Effects of temperature on microbial metabolic rates

Abstract

Prokaryotes (bacteria and archaea) are globally ubiquitous micro-organisms which play fundamental roles in biogeochemical cycles and ecosystem functioning. Understanding how these microbes are affected by temperature is key to our understanding of how ecosystem processes will be affected by and respond to climate change. This includes understanding both how temperature directly affects the biological rates of prokaryotes through to how community composition may change with temperature and the impacts that these responses have on overall community functioning. Combining meta-analyses with experimental work and mathematical modelling, I assessed the direct impacts of temperature on microbial biological rates, with the aim of understanding how these effects translate to community and ecosystem level changes. I performed a meta-analysis of prokaryotic growth and metabolic rates, spanning the entire temperature spectrum of life on earth, revealing that the metabolic rates of mesophilic prokaryotes are likely to rise with climate warming. I used experimental methods to reveal the phenotypic diversity of temperature fitness in microbial communities, suggesting that species sorting rather than direct thermal adaptation may play a major role in how ecosystems respond to climate change. This work also revealed a disparity in phylogenetic groups associated with cooler and warmer temperatures as well as a divergence in their growth strategies, with warmer adapted taxa tending towards growth specialism rather than yield specialism. I also tested how microbial carbon use efficiency — the proportion of carbon uptake allocated to growth — varies with temperature. I found a unimodal temperature dependence of this trait, a departure from previous understanding. This work shows that changes in the composition and function of microbial communities with global change are likely to have a profound impact on ecosystem responses to warming. I propose that through species sorting processes, microbial communities are likely to shift to warmer adapted taxa with higher metabolic rates on average, which tend to be less carbon efficient in their growth. Ultimately, this may lead to increased carbon efflux versus sequestration by the microbial components of ecosystems with climate warming.