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 (Q10) of SOC decomposition declined with vegetation restoration age increase. Higher soil moisture did not affect Q10 in the plantation and secondary natural forest soil, but increased Q10 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.

Background and aims Soil organic carbon (SOC) mineralization produces important CO2 flux from terrestrial ecosystems which can provide feedbacks to climates. Vegetation restoration can affect SOC mineralization and its temperature sensitivity (Q10), but how this effect is related to soil moisture remains uncertain. Methods We performed a laboratory incubation using soils of different vegetation restoration stages (i.e., degraded vegetation [DS], plantation [PS], and secondary natural forest [SFS]) maintained under different moisture and temperature conditions to explore the combined effects of vegetation restoration and soil moisture on SOC mineralization and Q10. Results We found that cumulative SOC mineralization in PS and SFS were about 11.7 times higher than that in the DS, associated with higher SOC content and microbial biomass. Increased soil moisture and temperature led to higher SOC mineralization in the SFS and PS. However, in the DS, soil moisture did not affect SOC mineralization, but temperature enhancement solely increased (158.7%) SOC mineralization at the 60%MWHC treatment. Furthermore, significant interactive effect of vegetation restoration and soil moisture on Q10 was detected. At the 60%MWHC treatment, Q10 declined with vegetation restoration age. Nevertheless, at the 30%MWHC treatment, Q10 was lower in the DS than that in the PS. Higher soil moisture did not affect Q10 in the PS and SFS, but enhanced Q10 in the DS. Conclusions Our results highlight that the responses of SOC mineralization and Q10 to vegetation restoration were highly dependent on soil moisture and substrate availability, and vegetation restoration reduced the influence of soil moisture on Q10.

Nitrogen (N) deposition is increasingly aggravating and has significant impact on the processes of forest soil carbon (C) cycling. However, how N deposition affects forest soil C cycling processes in the scenario of future drought-frequent climate is still unclear. Therefore, we conducted a 2.5-year experiment at two levels of N addition treatments (control and N addition) and three levels of moisture (well-watered: ca. 80% of field capacity, moderate drought: ca. 60% of field capacity, severe drought: ca. 40% of field capacity) to investigate the impact of N addition, drought, and their interaction on soil respiration (Rs) and soil organic carbon (SOC) content. The results showed that N addition significantly increased Rs and SOC content, and severe drought decreased Rs and SOC content. In a well-watered condition, N addition significantly increased annual mean Rs, but in moderate drought and severe drought condition, N addition did not obviously affect Rs. In the control group, severe drought significantly decreased annual mean Rs by 61.5%, and decreased SOC content in 0–10 cm and in 10–20 cm by 3.0% and 1.6%, respectively. However, in the N addition group, moderate drought and severe drought significantly decreased annual mean Rs by 27.6% and 70.5%, respectively. Meanwhile, compared to the well-watered condition, severe drought significantly decreased SOC content in 0–10 cm and in 10–20 cm by 12.4% and 11.9% in the N addition group, respectively. Severe drought also decreased aboveground and belowground biomass, fine root biomass, MBC, and specific respiration in N addition group. The Rs and SOC content were positively correlated with aboveground biomass, belowground biomass, and fine root biomass. These results suggest that under future global change scenarios, severe drought might offset the promotive effects of N deposition on soil respiration and C sequestration in the young subtropical forest. Moreover, the N deposition may enhance the suppressive effect of drought on soil respiration and C sequestration in the future.