The overarching goal of this session is to synthesize knowledge gained from model simulations, laboratory incubation experiments, and field studies, to produce a more coherent framework with which to link microbial ecophysiology to ecosystem level processes. While it is recognized that soil microbes play a critical role in mediating the flux of carbon between plants, soils and the atmosphere, many carbon cycling models do not include an explicit role for decomposer or mycorrhizal microorganisms. Therefore, there is a considerable effort underway aimed at understanding the physiological mechanisms which constrain microbial activity in soil, particularly with respect to the effects of water availability. When scaled up to the ecosystem level, such research would enhance our understanding of seasonal and geographical patterns in soil respiration, as well as soil and plant feedbacks to global climate change. The session will begin with a discussion of microbial physiological responses to changes in environmental conditions, focusing on recent carbon cycling models which explicitly incorporate the role of microbial physiology. Speakers will then discuss microbial community responses to both experimentally imposed drought stress and natural inter-annual climate variability, considering the physiological mechanisms which might underlie such community shifts. Finally, speakers will address the ways in which changes in microbial physiology and community structure might affect ecosystem processes, such as soil respiration and nutrient mineralization. Our speakers span a range of perspectives and experimental approaches, from simulation-based modeling studies to large-scale ecosystem manipulations. Ultimately, in a time of rapid global change, this holistic approach is required for a predictive framework that links individual microbial functions to ecosystem level processes.