Soils store enormous quantities of organic carbon, and the CO2 released from soils to the atmosphere through soil respiration is one of the most important fluxes in the global carbon cycle. Drought is predicted to have a profound impact on soil respiration. Many precipitation reduction experiments have shown that soil respiration decreases with decreasing moisture levels.  

Prof. ZHANG Yiping and his team of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study to assess the effects of long-term precipitation decrease on soil respiration in a tropical rainforest in Xishuangbanna. They aimed to determine the long-term effects of drought on soil respiration and the dependence of soil respiration on environmental parameters. They further wanted to evaluate the effects of changes in soil respiration on carbon cycling.

    The researchers created an artificial drought in January 2011 using a precipitation reduction treatment, in order to investigate the influence of precipitation on soil respiration under conditions drier than those normally experienced. The experiment included two treatments: a control treatment with ambient precipitation and a precipitation reduction treatment with partial throughfall exclusion. They measured soil respiration and environmental parameters (soil temperature and soil water content) monthly for three years.

   Over the three years of the study period, soil temperature showed no difference between two treatments, while soil water content decreased significantly in the precipitation reduction treatment, especially during the rainy season. Soil respiration increased significantly both annually and in the rainy season. The results showed that the influence of drought on soil respiration depended on a variety of factors and was seasonally dependent, with soil respiration being less sensitive to drought in the dry season. The precipitation reduction treatment significantly increased annual cumulative soil respiration both annually and during the rainy season. Compared with the annual soil respiration accumulation, the increment of annual soil carbon emissions in the reduction treatment was considerable and should not be ignored.  

   The study entitled “Effects of continuous drought stress on soil respiration in a tropical rainforest in southwest China” has been published online in Plant and Soil.