模拟氮沉降对小兴安岭地区人工红松林土壤氮转化的影响

Effects of Simulated Nitrogen Deposition on Soil Nitrogen Transformation in Artificial Korean Pine of Xiaoxing'anling Region

以我国小兴安岭地区凉水国家级自然保护区30年林龄的人工红松林为研究对象,建立对照(0 kg hm^(-2)a^(-1))、低氮(20 kg hm^(-2)a^(-1))、中氮(40 kg hm^(-2)a^(-1))和高氮(80 kg hm^(-2)a^(-1))四种模拟氮沉降水平的样地;采用室内培养试验,研究了短期模拟氮沉降对人工红松林土壤氮净矿化、净硝化速率和氧化亚氮排放的影响。结果表明,与对照处理相比,经过2年的模拟氮沉降处理,土壤的净矿化、净硝化速率都有降低趋势。与对照相比,低氮、中氮、高氮土壤净矿化速率分别降低了16.9%、20.6%和25.2%,土壤净硝化速率分别降低了16.7%、20.9%和25.5%,但是处理间差异没有达到显著水平。净硝化速率与净矿化速率呈显著正相关关系(P<0.05),表明净矿化速率降低减少铵态氮供应量可能是氮沉降处理降低净硝化速率重要原因。另外,模拟氮沉降处理导致土壤p H降低也不利于硝化作用。中氮和高氮处理土壤氧化亚氮累积排放量分别比对照高84%和40%,但是差异不显著。高的氮沉降量使硝化过程中氧化亚氮的排放比例增加,可能是中氮和高氮处理下净硝化速率下降而土壤氧化亚氮排放量却增加主要原因。研究结果表明,氮沉降会影响我国小兴安岭地区森林土壤氮矿化和硝化过程,但是由于实验开展观测时间较短,其影响规律还需长期实验验证。

In this study, the simulated nitrogen （N） deposition in field experiment with four N application levels, including control （0 kg hm^-2 a^-1）, low N （20 kg hm^-2 a^-1）, medium N （40 kg hm^-2 a^-1） and high N （80 kg hm^-2 a^-1）, was performed in an artificial Korean pine forest, Liangshui National Nature Reserve, Xiaoxing＇anling region, China, and a laboratory incubation experiment was carried to investigate the influence of short-term simulated N deposition on net N mineralization rate, net nitrification rate and nitrous oxide emissions. The results showed that the net N mineralization and nitrification rates decreased after simulated N deposition for 2 years compared with control. Net nitrification rate was significantly correlated with net N mineralization rate （P 〈 0.05）. The decrease in mineralization rate and in ammonium N application could be important reasons for the decreasing net nitrification rate. In addition, the simulated N deposition resulted in the decrease in pH, which was unfavorable to nitrification. The accumulated nitrous oxide emissions from soil increased in medium and high N treatments. The increase in the ratio of nitrous oxide emissions from nitrification in medium and high N treatments could be the main reason that the net nitrification rate decreased, but soil nitrous oxide emissions increased.