Predator contributions to belowground responses to warming

Background/Question/Methods

Identifying the factors that control soil CO₂ emissions will improve our ability to predict the magnitude of climate change-soil ecosystem feedbacks. Despite the integral role of invertebrates in belowground systems, they are excluded from climate change models. Soil invertebrates have consumptive and non-consumptive effects on microbes, whose respiration accounts for nearly half of soil CO₂ emissions. By altering the behavior and abundance of invertebrates that interact with microbes, invertebrate predators may have indirect effects on soil respiration. We examined the effects of a generalist arthropod predator on belowground respiration under different warming scenarios. Based on research suggesting invertebrates may mediate soil CO₂ emission responses to warming, we predicted that predator presence would result in increased emissions by negatively affecting these invertebrates. We altered the presence of wolf spiders (Pardosa spp.) in mesocosms containing a community of soil invertebrates. To simulate warming, we placed mesocosms of each treatment in ten open-top warming chambers ranging from 1.5-5.5°C above ambient at Harvard Forest, MA. We collected respiration data, microbial abundance, soil moisture, and soil temperature to determine the effects of predators on belowground systems. 

Results/Conclusions

As expected, CO₂ emissions increased under warming and we found an interactive effect of predator presence and warming, though the effect was not consistent through time. The interaction between predator presence and warming was the inverse of our predictions: mesocosms with predators had lower respiration at higher levels of warming than those without predators. CO₂ emissions were not significantly associated with microbial biomass or microinvertebrate density. We did not find evidence of consumptive effects of predators on the invertebrate community, suggesting that predator presence mediates response of microbial respiration to warming through non-consumptive means. In our system we found a significant interaction between warming and predator presence that warrants further research into mechanism and generality of this pattern to other systems.