NSFDEB-NERC:Mycorrhizal drivers of SOM formation and decomposition

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.

This is a 'Discovery Science' proposal, addressing a fundamental aspect of the terrestrial C cycle. As such, it has important implications in global change science, for ecosystem management, and for broader society. The focus of experiments and modelling efforts are on the understanding of feedbacks between vegetation and the soil biota with regards to the formation and decomposition of soil organic matter. We hypothesise significant shifts in the processing and ultimately longevity of soil organic matter in soils in response to vegetation change, which has profound implications to carbon storage and climate feedbacks for natural and managed ecosystems.

Results of this research are of immediate interest to the global change biology and climate sciences research communities, as well as to national and international policy makers. The aim of current modelling efforts in the atmospheric and ecosystem communities is to understand future CO2 burdens based on on-going and projected environmental conditions resulting from climatic change and human land use. The novel soil module developed here to reflect vegetation change will be integrated into ecosystem models currently used to assess carbon storage and release in ecosystems.

The result will further benefit statutory agencies and land managers concerned with carbon sequestration and storage in relation to land use. The Forestry Commission (and more specifically its research branch Forest Research) as well as commercial forestry operators and nature charities involved in tree plantation under current 'rewilding' schemes require more knowledge of the impact of vegetation change. National and regional land use policies will have to reflect all ecosystem services associated with land management decisions, and the proposed research would fill a gap in our knowledge regarding vegetation feedbacks on long term carbon storage.

Ultimately, these insights are for the benefit of society in general. Whether land cover change occurs as a consequence of global changes, or as a result of deliberate management, the consequences for belowground carbon storage have to be understood. Communities living and working in areas where changes occur (often areas of low agricultural productivity, such as UK uplands) are aware of the on-going and changing land-use demands, potential conflicts, and the challenges of earning a viable living. It is important that society has a robust science base upon which to develop rational policies for upland land-use, and that the ecosystem services provided in these areas can be sustainably managed. Furthermore, through their effects on biodiversity and landscape quality, 're-wilding' and forest regeneration will have significant implications for quality of life, health and aesthetic value.