烈冻融处理下两种酶活性分别高达21,4.3mg·kg^(-1)·h^(-1),持续冻结处理下两种酶活性分别低至16,3.1mg·kg^(-1)·h^(-1)。随着冻融的加剧和外源氮输入水平的提高,土壤中微生物生物量碳无明显的变化,微生物生物量氮则明显增加。剧烈冻融和N2处理组合下土壤微生物生物量氮质量分数最高,达516.69mg·kg^(-1)。【结论】未来氮沉降和气候变化带来的冻融交替的改变均会对青藏高原东缘高山土壤微生物群落和活性以及矿质氮库产生影响,由此对当地植物生长和布局带来实质性改变。

[Purposes]The effects of external nitrogen input and freeze-thaw alternation on alpine soil ecology were studied.[Methods]Alpine soil samples were collected from the eastern edge of Qinghai Tibet plateau.And then the effects of simulated external nitrogen input(CK:no exogenous nitrogen was added,N1:added 0.1 mg·g^(-1) external nitrogen,N2:added 0.4 mg·g^(-1) external nitrogen)and freeze-thaw alternation(severe freeze-thaw:temperature range-20~2℃,mild freeze-thaw:temperature range-2~2℃,continuous freezing:keep the temperature at-2℃)on soil microbes and mineral nitrogen pools were investigated.[Findings]The applying of exogenous nitrogen input did not affect the quantity of soil fungi significantly,but significantly increased the population of bacteria,as well as catalase and cellulase activities.The two enzymes were most active(20 and 4 mg·kg^(-1)·h^(-1),respectively)under N2 treatment.Freeze-thaw alternation also had significant influence on catalase and cellulase activities.And they were most active(21 and 4.3 mg·kg^(-1)·h^(-1),respectively)under severe freeze-thaw treatment.while under continuous freezing treatment,the lowest activities(16 and 3.1 mg·kg^(-1)·h^(-1),respectively)of these two enzymes were observed.As the degree of freeze-thawaggravated and amount of exogenous nitrogenincreased,MBC did not change significantly,while MBN greatly increased.The content of MBN was 516.69 mg·kg^(-1) under severe freeze-thaw and N2 treatment,which was the highest among all treatment.[Conclusions]The changes of soil microbial community and activity,as well as mineral nitrogen pool will be influenced by nitrogen deposition and freeze-thaw cycle,which will cause substantial changes to plant growth and distribution.