Soil Microbes Transform Inorganic Carbon Into Organic Carbon by Dark Fixation Pathways in Desert Soil

Abstract

Drylands are ecosystems that cover more than 40% of the terrestrial surface (Reynolds et al., 2007;Safriel & Adeel, 2005). These regions represent the major pool of soil inorganic carbon (SIC) and account for 15.5% of the world's soil organic carbon (SOC) storage (Lal, 2009), wherein the SIC pool is ten-fold higher than the SOC storage (Emmerich, 2003;Shi et al., 2012;Zamanian et al., 2016). Given that the carbon in SIC (85,000 years) has a longer mean residence time compared to SOC (35 years), vegetation (10 years), and atmosphere (5 years) (Monger et al., 2015), the dynamics of SIC in drylands may be of particular importance in the carbon cycles of terrestrial ecosystems, especially in the context of increased anthropogenic activity and global climate change (Gao et al., 2018;Zamanian et al., 2018Zamanian et al., , 2019. In addition, studies of soil organic matter in terms of formation, decomposition, transformation, and stabilization in drylands are relevant because of the mounting interest in investigating global carbon sequestration and soil nutrient condition in oligotrophic environments (Alonso-Sáez et al., 2010;Bay et al., 2018;Liang et al., 2017). Therefore, the dynamics and fate of the soil carbon pools in drylands are an essential and important topic of research.A growing body of research reveals that carbon transformation processes occur between these two carbon pools (SOC and SIC), which is significant for understanding the formation, turnover, and stability of soil carbon pools in drylands (Liang et al., 2017;Z. Liu et al., 2018Z. Liu et al., , 2020. Therein, soil microbes serve as a "microbial carbon pump" to regulate soil carbon dynamics via various metabolic pathways (Liang et al., 2017). In certain areas of drylands, SIC accumulation is closely related to SOC accumulation following vegetation rehabilitation (Gao et al., 2018;J. P. Wang et al., 2015), which involves a carbon transformation process from SOC to SIC ("SOC→SIC"). In the process of "SOC→SIC," soil microbes are assumed to link the two carbon pools through the decomposition of organic matter and forming carbonates via certain metabolic pathways