Identifying bacterial fixation pathway of mediating soil carbon stock changes along tropical forest restoration

Abstract

The mechanism mediating carbon accumulation changes along ropical forest restoration remains unclear. Here, we identified how functional bacteria, litter input, and abiotic variables control soil organic carbon stock changes along an age-chronosequence of tropical forest restoration. Over 51-yr recovery, significant increases in total organic carbon stocks (∼1.7 fold) were strongly associated with increases in copy number of carbon fixation bacterial genes (cbbL) (∼2.6 fold). The direct pathways of cbbL abundance, microbial and mineral-associated organic carbon explained 76 % of carbon stock variation. In contrast, litter carbon, soil water, and bulk density indirectly regulated carbon stocks through affecting cbbL abundance (68 %) and microbial carbon level (29 %). Furthermore, cbbL abundance had a higher contribution (71 %) to carbon fraction transformation than microbial carbon level (19 %). We suggest that tropical forest restoration controls carbon stocks primarily via direct bacterial fixation pathway mediated by litter carbon and physical soil variables. Our results are helpful to further understand the mechanism of tropical forest restoration regulating carbon transformation and accumulation.