Bacterial Community Composition and Diversity Changes Across an Agricultural Intensity Gradient

Abstract Ecological impacts associated with agricultural land use change are evident via the direct replacement of natural communities with managed production systems. These impacts are extensively studied, but the implications for soil biology and belowground diversity remain poorly understood. Due to their contribution to soil systems and ability to survive under harsh and changing conditions, soil bacteria are a good candidate to highlight belowground ecological community dynamics. Here, we use soil physicochemical assessment and 16S rDNA sequencing to investigate soil bacterial community assemblage across an agricultural intensity gradient in a semi-arid mixed-use agricultural landscape. We collected and assessed soil samples from distinct land use systems including remnant vegetation, old pasture, recently established vineyards and old vineyards and recently revegetated areas. We found that land use systems differed in soil physicochemical characteristics (specifically nitrogen and phosphorus) likely influenced by agricultural inputs and plant functional diversity. Land use and management practises were also linked to a shift in the soil microbiome, such that distinct bacterial communities were associated with specific land use systems. Counter to expectations, highest bacterial diversity was observed in the most intensively modified agricultural systems (vineyards). These systems were also broadly linked with a beneficial bacterial community shift (in the context of soil and plant health). The community composition of recently revegeted areas was also more similar to remnant habitat suggesting that bacterial community composition can respond quickly to above ground changes. Collectively, results suggest that while vineyard agriculture may reduce aboveground plant diversity, it can increase belowground bacterial diversity. We propose that this is in-part due to disturbance associated with the vineyard agricultural systems. These findings highlight the need to further explore practices influencing soil biological components in agricultural systems, and the potential to develop microbiome-based strategies to enhance soil health and agricultural productivity.