Role of fungal communities in carbon and nutrient cycling in forest soils under elevated atmospheric CO2 concentrations

Fungal communities are known to play influential roles in woodland ecosystems, yet much remains unknown about their diversity, functioning, and likely responses to environmental change. This project aims to address some of these knowledge gaps by investigating mycorrhizal fungal communities at the Birmingham Institute of Forest Research Free Air Carbon Dioxide Enrichment site (BIFoR FACE). The only facility of its kind in the northern hemisphere, BIFoR FACE is a large-scale experiment subjecting patches of mature temperate woodland to elevated CO2 levels (approx. 550 ppm) with the aim of illuminating likely effects of future increases in atmospheric CO2 on this kind of ecosystem. Though elevated CO2 levels are expected initially to enhance tree growth, it is predicted that this growth enhancement may be relatively short-lived as the availability of soil nutrients - in the northern hemisphere, primarily nitrogen - could become limiting in the longer term. A fuller appraisal of this "progressive nitrogen limitation" (PNL) hypothesis demands consideration of fungal communities as ectomycorrhizal fungi in particular can supply significant quantities of otherwise inaccessible nitrogen to their plant hosts, although the extent to which this occurs varies between different species and environmental conditions. One possible scenario with some empirical support is that under elevated CO2 trees will invest more carbon in their mycorrhizal symbionts and receive more nitrogen from these fungi in return, alleviating PNL. Conversely, experimental evidence from boreal forest ecosystems has suggested that greater allocation of carbon from trees to mycorrhizal fungi can lead to increased amounts of nitrogen being locked up in proliferating mycorrhizal biomass, rather than being transferred to tree hosts, thus exacerbating PNL. This project will use molecular techniques firstly to characterize the mycorrhizal fungal communities present in elevated- and ambient-CO2 plots at the BIFoR FACE site, determining whether differences in community composition are apparent between the two conditions. This will then form the basis for investigating possible changes in mycorrhizal nutrient acquisition and transfer under elevated CO2, whether through community compositional shifts or altered functioning under different conditions, thus connecting mycorrhizal fungal responses to elevated CO2 with their wider effects in terms of nutrient cycling and tree growth.