As climate change alters precipitation patterns globally, projections suggest the Midwestern United States will experience more intense and longer lasting droughts, increasing plant water stress and potentially altering ecosystem structure and function. To explore the potential consequences of drought stress on a tallgrass prairie community, we established a field experiment in West Lafayette, IN that examined how the timing and duration of drought impacts plant communities.
Precipitation was manipulated from April-September in 2016 and 2017 to create dry periods that varied in duration (7, 14, or 21 weeks) and timing over the growing season (beginning (B), middle (M), and end (E)), resulting in a total of 8 treatments, B, M, E, BM, ME, BE, BME, and an ambient control (C). During exclusion periods, precipitation was reduced by 100% in experimental plots using rainout shelters. Harvests were conducted in August and October of each experimental year. We hypothesized that aboveground net primary productivity (ANPP) would be reduced in all drought treatments and that this reduction would be greater for longer droughts. We expected plant composition to shift towards forb-dominated communities under drought conditions, and plots receiving earlier droughts to be more diverse, as reduced aboveground biomass would reduce competition for light.
Results/Conclusions
Drought treatments reduced soil moisture during each experimental period, and the effect of dry conditions depended on their length and timing. Greater precipitation in 2017 likely contributed to greater productivity in October 2017, and in 2017 compared to 2016. Across all harvests, ANPP was smaller in BM and BME plots and greater in E and BE plots. Drought had little effect on diversity but altered plant functional type composition. Short droughts late in the season (E and BE) increased productivity, advanced senescence, and reduced forb abundance. Longer droughts in the beginning of the growing season (BM and BME) reduced productivity. Senescence was delayed in BM treatments.
We suggest that plants responded to dry conditions and other environmental cues characteristic of the end of the growing season by promoting late season growth and senescence when resources became increasingly depleted as the drought progressed. ANPP was reduced under longer, early droughts, but senescence was only delayed when dry conditions were relieved before the end of the growing season, suggesting senescence responds to soil moisture. Productivity, senescence and composition were generally resistant to change in this community, but the timing or duration of drought can impact this resistance.