The impact of altered precipitation variability on annual weed species

? Premise of the study: Climate change models predict increasing variability in precipitation across the globe, with an increase in the incidence of large precipitation events but decreasing overall event frequency. Research with annual species in arid and semiarid ecosystems has demonstrated that precipitation variability can influence plant community dynamics; however, less is known about the impact of precipitation variability in less water-limited ecosystems, including economically important agricultural systems. ? Methods: We conducted three greenhouse experiments to determine how variation in total precipitation and the interval between precipitation events affected emergence and growth of two common annual midwestern weed species, Chenopodium album (Chenopodiaceae) and Setaria faberi (Poaceae). ? Key results: Both species responded to precipitation variability; however, the effect depended on life stage and precipitation amount, indicating that responses are highly context-dependent. Emergence of both species increased with longer intervals between precipitation events at low total precipitation, but species' responses varied under typical precipitation amounts. Individual seedling biomass of both species depended on interactions between total water and intervals, but species' responses differed; Setaria faberi biomass was reduced with longer intervals, but Chenopodium album had either a positive or no response. ? Conclusions: Our results suggest that changes in precipitation variability likely will affect the composition and relative abundance of agriculturally important weeds. These results are important for understanding how changes in the temporal variability of precipitation due to global climate changes could impact plants in non-arid communities.