Soluble organic nitrogen (SON) and inorganic N are two crucial nitrogen (N) forms in the cycling of N within terrestrial ecosystems, acting as either a "source" or a "sink" to the environmental N release. The mineralization, retention, leaching, and plant absorption of N in terrestrial ecosystems are closely related to SON. As a result, the role of SON in soil material circulation and nutrient flow has attracted much attention and has become one of the hotspots in various research fields, such as ecology, environmental science, soil science, and hydrology. We reviewed the research progress on soil SON, including the definition and quantification, the size and composition, the absorption and utilization by plants and microorganisms, the sources and influencing factors, and the transformation, migration, and leaching loss of SON. SON is a complex collection of multi-component soluble organic matter, mainly as recalcitrant components (difficult to degrade), with relatively low proportion as labile components (easily degradable). Due to the difference in the turnover time among recalcitrant and labile components, the roles of SON in N cycling and turnover cannot be fully represented by the SON quantity. Therefore, to accurately reflect the role of SON in N turnover, N uptake, and N leaching, it is necessary to establish new methods and distinguish between recalcitrant and labile SON components in future studies. When studying the role of SON in N conversion and N absorption, it is essential to focus on its labile components. When studying the contribution of soil SON to N leaching or runoff loss, it is necessary to focus on the recalcitrant components.
可溶性有机氮(SON)和无机氮是陆地生态系统氮循环过程中重要的氮素形态,互为“源”和“汇”。陆地生态系统中氮素和其他营养元素的矿化、固持、淋溶和植物吸收均与SON有密切的联系。SON在土壤物质循环和养分流动等动态过程中的作用越来越受到关注,已成为生态学、环境学、土壤学、水文学等研究领域的热点之一。本文综述了国内外对土壤SON的研究进展,包括SON的定义和测定、SON库容大小和组成、植物和微生物对SON的吸收利用、SON来源及其影响因素、SON在土壤中的转化运移和淋失等。综合国内外研究结果发现,土壤SON是一个复杂的多组分可溶性有机物的混合物,主要为难降解的物质(惰性成分),能快速矿化分解的物质(活性成分)占比较低。由于惰性成分和活性成分在周转速率上的差异,SON在生态系统氮循环中的地位不能完全通过SON的容量特征来反映。因此,为了更准确地反映SON在氮周转、氮吸收和氮流失中的作用,未来需要创新研究方法并对SON组分加以区分:研究SON在氮转化和氮吸收中的作用时,重点关注SON中的活性成分;研究SON在氮淋溶径流损失中的贡献时,则重点关注SON中的惰性成分。.
Keywords: leaching; migration; mineralization; soluble organic N; transformation.