不同水分条件下土地利用方式对我国热带地区土壤硝化过程及NO和N_(2)O排放的影响

Effects of Land-use Conversion on Soil Nitrification and NO&N_(2)O Emissions in Tropical China Under Different Moisture Conditions

热带地区雨热条件丰富,硝化过程产生的硝态氮不利于氮素养分的保持,同时会带来氮氧化物排放等环境负面效应.橡胶树和茶树在热带地区广泛种植,不同土地利用方式土壤硝化速率和氮氧化物排放的差异尚不清楚.以海南白沙地区典型橡胶林和茶园土壤为研究对象,分别采集5 a(T5)和15 a(T15)茶园土壤和附近橡胶林(XJ)土壤,设置低(50%WFPS-L)和高(80%WFPS-H)两种不同水分含量,在25℃进行71d室内培养试验,探究不同土地利用方式和不同水分含量对土壤净硝化速率、NO和N_(2)O排放的影响.结果表明:①橡胶林改为茶园后,在高含水量条件下,显著降低了土壤净硝化速率、NO和N_(2)O排放,整体呈现XJH>T15H>T5H的趋势,XJH处理土壤净硝化速率、NO和N_(2)O排放分别高达4.2 mg·(kg·d)^(-1)、1.4 mg·kg^(-1)和14.3 mg·kg^(-1)(以N计);在低含水量条件下,茶园土壤显著降低了土壤NO排放,N_(2)O排放在各土壤间差异不显著,净硝化速率在XJ和T15处理之间无显著差异;土壤NO排放和净硝化速率呈极显著正相关(P<0.01).②XJH净硝化速率高于XJL,茶园土壤呈相反趋势;XJ和T15的NO排放对水分的响应和净硝化速率趋势一致,高硝化速率促进NO排放,而T5处理NO排放受含水量影响不显著;相比低含水量处理,高含水量各处理显著促进N_(2)O排放.结果表明,土壤有机质(SOM)、全氮(TN)、pH和含水量是影响土壤净硝化速率、NO和N_(2)O排放的关键因子,高含水量条件下橡胶林转为茶园的种植模式显著降低了土壤净硝化速率和对环境的负面影响.

Rain and heat conditions are abundant in tropical areas,and rubber and tea are widely planted in this region;the nitrification process produces nitrate content,which is not conducive to the maintenance of nitrogen nutrients,and has negative environmental effects(nitrogen oxide emissions).The characteristics of soil nitrification rate and nitrogen oxide emission under different land use patterns remain unclear.An incubation experiment was conducted under the 5 a(T5)and 15 a(T15)tea plantation soils and the nearby typical rubber plantation(XJ)soils in Baisha county of Hainan province under two moisture contents(50%WFPS-L and 80%WFPS-H)for 71 d at 25℃.The results showed that:①after the rubber plantation was converted to a tea plantation,the net nitrification and soil NO and N_(2)O emissions were significantly reduced under high moisture content.The overall trend was in the order of XJH>T15H>T5H,and the values of soil net nitrification and NO and N_(2)O emissions were as high as 4.2 mg·(kg·d)^(-1),1.4 mg·kg^(-1),and 14.3 mg·kg^(-1)in the XJH treatment,respectively.Under the low moisture content,soil NO emissions in tea field soil were significantly reduced relative to those in rubber plantation soil,N_(2)O emissions had no significant difference among different treatments,and net nitrification had no significant difference between the XJ and T15 treatments.There was a significant positive correlation between NO emissions and net nitrification rate(P<0.01).②The net nitrification of XJH was higher than that of XJL,but the net nitrification values under different moisture contents in tea field soil was in contrast to that in rubber plantation soil.The NO emissions of XJ and T15 under different moisture contents were consistent with the trend of net nitrification,and the high nitrification promoted NO emissions,whereas NO emissions of T5 were not significantly affected by moisture content.The high moisture content treatment significantly promoted N_(2)O emissions relative to those under the low moisture content treatment.The results showed that SOM,TN,pH,and moisture content were the key factors affecting soil net nitrification rate,NO,and N_(2)O emissions.The conversion of the rubber plantation to a tea plantation significantly reduced the net nitrification rate and negative impact on the environment under high moisture content.