土壤轻组有机质研究进展

Advance of research on light fraction organic matter in soil

土壤有机质在碳和氮循环及维持土壤生产力等方面具有重要作用,利用密度分组技术可将土壤有机质分成轻组和重组.轻组密度一般<2.0 g.cm-3,通常用密度浮选法分离得到,早期分离轻组的重液是有机溶剂,目前多用水溶性无机盐,结合密度和颗粒大小的分离技术在近年来得到迅速发展.轻组主要由可识别的不同分解阶段的植物残体组成,还包括孢子、种子、动物残体、微生物的残骸以及一些吸附在碎屑上的矿质颗粒.土壤轻组仅占土壤质量的一小部分,但轻组的碳含量一般显著高于全土.轻组物质的碳氮比高,周转速度快,是易变有机碳的良好指标.土壤轻组一般具有明显的季节变化,并大部分聚集在土壤表层,随土层深度的增加而下降.土壤轻组主要受残留物输入的时间、数量、组成以及环境因素的影响,同时轻组对耕作经营措施、作物轮作制度、土地利用、施肥等变化的响应非常敏感.密度分组与颗粒大小分组技术的结合是今后研究轻组的主要技术手段,土地利用和经营管理的变化对土壤轻组数量和性质的时空动态影响是未来的主要研究方向.

Soil organic matter （SOM） plays an important role in carbon and nitrogen cycles and maintaining soil productivity. SOM can be divided into light fraction and heavy fraction using the density fractionation technique. Light fraction （density 〈 2. 0 g.cm^-3 general） is separated from the heavy fraction by flotation in a high density organic or inorganic solutions after a certain degree of disruption or even complete dispersion of the soil. Size-density fractionation combining size and density fraction techniques becomes the main technique recently. Light fraction consists of visible partly decomposed plant material at various stage of decomposition, includes spore, seed, animal and microbial debris and some soil minerals particle associated with plant debris. The dry weights of the light fraction are small and represent only a small percentage of the dry weights of the whole soil, but light fraction had a high concentration of organic carbon relative to that of the whole soil and has a wide C/N ratio and rapid turnover, is a good indicator for labile organic carbon. Amounts of soil light fraction change with seasonal dynamics, and light fraction enriches in soil surface layer and declines along with soil depth increasing. Soil light fraction is affected by the input time, amounts and composition of the residues and environment factor. Since light fraction is labile organic matter pool, it is sensitive to the changes of tillage management practices, rotation of crops, land use and fertilization. Size-density fracfionation is the main technique for light fraction research in the future. That effect of changes of land-use and management on the amounts and characters of soil light fraction would be the main research direction in the future.