南方红壤丘陵区土壤侵蚀-沉积作用对土壤酶活性的影响

Effects of Soil Erosion and Deposition on Soil Enzyme Activity in Hilly Red Soil Regions of South China

土壤酶与土壤矿质营养元素循环、能量转移等密切相关。明确土壤酶对土壤侵蚀—沉积作用的响应机制,有助于进一步把握土壤侵蚀在全球碳循环中的作用。通过分析湘中红壤丘陵区松林坡面侵蚀区及沉积区土壤酶活性的变化特征,揭示了酶活性与土壤主要养分因子之间的关系,并在此基础上深入探讨了土壤侵蚀—沉积作用对土壤酶活性的影响。结果表明：沉积区绝大多数土层土壤有机碳（soil organic carbon,SOC）、全氮（total nitrogen,TN）、可溶性有机碳（dissolved organic carbon,DOC）、脲酶、酸性磷酸酶及过氧化氢酶活性均要显著高于侵蚀区。土壤沉积作用明显提高了土壤养分含量及酶活性。其次,侵蚀区与沉积区土壤养分含量及酶活性差异在侵蚀干扰较为严重的表层（0~30 cm）土壤表现较为明显,随着土壤深度的增加差异逐渐减小。侵蚀区与沉积区SOC、TN、DOC及酶活性均随土壤深度的增加呈现总体下降的趋势。相关性分析表明,土壤脲酶、酸性磷酸酶、过氧化氢酶之间及其与SOC、TN、DOC之间均存在极显著正相关关系（p〈0.01）。此外,偏冗余分析结果进一步表明SOC是解释土壤酶活性动态变化的主要因子,其解释量达7.5%,侵蚀诱导SOC在坡面的再分布是影响土壤酶活性的重要途径之一。

【Objective】Soil enzymes catalyze nutrient recycling in forms available for plants and other organisms and are actively involved in soil energy transfer processes. Therefore,soil enzyme is an important driving factor in soil organic carbon dynamic and plays an extremely important role in the global carbon cycle. Knowledge of the mechanism of soil enzymes responding to soil erosion and deposition contributes to further understanding of the role of soil erosion in the global carbon cycle. Therefore,the purposes of this study were to elucidate the response of soil enzyme activities to long-term water erosion and quantify the relationships between soil basic physico-chemical parameters and enzyme activities. 【Method】In this research,soil samples were collected separately from the soil layers（0～5,5～10,10～20,20～30,30～40,40～60,60～80,80～100 cm）of the erosional and depositional sites along a slope covered with pine trees in the hilly red soil region of South Hunan for the analysis of basic physico-chemical properties and enzyme activities in the soil. Soil organic carbon（SOC）,total nitrogen（TN）,dissolved organic carbon（DOC）and activities of-four kinds of soil enzymes（i.e. urease,catalase,acid phosphatase and sucrase）were measured. Pearson correlation analysis and partial redundancy analysis were performed to analyze relationships between the soil enzyme activities and the soil physico-chemical properties and explore the most important physico-chemical factors influencing the soil enzyme activities. The findings in this study may provide some fundamental theoretical bases for exploration of the roles of the soil enzymes in soil carbon dynamic as affected by soil erosion. 【Result】Results show that the depositional soils were higher than the erosional soils in content of SOC,TN,DOC. Soil deposition significantly improved soil fertility. Furthermore,the content of SOC,TN and DOC in the surface soils at the erosional and depositional sites was significantly greater than that of their respective one in the deep soils. In the soil profiles,the contents of SOC,TN and DOC all displayed a downward trend with increasing soil depth. Water erosion had not only a significant effect on soil nutrition distribution in the eroded slope,but also a great impact on soil enzyme activities in soils different in slope position. All the four enzymes,except for sucrase,were much higher in activity in the depositional soils than in most erosional soils. Soil deposition apparently improved soil enzyme activities. The same as the content of SOC,TN and DOC,activities of the four soil enzymes declined with soil depth in the profile. In addition,correlation analysis reveals that positive correlations existed between urease,acid phosphatase and catalase. Furthermore,significant positive correlations（p〈0.05）between soil nutrition parameters（SOC,TN,DOC）and enzyme activities（urease,acid phosphatase and catalase）were observed. All these findings prove that under the influence of long-term water erosion,soil enzyme activities and nutrition level presented a similar curve in dynamic. Partial redundancy analysis shows that SOC,TN and DOC together were responsible for 39.7% of the variation of the enzyme activity and SOC explained up to 7.5% of the variation of the enzyme activity,whereas,TN and DOC did 0.1% and 3.5%,respectively,which demonstrates that SOC is a factor more influencing on soil enzyme activities than all the other measured physicochemical parameters. Erosion-induced SOC redistribution in the soil on a slope is one of the major routes via which soil erosion affects soil enzyme activities. This study is quite limited to the soil on the slope covered by pine trees in a hilly red soil region. 【Conclusion】Therefore,more efforts should be devoted in future studies to further elucidate mechanisms of soil enzymes responding in activity to long-term water erosion in soils different in type and land use.