We have completed our 3 stated objectives.
Project 1. Changes in temperature alter the relationship between biodiversity and ecosystem functioning.
We used high-throughput experiments with microbial communities to investigate how changes in temperature affect the relationship between biodiversity and ecosystem functioning. We found that changes in temperature systematically altered the relationship between biodiversity and ecosystem functioning. As temperatures departed from ambient conditions the exponent of the diversity-functioning relationship increased, meaning that more species were required to maintain ecosystem functioning under thermal stress. This key result was driven by two processes linked to variability in the thermal tolerance curves of taxa. First, more diverse communities had a greater chance of including species with thermal traits that enabled them to maintain productivity as temperatures shifted from ambient conditions. Second, we found a pronounced increase in the contribution of complementarity to the net biodiversity effect at high and low temperatures, indicating that changes in species interactions played a critical role in mediating the impacts of temperature change on the relationship between biodiversity and ecosystem functioning. Our results highlight that if biodiversity loss occurs independently of species’ thermal tolerance traits, then the additional impacts of environmental warming will result in sharp declines in ecosystem function.
Project 2. Scaling the temperature dependence of metabolism from individuals to ecosystems: the role of biotic interaction.
It is now widely recognized that massive variation in the temperature dependence of metabolism (i.e. the activation energy, Ea) exists among species. If variation in Ea is prevalent then a simple linear scaling from individuals to ecosystems, assuming the ecosystem rate is the sum over all individuals, is unlikely to hold. We carried out a large scale experiment to understand how the interspecific differences in thermal responses and the nature of the ecological interactions (eg., competition, facilitation, predation) shape the overall temperature response of microbial ecosystems. We isolated 5 bacteria species from a naturally warmed aquatic environment in Iceland and characterized the temperature dependence of their metabolic rates and also the interspecific biological interactions. We then built an artificial microbial communities using the isolated species and further characterized the metabolic thermal response of the entire community. Our results show how it is possible to predict the response of the community to a rise in temperature by understanding the thermal traits and the nature of the interactions between the individuals. We found that facilitation amplifies the temperature dependence of microbial community metabolism.
Project 3. Metabolic adaptation dampens the temperature dependence of microbial community respiration.
Microbial respiration controls a key flux in the global carbon cycle. Respiration rates increase exponentially with temperature in the short-term, but studies have shown that the sensitivity of respiration to temperature becomes dampened as microbial communities ‘adapt’ to warming. Quantification of the mechanisms that underpin the long-term temperature dependence of microbial community respiration has so far remained elusive. Using bacterial microcosms, we show that the temperature sensitivity of microbial community respiration declined by 65% after >100 generations of adaptation to temperature change. Parallel experiments evolving bacteria in mono- and polycultures revealed that evolutionary change in taxon-level traits causally explained the decline in the long-term temperature dependence of microbial community respiration. This finding provides the basis for a robust representation of microbial eco-evolution in carbon cycle models.
