19 Sep 2023
 | 19 Sep 2023
Status: this preprint is open for discussion.

Non-mycorrhizal root-associated fungi increase soil C stocks and stability via diverse mechanisms

Emiko K. Stuart, Laura Castañeda-Gómez, Wolfram Buss, Jeff R. Powell, and Yolima Carrillo

Abstract. While various root-associated fungi could facilitate soil carbon (C) storage and therefore aid climate change mitigation, so far research in this area has largely focused on mycorrhizal fungi, and potential impacts and mechanisms for other fungi are largely unknown. Here, we assessed the soil C storage potential of 12 root-associated, non-mycorrhizal fungal isolates (spanning nine genera and selected from a wide pool based on traits potentially linked to soil C accrual) and investigated fungal, plant and microbial mediators. We grew wheat plants inoculated with individual isolates in chambers allowing continuous 13C labelling. After harvest, we quantified C persistence, and pools of different origin (plant vs soil) and of different stability with long-term soil incubations and size/density fractionation. We assessed plant and microbial community responses, as well as fungal physiological and morphological traits in a parallel in vitro study. While inoculation with three of the 12 isolates resulted in significant total soil C increases, soil C stability improved under inoculation with most isolates – as a result of increases in resistant C pools and decreases in labile pools and respired C. Further, these increases in soil C stability were positively associated with various fungal traits and plant growth responses, including greater fungal hyphal density and plant biomass, indicating multiple direct and indirect mechanisms for fungal impacts on soil C storage. We found more evidence for metabolic inhibition of microbial decomposition than for physical limitation under the fungal treatments. Our study provides the first direct experimental evidence in plant-soil systems that inoculation with specific non-mycorrhizal fungal strains can improve soil C storage, primarily by stabilising existing C. By identifying specific fungi and traits that hold promise for enhancing soil C storage, our study highlights the potential of non-mycorrhizal fungi in C sequestration and the need to study the mechanisms underpinning it.

Emiko K. Stuart et al.

Status: open (until 03 Nov 2023)

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Emiko K. Stuart et al.

Emiko K. Stuart et al.


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Short summary
We inoculated wheat plants with various types of fungi whose impacts on soil carbon are poorly understood. After several months of growth, we examined both their impacts on soil carbon and the underlying mechanisms, using multiple methods. Overall, the fungi benefited the storage of carbon in soil mainly by improving the stability of pre-existing carbon, but several pathways were involved. This study demonstrates their importance for soil carbon storage and, therefore, climate change mitigation.