Drought differentially affects autotrophic and heterotrophic soil respiration rates and their temperature sensitivity

Abstract

Climate change predictions indicate that extreme drought is likely to become more frequent in the future. In this study, the impact of drought on soil respiration (Rs) and its autotrophic (Ra) and heterotrophic components (Rh) were studied in a cultivated Black Chernozemic soil in central Alberta, Canada. The mean Rs was 24.4% lower in the drought relative to the plots with ambient precipitation (P < 0.001), with a larger decrease in Ra (26.8%) relative to Rh (21.0%), and a higher (P < 0.05) contribution of Rh to Rs under drought (52.8%) than under the ambient condition (47.7%). Both Rs and its Ra and Rh components had an exponential relationship with soil temperature and a quadratic relationship with soil water content. Drought caused a greater decrease in the tipping point of soil water content for Rh (a 39.6% reduction) than for Ra (a 15.1% reduction) relative to the ambient precipitation treatment. In addition, drought resulted in a greater increase in the temperature sensitivity (Q10 values) of Ra (a 45.0% increase) than that of Rh (a 14.1% increase) relative to the ambient precipitation treatment. The results suggest that drought amplified the water limitation effect on CO2 emission, especially that from microbial respiration, and resulted in a tighter relationship between temperature and root or autotrophic respiration, based on this 1-year study. We conclude that it is important to assess the impact of drought on soil respiration components rather than the total soil respiration, and such differential effects of drought on soil respiration components should be incorporated into global carbon circulation models.