Microbiome manipulation and enhanced weathering influence tree growth in reforestation

Abstract Limiting future warming invokes the need to maximize the natural carbon sequestration capacity of forests. Here we report on a large-scale (11.5 hectare) field trial testing co-deployment of two strategies to increase forest carbon capture: enhanced rock weathering via addition of crushed silicate rock, and modification of the soil microbiome. Individual monitoring of 6400 trees over four years revealed that silicate rock amendment augmented aboveground carbon stocks by 27% in broadleaf stands only. Inoculating trees with soils from nearby mature forest tended to boost their growth, but effect sizes varied strongly among tree species and diminished through time. We conclude that co-deploying early-stage reforestation with enhanced rock weathering can increase forest carbon sequestration by up to 787 kilograms carbon per hectare in the first four years post-planting. Soil microbiome enrichment could potentially be harnessed for ecological restoration, although more investigation is required to verify the underlying ecological mechanisms.