Effects of Soil Texture and Heterogeneity on Optimal Water Content for Carbon Decomposition

Abstract:

Soil is the largest pool of terrestrial organic carbon in the biosphere. The patterns and controls of soil organic carbon storage are critical for understanding the coupled interactions between biosphere behavior and climate change. Although soil carbon stocks are positively correlated with mean annual precipitation at global scale, moisture is considered to promote carbon decomposition in most macroscale soil carbon models, which include a scaling factor that increases with water content. Therefore, more mechanistic understanding of soil moisture effects on carbon accumulation and cycle are needed. The microbial activity, substrate availability, and gas transfer in soil react differently with water content, and their interactions result in an optimal water content for carbon decomposition. We develop a physical based microscale model to study the effects of soil texture and heterogeneity on the optimal moisture as well as the carbon destabilization. X-ray computed tomography of soil samples with different clay content and pore distribution are used to study the impact of soil texture and heterogeneity on the optimal water content and carbon release. After thorough modeling studies, we introduce a scaling factor, which reflects the optimal effect of water moisture, to the macroscale carbon model. This scaling factor exhibits a strong physical mechanism and can improve the accuracy of predicting carbon storage and cycle in soil.