Microbiome manipulation and enhanced weathering stimulate CO2 removal in reforestation

Limiting future warming requires both drastic reductions in carbon emissions, and removal of past emissions from the atmosphere. Socioeconomic and biophysical limits on the efficacy of nature-based carbon dioxide removals (such as reforestation) mean that the natural carbon sequestration capacity of forests should be maximized, wherever reforestation is implemented. Here we report on a large-scale (11.5 ha) field trial testing co-deployment of two strategies to increase forest carbon capture: modification of the soil microbiome, and enhanced rock weathering (ERW) via addition of crushed silicate rock. Individual monitoring of 6,400 trees over three years revealed that individual saplings grew 7% larger, on average, when inoculated with soils from nearby mature forest. Meanwhile, the ERW treatment augmented aboveground carbon stocks by 27% and elevated plant tissue nutrients. We conclude that co-deploying early-stage reforestation with microbial enrichment or ERW can increase forest carbon sequestration by 69–159 kg C ha ^− 1 in the first three years post-planting.