Results/Conclusions We found that the presence of summertime fog (both through its impacts on drip and shading) was an important control on soil respiration rates and patterns, enabling greater plant and microbial activity in the absence of rain. Over the summer fog period, autotrophic respiration (root and associated microbial respiration) dominated soil respiration rates and patterns, and increased in percent contribution (54-75%) with decreasing soil moisture and increasing soil and air temperature. However, observations on shorter timescales demonstrated that following summertime moisture pulses, heterotrophic respiration (microbial decomposition) was much more dynamic, in some cases contributing up to 90% of the elevated respiration response immediately after the wetting event. Our results suggest that microbial decomposition is more responsive to seasonal and episodic moisture inputs. Thus, alterations to the amount, frequency, and seasonality of moisture pulses likely have very different implications for autotrophic and heterotrophic respiration sources and the total carbon respired in arid ecosystems.