营林措施对森林土壤N_2O排放影响的研究进展

Advancement in Researches on Effect of Forest Management on Soil N_2O Emission in Forest Soils

森林土壤是大气N_2O重要的排放源。施肥、采伐、火烧、林下植被管理等营林措施和土地利用变化改变了土壤理化性质和土壤微气候,显著影响森林土壤N_2O的产生与排放。综述了森林土壤N_2O排放对不同营林措施的响应,探讨了营林措施影响土壤N_2O排放的主要机理,并提出目前研究的不足和未来研究的重点。总体而言,森林转变为农田、草地后增加了土壤N_2O排放,而农田和草地恢复成人工林后减弱了土壤N_2O排放;天然林转换为人工林或次生林后土壤N_2O排放没有明确结论;森林生态系统"氮饱和"程度使得森林土壤N_2O排放对施肥呈非线性响应,即初期无明显响应、中期缓慢增加和后期急剧增加;火烧一般增加土壤N_2O排放;采伐改变土壤温度、含水量、有机碳的分解和利用等,从而增强森林土壤N_2O排放能力;剔除林下植被提高土壤温度,加快了表层土壤有机碳的分解矿化,促进土壤N_2O排放;种植固氮植物增加了土壤有机碳和土壤氮含量,土壤N_2O排放增强。今后的研究应更多地关注多种因素和气候变化对林地土壤N_2O排放影响的内在机理以及氨氧化细菌、硝化细菌和反硝化细菌等微生物对各种干扰因素的响应机制。

【Objective】Nitrous oxide（N2 O）is an important kind of greenhouse gas,and forest soil is the main source of atmospheric N2 O,posing a great uncertainty in budgeting of atmospheric N2 O. Forest management,like fertilization,felling,litter burning,understory management and land-use change in forests would affect soil properties and soil micrometeorology,and hence production and emission of N2 O from forest soils significantly.This paper discussed responses of forest soil to different management practices in N2 O emission,explored major mechanisms of forest management affecting soil N2 O emission,and highlighted shortages of the current researches and focal points of future studies.【Method】With reference to the databases of Scopus,Web of Science,SDOS and China National Knowledge Infrastructure（CNKI）,current studies on N2 O emission from forest soils were reviewed,and findings of the researches on influences of forest management on soil N2 O emission in recent 20 years were systematically summarized,mechanisms of forest management affecting soil N2 O emission discussed,and shortages of the current studies and prospects of the researches in this field in future described.【Result】Reclamation of forests into agricultural land or grassland would increase soil N2 O emission,whereas the reverse course would did the other way around. How replacement of natural forest with artificial or secondary forest to soil N2 O emission is still unclear. The response of N2 O emission from forest soils to fertilization exhibited a nonlinear curve,consisting of no significant response at the early stage,linear increase at the middle stage,and exponential increase at the late stage,depending on degree of＂N saturation＂of the forest ecosystems. It was generally held that burning stimulated soil N2 O emission;felling affected soil temperature,water content,organic matter decomposition and utilization,thus enhancing soil N2 O emission capacity;and removing understory increased soil temperature,sped up decomposition and mineralization of organic carbon in the surface soil layer,thus promoting soil N2 O emission. Planting N-fixing plants also increased soil N2 O emission. 【Conclusion】Therefore,future researches should focus on the following four aspects 1）to define sources of soil N2 O in the forests of North China and of South China by means of the 15 N-18 O labeling technique in combination of molecular biology,and workout non-linear curves of the responses of N2 O emission to increased N fertilizer application,through multi-dosage multi-form（ammonium nitrogen fertilizer,nitrate nitrogen fertilizer and amide nitrogen fertilizer）N fertilizer application experiments at different latitudes and under climate conditions;2）to use molecular biological and matagenomic methods and techniques to determine effects of forest management on abundance and composition of N2 O producing bacterial communities,and quantify the coupling relationships between soil N2 O emission and major soil microbial functional groups,such as nitrifiers,denitrifiers ammonia-oxidizing bacteria,etc.;3）to extend the observation in period and frequency of soil N2 O emissions after different forest fire chronosequence;and 4）to unfold research about response of soil N2 O emissions to select-cutting,especially in North and South China,rich in coniferous forest and rainforest,respectively.