2018 ASHS Annual Conference

The microbiota in the root rhizosphere is essential for mutualistic benefits with plant growth. Due to the dynamic and complex environment, the community of rhizosphere microbes is highly affected by root growth and abiotic factors. Humic substances (HS) are widely used as soil organic amendments to improve plant root growth and soil properties, and also to enhance soil microbial activities due to the additional carbon input. However, there is limited information on the effects of HS on the rhizosphere microbial composition, especially in vegetable crop systems. In this two-year field experimental study, we applied HS as carbon input, and evaluated their responses under two distinctive environmental factors: soil type (clay, sandy) and water content (deficit, well-watered) to illustrate the shaping effects of abiotic factors on the microbial activity of a bell pepper rhizosphere. The results using a path analysis revealed that soil type was the main factor driving the microbial changes. Clay soil tended to increase bacteria population through changes in root length, soil pH and K content, and fungi population through the enhancement in pepper yield. HS application acting as organic input may have a long-term positive influence on soil microbial activity through improvements in soil organic carbon content, and this benefited more to bacteria community. Water content became a less influential factor compared to soil type and organic input on the microbial activity. Higher water content tended to increase fungal biomass but decrease soil respiration through the enhancement in pepper aboveground growth. This study distinguished key abiotic factors that affected the rhizosphere microbial biomass in a bell pepper growth system, which can act as a reference to establish applied approaches to improve the persistence and benefits from rhizosphere microbial community.