Metagenomics reveals divergent functional profiles of soil carbon and nitrogen cycles in an experimental drought and phosphorus-poor desert ecosystem

Abstract

Carbon (C) and nitrogen (N) cycles are fundamental biogeochemical processes in terrestrial ecosystems. The specific contribution of soil biodiversity toward these processes in hyper-arid desert environments with limited availability of water and phosphorus (P) remains ambiguous. This study performed a three-year pot experiment to determine the importance of biodiversity among dominant soil microbes in C and N cycling under varying conditions of water (drought and well-watered) and P (no, low, medium, and high) supply. The dissolved organic C (DOC) and ammonium nitrogen (NH₄⁺-N) concentrations and cellulase and nitrite reductase activities were 11 %, 18 %, 49 %, and 14 % lower, respectively, under drought with no-P supply conditions (stress scenario) compared with well-watered with high-P supply conditions (accommodative scenarios); however, the nitrate nitrogen (NO₃⁻-N) concentration and ammonia monooxygenase activity under these stress conditions were 16 % and 44 % higher. The relative abundances of the C-cycling genes (60 %) associated with all C-cycling processes (e.g., frdB, mcmA1, and IDH3), while N-cycling genes (57 %) were associated mainly with dissimilatory nitrate reduction and N degradation (e.g., nrfA, gltS, and glnA). The dominant microbe diversity, mainly copiotrophic bacteria in Acidobacteria, was lower under drought with no-P supply compared with the well-watered with high-P supply treatment. The relative abundances of these two genes, the dominant microbe biodiversity, and soil DOC and NH₄⁺-N concentrations were strongly positively correlated. This research indicates that drought and/or low-P conditions can impede nitrification and soil organic matter reduction and decomposition and promote denitrification. Additionally, the findings emphasise the importance of dominant soil microbe biodiversity in driving desert soil C and N cycling. These results could provide evidence-based recommendations for the sustainable preservation of the composition and capabilities of desert ecosystems and further contribute to addressing desert ecosystem imbalances caused by global climate change by increasing soil fertility and greening desert landscapes.