In-situ soil greenhouse gas fluxes under different cryptogamic covers in maritime Antarctica

Abstract

Soils can influence climate by sequestering or emitting greenhouse gases (GHG) such as carbon dioxide (CO2),methane (CH4), and nitrous oxide (N2O). We are far from understanding the direct influence of cryptogamiccovers on soil GHGfluxes, particularly in areas free of potential anthropogenic confounding factors.We assessed the role of well-developed cryptogamic covers in soil attributes, as well as in the in-situ exchange ofGHG between Antarctic soils and the atmosphere during the austral summer. We found lower values of soil or-ganic matter, total organic carbon, and total nitrogen in bare areas than in soils covered by mosses and, particu-larly, lichens. These differences, together with concomitant decreases and increases in soil temperature andmoisture, respectively, resulted in increases in in-situ CO2emission (i.e. ecosystem respiration) and decreasesin CH4uptake but no significant changes in N2Ofluxes. We found consistent linear positive and negative relation-ships between soil attributes (i.e. soil organic matter, total organic carbon and total nitrogen) and CO2emissionsand CH4uptake, respectively, and polynomial relationships between these soil attributes and net N2Ofluxes.Our results indicate that any increase in the area occupied by cryptogams in terrestrial Antarctic ecosystems (dueto increased growing season and increasingly warming conditions) will likely result in parallel increases in soilfertility as well as in an enhanced capacity to emit CO2and a decreased capacity to uptake CH4.Suchchanges,un-less offset by parallel C uptake processes, would represent a paradigmatic example of a positive climate changefeedback. Further, we show that the fate of these terrestrial ecosystems under future climate scenarios, as wellas their capacity to exchange GHG with the atmosphere might depend on the relative ability of different above-ground cryptogams to thrive under the new conditions.