Bacterial necromass recycling promotes diversity maintenance in bacterial communities via resource partitioning

Understanding how high species diversity is maintained in natural bacterial communities is a central question in microbial ecology. Due to the versatile heterotrophic capacities of bacteria and the rich nutrients released by deceased bacterial cells, necromass recycling plays an important role in sustaining bacterial growth. Such nutrient cycling within communities can provide additional resource niches for bacteria, but its potential effects on bacterial diversity maintenance have been neglected. Here we conducted two independent experiments and studied the assembly of 276 soil-derived bacterial communities sustained by a wide range of bacterial necromass combinations, from single-species necromass to combinations of up to nearly 1,000 species. Our results highlight the existence of a species-rich bacterial necrobiome in soil. We found that the composition of necromass-decomposing communities was determined by the various organic compounds in the different necromass combinations, and the increases in necromass-producing species constantly promoted species diversity of necromass-decomposing communities. Moreover, the average niche breadth and overlap of coexisting necromass-decomposing species in utilizing distinct single-species necromass decreased with increases in necromass diversity, supporting the hypothesis of resource partitioning in utilizing different single-species necromass. Our study provides insights into diversity maintenance in bacterial communities from a perspective of internal nutrient cycling.