A shift from competition to facilitation amplifies the temperature-dependence of microbial community respiration

The respiratory release of CO2 by microbes is a dominant component of the global carbon cycle. However, large uncertainties exist about the effects of climatic warming on the respiration of microbial communities due to lack of mechanistic, empirically-tested theory that accounts for dynamic species interactions. We developed a general mathematical model which predicts that thermal sensitivity of microbial community respiration increases as species interactions become more positive, i.e., change from competition to facilitation. This is because facilitation disproportionately increases positive feedbacks between the thermal sensitivities of species-level metabolic and biomass accumulation rates at warmer temperatures. We experimentally validated this prediction in bacterial communities of 8 taxa, finding that a shift from competition to facilitation after a month of co-adaptation caused a 60% increase in the thermal sensitivity of their respiration relative to de novo communities that had not co-adapted. Thus, rapid changes in species interactions can profoundly change the temperature-dependence of microbial community respiration and should be considered in climate change models.