Effects of black carbon (BC) on soil multifunctionality in soil exposed to plastic mulch film (PMF)

Black carbon (BC) formed after straw incineration remains in farmland soil and coexists with mulch residues in soil. Studies have not yet determined whether BC formed by direct incineration further affects the soil multifunctionality (soil nutrients, enzyme activity, microbial community structure, and function) of agricultural soil exposed to different plastic mulch film (PMF). In this study, we conducted a soil microcosmic experiment by adding BC formed by direct burning of straw and PMF fragments (polyethylene (PE) and biodegradable PMF (BP)) into soil at the dosages of 1%, and soils were sampled on the 15th, 30th, and 100th day of soil incubation for high-throughput sequencing. The results showed that PE and BP PMF underwent photo-oxidation and mechanical degradation after soil burial incubation, and BP also underwent biodegradation, accompanied by the release of microplastics (MPs). BC altered the pH and nutrients content (TK, TP, AP, AN, NH4+-N, and NO3--N) in PMF-exposed soils, which affected the activities of urease, phosphatase, peroxidase and catalase. Furthermore, the incubation time was the most influential factor driving the variations in microbial diversity and abundance, and significant effects of PMF type was also detected. Meanwhile, BC reduced the richness of bacterial and fungal communities and fungal diversity in PMF-exposed soils. Exposure to PMF and BC led to significant changes in the proportion of dominant phyla and genus of bacteria and fungi. It was also found that BC affected microorganisms by influencing soil properties, and AN was the main influencing factor. In addition, FAPRPTAX analysis indicated that the addition of BC and PMF affected C and N cycling in soil, including cellulolysis and ureolysis. These findings provided new insights into the response of soil multifunctionality to BC and PMF debris, and further studies are needed to explore the effects of coexistence of BC and PMF on soil microbial composition and function.