Effects of drought and rainfall events on soil autotrophic respiration and heterotrophic respiration

The changes of surface vegetation cover, caused by the return of farmland to forest and grassland, can not only effectively control soil erosion, but also significantly increase soil organic carbon reserves. However, few studies are currently available on the control mechanism of soil CO2 emission after artificial vegetation restoration, particularly on sloping land. This lack of knowledge increases the uncertainty of quantitative estimations of the effect of soil carbon cycle in conversions of cultivated land to forest. This study selected three different plantation types from re-forested hillslopes and monitored both soil respiration and its component changes. The goal was to describe the responses of soil heterotrophic respiration (Rh), soil autotrophic respiration (Ra), and total soil respiration (Rt) to drought and precipitation. Furthermore, the effects of climate warming and drought on soil respiration were evaluated in these reforested areas. A two-year experiment was conducted in the Haihe River Basin of China to study the effects of drought and precipitation on Rt and Rh. The results showed that: (1) soil drought significantly decreased soil respiration carbon emissions. In 2014, rainfall was 20.25 % lower than in 2013, and soil respiration carbon emissions were 5% lower (95 % confidence interval from 1% to 8.1 %). (2) Rainfall significantly increased carbon emissions from soil respiration by 33 % after rainfall (95 % confidence interval from 29.9%–36.5%). (3) Ra and Rh showed different responses to climate warming and drought, where Rh is more sensitive to drought than Ra, and the percentage of Rh in Rt (PRh) was positively correlated with soil moisture. These results show that the increase in soil respiration after vegetation restoration may not be as strong as predicted for semi-humid regions. Climate warming also results in lower soil moisture and less precipitation, which neutralizes part of the positive feedback from the soil-carbon climate.