Effects of Increased Temperature, Elevated CO2 Concentrations and Drought on Soil Structure and Gas Diffusion in a Submontane Grassland Soil

Global climate change, driven by rising atmospheric CO2 concentrations, is increasing the frequency and duration of extreme weather events, such as droughts and heavy rainfalls. The implications of these changes for soil-plant interactions in managed grasslands remain poorly understood. To investigate the combined effects of increased CO2 (+300 ppm) and elevated temperature (+3 °C), along with a 2-month summer drought, we conducted a study using undisturbed topsoil and subsoil samples from a 10-year climate change experiment (ClimGrass) in a submontane grassland in Gumpenstein, Austria. We hypothesize that elevated CO2 and temperature will enhance above- and below-ground biomass, leading to increased root growth and a corresponding rise in soil porosity, particularly of the proportion of biogenic macropores, which is expected improve aeration and boost gas diffusion rates.

We analyzed potential changes in soil structure by scanning 66 undisturbed samples with a high-resolution x-ray computed tomography system (only topsoil). Additionally, we measured water retention curves and oxygen diffusion rates (single chamber method) at different matric potentials (-60,  -150,  -300 hPa) for the topsoil and subsoil, to examine how potential changes in total porosity, pore size distribution and pore connectivity affect gas exchange from the soil to the atmosphere at different moisture levels. As was expected, first results indicate that elevated CO2 led to a lower bulk density and a higher amount of macropores, which also caused gas diffusion rates to increase. The moderating effects of elevated temperatures and droughts will also be discussed.