Temperature and trophic structure are more important than species sorting for ecosystem functioning

Background/Question/Methods

Climate influences ecosystem functioning through its direct effect on the biological rate of species and indirectly through its effect on species distribution and interactions. Understanding the relative importance of these factors is crucial for predicting the impact that climate change will have on ecological systems. In this study, we tested how ecosystem functioning (nutrient processing, respiration and microbial biomass) is affected by temperature, local adaptation and trophic structure. According to metacommunity theory, we expect that environmental filtering selects species that will maximize ecosystem functioning locally (species-sorting). Alternatively, metabolic theory and consumer-resource theory respectively predict that temperature and trophic structure are the most important drivers of ecosystem functioning. To test these contrasting hypotheses, we used the natural ecosystems held within Sarracenia purpurea leaves, which contain comparable communities across the latitudinal range of the species. We collected entire communities from five sites (Florida to Quebec) and created a common garden, factorial experiment using five incubators mimicking the mean June temperatures at each site.

Results/Conclusions

As predicted by consumer-resource theory, our results show that S. purpurea microbial communities were more efficient at processing nutrients and respiring in warmer temperatures, independent of their origin. There was consequently no evidence of a species-sorting effect. Even if the origin of the community had a strong impact on ecosystem functioning, there was no predictable pattern for how it interacts with temperature. We also found that trophic regulation (top-down control) increased with temperature, in agreement with consumer-resource theory. Our results show that for the S. purpurea microbial system, the highly conserved functional structure of the food web throughout its range contributes to maintain functioning and therefore that allometric scaling could be used to approximate climate change impacts on ecosystem functioning