OOS 73

Rewetting Dry Soil: The Century’s Unifying Problem in Soil Microbial Ecology

A pulse of carbon dioxide (CO2) is released when water is added to dry soils. These pulses may have profound ecological importance and can dominate the annual heterotrophic respiration of terrestrial ecosystems. This phenomenon was already observed about a century ago, and has been termed the ‘Birch effect’ after one of its first observers. Pulses of CO2 are often assumed to be microbial mediated. However, a century of work shows that the connection between the CO2 pulse released when rewetting a dry soil and the microbial decomposers require a more nuanced explanation. Here, we will consider the microbial dynamics and strategies to describe the ecosystem response to drying-rewetting events. The explosive dynamics of the rewetting pulse creates an excellent arena for elucidating the microbial mechanisms that can characterize ecosystem biogeochemistry and capture temporal dynamics driving ecosystem processes. In addition, the microbial dynamics and strategies during drying-rewetting will become more relevant as the climate continues to change, creating more frequent and extreme fluctuations in rainfall patterns. Our session will synthesize current knowledge on the causes for the respiration pulse upon rewetting a dry soil and highlight fruitful avenues for future research. The session starts with an introduction to define the current state-of-the-art understanding of the microbial control of the rewetting pulse. After this, a series of research frontier case studies will offer results and insights from soil ecology, microbial ecology and biogeochemistry. The last presentation will identify the knowns and unknowns in models to account for the microbial control of the respiration pulse upon rewetting. We hope to stimulate an ongoing discussion about how our continued efforts to address one of the most prominent drivers of soil microbes, soil moisture, can elucidate the links between their temporal dynamics and functioning and will lead soil microbial ecology into the new century.