Ecological responses of soil bacteria to rapid and slow temperature fluctuations.

Fluctuating temperatures profoundly affect microorganisms' coexistence, biogeographic distributions and responses to future climate change. However, how microorganisms respond to fluctuating temperatures with different frequencies in natural communities remains unknown. We conducted a 120-day temperature manipulation experiment with soil-bacterial communities subjected to constant low, medium and high temperatures, as well as fluctuating temperatures with three different frequencies. Four groups of temperature-responsive species were identified, including species favoured by constant high or low temperature, and species favoured or disfavoured by rapid temperature fluctuations. Further analyses confirmed that species in the first two groups only responded to the constant temperatures, and their performances at all fluctuating temperatures were roughly equal to their time-averaged performances at high and low temperatures. Species in the last two groups showed specific responses to frequent temperature transitions. Our results revealed that the performances of bacterial species under slow temperature fluctuation closely resembled their time-averaged performances at high and low temperatures, but deviated from those at medium temperature, due to the nonlinearity of temperature-dependent performances. Our study highlights that soil bacteria show unique responses to both rapid and slow temperature fluctuations compared to medium temperature, which is crucial to understand microbial community dynamics in variable thermal environments.