Abstract
Rainfall variability is a key driver of ecosystem structure and function in grasslands worldwide. Changes in rainfall patterns predicted by global climate models for the central United States are expected to cause lower and increasingly variable soil water availability, which may impact net primary production and plant species composition in native Great Plains grasslands. We experimentally altered the timing and quantity of growing season rainfall inputs by lengthening inter-rainfall dry intervals by 50%, reducing rainfall quantities by 30%, or both, compared to the ambient rainfall regime in a native tallgrass prairie ecosystem in northeastern Kansas. Over three growing seasons, increased rainfall variability caused by altered rainfall timing with no change in total rainfall quantity led to lower and more variable soil water content (0–30 cm depth), a ~10% reduction in aboveground net primary productivity (ANPP), increased root to shoot ratios, and greater canopy photon flux density at 30 cm above the soil surface. Lower total ANPP primarily resulted from reduced growth, biomass and flowering of subdominant warm-season C4 grasses while productivity of the dominant C4 grass Andropogon gerardii was relatively unresponsive. In general, vegetation responses to increased soil water content variability were at least equal to those caused by imposing a 30% reduction in rainfall quantity without altering the timing of rainfall inputs. Reduced ANPP most likely resulted from direct effects of soil moisture deficits on root activity, plant water status, and photosynthesis. Altered rainfall regimes are likely to be an important element of climate change scenarios in this grassland, and the nature of interactions with other climate change elements remains a significant challenge for predicting ecosystem responses to climate change.
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Acknowledgements
Brett Danner, Chris Harper, Michelle Lett, Ken McCarron, Roger Baldwin, Scott Heeke, John Kraft and Jen Olivigni ably performed the field and laboratory work, and Jim Larkins, Dennis Mossman, and Tom VanSlyke supplied essential support during construction of the rainout shelters. This research was supported by the USDA National Research Initiative Competitive Grants Program, the Office of Science, Biological and Environmental Research Program (BER), U.S. Department of Energy, through the Great Plains Regional Center of the National Institute for Global Environmental Change (NIGEC) under Cooperative Agreement No. DE-FC03–90ER61010, and the National Science Foundation Konza Long Term Ecological Research program. Contribution number 03-344-J of the Kansas Agricultural Experiment Station.
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Fay, P.A., Carlisle, J.D., Knapp, A.K. et al. Productivity responses to altered rainfall patterns in a C4-dominated grassland. Oecologia 137, 245–251 (2003). https://doi.org/10.1007/s00442-003-1331-3
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DOI: https://doi.org/10.1007/s00442-003-1331-3