增温和氮添加对中亚热带杉木人工林土壤氮矿化和N_(2)O排放的影响

Effects of Warming and Nitrogen Addition on Soil Nitrogen Mineralization and N_(2)O Emission in a Mid-subtropical Cunninghamia lanceolata Plantation

[目的]研究增温和氮沉降对中亚热带森林土壤氮矿化和氧化亚氮(N_(2)O)排放的影响,以期深入认识全球变化背景下中亚热带森林土壤氮循环过程。[方法]选取经过野外增温和氮添加处理的中亚热带杉木人工林土壤,将野外非增温处理和增温处理的土壤置于不同温度(20、25℃)培养箱中,同时对野外氮添加处理的土壤继续添加不同梯度的氮素(0.1、0.2 g·kg^(−1),以干土计),进行为期28 d的室内培养,研究增温和氮添加对土壤氮矿化和N_(2)O排放的影响。[结果]与对照相比,增温和氮添加及二者交互处理增加了土壤铵态氮、硝态氮和矿质氮含量,且氮添加水平越高增加越明显,增温处理增加不显著。与对照相比,培养28 d后增温处理的土壤净铵化速率、净硝化速率和净氮矿化速率变化不显著,低氮、增温+低氮显著增加土壤净硝化速率,而高氮、增温+高氮显著降低土壤净氮矿化速率。与对照相比,增温和氮添加及二者交互处理总体降低土壤N_(2)O排放速率,土壤N_(2)O累积排放量也显著降低(P<0.05),其中,单独增温、低氮、高氮、增温+低氮和增温+高氮处理土壤N_(2)O累积排放量显著低于对照50%、21%、29%、62%和31%。增温和氮添加及二者交互处理显著降低土壤pH值。相关性分析表明:土壤N_(2)O排放速率与土壤pH值呈显著正相关,与硝化速率呈显著负相关,而与土壤铵化速率无显著相关。[结论]增温和氮添加降低土壤pH值,同时抑制土壤N_(2)O排放,因此,全球变化背景下中亚热带森林土壤中存留的硝态氮可能以淋溶方式损失。

[Objective]To study the effects of warming and nitrogen deposition on soil nitrogen mineralization and nitrous oxide(N_(2)O)emission in mid-subtropical forests for further understanding soil nitrogen cycling process in subtropical forests under the background of global change.[Method]The soils taken from a mid-subtropical Cunninghamia lanceolata plantation treated with field warmed and nitrogen addition were selected,and the field un-warmed and warmed soils were placed in incubators at different temperatures(20,25℃).The soil was continuously added with different gradients of nitrogen(0.1、0.2 g·kg^(−1))for 28 days of indoor cultivation to study the effects of warming and nitrogen addition at different concentrations on soil nitrogen mineralization and N_(2)O emissions.[Result]Compared with the control,soil ammonium,nitrate and mineral nitrogen contents were increased by warming and nitrogen addition and their interaction treatment,and the increase was more obvious with the higher level of nitrogen addition,while the increase was not significant in warming treatment.Compared with the control,the net ammonification rate,net nitrification rate and net nitrogen mineralization rate of soil treated with warming after 28 days of culture had no significant changes.Low nitrogen,warming+low nitrogen treatments could significantly increase soil net nitrification rate,while high nitrogen,warming+high nitrogen could significantly decrease soil net nitrogen mineralization rate.Compared with the control,warming and nitrogen addition and their interaction treatment reduced the soil N_(2)O emission rates,and the cumulative soil N_(2)O emissions was also decreased significantly(P<0.05).The cumulative soil N_(2)O emissions under the treatments of low nitrogen,high nitrogen,warming+low nitrogen and warming+high nitrogen were significantly lower than those of the control by 50%,21%,29%,62%and 31%,respectively.At the same time,warming,nitrogen addition and their interaction treatments also significantly decreased the soil pH value.Correlation analysis showed that soil N_(2)O emission rate was positively correlated with soil pH and was negatively correlated with the soil net nitrification rate,but not significantly correlated with soil ammonium rate.[Conclusion]Warming and nitrogen addition reduce soil pH and inhibit soil N_(2)O emission.Therefore,nitrate nitrogen retained in mid-subtropical forests soils may be lost by leaching under the background of global change.