Soil aggregate-related organic carbon and relevant enzyme activities as affected by tea (Camellia sinensis L.) planting age in hilly region of southern Guangxi, China

Abstract

It is essential to reveal the variations in the activities of carbon (C)-cycling enzymes in soil aggregates of different sizes, so as to shed more light on the soil organic C (Corg) dynamics in the tea plantation ecosystems. In this study, the activities of cellobiohydrolase, xylanase, β-glucosidase, and invertase were detected in soil aggregates obtained at the depth of 0–20 cm from tea plantations of various ages (8, 17, 25, and 43-yr.) in hilly region of southern Guangxi, China. Soil aggregates were divided into >2, 2–1, 1–0.25, and <0.25 mm fractions through a dry sieving procedure. This study hypothesized that the potential of soil Corg decomposition would be higher at early stage (in the initial 17-yr.) than that at late stage (after 17-yr.). Our results suggested that, irrespective of the tea planting age, soil aggregate-related Corg contents were mainly distributed in the >2 and 2–1 mm fractions, and soil aggregates at the >2 mm sizes had the highest activities of C-cycling enzymes. Notably, the C-cycling enzyme activities in soil aggregates were closely correlated with Corg availability, and Corg contents might not exert a vital part. On the other hand, tea planting for a long time could promote soil Corg to be accumulated. At early stage, the accumulated soil Corg was primarily derived from the >2 mm fractions; meanwhile, the C-cycling enzyme activities in the >2 mm fractions were also markedly elevated, indicating that the accumulated Corg in soils at early stage was more easily decomposed and showed a higher potential of decomposition than that at late stage, thus supporting our hypothesis. Overall, the youthful tea plantations in the initial 17-yr. showed an increasing trend with respect to the potential of soil Corg decomposition; however, when tea plantations became mature, the potential of soil Corg decomposition was reduced in hilly region of southern Guangxi, China.