Changes in soil organic carbon and nitrogen mineralization and their temperature sensitivity in response to afforestation across China’s Loess Plateau

Abstract

Afforestation on abandoned cropland has great potential to increase soil organic carbon (OC) and nitrogen (N). Identifying the effect of afforestation on mineralization of OC and N as well as their temperature sensitivity at large spatial and temporal scales is essential to understand soil OC and N dynamics. In this study, we measured mineralization of soil OC and N at standard temperatures (15 and 25 °C) by laboratory incubation, and calculated their temperature sensitivity (Q10). Soil samples were collected from cropland (0 years, selected as a control) and adjacent woodlands with different afforestation age (10, 20 and 30 years) at five sites from north to south on China’s Loess Plateau. The objectives were to understand how long-term afforestation affects OC and N mineralization and their Q10 and whether such effects depend on afforestation age and soil texture. The results showed that afforestation increased OC and N mineralization, but this effect was not affected by afforestation age (10–30 years). The Q10 of OC and N mineralization increased in the first 10 years of afforestation but decreased in the late stage. Furthermore, the increases of OC and N mineralization by afforestation were higher at sites with fine-textured soils than those at sites with coarse-textured soils. However, the Q10 increased at sites with a relatively high sand content but decreased or remained unchanged at sites with a relatively high clay content. The changes in OC and N mineralization and their Q10 were related to soil OC and N contents, pH and clay content. Overall, we concluded that long-term afforestation would contribute to the stability of soil OC and N in afforested ecosystems. Soil texture is an important factor controlling OC and N mineralization and their Q10, and should be considered when predicting soil OC and N dynamics in response to temperature change in different landscapes.