A diversity of fungal pathways contribute to improved soil carbon stability and storage

While various fungi could facilitate soil C storage and climate change mitigation via carbon (C) cycling, standard soil C tests that measure only bulk soil C cannot disentangle mechanisms underpinning fungal influences and so far research has largely focused on mycorrhizal fungi. Here, we assessed the soil C storage potential of 12 non-mycorrhizal fungi, selected from a wide pool based on traits potentially linked to soil C accrual. We grew wheat plants inoculated with individual isolates in chambers designed to differentiate plant- and soil-derived C using stable isotope analysis. After harvest, we conducted long-term soil incubations and high throughput fractionation to determine fungal impacts on soil C pools. While only some isolates resulted in significant total soil C increases, most significantly improved soil C stability by increasing the stable pools of soil C, providing the first direct experimental evidence that inoculation with specific fungi can improve soil C storage by stabilising existing C. These increases were positively associated with fungal and plant growth characteristics, indicating direct and indirect mechanisms for fungal impacts on soil C storage. Our study highlights the need for more research on the roles of non-mycorrhizal fungi in C cycling and for higher resolution methods to understand fungal impacts on soil C storage, as these fungi hold promise for soil C sequestration strategies.