Mining activities accelerate the decomposition of organic matter from aquatic ecosystems through soil microbes

Mining activities have been shown to affect the rate of carbon decomposition in aquatic ecosystems by altering the traits of the organic matter (e.g., leaf litter). However, the ecological function of soil microbes that enter aquatic ecosystems in association with organic matter is not known. Here, standardized cotton strip assays (CSA) were used to quantify the effects of soil microbial colonization location (mine vs. forest riverbank) and time (7 days vs. 14 days) on cellulose decomposition in aquatic ecosystems. The CSA results showed that the mine riverbank location and microbial colonization time had significant effects on the microbial community structure, microbial biomass, and functional genes of cellulose decomposition. Compared with the forest riparian zone, the fungal biomass and bacterial cellulose-decomposing gene (GH48) abundance of cotton strips colonized in the mine riparian zone for 14 days were 12.5-times and 54.93-times higher than that of the cotton strips colonized in the forest riparian zone, respectively, while the fungal cellulose-decomposing gene (cbhI) was detected only after 14 days of colonization. After 90 days of stream incubation, the decomposition rate and GH48 gene abundance of cotton strips colonized in the mine riparian zone for 14 days were significantly higher than those of cotton strips colonized in the forest riparian zone. However, the abundance of the cbhI gene in cotton strips colonized for 14 days was significantly higher than that in cotton strips colonized for 7 days. These results show that bacteria were mainly affected by the microbial colonization environment, while fungi were mainly affected by colonization time. Mining activities accelerate the decomposition of organic matter in aquatic ecosystems by increasing soil fungal biomass and bacterial cellulose decomposition genes. To reduce the carbon loss of aquatic ecosystems, it is necessary to study the potential influence of soil microbes on the decomposition of organic carbon in riparian zones.