NSFDEB-NERC:Mycorrhizal drivers of SOM formation and decomposition

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Soils in natural temperate ecosystems store substantial amounts of carbon in the form of soil organic matter. This represents a vital service by these ecosystems (including forest, grasslands as well as wetlands), as these organic matter reservoirs have been built up from decaying vegetation that previously fixed carbon in its biomass from atmospheric CO2. There is significant uncertainty regarding the persistence of this reservoir of carbon in soils, both from climatic influences and changes in land use. The influence of temperature on the formation of plant biomass as well as decay processes are well researched, but have so far been largely considered separately. More recently, it has emerged that fundamental differences in the way in which vegetation interacts with microbial organisms in the soil have significant impact on the storage of carbon in soil organic matter. The symbiotic relationship of plants with particular forms of fungi (mycorrhizas) is of particular interest. The role of these fungi in the supply of nutrients to plants is well established, but recent findings highlight important influences of these organisms also on the formation and decomposition of organic matter. Changes in vegetation form can drastically influence the type of fungal (i.e. mycorrhizal) diversity in the soil, with direct implications for organic matter formation and decay. However, the interaction between vegetation form, fungal association and soil organic matter storage has not been investigated systematically.This research addresses the way in which changes in vegetation that also alter the type of mycorrhizal fungal association results in changes in organic matter storage. Specifically, we will investigate a switch from grasslands to coniferous forests. This kind of vegetation change is relatively common in temperate regions due to an encroachment of trees near treelines, following a warming climate, and managed land use changes where upland pasture may be planted with commercial forestry or for 'rewilding' efforts. Our methodology combines experimental decomposition studies with ecosystem model development to enable a new generation of predictive models (based on existing modelling tools) able to incorporate plant-microbial interactions. Land managers and policy makers alike require a full understanding of the consequences of this kind of vegetation change on soil carbon storage, as apparent benefits in carbon uptake by vegetation may be annulled by corresponding losses in storage within the soil.