Linking soil C cycling and microbial diversity under regenerative management in Northern California (USA) vineyards

Abstract

Regenerative agriculture (RA) practices aim to minimize soil disturbance, keep soil covered, maintain living roots underground, and integrate livestock to improve soil health and sustainability. Inputs from animals and living roots increase carbon (C) cycling and the associated microbial activities, which can promote C sequestration in soil. Studies have shown that RA practices, such as cover cropping, no-till, and sheep-grazing, can increase C stock and microbial diversity. Grapevine (Vitis vinifera L.) cultivation has been suggested to have a greater overall potential to store soil C than annual crops due to the vine’s deep-reaching roots and C exudation. Worldwide, vineyards occupy an extensive range of soil types with distinct subsoil mineralogy and physiochemical properties that may lead to significant variability in the potential of C stabilization and accrual in the subsoil depths. Despite the promising outcomes of RA practices on soil C and microbial diversity, the role of microbial communities in C sequestration, particularly in subsoil layers, is poorly understood. In a field trial, we surveyed the vertical distribution of indicators of C pools, microbial activity, and diversity before applying tillage and grazing treatments in three Northern California (USA) vineyards. After the use of RA practices for two years, we examined the short-term effects of no-till and grazing practices on soil C dynamics at different soil depths (0-15 cm, 15-30 cm, 30-60 cm, and 60-100 cm) in one of the vineyards. Further, we investigated how soil microbial communities and soil C pools shift across subsoil layers by characterizing bacterial and fungal taxonomic composition and diversity across the four soil depths. We performed 16S and ITS amplicon sequencing to measure bacterial and fungal taxonomic abundance and alpha and beta diversities, respectively. Microbial community composition, diversity, and enzymatic activity are expected to correspond to changes in C dynamics at deeper soil depths. We expect the C pool and microbial diversity indicators to reflect trends along the vertical soil profile under various RA practices. Our long-term goal is to provide insights into how RA practices affect the linkages among microbial communities, soil C dynamics, and soil properties in California vineyards, which will help growers make management decisions to improve crop productivity and resiliency while coping with the challenges of climate change.