The impact of altered precipitation patterns on plant productivity, soil respiration and plant water-use efficiency in a northern Great Plains grassland

Precipitation patterns are expected to shift towards larger but fewer rain events, with longer intermittent dry periods, associated with climate change. The larger rain events may compensate for and help to mitigate climate change effects on key ecosystem functions in semi-arid grasslands. I experimentally manipulated the amount and frequency of simulated precipitation added to treatment plots that were covered by rain shelters, and measured the response in plant productivity, soil respiration and water-use efficiency in a native, grassland near Lethbridge, Alberta. The observed responses were compared to the predictions of a conceptual ecosystem response model developed by Knapp et al. 2008. Two experiments were conducted during 14 weeks of the growing season from May-August. The first experiment applied total growing season precipitation of 180 mm (climate normal), and the second experiment applied total precipitation of 90 mm (reduced amount). In both experiments, precipitation was applied at two frequencies, 1 rain event every week (normal frequency) and 1 rain event every two weeks (reduced frequency).Plant productivity decreased in response to larger but fewer rain events in the first experiment, but was not significantly different in the second experiment. Soil respiration rate was significantly higher for the larger but fewer rain events in the second experiment, as well as for the normal (NN+NR) compared to the reduced (RN+RR) amount treatments. Stable carbon isotope composition of plant tissue was largely insensitive to precipitation alterations, but showed significantly lower δ13C values for the normal compared to the reduced amount treatments. The results of this study have implications for understanding the mechanisms underlying ecosystem responses to anticipated precipitation change in the Great Plains.