Soil potentially toxic elements promote carbon metabolism in alpine meadows on the Qinghai-Xizang Plateau

Abstract

Potentially toxic elements (PTEs) of soil are crucial for sustaining the equilibrium of grassland "vegetation-soil-microorganism" systems and influencing terrestrial biogeochemical cycles. This study investigated how PTEs influence microbial community structure and carbon metabolism by comparing soil microbial differences under fencing enclosure (FE), winter grazing (WG), and artificial unicast oat (AU) management practices. This was done in alpine meadows using metagenomic sequencing techniques. The results indicated that management measures significantly changed the distribution of the Cr, Hg, and As, with Cr and As being the highest in AU and Hg being the highest in FE. In the purine metabolic pathway, Hg had a significant positive effect on soil microbial biomass carbon (SMBC) metabolism, which was catabolized by the prokaryote Chloroflexi and the fungal organism Chytridiomycota during guanosine triphosphate (GTP) catabolism and xanthosine monophosphate (XMP) synthesis to promote soil SMBC cycling. Cr had a significant negative effect on soil organic carbon (SOC) and SMBC metabolism during the synthesis of xanthonsine, urate, 5-hydroxy-2-oxo-4-ureido-2,5-dihydro-1H-imidazole-5-carboxylate and CO₂. Additionally, the enrichment and decomposition of Cr by the prokaryotic organisms Proteobacteria and Verrucomicrobia, inhibited SMBC and SOC transformation and affected soil CO₂ emissions. Further, by comparing resistance genes, it was found that alpine meadows were more resistant to Hg and Cr and that fungal organisms were more tolerant to Cr than prokaryotes. Overall, Cr and Hg interact with microorganisms to influence SOC and SMBC metabolic processes and have a positive effect on carbon sequestration in alpine meadows.