Assembly and Source of the Lithobiontic Microbial Community in Limestone

Due to its unique rock properties (e.g., porous nature, rough texture, and high calcium and magnesium content), limestone exhibits a high degree of bioreceptivity. However, the mechanisms underlying the establishment of limestone lithobiontic microbial communities (LLMCs) and the extent to which their composition is influenced by the surrounding environment remain enigmatic. Herein, after collecting limestone sand samples, we applied various treatments: rain shelter (RS), organic acid (Oa), nutrients (Nut), inorganic acid (Ia), inorganic acid combined with nutrients (Ia+Nut15), and a blank control (CK). Subsequently, we sampled the treatments after a duration of 60 days. In addition, we collected rotted wood, concrete fences, and soil from the surrounding environment as microbial sources, while using treated limestone samples as microbial sinks. This study yields the following findings: (1) Limestone exhibits high bioreceptivity, allowing rapid microbial colonization within 60 days. Furthermore, compared to the surrounding environment, limestone can accommodate a greater diversity of microbial species. (2) The fungal and bacterial community compositions were explained by surrounding sources to the extent of 35.38% and 40.88%, respectively. The order of sources, in terms of contribution, is as follows: unknown sources > soil > rotted wood > concrete fences. (3) Higher concentrations of Ia and Ia+Nut15 treatments facilitate the colonization of fungi from the surrounding environment onto limestone while inhibiting bacterial colonization. (4) The process of establishing LLMCs is primarily driven by stochastic processes. However, Ia and Ia+Nut15 can mediate transitions in the establishment processes of bacterial communities, while Ia is solely responsible for mediating transitions in the establishment process of fungal communities. Our study offers a fresh perspective on the establishment and origins of microbial communities in limestone habitats. We believe that limestone serves as an excellent substrate for microbial colonization and holds immense potential in ecological restoration efforts within degraded karst areas.