Effects of Moisture and Temperature on Soil Organic Carbon Decomposition along a Vegetation Restoration Gradient of Subtropical China

Vegetation restoration can affect the process of soil organic carbon (SOC) decomposition, but how this effect is related to soil moisture and temperature remains uncertain. Thus, we performed an incubation of 120 days using soils of degraded land, plantation forest, and secondary natural forest, at two levels of temperature under two moisture levels. We found that the amount of cumulative SOC decomposition in the plantation and secondary natural forest soil was ca. 11.7 times higher than that in the soil from degraded land. Higher soil moisture and temperature treatment increased SOC decomposition in the plantation and secondary natural forest soils. However, in the soil from degraded land, higher soil moisture did not increase SOC decomposition, and higher temperature only increased SOC decomposition in the 60%WHC treatment. The amount of cumulative SOC decomposition was positively correlated with soil MBC and DOC content. The responses of SOC decomposition and the decomposability of DOC to moisture and temperature along the vegetation restoration gradient were highly consistent. Furthermore, in the 60%WHC treatment group, the temperature sensitivity (Q(10)) of SOC decomposition declined with vegetation restoration age increase. Higher soil moisture did not affect Q(10) in the plantation and secondary natural forest soil, but increased Q(10) in the soil from degraded land. Our results indicate that higher soil temperature and moisture would stimulate SOC decomposition, but it is highly dependent on labile carbon supply and microbial metabolic activity along the vegetation restoration gradient.