华西雨屏区植被恢复对紫色土酸化的影响

Effect of vegetation restoration on Purple soil acidification in rainy area of Western China

退耕还林是控制水土流失、恢复森林植被和改善生态环境的重要举措。植被恢复进程中会发生土壤酸化,进而影响植物生长,厘清不同还林树种对土壤酸化的影响程度及作用机制有助于更好地评估退耕还林工程的整体生态效益。以华西雨屏区紫色土坡耕地(玉米)为对照,分析了退耕20a后柳杉纯林、柳杉-光皮桦混交林、慈竹林和茶园土壤pH的变化及其垂直分异。结果表明:玉米地、慈竹林、茶园、混交林和柳杉纯林0—50 cm土壤pH平均值分别为5.66、5.55、5.12、5.03和5.00,相较于玉米地,柳杉纯林、混交林和茶园土壤pH值显著下降(P<0.01),土壤酸化严重。相较于玉米地土壤pH值的均匀分布,植被恢复不同类型人工林pH值随土壤深度的增加而增加,10—50 cm土壤pH值(4.89—5.90)显著高于0—10 cm土壤pH值(4.72—5.21)(P<0.01),表层土壤酸化最明显。土壤pH值与土壤有机质含量呈极显著负相关,而与风化指数Na/K比值呈显著正相关,有机质含量和Na/K比值共同解释了土壤pH值变化的53.9%,表明植被恢复引起的土壤有机质积累与长石类矿物风化是驱动紫色土酸化的重要过程。通过对紫色土人工林酸化特征及其过程的揭示,可为华西雨屏区森林生态系统恢复及其管理提供科学依据。

The Chinese Grain for Green Project is crucial for controlling water and soil erosion, rehabilitation forest vegetation, and improvement of the environment. Soil acidification could be induced during the vegetation restoration, which has a negative impact on plant growth. It is important to clarify the degrees and mechanisms of the influences of reforestation species on soil acidification in order to achieve a better ecological benefit of the Grain for Green Project. In this study, we used the Purple soil of sloping farmland(planted Zea mays) as control group(SF) in rainy area of western China, and analyzed the changes and profile distribution of soil pH value after a 20-year farmland to artificial forestland with plant species of Cryptomeria fortune(CF), Cryptomeria fortune & Betula luminifera(MF), Neosinocalamus affinis(NA) and Camellia sinensis(CS). Results showed that the weighted average value of soil pH in the top 50 cm was 5.66 for SF, 5.55 for NA, 5.12 for CS, 5.03 for MF, and 5.00 for CF. Soil pH value of CF, MF and CS decreased significantly compared with SF(P<0.01), and these soils exhibited severe acidification. In addition, vegetation restoration increased the degree of vertical variations of soil pH for SF that showed a uniform profile distribution. By contrast, soil pH for artificial forests exhibited greater profile differentiations. Soil pH values(4.89—5.90) of the 10—50 cm layer for different artificial forests were significantly higher(P<0.01) than those(4.72—5.21) of the 0—10 cm layer suggesting that soil acidification was most intense for the top 10 cm. There were significantly negative correlations between soil pH value and soil organic matter content, while significantly positive correlation between soil pH value and Na/K ratio of weathering index was observed. 53.9% of the variation for soil pH was explained by soil organic matter content and Na/K ratio, indicating that the acidification of Purple soil in this area were driven by the accumulation of soil organic matter during the process of returning farmland to forests and sorts of feldspar weathering. By revealing the acidification characteristics and its processes for Purple soil, this study provides a scientific basis for future vegetation restoration and ecosystem management in rainy area of western China.