Soil depth and agricultural irrigation activities drive variation in microbial abundance and nitrogen cycling

• Published in: Catena (Giessen) 2022-12, Vol.219, p.106596, Article 106596
• Main Authors: He, Junqi, He, Yi, Gao, Wande, Chen, Yunfei, Ma, Guixiang, Ji, Ruiqing, Liu, Xiuhua
• Format: Article
• Language: English
• Subjects: Critical zone; Environmental filtering; Farmland abandonment; Irrigated agriculture; Nitrogen-cycling microorganisms
• ISSN: 0341-8162; 1872-6887
• DOI: 10.1016/j.catena.2022.106596

•Environmental filtering by depth drives microbe abundance along resource gradients.•Soil depth plays a crucial role in driving microbial abundance, but not diversity.•Nutrient resources were a control factor of microbial abundance in summer rather than in winter.•Land use pattern of agricultural activities speed up the biogeochemical cycle of N. Understanding the vertical diversity and abundance of soil microorganisms in shifting environments is crucial for the improvement of crop yield, tackling climate change and optimizing biogeochemical cycles in the Earth’s critical zone. In this study, a comprehensive survey of soil microbial communities was conducted in fields in an irrigated area and an abandoned area in western China. In total, 40 soil cores (600 cm deep) were taken from land under irrigation–fertilization management (IL; 34 cores) and abandoned land (AL; six cores) from July 2013 to April 2018. Spatiotemporal variation in the abundance of soil bacteria, fungi and nitrogen (N)-cycling microbes was evaluated. Soil depth was found to drive soil microbial abundance, but not diversity, throughout the vertical soil profile. The results suggest that in winter, the abundances were mainly driven by environmental variables (depth and temperature), but in summer, by depth, temperature and nutrient status. Depth had strong direct effects, and indirect impacts via temperature and TN, on microbial abundance in summer. The sequence counts for some prokaryotic taxa presented clear, mid-profile peaks in the vertical soil profiles. These distributions may be partially explained by soil texture. Consequently, the environmental filtering associated with depth controls local microbial abundance along resource gradients in the soil profile. Other factors, including temperature, moisture, pH and nutrients, were secondary regulators of microbial abundance. Further, irrigated agriculture land use could accelerate N cycling, increase nitrate leaching, and N2O and N2 production. Such findings, which enhance our understanding of how soil microbial communities respond to environmental changes and N-cycling pathways in the deeper soil profile, could improve field nitrogen management.