Soil functional responses to drought under range-expanding and native plant communities

1. Current climate warming enables plant species and soil organisms to expand their range to higher latitudes and altitudes. At the same time, climate change increases the incidence of extreme weather events such as drought. While it is expected that plants and soil organisms originating from the south are better able to cope with drought, little is known about the consequences of their range shifts on soil functioning under drought events. 2. Here, we test how range-expanding plant species and soil communities may influence soil functioning under drought. We performed a full-factorial outdoor meso-cosm experiment with plant communities of range expanders or related natives, with soil inocula from the novel or the original range, with or without summer drought. We measured litter decomposition, carbon mineralization and enzyme activities, substrate-induced respiration and the relative abundance of soil saprophytic fungi immediately after drought and at 6 and 12 weeks after rewetting. 3. Drought decreased all soil functions regardless of plant and soil origin except one; soil respiration was less reduced in soils of range-expanding plant communities, suggesting stronger resistance to drought. After rewetting, soil functioning responses depended on plant and soil origin. Soils of native plant communities with a history of drought had more litter mass loss and higher relative abundance of saprophytic fungi than soils without drought and soils of range expanders. Functions of soil from range expanders recovered in a more conservative manner than soils of natives, as litter mass loss did not exceed the control rates. At the end of the experiment, after rewetting, most soil functions in mesocosms with drought history did not differ anymore from the control. 4. We conclude that functional consequences of range-expanding plants and soil biota may interact with effects of drought and that these effects are most prominent during the first weeks after rewetting of the soil.