Effect of nitrogen loss on deep soil organic carbon decomposition

Ms Wenjing Zeng1

1 College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, People’s Republic of China

More and more deep soil is exposed to the surface as a consequence of anthropogenic activities. The effect of nitrogen (N) loss through biological, chemical and physical processes is widespread on deep soil organic carbon (SOC). Despite researchers have realized the different regulatory mechanisms of SOC decomposition in response to increasing N availability in topsoil and in subsoil, very few experiments have considered the effect and mechanism of N loss on deep SOC. In this study, we selected grassland soil samples from 0-10 cm, 10-20 cm, 20-40 cm, 40-60 cm, 60-100 cm soil depths and conducted 411-day incubation using ion exchange membrane to imitate N loss. Microbial respiration and the related variables including environmental factor (soil pH), substrate quality (SOC and total N of light and heavy fraction, dissolved C and N, and their ratios of C and N), and microbial attributes (active microbial biomass, microbial biomass C and N, the ratio of r and K strategies, extracellular enzyme activities, and microbial C efficiency) were measured during the incubation period. Our results indicated that the effect of N loss on SOC decomposition was nonlinear with the increase of soil depth. N loss significantly increased SOC decomposition in the surface, decreased in the middle layer, and increased in the deep layer. The increase of SOC decomposition in subsoil was twice that in topsoil. The difference of SOC decomposition at different depth was caused by the influence of substrate availability and environmental factors on the microorganism. The decrease of N availability mainly affected the SOC decomposition through the reduction of available N in topsoil, whereas through the increase of soil pH in subsoil. Our study provides new evidence of the vulnerability of deep SOC to global changes and is meaningful to accurately predict deep SOC dynamic in response to global N deposition.

Biography: Wenjing Zeng received her Ph.D. in Ecology from Peking University in January, 2019. Now, she is a postdoctoral fellow at the College of Urban and Environmental Sciences, Peking University and foucuses on the effect of nitrogen availability on soil organic carbon stability.

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