摘要:
有机氮是土壤氮素的主要存在形式,土壤中有机氮大多以聚合物形式存在,经过一系列复杂的生物和非生物过程转变成可溶性有机氮。本文总结了不同生态系统可溶性有机氮的研究现状,指出当前可溶性有机氮的研究主要集中在森林生态系统、草地生态系统和农业生态系统,在不同的生态系统中,由于土壤类型、土地利用类型、覆盖的植被类型、土壤管理措施和环境因素等的不同,土壤可溶性有机氮的含量和组分均存在差异。本文还综述了当前可溶性有机氮生物转化过程的研究现状,指出可溶性有机氮含量与土壤微生物的数量、组分及胞外酶的活性有关,其生物转化过程为:在土壤微生物(细菌、真菌等)及胞外解聚酶如蛋白酶、几丁质酶等的作用下,大分子有机氮降解为小分子有机氮,被植物和微生物直接吸收利用,或进一步降解为NH+4和NO-3被植物和微生物吸收利用。认为未来应该加强土壤有机氮转化代谢过程的调控机制研究。
Abstract:
In soil,nitrogen mostly exists in the form of organic polymers,which can transform into soluble organic nitrogen(SON)through a series of complex biological and non-biological processes.In this paper,SON refers to the organic nitrogen extracted by water or salt solution,rather than the dissolved organic nitrogen(DON)collected in situ.Currently,the research on SON largely focuses on forest-,grassland-and/or agro-ecosystems.There are differences in the content and composition of the soil SON in different ecosystems that vary in soil type,land use,vegetation,soil management and/or environmental factors.A great deal of the information obtained thus far indicates a correlation between SON content and the quantities and components of the microorganisms in soil,the activities of extracellular enzymes,etc.The transformation process may include breakdown of the polymeric nitrogen by bacteria,fungi and/or extracellular depolymerases secreted by microbes in soilor plants into soluble subunits that can be utilized by microorganisms or plants.The soluble subunits may also be further degraded into ammonium(NH+4)and nitrate(NO-3),which are the preferred N source for bacteria,fungi and plants.At present,few study targets the microbes that are capable of degrading organic nitrogen into subunits,while only a few reported the degradation and absorption of organic nitrogen by mycorrhizal fungi.Thus,future studies ought to be directed toward the understanding of the regulatory mechanisms of soil organic nitrogen transformation.
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