长白山天然次生林土壤微生物量对氮沉降的响应

土壤微生物作为土壤养分的生物驱动因素,氮沉降会改变其活性和生物量,从而打破土壤养分循环动态平衡。氮沉降对热带、亚热带森林以及温带原始林生态系统土壤微生物量影响的研究较多,但对温带天然次生林影响的研究鲜有报道。于2016年5月(春)、7月(夏)和9月(秋)分别对长白山模拟10年氮沉降的控制试验样地——白桦山杨次生林进行了野外调查。控制试验分为3个氮添加处理,对照(CK 0 kg N hm~(-2)a~(-1))、低氮(LN 25 kg N hm~(-2)a~(-1))和高氮(HN 50 kg N hm~(-2)a~(-1)),按照土壤层(0—10 cm和10—20 cm)分别测试了不同处理的土壤微生物量碳(MBC)和氮(MBN)、土壤全碳(TC)、全氮(TN)和全磷(TP)、p H、土壤可溶性有机碳(DOC)和氮(DON)等指标。结果表明:1)土壤p H在氮沉降的作用下显著降低;上层土壤TC、TN在氮沉降下变化较小,下层土壤TC、TN的含量显著增加;氮沉降下春、夏两季土壤TP含量上升,LN处理在秋季对TP有抑制作用;氮沉降对DOC、DON的影响不显著。2)上层土壤MBC春季到秋季呈现递减的趋势,下层土壤呈现先升后降的趋势,HN对MBC有抑制作用,LN对下层土壤MBC有促进作用;土壤MBN由春季到秋季呈现递减的趋势,且上、下层土壤MBN差异显著;氮处理对春、秋两季MBN有促进作用,夏季有抑制作用;氮沉降使春、秋两季MBC/MBN降低,夏季土壤MBC/MBN升高。3)氮处理、季节变化和土层深度对MBC、MBN存在显著影响,其交互影响也显著。总之,长期氮沉降在生长季对土壤微生物量的影响具有季节性差异,且受到土层深度的影响。未来研究在重视年际变化的同时,也要注重时空动态对氮沉降作用表现出的差异性。

Response of soil microbial biomass to nitrogen deposition in natural secondary forests in Changbai Mountains

Soil microorganisms are soil nutrient biological driving factors, and nitrogen deposition can change its activity and biomass, which can break the soil nutrient cycling and dynamic equilibrium. The influence of nitrogen deposition on soil microbial biomass in tropical, subtropical and temperate virgin forest ecosystems is increasingly investigated, however, there are less reports from temperate natural secondary forests. We conducted field surveys in May (spring), July (summer) and September (autumn) of 2016 in the control test sample-Betula platyphylla-Populus davidiana natural secondary mixed forest, in which we simulated nitrogen deposition from 2006 in the Changbai mountains. The control trial was divided into three nitrogen-adding treatments:Control (CK 0 kg N hm^-2 a^-1), Low-nitrogen (LN 25 kg N hm^-2 a^-1) and High-nitrogen (HN 50 kg N hm^-2 a^-1). According to the soil layer (0-10 cm and 10-20 cm), we separately tested the soil microbial biomass carbon (MBC) and nitrogen (MBN), soil total carbon (TC), nitrogen (TN) and phosphorus (TP), pH, soil dissolved organic carbon (DOC) and nitrogen (DON). The results showed that, 1) the soil pH significantly declined under the effect of nitrogen deposition. The TC and TN in the upper layer of the soil were less impacted by nitrogen deposition, and nitrogen deposition significantly increased the TC and TN content of the deeper soil. Nitrogen deposition also increased the TP content of the soil in spring and summer. In autumn, the LN treatment inhibited TP. The impact of nitrogen deposition on DOC and DON were not significant. 2) The upper soil MBC showed a decreasing trend in spring and autumn, and the deeper soil increased first and then decreased. HN had an inhibitory effect on MBC, and LN promoted MBC in the deeper soil. The soil MBN showed a decreasing trend from spring to autumn, and the difference between the upper and deeper soil MBN was significant. Nitrogen treatment promoted MBN in spring and autumn, and had an inhibitory effect in summer. Nitrogen deposition also reduced MBC/MBN in spring and autumn and increased MBC/MBN in summer soil. 3) The effects of nitrogen treatment, seasonal variation and soil depth on MBC and MBN were significant, and had significant interacting effects. In summary, the effect of long-term nitrogen deposition on soil microbial biomass in the growing season has seasonal differences and is influenced by the depth of the soil layer. Future research should pay attention to the interannual change, but also investigate the difference between spatiotemporal dynamics and nitrogen deposition.