Microbial adaptations to envrionmental change: a moving target for global change ecology

Background/Question/Methods As the abiotic conditions that structure biological communities and elicit physiological responses continue to change at an unprecedented rate, we need to understand how biological responses to global change will affect ecosystem functioning. A number of studies have detected shifts in the structure of microbial communities in response to experimental warming, elevated CO22 altered precipitation, and increased N deposition. However, since the links between microbial phylogeny and function are poorly understood, it can be challenging to predict how these changes in community structure will affect the rates of specific processes. It is often assumed that the high diversity of microbial communities makes them functionally redundant, and thus changes in community composition should have no direct effects. This paradigm has resulted in model structures that famously represent microbes as ‘black boxes'. Recently, significant progress has been made in linking microbial community structure to function, and efforts have been made to incorporate microbial physiology into biogeochemical models.

Results/Conclusions Most efforts to predict the rates of microbially driven processes under future climates have extrapolated contemporary relationships between abiotic drivers and process rates, derived from either short-term lab studies under artificial conditions, or from large-scale patterns across resource or climate gradients. This approach assumes that the nature of these relationships will not change through time. However, recent studies have shown that microbial communities can acclimate to changing environments over time. For example, we recently found that the temperature sensitivity of soil respiration decreased in response to experimental warming in forest mineral soils. This mechanism may contribute to the ephemeral stimulation of respiration following experimental warming that has been observed at many sites, and has important implications for soil C responses to climate change. Other research suggests the ability of microbes to adapt to environmental change can be constrained by nutrient availability. In aquatic systems, the ability of bacteria to acclimate to temperature regimes, possibly through modifcations in cell wall structure, can be limited by P. Similarly, in soils, N availability can modify the balance of r vs K selected microbes, thus altering the ability of microbial communities to utilize short-lived pulses in C availability due to rhizodeposition or precipitation events. Ongoing research will elucidate the specific nature of biological adaptation and acclimation that will enable us to better constrain ecosystem response to global change and manage for preferential outcomes.