陆地生态系统中水溶性有机物动态及其环境学意义

Dynamics of dissolved organic matter in terrestrial ecosystem and its environmental impact

水溶性有机物 (DOM )是陆地生态系统中最活跃的有机碳库 ,也是土壤圈层与相关圈层进行物质与能量交换的重要表现形式 ,它对重金属、养分元素和有机污染物的活化、迁移与生态毒性有较大影响 .在农业土壤溶液中DOM浓度通常在 10～ 80mgC·L-1,湿地土壤中多数在 2 5～ 5 0mgC·L-1,与森林土壤剖面淋滤水中的DOM相近 .但在某些微域土壤环境 (如根际和有机肥施用点附近 )中DOM浓度可高达2 0 0～ 10 0 0mgC·L-1.不同来源的DOM在土壤中的迁移性与降解性明显不同 ,含低分子量组分或亲水性组分较多的DOM不易被土壤吸持而易被微生物降解 .pH值相对较高的土壤 (如石灰性土壤 )对DOM吸附较弱 ,但pH较低和含有大量氧化物的土壤 (如红壤、赤红壤和砖红壤等 )则对DOM的吸附较强 .施用石灰、土壤淹水或干湿交替、温度升高等有利于土壤保持较高的DOM浓度 .由于DOM 金属配合物的形成 ,DOM能明显促进土壤重金属活化和向下迁移 ,而且DOM中低分子量或亲水性组分所占比例越低活化作用越强 .同样地 ,由于DOM具有两亲性质 ,也能明显提高疏水性有机污染物 (如农药和持久难降解有机污染物 )的水溶性 ,增加其对环境污染的风险 ,特别是含疏水性组分越多的DOM这种作用越强 .可以认为 。

Dissolved organic matter (DOM), the most active organic carbon pool in terrestrial ecosystem, has a greater effect on the mobilization, translocation, and ecological toxicity of many inorganic and organic pollutants in environment. The DOM concentration in farmlands varies from 10 to 80 mgC·L -1 , while most of wetlands contain 25～50 mgC·L -1 of DOM, which is similar to the leachate from forest soils. However, soil DOM can be increased to above 200～1000 mgC·L -1 in the rhizosphere or in the plots amended with organic manures. Generally, soil DOM containing a great deal of lower molecular weight fractions or hydrophilic fractions is more mobile and readily biodegradable, compared to the DOM with larger molecular weight or hydrophobic fractions. However, soils with lower pH and higher amount of oxides can adsorb DOM more strongly, and as a result, the mobile DOM in the soils will be reduced. Liming, water-logging, dry-wet recycling and higher temperature can increase the concentration of soil DOM. Furthermore, DOM can enhance the dissolution and translocation of inorganic and organic pollutants, due to the formation of DOM-pollutant complex, resulting in environmental risks. It was suggested that the dynamics of DOM in terrestrial ecosystem and the transportation flux and model of DOM or its associated pollutants from terrestrial to aquatic ecosystem should be considered in future research.