Distribution characteristics of soil aggregates and its organic carbon in different tea plantation age

Soil organic carbon( SOC) is a complicated composition,which could be influenced by many factors such as land use,soil management regimes,soil property and even climate.Understanding its dynamics can know which of the parts are active or passive due to either physical protection or biochemical resistance,or both.The labile fractions,such as water-soluble organic carbon( WSOC) and microbial biomass carbon( MBC),have a much shorter turnover time and thus have been suggested as an early indicator of the effects of either soil management or cropping systems on total organic carbon( TOC) quality.As an important component of soil structure and fertility,soil aggregates have huge effects on the physical,chemical and biological properties of soil.Investigating the formation and stabilization of soil aggregates is very necessary to understand dynamics of soil organic matter.Tea plantation age has great potential to affect soil aggregates and carbon pools.Therefore,knowledge about the different tea plantation ages effecting on soil aggregate and SOC distribution is essential for understanding the carbon pools changes of tea plantation ecosystem.Therefore,in the present study,we compared the distribution patterns of organic carbon within soil aggregates among four different plantation ages( 12—15,20—22,30—33and 50 years old) located in Zhongfeng Township of Mingshan County,Sichuan.The results showed that:( 1) Thegreatest proportion of aggregates was observed at the size of 2 mm in each tea plantation which approximately accounted for 70—80% of all aggregates.SOC contents of aggregate fractions in the 0—20 cm soil layer were the highest in the tea plantation of 20—22 years old.( 2) SOC contents of aggregate fractions increased gradually with decreasing particle size,and the maximum values of SOC contents were found in the aggregate fractions of 0.25 mm diameter in tea plantations of 50 years old.SOC contents of aggregate fractions in the 0—20 cm soil layer were higher than those of 20—40 cm soil layer.The contents of WSOC and MBC in the aggregate fractions decreased after an increase along with rising ages of the tea plantations.The maximum values of the contents of WSOC and MBC in the aggregate fractions were found in the tea plantation of 30—33 years old.The contents of WSOC in the smaller size aggregates were higher and the contents of MBC in the smaller size aggregates were lower.( 3) 70% of organic carbon resulted from the aggregate at size of 2 mm.SOC storage presented an increasing trend in different soil layers aggregates of all particle sizes along with rising age of the tea plantations.SOC storage of aggregate fractions in the 0—20 cm soil were higher than those of 20—40 cm soil layer,and the maximum values of SOC storage in the aggregate fractions were observed at size of 0.25 mm diameter.The results partly explored the distribution characteristics of SOC of aggregates in different tea plantation ages,and it would provide theoretical guidance for returning farmland to tea and improvement of soil quality in the study area.