Bacterial community succession and influencing factors for Imperata cylindrica litter decomposition in a copper tailings area of China

Litter decomposition is a critical component of the ecological nutritional transformation process. In a copper mining area, the litter from Imperata cylindrica is the major indicator for restoring heavy metal-polluted copper mining lands. Large amounts of litter are generated at the end of the plant growing season during the process of vegetation restoration in copper mining areas, and the microbial dynamics play an important role in soil nutrient turnover during the decomposition of litter. Investigating the characteristics and interactions of bacterial communities during litter decomposition will clarify the driving mechanisms of organic matter and nutrient cycling in copper mining areas that harbor contaminated soils. Here, we report the results of an in situ decomposition experiment that lasted for a total of 460 days from three of the 16 copper mining subdams with heavy metal pollution and different phytoremediation histories (e.g., 50, 22 and 5 years) to explore the bacterial communities as the driving factors of litter decomposition. The total carbon contents of the litter decreased by 62.6% and 71.5% in the decomposition process at those sites with phytoremediation histories of 50 and 22 years (S516 and S536), respectively, but decreased by only 25.8% at the site with a phytoremediation history of 5 years (S560). The optimal C/N ratios in the three different restoration stages varied and were 65.5, 86.7 and 39.3 in S516, S536, S560, respectively. Litter decomposition enriched the heavy metal contents such as cadmium, copper (Cu), lead and zinc (P < 0.05) in litter. Proteobacteria and Actinobacteriota were the dominant bacterial phyla during the different litter decomposition stages, which accounted for 91.66% of the relative abundances in the bacterial communities. Moreover, the role of Friedmanniella, which had the highest betweenness centrality (BC) value, was critical in sustaining both the structure and function of the bacterial communities during the early decomposition stage. However, Quadrisphaera, with the maximum BC value (1074.8), became the dominant genus as litter decomposition progressed. The most crucial factors that affected the litter bacterial communities were the litter pH and copper contents. The obtained results will be helpful to provide a further understanding of litter decomposition mechanisms and will provide a scientific basis for improving the effectiveness of material circulation and nutrient transformation in degraded copper mining ecosystems.