桂南茶园土壤团聚体酶活性对植茶年限的响应

Response of soil aggregate-associated enzyme activities to tea planting age in the hilly region of southern Guangxi, China

揭示桂南茶园土壤团聚体碳氮磷循环相关酶活性对植茶年限的响应机制,可为广西茶园提升土壤肥力、保障土壤健康以及促进土壤资源可持续利用奠定理论基础。以植茶年限分别8年、17年、25年和43年的南山白毛茶园土壤为研究对象,在0-20 cm土层采集原状土样,通过改良干筛法将土样分为>2 mm、1-2 mm、0.25-1 mm和<0.25 mm粒径团聚体,并测定各粒径团聚体β-葡萄糖苷酶、蔗糖酶、脲酶、蛋白酶以及酸性磷酸酶活性。不同植茶年限土壤团聚体组成以>2 mm粒径团聚体为主,其含量显著高于其他粒径团聚体,平均值为52.57%。随着植茶年限的延长,>2 mm粒径团聚体含量先升高后降低,在植茶17年时处于较高水平。茶园土壤β-葡萄糖苷酶、蔗糖酶、脲酶和蛋白酶主要分布在>2 mm粒径团聚体中,其活性分别为213.09-302.18 mg kg^-1 h^-1、512.39-651.03 mg kg^-1 h^-1、47.36-58.96 mg kg^-1 h^-1和74.49-94.45 mg kg^-1 h^-1;而土壤酸性磷酸酶活性受团聚体粒径变化的影响较小。随着植茶年限的延长,土壤β-葡萄糖苷酶、蔗糖酶、脲酶以及蛋白酶活性先升高后降低,在植茶17年时处于较高水平,其值分别为337.07、719.48、69.67 mg kg^-1 h^-1和112.01 mg kg^-1 h^-1;而土壤酸性磷酸酶活性则逐年升高。在团聚体分级过程中,各类酶活性有不同程度损失。不同植茶年限土壤β-葡萄糖苷酶、蔗糖酶、脲酶、蛋白酶以及酸性磷酸酶活性的平均回收率分别为80.72%、83.53%、80.13%、78.55%以及84.60%。作为土壤酶的主要载体,>2 mm粒径团聚体的形成与稳定对于促进土壤有机碳及养分循环具有重要意义。在茶园管理中,植茶17年以后应重视土壤>2 mm粒径团聚体的崩解与破坏问题,以保障土壤质量及维持土壤有机碳及养分利用效率。

Research on the changes of soil C-, N-, and P-cycling enzymes′ activities in aggregate fractions with different sizes is essential for improving our understanding of the variations in soil organic C and nutrients in the tea plantation ecosystems. Activities of soil β-glucosidase, invertase, urease, protease, and acid phosphatase were analyzed in aggregate fractions that were collected from 0-20 cm depth in tea plantations of various ages(8 a, 17 a, 25 a, and 43 a) in the hilly region of southern Guangxi, China. Soil aggregates were classified into >2 mm, 1-2 mm, 0.25-1 mm, and <0.25 mm fractions by an improved dry-sieving procedure. Across the four tea planting ages, the distribution of soil aggregates showed that the dominant aggregates were >2 mm fractions with a mean value of 52.57%, and these fraction proportions in the 17 a of tea plantations were the highest in all tea plantations. Irrespective of the tea planting age, soil aggregate-related enzymes were mainly distributed in the >2 mm fractions, except for the acid phosphatase. In these fractions, the activities of soil β-glucosidase, invertase, urease, and protease were 213.09-302.18 mg kg^-1 h^-1, 512.39-651.03 mg kg^-1 h^-1, 47.36-58.96 mg kg^-1 h^-1, and 74.49-94.45 mg kg^-1 h^-1, respectively. Soil β-glucosidase, invertase, urease, and protease activities first increased and then decreased alongside the tea planting age, and the 17 a of tea plantations had significantly higher levels compared with the other plantations. However, soil acid phosphatase activity continuously increased during tea planting. Long-term tea planting could promote soil organic matters(OM) to be accumulated. Notably, the youthful tea plantations in the initial 17 a. showed an increasing trend with respect to the potential of soil OM decomposition;however, when tea plantations became mature, the potential of soil OM decomposition was reduced. In the process of aggregate fractionation, the mean recovery rates of soil β-glucosidase, invertase, urease, protease, and acid phosphatase activities were 80.72%, 83.53%, 80.13%, 78.55%, and 84.60% across the four tea planting ages, respectively. As the major carriers for soil enzymes, the >2 mm fractions played an important role in the cycles of soil organic C and nutrients. Therefore, after 17 a of tea planting, the development and implementation of a suitable management protocol is critically important to promote the >2 mm fraction formation, so as to maintain the utilization efficiencies of soil organic C and nutrients in the hilly region of southern Guangxi, China.