| Soil organic carbon (SOC) pool can effectively characterize the carbon sequestration capacity of soil, and the labile organic carbon pool play an important role in nutrient cycling and sensitive response to the land use change. Study on the dynamics of soil carbon pool in typical area of returning farmland to tea of hilly region in the Western Sichuan so as to understand the change and effect evaluation during process of ecological restoration is of great importance. This research regarded different ages of returning farmland to tea (2-3,9-10 and 16-17 years old) located in Zhongfeng Township of Mingshan Area as a study plot, and the farmland was used as contrasts. A combination of field investigation and laboratory analysis methods are using to explore the soil organic carbon pool and the characteristics of soil organic carbon mineralization under different culture conditions with farmland conversion to tea plantations, in order to reveal the carbon source or sink effect with farmland conversion to tea plantations and provide a theoretical basis for the sustainable use of tea plantation soils. The main results are as follows:(1) Contents of soil total organic carbon (TOC), labile organic carbon (LOC), and non-labile organic carbon (NLOC) had been increased with the increasing age of tea plantations. And the contents in 0-10 cm soil layer were significant higher than that in 20-40 cm. In 0-10 cm,10-20 cm and 20-40 cm soil layers, total organic carbon concentration with RT16-17 increased by 5.67%,5.67% and 0.78% compared with the control, and the density of soil total organic carbon, labile organic carbon, and non-labile organic carbon with RT16-17 were significant higher than CK at the soil layers of 0-10 cm, 0-20 cm, and 0-40 cm, showing the carbon sequestration capacity increased. With the increasing age of tea plantations, the efficiency ratio of labile organic carbon was significant increased by 107.83%,99.13% and 88.26% compared with the control. Meanwhile, carbon pool management index increased linearly with the increasing age of tea plantations. The results showed the farmland conversion to tea plantations have a positive role in the sustainable use of soils in the study area to some extent.(2) Contents of soil particulate organic carbon (POC), microbial biomass carbon (MBC), and water soluble organic carbon (WSOC), first reduced and then increased with the increasing of the tea plantations’ age. The contents of POC, MBC, and WSOC with RT16-17 increase by an average of 29.04%,36.35%, and 4.66% compared with the control, while the easily mineralizable carbon (EMC) content was significantly lower than CK. With the increasing year of returning farmland to tea plantations, soil microbial quotient gradually increased while the proportion of POC and WSOC to TOC first reduced and then increased, but they were all higher with RT9-10, increase by 31.63%,67.15%, and 7.00%, respectively. Meanwhile, the mineralized percentage with tea plantation soils was also higher in the 9-10 years, yet still significantly lower than CK. The decreasing of EMC content and mineralized percentage showed the effect of Soil carbon sequestration with RT16-17. In addition, soil LOC fractions and their proportion to TOC of 0-10 cm layer were generally higher than that of 20-40 cm.(3) Under different temperature conditions, the cumulative amount of SOC mineralization at all the plots was the largest under 35℃, but the increase in 15-25℃ interval was higher than that in 25-35℃ interval. Compared with the control, tea plantation soils showed lower cumulative mineralization amount, the cumulative amount of SOC mineralization with RT16-17 was significantly lower than that with RT9-10, decreasing by 22.75%,24.67%, and 23.57%, respectively. Meanwhile, the Qio value of farmland conversion to tea plantation soils significant decreased when compared with CK, but the Qio value of different soil layers were little changed. Moreover, with the different soil moisture conditions, the cumulative amount of SOC mineralization at all the plots was the largest under 60% of the water-holding capacity (WHC), and SOC mineralization amount significantly decreased after farmland conversions to tea plantations. And the SOC mineralization amount with RT16-17 under 20%,40%,60%, and 80%WHC decreased by 40.61%,33.36%,24.68%, and 31.25% respectively when compared with RT9-10.(4) There are significant differences in SOC mineralization amount between different tea plantation years with different aggregate sizes, the cumulative amount of SOC mineralization with>5 mm aggregate was significantly lower than that with 1-0.5 mm and 0.5-0.25 mm, but its contribution to the TOC mineralization was the highest. Meanwhile, the SOC content with<0.25 mm aggregate was higher, yet its cumulative mineralization was less than that with 1-0.5 mm and 0.5-0.25 mm, this showed the role of carbon sequestration. Compared with CK, RT16-17 with the lower SOC mineralization amount and higher SOC content suggested the benefits of carbon sequestration enhancement by converting farmland to tea plantations.(5) The first-order kinetics equation well described the SOC mineralization dynamics under different conditions, which is important to predict the dynamics of SOC mineralization in the study area. |
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