Responses of microbial populations and processes to pulses of precipitation in semiarid forest ecosystems

Understanding how abiotic factors regulate soil microbial activity is key in understanding the responses of terrestrial ecosystems to anticipated climate change. Soil microbes catalyze biogeochemical reactions and the exchange of nutrients between heterotroph and autotroph organisms, as well as between the soil and atmosphere. Semiarid forests are driven by "pulses" of precipitation (episodic and irregular events of precipitation) which activate soil microbial activity and their processes. Our knowledge on the functioning of semiarid forest ecosystems in response to pulse events has increased substantially over the last decade. However, a comprehensive paper synthesizing this literature and making conceptual progress at global scale is yet missing. This paper is a review of the current knowledge on microbial populations and their processes in forest semiarid ecosystems after pulse events. First, we briefly describe distribution and abundance of soil microbial biota in these systems. Second, we review ecosystem processes, and how they are regulated by microbial communities. These ecosystem processes include soil respiration, carbon and nitrogen dynamics and decomposition. Third, we address the effects that climatic change may exert on these populations and processes. The effects described are increased CO2 concentrations, elevated temperatures and changes in precipitation regimes.