Deciphering microbiomes dozens of meters under our feet and their edaphoclimatic and spatial drivers

Microbes inhabiting deep soil layers are known to be different from their counterpart in topsoil, yet remain under investigation in terms of their structure, function, and how their diversity is shaped. The microbiome of deep soils (> 1 m) is expected to be relatively stable and highly independent from climatic conditions. Much less is known, however, on how these microbial communities vary along climate gradients. Here, we used amplicon sequencing to investigate bacteria, archaea, and fungi along fifteen 18-m depth profiles at 20–50 cm intervals across contrasting aridity conditions in semi-arid forest ecosystems of China's Loess Plateau. Our results showed that bacterial and fungal α diversity and bacterial and archaeal community similarity declined dramatically in topsoil and remained relatively stable in deep soil. Nevertheless, deep soil microbiome still showed the functional potential of N cycling, plant-derived organic matter degradation, resource exchange, and water coordinat...