Resilience of soil microbial communities impacted by severe drought and high temperature in the context of Mediterranean heat waves

In the context of Climate Change, the increasing of frequency and intensity of droughts and heat waves constitutes a serious threat for agroecosystems in the Mediterranean region. Soils and their functions may be impacted by these extreme events through changes in the biomass, composition and activities of edaphic microbial communities. We designed an experiment to investigate changes over time in the microbial biomass, composition (EL-FAME profiles) and functions (catabolic responses) after severe drought and high temperature disturbances. Impacts were assessed using indoor soil microcosms under controlled drought and high temperatures, mimicking various stress scenarios and durations in conditions of severe drought and heat wave. Drought and heat wave restructured the soil microbial communities over the course of the experiment. This may be a consequence of inhibition and/or killing of sensitive species and selection of tolerant species by the disturbances applied, but also of the proliferation of fast-growing species after environmental soil conditions had been restored. Heating dry soil at 50 C had a stronger effect than only drying. Moreover, above a critical threshold of heat wave duration, soil microbial communities may have undergone a drastic biomass killing and restructuring associated with a shift in physiological traits. In this experimental context, resilience of microbial catabolic functions was not observed and in consequence ecosystem processes such as carbon mineralization and sequestration in soil may be affected. (C) 2011 Elsevier Masson SAS. All rights reserved.