Severe drought-induced community tolerance to heat wave. An experimental study on soil microbial processes

The purposes of this study were to identify the influence of a severe drought period on the impact of a subsequent heat-drought disturbance on the microbial community of a Mediterranean agricultural soil and particularly to highlight the long-term effects on the microbial catabolic profiles.<br/>We performed an experiment in microcosms and applied the MicroResp (TM) method on soil microbial communities.<br/>A 21-day combined heat-drought disturbance had less impact on soil microbial communities pre-exposed to a 73-day severe drought than on those that were not pre-exposed. These differences were observed not only for biomass and physiological traits (basal respiration, qCO(2)), but also for catabolic microbial structure evolution during the recovery time.<br/>These observations suggest that the physiological stress imposed by the initial severe drought changed the microbial catabolic structure or physiological state and favoured a portion of the microbial community best adapted to cope with the final heat-drought disturbance. Consequently, the initial severe drought may have induced a community tolerance to the subsequent heat wave. In this study, we also note that resilience was, more than resistance, an indicator of pre-exposure to stress. In the context of assessing the effects of extreme climatic events on soil microbial processes, these results suggest that future studies should take into account the historic stress of habitats and resilience parameters.