Soil fertility determines whether ectomycorrhizal fungi accelerate or decelerate decomposition in a temperate forest

• Published in: The New phytologist Vol. 239; no. 1; pp. 325 - 339
• Main Authors: Mayer, Mathias, Matthews, Bradley, Sandén, Hans, Katzensteiner, Klaus, Hagedorn, Frank, Gorfer, Markus, Berger, Harald, Berger, Torsten W., Godbold, Douglas L., Rewald, Boris
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01-07-2023
• Subjects: Acceleration; Carbon; carbon cycle; Carbon dioxide; Community composition; Deceleration; Decomposition; Ectomycorrhizas; Efflux; Fagus sylvatica (beech) forest; Fertility; Forest soils; Forests; Fungi; Gadgil effect; Girdling; Mycorrhizae; Nitrogen; nitrogen mining; Organic matter; Organic soils; plant–soil feedback; Positive feedback; priming; Soil; Soil dynamics; Soil fertility; soil fungal communities; Soil Microbiology; Temperate forests; tree girdling; Trees - microbiology; priming; soil fungal communities; nitrogen mining; Gadgil effect; carbon cycle; Fagus sylvatica (beech) forest; plant-soil feedback; tree girdling
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.18930

Summary
Ectomycorrhizal (ECM) fungi can both accelerate and decelerate decomposition of organic matter in forest soils, but a mechanistic understanding of this differential influence is limited.
Here, we tested how ECM fungi affect decomposition along a natural fertility gradient in a temperate forest of European beech. Trees were girdled to reduce belowground carbon supply to the soil.
Girdling shifted soil fungal community composition and decreased hyphal biomass production and soil CO2 efflux, indicating a reduced ECM fungal activity. Girdling also affected decomposition processes, but the effects depended on fertility. Our results indicate that ECM fungi decelerate decomposition under conditions of low fertility while under conditions of high fertility ECM fungi and their host roots have an accelerating effect.
We conclude that both acceleration and deceleration of decomposition of organic matter by ECM fungi can occur within a forest, with soil fertility determining the direction and magnitude of these effects. We suggest a positive feedback between fertility, stand productivity and soil carbon and nitrogen dynamics that is mediated to a large extent by ECM fungi.