Altered germination of agricultural weeds in response to precipitation variability

Robinson, T.M.P. and K.L. Gross

Presented at the All Scientist and GLBRC Sustainability Meeting (2009-05-05 to 2009-05-07 )

Global climate change models predict widespread changes in precipitation frequency and intensity, with larger, but less frequent rain events. In addition to these predictions of changes to within season rainfall, some models predict a 50% reduction in summer rainfall for the Great Lakes Region. Changes in total seasonal rainfall and increased variation in rainfall during a season may have significant and interacting impacts on plant communities, particularly annual dominated agricultural weed communities. We conducted three greenhouse experiments to examine how germination and early growth of LTER microplot weeds responded to changes in the interval between watering events at two precipitation levels. The dominant grass (Setaria faberi) and the dominant forb (Chenopodium album) both responded to water manipulations, but the response varied between species and life history stage. Germination of both species increased with large, infrequent rain events at low water, but neither responded at higher levels of total water. Chenopodium album growth showed a positive or neutral response to longer, less frequent rain at average or low total water respectively, while Setaria faberi growth always decreased with longer, less frequent rain events. Both germination and growth responses played a role in structuring experimental communities, and it is likely that greater competition due to high germination exacerbated the direct growth reductions for Setaria faberi in a community context. Our results suggest that the response of agricultural weed communities to predicted changes in precipitation regimes may be complex, with the existence of opposing effects at different life history stages and differences between species. In communities dominated by Setaria faberi we would predict reductions in productivity in the future, but that other less sensitive weed species may buffer these communities from large shifts in total productivity.