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Extreme weather events are a growing focus of global climate change research. Extreme events, which occur abruptly and unpredictably, are often more detrimental to terrestrial vegetation than gradual shifts in climate. One type of event, the summer heat wave, may already be increasing in some areas of the world. Large-scale reductions in Net Primary Productivity and mortality have been reported during heat waves in forested ecosystems. Unfortunately, our understanding of how abrupt heat-stress affects woody species during heat waves lags behind our knowledge of herbaceous species that have been more widely studied in experimental manipulations. A few studies of herbaceous species also suggest that the coupling of soil heating to air heating can change the overall plant response to heat waves. To investigate air vs. air+soil heating in woody species, we manipulated the temperature of both shoots and roots separately for both white and black oak seedlings by insulating the soil during heat-stress to the shoot (35 vs. 40°C for 4 days, white oak; 35°C for 8 days, black oak). Interestingly, at moderate heat-stress temperature (35°C), net photosynthesis declined and internal CO2 concentration of leaves increased more when the roots were insulated in both species. Hence, concurrent soil warming prevented metabolic damage to leaves during moderate heat-stress, suggesting that direct heat to the roots increased shoot thermotolerance. In both experiments, differences in air vs. air+soil heating effects on root respiration were directly related to differences in soil temperatures, such that root respiration was higher with air+soil heating. In neither experiment were soil temperature effects related to plant water status. These results suggest that both direct and indirect effects of soil warming may occur in woody species during a heat wave, but that the response may depend on the severity and duration of the heat-stress. Future research is needed to determine the underlying mechanism for differences between air vs. air+soil heating during a heat wave.