洞庭湖湿地土壤环境及其对退田还湖方式的响应

土壤物理、化学和生物学特性是构成土壤环境的主要组分，综合影响湿地生态系统的调蓄功能和演替恢复。本文以农田（水田和旱地）和自然湿地系统（苔草地和芦苇地）为对照，以3种退田还湖生态系统（种植杨树、芦苇和自然恢复）为研究对象，采用主成分和聚类分析，探索湿地土壤总体环境与生态系统演替过程的相关性。研究结果表明，土壤总体环境与生态系统恢复有很好的一致性。退田还湖为自然水域后，土壤环境的恢复接近于自然湿地系统，在3种退田还湖方式中恢复最好；杨树林地对土壤环境的恢复效果优于人工芦苇地，在一定程度上对湿地土壤环境有所改善，特别是对土壤有机质积累、土壤粘粒形成等过程的改善，但是其土壤环境与苔草等自然湿地发育的土壤仍然有较大差异；因子重要性分析表明水文情势是控制湿地土壤环境恢复的决定性因素，其次是人类干扰强度和方式。

Characteristics of the soil environment of Dongting Lake wetlands and its response to the converting farmland to lake project

Long-term monitoring of soil properties is important for management and restoration of the Dongting Lake wetland after implementation of the converting farmland to lake (CFTL) project. Soil physical, chemical and biological properties are important components of the soil environment, and they affect water regulation and vegetation succession of wetland ecosystems. Although there have been reports on changes in soil properties, including soil particle size composition, C, N and P contents, microbial biomass C, N, P, and enzyme activities after CFTL, there is still a lack of information evaluating the ecological consequences of the CFTL project on the soil environment. Therefore, the objectives of this study were to explore correlations between soil environmental conditions and the processes of ecosystem restoration and succession, and to investigate the key factors controlling the recovery of the soil environment in degraded ecosystems of the Dongting Lake wetland. Three types of CFTL projects (poplar plantation, reed plantation, and natural restoration, e.g. aquiculture), farmland (dryland and paddy) and natural wetland ecosystems (reed marsh and Carex marsh) were selected, and soil samples were taken at depths of 0-30 cm (topsoil), 30-60 cm (subsoil), and 60-100 cm (deep soil) in November 2006. Soil physical, chemical and biological properties including soil particle size composition (sand, 2.0-0.05 mm; silt, 0.05-0.002 mm; clay, <0.002 mm), soil organic matter (SOM), total nitrogen, total phosphorus, total potassium, and invertase, urease, catalase, and alkaline phosphatase activities were determined. Principal component analysis and cluster analysis were used to interpret the data. Clear relationships between soil environmental conditions and ecosystem restoration were found. The soil environment of the aquiculture ecosystem was very similar to that of the Carex marsh, indicating that natural restoration is the best approach to wetland restoration among the three types of CFTL. The soil environment of the poplar plantation was significantly different from that of the natural marsh. However, the poplar plantation performed better in improving the ecosystem function of SOM accumulation and clay particle formation than did the reed plantation. The soil environment of the paddy was very similar to that of the aquiculture ecosystem and the Carex marsh, but the soil of the dryland was different from that of the natural wetland, suggesting that the hydrological regime is the most important factor affecting restoration of the soil environment, and that human disturbance is of lesser importance. Importance analysis and one-way analysis of variance based on factor scores both showed that accumulation of clay, TP, TK, and SOM in the topsoil were the most important processes separating the group of relatively dry systems (dryland, poplar and reed plantations, and the reed marsh ecosystem) and the group of submersed ecosystems (Carex marsh, aquiculture and paddy ecosystems). This suggests that submersion can improve the capacity of the soil environment to accumulate clay, SOM, P, and K. However, ecosystems with fertilizer input (dryland, and the poplar and reed plantations) possess higher N accumulation and urease enzyme activity, implying that fertilization can help to maintain the supply of N, but on the other hand may increase the risk of N contamination.