Effect of tea plantation age on the distribution of soil organic carbon fractions within water-stable aggregates in the hilly region of Western Sichuan, China

Establishment of tea plantations (Camellia sinensis L.) could markedly change the pools of soil organic carbon (SOC) and labile organic carbon (LOC). However, the effects of different chronosequence phases on the quantity and quality of SOC in such plantations were poorly understood. In this study, we investigated SOC dynamics following farmland conversion to tea plantations of 16-, 23-, 31-, and > 50 years old in Zhongfeng Township of Mingshan County, Sichuan, which is in southwest China. We specifically examined the effects of the age of various tea plantations on the concentrations of SOC and LOC, including readily oxidizable carbon (ROC), water soluble organic carbon (WSOC), microbial biomass carbon (MBC), particulate organic carbon (POC), and mineralizable organic carbon (MOC) within soil water-stable aggregates. We found that the contents of very coarse fraction (> 5 mm) and very fine fraction (< 0.25 mm) dominated in the soil of the different tea plantations. Importantly, contents of water-stable aggregates at the size of > 5 mm and mean weight diameter (MWD) in 23 year old tea plantation were seen to be higher when compared with > 50 years, indicating that maximum soil stability was within soil macro-aggregates. SOC, ROC, POC, MBC, and MOC contents were reduced with the decreasing of particle size except for WSOC. On the whole, the SOC concentrations in > 50 yr. of tea plantations at two soil depths were significantly lower than those of 23 yr. In addition to WSOC, other LOC contents changed in trends parallel to SOC, demonstrating that tea plantation reaching up to about 23 years contributed more to the soil quality than > 50 yr.