Microbial distribution patterns and driving factors related to nitrogen cycling in karst Tiankeng soil

Soil nitrogen (N) cycling is one of the most critical biogeochemical cycles, and N cycling-related microorganisms are the primary driving force behind N cycling in natural environments. The large karst sinkholes in China, known as Tiankengs, harbor abundant unique biological resources due to their particular environmental conditions. However, N cycling-related microorganisms in Tiankeng soils and their connection to ecosystem processes remain poorly studied. In this study, we investigated the distribution patterns and genomic diversity of N cycling-related microorganisms both inside and outside the Luohun cave Tiankeng in Guizhou, China, utilizing high-throughput sequencing and other techniques. The results indicated that the diversities and abundances of denitrifying bacteria, ammonia-oxidizing bacteria, and ammonia-oxidizing archaea communities inside the Tiankeng were higher than those outside the Tiankeng; however, the microbial network relationships were more fragile inside the Tiankeng. The most abundant species of denitrifying bacteria, ammonia-oxidizing bacteria, and ammonia-oxidizing archaea inside the Tiankeng were unclassified_p_Proteobacteria (47.8%), unclassified_k_norank (AOB, OTU121, 37.3%), and unclassified_g_norank_f_norank_o_norank_c_environmental_samples (55.7%), respectively; outside the Tiankeng, they were unclassified_k_norank_d_bacteria (54.5%), unclassified_k_norank (AOB, OTU121, 48.1%), and unclassified_k_norank (AOA, OTU70, 49.6%), respectively. Additionally, the N content inside the Tiankeng was significantly lower (P < 0.05) under the influence of these N cycling-related microorganisms, whereas the nutrient contents were higher than that outside the Tiankeng. To the best of our knowledge, this is the first report on the crucial microbial distribution patterns driving N cycling in karst Tiankengs and provides new insights into the structure and potential functions of N cycling-related microorganisms in the unique ecological environment of fragile Tiankeng ecosystems.