森林土壤碳、氮淋失过程及其形成机制研究进展

Research on Process and Mechanism of Carbon and Nitrogen Leaching for Forest Soils

大气氮沉降对森林生态系统碳截存和损耗过程的影响已引起广泛关注,但对沉降氮在森林生态系统中的去向、增氮对土壤中碳/氮转化过程的影响以及土壤氮饱和前后土壤渗漏液中溶解性有机碳(DOC)和溶解性有机氮(DON)动态等方面的研究还不够深入。本文论述了近年来国内外在土壤氮饱和及土壤碳、氮淋溶领域的最新研究进展,从系统论的角度阐述土壤氮饱和过程及内涵;通过论述DOC和DON含量及其结构组成变化来揭示其对增氮/氮沉降的内在响应机理;论述了增氮对土壤无机氮转化的影响以及生物和非生物因素对沉降氮固持的贡献。指出土壤氮饱和为土壤中的有效氮随时间增加超过了土壤中生物和非生物的持留能力,导致土壤氮的净矿化、净硝化、NO-3流失以及土壤酸化等过程发生一系列非线性变化。初步认为土壤中DOC和DON对增氮的不同响应归因于氮素饱和过程的三个不同阶段。对于特定的生态系统来说,需要清楚地认识土壤氮素矿化、硝化、反硝化和固持等过程,才能明晰土壤氮素状态以及随时间的演变。另外,指出在上述三个研究领域中存在的问题,并提出拟解决的途径以及未来的可能研究方向,以期对该领域的研究提供参考。

Abroad attention has been drawn to effects of nitrogen deposition on process of carbon sequestration and depletion for forest ecosystem. However, further research is needed on fate of deposited nitrogen in forest ecosystem, impact of nitrogen increase on conversion process of soil carbon and nitrogen, and dynamics of dissolved organic carbon （DOC） and dissolved organic nitrogen （DON） in soil solution during pre- and post-soil nitrogen saturation. In this paper, new research advance on fields of soil nitrogen saturation and soil carbon/nitrogen leaching is discussed firstly. Secondly, process and meaning of soil nitrogen saturation are demonstrated by system approach. Inherent response mechanism of nitrogen increase and deposition on the composition and structure change of DOC/DON is analyzed. Finally, influence of nitrogen increase on conversion of soil inorganic nitrogen and contribution of biotic and abiotic factors on sequestration of deposited nitrogen. To sum up, we think soil nitrogen saturation is a state of available nitrogen increase with time and exceeds capacity of biotic and abiotic hold in soil, and then processes such as nitrogen mineralization, nitrification, leaching and soil pH occur in non- linear change. Different responses of soil DOC and DON to added nitrogen are attributed to three stages of soil nitrogen saturation, which is related to the persisting time and quantity of nitrogen deposition or added mineralized nitrogen. As far as a certain terrestrial ecosystem is concerned, processes of nitrogen mineralization, nitrification, de-nitrification, immobilization and ammonium fixation in soil need to be deeply studied to make clear status of soil available nitrogen and temporal variability. Furthermore, uncertain questions, possible countermeasures and potential directions are pointed out in three research fields above to provide some reference for researchers.