冻融期温带森林土壤N_2O排放对模拟大气氮沉降的响应

Effects of simulated N deposition on N2O emssion from temperate forest soil subject to freezing-thawing process

为研究大气氮沉降在冻融期对森林土壤温室气体N2O交换通量的影响,采用不同形态氮(硝态氮、铵态氮和混合态氮)和不同水平(对照0kg.hm-2.a-1、低氮处理50kg.hm-2.a-1和高氮处理150kg.hm-2.a-1)的氮输入,使用静态箱/气象色谱法研究模拟氮沉降对北京西山地区温带森林土壤N2O排放通量的影响。1年模拟氮沉降后研究结果表明,2012年冻融期间温带森林土壤表现为N2O的排放源,排放通量显著增大并出现高峰期,土壤完全解冻后N2O排放通量有所降低且趋于稳定,冻融期N2O排放通量占2011年全年的37.4%。不同水平的氮沉降对土壤N2O排放均有显著的促进作用(P=0.028),且这种促进作用随氮沉降水平的升高而增强,低氮和高氮输入土壤N2O的平均排放通量分别为19.4和35.1μg.m-2.h-1,而对照处理仅为13.9μg.m-2.h-1;不同形态的氮输入对冻融期N2O的排放无显著性差异,硝态氮、铵态氮和混合态氮输入土壤N2O的平均排放通量分别为28.63、25.91和28.67μg.m-2.h-1。土壤pH值在短期内随着施氮量增加具有降低的趋势,但差异不显著;冻融过程中土壤硝态氮含量逐渐降低,冻结过程中土壤硝态氮含量显著高于解冻期和解冻后,不同水平氮输入后土壤铵态氮和硝态氮含量均趋向氮处理样地高于对照样地,但高、低氮与对照之间差异不显著。不同水平(高、低氮)氮输入样地N2O排放通量与铵态氮含量具有极显著正相关关系,而与pH值和硝态氮均无显著相关关系,可见铵态氮含量对土壤N2O的排放起着显著地促进作用。

The experiment, was conducted to investigate the effects of three forms （NO3--N （SN）, NH4＋-N （AS） and mixed nitrogen （AN）） and three levels （Control （CK） 0 kg N·ha-1·y-1, low nitrogen （LN） 50 kg N·ha-1·y-1 and high nitrogen （HN） 150 kg N·ha-1·y-1） of nitrogen application on N2O fluxes from temperate forest soil in Beijing mountain area, using static and dynamic chambers, for the study of the influence of atmospheric nitrogen deposition on soil greenhouse gas （N2O） exchange fluxes in the freezing-thawing process. After one year of simulated N deposition experiment, the temperate forest soil during Freezing-thawing acted the performance of the N2O emission source. N2O fluxes were greatly increase and reached the peak, but it gradually decreased and tended to be stable after fully thawing, N2O emission accounted for 37.4% of the whole year＇s emission in the freezing-thawing process. Soil N2O fluxes amount were larger by HN treatment than that by LN and CK treatment （P=-0.028）, and this effect was significantly elevated by nitrogen addition in the order HN〉LN〉CK. The average N2O fluxes with addition of LN and HN were 19.4 and 35.1 μg·m2·h-1, and the CK was only 13.9 μg·m-2·h-1. The pairwise differences between the three N-forms treatments were not significant in cumulative N2O fluxes. The average N2O fluxes with addition of SN, AS and AN were 28.63, 25.91 and 28.67 μg·m-2·h-1. Soil pH value tended to decrease by N treatment in the short term while the difference was not significant between any two of N-levels or between any two of N-forms. Soil NO3--N content gradually decreased in the process of freeze-thaw： in the process of frozen value of soil NO3--N content was significantly larger than that in the thawing period and after thawing; NH4＋-N nitrogen and NO3--N content tended to increase after three levels of soil nitrogen addition, but no significant difference was abserved among the control, low and high nitrogen. N2O emission had a very significant positive correlation with NH4＋-N content, but no correlation with pH value and NO3--N content in three levels nitrogen addition, which showed that NH4＋-N content played a significant role of promoting N2O emission.