三峡库区岸坡消落带草地、弃耕地和耕地土壤微生物及酶活性特征

为研究不同用地方式对三峡库区消落带土壤性质的影响,选取三峡库区重庆忠县汝溪河流域典型消落带为研究区域,研究不同用地类型(草地、弃耕地、耕地)、不同土层间(0—10 cm、10—20 cm)土壤微生物、土壤酶活性和土壤化学性质的各自特征及其相互关系,旨在为该地区消落带生态恢复实践提供理论依据。研究发现:除蛋白酶活性、全磷含量、碱解氮含量外,不同用地类型对土壤各生化特性均产生了显著影响;与之不同,土层仅对细菌数量、放线菌数量、真菌数量、蔗糖酶活性、脲酶活性以及土壤有机质含量产生显著影响,但对其他生化性质影响不显著;用地类型与土层两者的交互作用仅对蔗糖酶活性影响显著。同时,弃耕地土壤的细菌数量在3种用地类型中最高;真菌、放线菌数量在草地中最高,耕地次之,弃耕地最低。弃耕地中的过氧化氢酶、蔗糖酶、蛋白酶和脲酶活性与其他两种用地类型相比较高,而耕地中磷酸酶活性则显著高于弃耕地和草地土壤。草地土壤全氮、有效磷以及速效钾含量均显著低于耕地,而草地0—20 cm土层的有机质含量却显著高于弃耕地和耕地;3种用地类型的全磷、全钾、碱解氮含量差异均不显著,弃耕地的pH值显著高于另外两种用地类型。另一方面,三峡库区消落带土壤的各生化指标间存在一定的相关性。pH值和微生物数量及酶活性间的关系最为密切,土壤真菌和放线菌数量与土壤有机质含量呈极显著正相关。研究结果表明,与弃耕地和耕地相比,草地在稳定消落带土壤环境、固持土壤营养元素、提高土壤肥力方面作用更为显著;相对而言,耕地的土壤微生态环境较差,故在消落带实施退耕还草、恢复草本植被等具有重要意义。

Responses of soil microorganisms and soil enzyme activities to different land use patterns in the water-level-fluctuating zone of the Three Gorges Reservoir region

The water-level fluctuating zone of the Three Gorges Reservoir (TGR) region contains several different land use types which have been altered or newly established since the commencement of the dam's operations. This study sought to examine the variation of soil microorganisms (the quantity of bacteria, actinomycetes and fungi), soil enzyme activity, soil nutrient content and the relationship among these factors under three land-use regimes in the Ruxi river basin area: grassland, abandoned farmland and farmland. 30 sampling plots from 11 grassland, 16 abandoned farmland and 3 farmland in Ruxi river basin (a typical region in the TGR area) were set up. All samples were collected in the same month and from the same elevation to control for seasonal and flooding influences on soil microbiology. Soil samples were collected from the 0-20 cm and 20-40 cm soil layers for each sampling plots. Results showed that there were significant differences among land uses in certain soil biochemical properties. Of the three types of land use patterns, abandoned farmland displayed the highest quantity of bacteria, while the amounts of fungi and actinomycetes were the greatest in grassland. The activity of hydrogen peroxidase, invertase, protease and urease were also higher in abandoned farmland than in the other two land patterns. However, phosphatase activity was significantly higher in farmland than in abandoned farmland and grassland. Total nitrogen (TN), available phosphorus (AP) and available potassium (AK) concentrations were significantly lower in grasslands compared to farmland, while the organic matter (OM) content was significantly higher there than in abandoned farmland and farmland. There were no significant differences among total potassium (TK), total phosphorus (TP) or available nitrogen (AN) content or protease activity under the three kinds of land use patterns. Soil depth only had a significant impact on the quantity of soil microbes, invertase activity, urease activity and OM content. Furthermore, the effect exerted by land use type in combination with soil depth was only significant in invertase activity. The pH value of the abandoned farmland was significantly higher than the other two patterns of land use. An analysis of correlation of the relationships among the soil biochemical characteristics indicated that the most significant association existed between the pH value and the soil biological characteristics, suggesting that pH is a decisive influence on the other biochemical parameters in this region. In addition, the quantity of fungi and actinomycetes in soil were significantly positively correlated with OM content underling the important role these species play in improving soil fertility in this area. Compared to abandoned farmland and farmland, grassland plays an important role in stabilizing the soil environment by retaining soil nutrients and improving soil fertility in the fluctuating zone of the TGR region. Therefore, it is suggested that more land should be converted from farmland to grassland.