Aggregate-associated carbon compositions explain the variation of carbon sequestration in soils after long-term planting of different tea varieties

Strategies to increase carbon (C) sequestration in tea plantation soils are pertinent to mitigating global climate change, but little is known about the variation in C sequestration in soils planted with different tea varieties. In the current study, we collected 0–20 and 20–40 cm layer soil samples from a tea plantation planted with four tea varieties (Chuancha No.3 (CC3), Chuanmu No. 217 (CM217), Chuannong Huangyazao (CN), and C. sinensis ‘Fuding Dabaicha’ (FD)). Soil organic carbon (SOC) stock and composition in the bulk soil and aggregate fractions, as well as the SOC stability index (SI), were investigated. Both SOC stock and composition in the bulk soil or aggregate fractions were variable among the soils after planting different tea varieties. Overall, the highest SOC stock (0–40 cm) was observed in FD soil, followed by CN, CC3, and CM217 soil. This difference was dominated by the SOC stock associated with macroaggregates, and the highest macroaggregate-associated SOC stock was detected in FD soil in both soil layers. Moreover, FD soil showed the highest proportion of macroaggregates in both soil layers, accumulated the greatest recalcitrant organic carbon (ROC) and further contributed to the highest SI values of SOC associated with most aggregate fractions. In contrast, CN topsoil (0–20 cm) accumulated the greatest labile organic carbon (LOC) in most aggregate fractions, which had a positive correlation with the amount of C return by pruning litter. Ultimately, long-term planting of FD promoted macroaggregate formation, and ROC accumulation in aggregates greatly contributed to maintaining high C sequestration in the tea plantation soils and showed a high potential for future C budgets; in contrast, the tea plantation soil planted with CN could be a potential C source because of high C return.