Divergent response of upper layer soil organic and inorganic carbon to biotic and abiotic factors in afforestation by aerial seeding in desert, China

In arid lands, soil inorganic carbon (SIC) is as important as soil organic carbon (SOC), and both of was governing by climate, vegetation, soil properties and human activities. However, there has been limited focus on the relative importance of abiotic and biotic factors in governing content of SOC and SIC in desert. To address this gap, we determine the variations of upper layer (0–20 cm) SOC and SIC content and their controlling factors following the nearly 40 years afforestation by aerial seeding in the edge of the Tengger Desert, China. The results showed that upper layer SIC was rapidly increased in the first 10 years and subsequently stabilized at 2.0 g kg⁻¹, when it was about twice of SOC. The correlation and random forest analysis indicated that soil physicochemical properties, including clay and silt content, calcium, available kalium, electrical conductivity, total nitrogen and phosphorus, have higher correlation with SOC than the other properties. In contrast, calcium and bacterial richness indexes (ACE and Chao1) were found to be crucial in determining the variation of SIC. Similarly, the structural equation model and variance partitioning analysis illustrated that soil physicochemical properties and microbial diversity have different effects on SOC and SIC. Furthermore, the linear mixed-effects model determined that soil physicochemical properties and microbial diversity have relative effects of 70.38 % and 29.62 % on variation of SOC, and of 19.91 % and 80.09 % on variation of SIC, respectively. In conclusion, our study demonstrates the divergent response of SOC and SIC to biotic and abiotic factors, and underscores the significance of bacterial richness in determining SIC in desert with enriched calcium and alkali. Our findings provide an improved understanding between soil carbon and biotic factors after plantation in desert.