Relating fungal functional diversity to C-cycling in sub- and Maritime Antarctic soils

The decomposition of organic matter is a critical process to the functioning of terrestrial ecosystems. This process is largely driven by saprotrophic (decomposer) fungi in soil and plant litter. Saprotrophic fungi therefore have pivotal roles in the release of carbon (C) from terrestrial ecosystems, in the form of CO2 (a climate-forcing gas), to the atmosphere. Currently, little is known of the specific roles of individual fungal species, i.e. functional diversity, in the degradation of particular C components in the sub- and Maritime Antarctic. The first step in characterising functional diversity is to identify the soil C components (fractions, particle sizes and ages) with which decomposer fungi in soil are associated. Establishing baseline fungal taxonomic and functional diversity and characterizing the soil C components - central aims of this proposal - are fundamental to understand the impacts of environmental change on Antarctic ecosystems. Why the sub- and Maritime Antarctic? Soils in these regions have relatively high stocks of C because of the slow decomposition of organic matter and the tundra vegetation present. For example, soils from South Georgia and Signy Island contain 30 to 40% C. The potential temperature responses of these soils and the C fractions they contain are also important to understand because the terrestrial Maritime Antarctic has been warming rapidly, at c. 0.2-0.4 degrees C per decade over the past 50-100 years, one of the fastest rates of warming recorded. The temperature sensitivity of young and older C fractions in releasing CO2 to the atmosphere is much debated, particularly for peatlands and permafrost soils, such as those that occur in the sub- and Maritime Antarctic. We will determine the associations of specific fungal taxa with specific organic fractions in the field at three sites in the sub- and Maritime Antarctic, and characterise by age and organic geochemistry, the C components of these fractions. In the laboratory, the specific C fractions mineralised by 'key' species of fungi will be determined, together with responses to temperature increases and freeze-thaw cycles. The outcomes of the project will be: (1) a better understanding of the roles of particular groups of fungi in the C cycle, (2) a benchmark for future studies (e.g. in arctic or temperate soils) of the functional roles of fungal mycelia in relation to C mineralisation will have been obtained, and (3) the effects of temperature increases / freeze-thaw on C mineralisation will have been determined.