Differential response of subterranean microbiome to exogenous organic matter input in a cave ecosystem

As a recurrent climatic phenomenon in the context of climate change, extreme rainstorms induce vertical translocation of organic matter and increase moisture content in terrestrial ecosystems. However, it remains unclear whether heavy rainstorms can impact microbial communities in the deep biosphere by modulating organic matter input. In this study, we present findings on the different responses of bacterial and fungal communities in a subsurface cave to rainstorms and moisture variations through field surveys and microcosm experiments. During periods of rainstorms, the influx of dissolved organic matter (DOM) from soil overlying the cave into cave sediments significantly enhanced the correlation between core bacteria and environmental factors, particularly fluorescence spectral indices. The resource utilization of core bacteria was diminished, while the functional diversity of core fungi remained relatively unaltered. We also performed simulated experiments with restricted external DOM inputs, in which DOM content was observed to decrease and microbial diversity increase in response to artificially increased moisture content (MC). The niche breadth of core bacteria decreased and became more closely associated with DOM as the MC increased, while the niche breadth of core fungi remained predominantly unchanged. Compared to fungi, cave bacteria exhibited higher sensitivity towards variations in DOM. The core microbiome can efficiently utilize the available organic matter and participate in nitrogen- and sulfur-related metabolic processes. The study systematically revealed distinct microbial responses to rainstorm events, thereby providing valuable insights for future investigations into energy utilization within deep biospheres.