冻融作用对土壤物理、化学和生物学性质影响的研究进展

Research Progress on the Effects of Freezing and Thawing on Soil Physical, Chemical and Biological Properties

冻融是作用于土壤的非生物应力,对元素生物地球化学循环过程影响显著。文章综述了冻融作用对土壤物理、化学和生物学性质的影响,分析了影响冻融理化效应的主控环境因子。结果表明:冻融循环可使土壤大团聚体破碎成小团聚体,细颗粒物表现出向中等大小颗粒物聚集的趋势;但冻融作用对团聚体水稳性的影响不一。由于土壤孔隙间冰晶膨胀,推动土壤颗粒发生相对位移,导致土壤孔隙度增加,容重随之降低。冻融初期,低温导致大量水分向冰晶转化,促使水分向土壤表层迁移;经反复冻融后,冰晶充分占据土壤孔隙,使水分移动空间变小、路径增长,造成不同深度土层含水率差异显著;水分状况改变又反过来对土壤冻融过程产生影响。冻融过程会增强土壤硝化作用和促进溶解性有机酸的释放,从而导致土壤溶液pH降低。冻融作用能够提高土壤有机碳(SOC)矿化速率,导致有机碳组分的固定与活化产生分异。冻融循环通过改变土壤理化性质和生物学性状,影响氮、磷素迁移转化方向和赋存形态以及温室气体N_2O等的排放。此外,冻融作用还显著影响土壤微生物群落结构,指示土壤微生物群落演替方向。冻融循环次数、温度和土壤含水率是影响上述冻融作用效应的关键因素。

Freezing and thawing is a non-biological stress on the soil and has significant impacts on the biogeochemical cycling process of the elements.This paper summarized the effects of freezing and thawing on the physical,chemical and biological properties of soil,and analyzed its main environmental factors.The results showed that the freezing-thawing cycle broke down the large soil aggregates into small aggregates.The fine particles tended to form medium size particles,but the effect of freezing and thawing on the water stability of aggregates was different.Due to the expansion of ice crystals in soil pores,the relative displacement of soil particles was promoted,which led to the increase in soil porosity and the decrease in bulk density.In the early stage of freezing and thawing,the low temperature led to the transformation of a large amount of water to the ice crystals,which promoted the migration of water to the soil surface.After repeated freezing and thawing,the ice crystals occupied the soil pores completely,so that the water movement space became smaller and the path grew,which resulted in significant differences in soil moisture content.The changes in water condition also affected the freezing and thawing process.Freezing-thawing processes enhanced soil nitrification,promoted the release of soluble organic acids,and decreased soil p H value.Freezing and thawing improved the mineralization rate of soil organic carbon,leading to the differentiation and activation of organic carbon components.By changing soil physical,chemical and biological properties,the freezing-thawing cycle affected the transformation direction of nitrogen and phosphine migration and the emission of greenhouse gas N2O.In addition,freezing and thawing also significantly affected soil microbial community structure,indicating the succession of soil microbial communities.The number of freezing-thawing cycles,temperature and soil moisture content are the key factors to influence the above freezing and thawing effects.