Dynamics of bacterial function characteristics in soil aggregates during the tea-planting process

Abstract

Increasing knowledge of how tea-planting age impacts the relationships of soil aggregates with microbial (particularly bacterial) function characteristics may help elucidate the principles to improve soil carbon (C) sequestration and soil health in the tea garden ecosystem. In this study, the bacterial metabolism activity and function diversity (as determined by Biolog Eco MicroPlates) were measured in different sized aggregates in soil (with a depth of 0–20 cm) from tea gardens of different ages (8, 17, 25, and 43 years) in the southern region of Guangxi, China. Soil aggregates were classified into micro-aggregates (<0.25 mm), small (0.25–1 mm), medium (1–2 mm), and large (>2 mm) macro-aggregates by complying with an optimal moisture sieving procedure. In all tea gardens, soil large macro-aggregates, with the highest levels of bacterial metabolism activity (as indicated by the average well color development, AWCD) and function diversity (as indicated by the Shannon and McIntosh indices), contributed significantly to the organic C decomposition and nutrient release as well as to the material circulation and energy flow. As the major parts of whole soil, large macro-aggregates were more centralized in the 17-year tea gardens, indicating that these tea gardens provided a relatively favorable soil condition for the bacterial growth and proliferation thereby promoting bacterial metabolism activity and function diversity. After 17 years of tea planting, the large macro-aggregates’ disintegration in soil could partially interpret the bacterial functions’ degradation. Also, soil microbial quotient (the rate of soil microbial C to organic C) and soil pH acted as critical promoters for soil bacterial function characteristic dynamics in the tea-planting process. After 17 years of tea planting, therefore, promoting the formation of soil large macro-aggregates is necessary to maintain soil bacterial metabolism activity and function diversity as well as to facilitate nutrient cycling for tea plant growth in the southern region of Guangxi, China.