氮添加对西南亚高山针叶林不同深度土壤甲烷吸收潜力的影响

Effects of Nitrogen Addition on Soil Methane Uptake Potentials at Different Depths of a Subalpine Coniferous Forest in Southwest China

森林土壤是重要的大气CH 4汇,氮添加可能增加、抑制或不影响森林土壤CH 4吸收。亚高山针叶林是中国西南森林的主体,针对氮添加对亚高山针叶林土壤CH 4吸收影响的研究并不充分。本研究依托贡嘎山亚高山针叶林开展氮沉降(氮添加)试验,结合室内微宇宙实验及微生物功能基因分析,测定不同深度土壤在标准实验条件下的CH 4吸收速率,明确亚高山针叶林不同深度土壤CH 4吸收潜力对氮添加的差异性响应规律及CH 4氧化功能基因的调控作用。结果显示:(1)同一氮添加处理下,土壤CH 4吸收速率由大到小为矿质层0~5 cm、矿质层5~10 cm、有机层,氮添加未改变土壤CH 4吸收潜力的剖面垂直分布规律。(2)氮添加对有机层CH 4吸收速率无显著影响(P>0.05),但促进了矿质层土壤的CH 4吸收速率。低氮和高氮添加分别促进矿质层0~5 cm土壤CH 4吸收142%和58%,促进5~10 cm土壤CH 4吸收2550%和650%。(3)CH 4氧化功能基因丰度是调控不同土层CH 4吸收速率的重要因素,而较高的铵态氮浓度会改变功能基因丰度与CH 4吸收速率的相关关系。本研究深化了氮添加对西南典型亚高山森林土壤CH 4吸收影响的认识,可为大气氮沉降背景下区域森林土壤CH 4汇的准确核算提供科学依据。

Forest soils are important atmospheric CH 4 sinks.Nitrogen addition may increase,inhibit,or not affect CH 4 uptake in forest soils.Subalpine coniferous forests are the mainstay of forests in southwest China,which are largely affected by elevated atmospheric nitrogen(N)deposition.Unfortunately,there was not adequate research on the effect of nitrogen addition on CH 4 absorption in subalpine coniferous forest soil.Previous studies mostly concerned about the general functions of N deposition on CH 4 uptake as per a whole soil profile;however,the distribution of soil CH 4 uptake potential at different soil depths and how it is affected by N deposition had remained unclear.In this study,simulated N deposition(i.e.N addition)experiments were conducted at a plot of typical subalpine coniferous forest located at the east flank of Mt.Gongga,southwest China to explore the effect of N addition on soil CH 4 uptake potential at different soil depths;soil samples were collected from organic layers,0-5 cm and 5-10 cm mineral layers,separately and then incubated under controlled laboratory conditions(60%of water holding capacity,aerobically at 20℃in dark).Soil physicochemical properties and the abundance of microbial functional genes associated with CH 4 oxidation were determined to reveal the factors regulating CH 4 uptake.It had following findings.(1)By the same quantity of nitrogen addition,CH 4 uptake rate varied along soil depths,with the highest value observed at a depth of 0-5 cm in the mineral layer,followed by 5-10 cm in the mineral layer,and the lowest rate to be found in the organic layer.Nitrogen addition did not change the vertical distribution of soil CH 4 absorption potential profile.(2)N addition had no significant(P>0.05)effect on CH 4 uptake rate in the organic layer,but it worked in the mineral layers.Compared to the control group,in the depth of 0-5 cm mineral soil low N(8 kg N·ha-1·a-1)addition and high N(40 kg N·ha-1·a-1)addition promoted CH 4 uptake by 142%and 58%,respectively,whereas in 5-10 cm soil their promotion were 2550%and 650%,respectively.(3)The abundance of CH 4 oxidation functional genes played an important role in regulating the uptake rate of CH 4 in different soil layers.And higher concentrations of ammonium could weaken the relationship between the abundance of functional genes and the uptake rate of CH 4.This study deepens an understanding of the effect of N addition on soil CH 4 uptake in typical subalpine forests soils in southwestern China,and provides a scientific basis for accounting of CH 4 sink in regional forest soils under the background of atmospheric nitrogen deposition.