Rhizosphere microbial biomass is affected by soil type, organic and water inputs in a bell pepper system

Effects of environmental and management factors on the diversity and abundance of rhizosphere microbes in unmanaged ecosystems are well established. However, there is limited information about these interactions in vegetable cropping systems. In this two-year field study, we used organic amendments (humic substances, HS) and water supply (deficit irrigation) as soil management factors to characterize changes in bell pepper rhizosphere microbial population under two distinct soil types (clay and sandy). Path analysis revealed that soil type was the main factor constructing the microbial population. Clay soil indirectly increased bacterial biomass through the changes in root length, soil pH, P and K contents, while increased fungal biomass was linked with the enhanced above-ground plant yield. As organic inputs, HS had long-term positive influences on soil microbial activity through improvements in soil organic carbon content, which was also positively correlated with bacterial population. Water input became a less influential factor-deficit irrigation indirectly decreased fungal biomass but increased soil respiration through the reduction in pepper yield. These findings provide a better understanding of external factors controlling the abundance of rhizosphere microbiota under intensively managed cropping systems, and potential strategies to improve beneficial microbial diversity and soil health.