Response of plant biomass and soil respiration to experimental warming and precipitation manipulation in a Northern Great Plains grassland

The interacting effects of altered temperature and precipitation are expected to have significant consequences for ecosystem net carbon storage. Here we report the results of an experiment that evaluated the effects of elevated temperature and altered precipitation, alone and in combination, on plant biomass production and soil respiration rates in a northern Great Plains grassland, near Lethbridge, Alberta Canada. Open-top chambers and rain shelters were used to establish an experiment in 2011 with two temperature treatments (warmed and control), each combined with three precipitation treatments (minus 50%, ambient (no manipulation), and plus 50%). A smaller experiment with only the two temperature treatments was conducted in 2012, a year with less rain than 2011. Our objectives were to determine the sensitivity of plant biomass production and soil respiration to temperature and moisture manipulations, and to test for direct and indirect effects of the environmental changes on soil respiration rates. The experimental manipulations resulted primarily in a significant increase in air temperature in the warmed treatment. There were no significant temperature or precipitation treatment effects on soil moisture content. Aboveground biomass was not significantly affected by the experimental manipulations, but the warmed plots of the ambient precipitation treatment showed an increase in root biomass relative to the control plots in 2011. The warmed treatment increased the cumulative loss of carbon in soil respiration (July–September) compared to the control by 497 g C m−2 during 2011, and by 185 g C m−2 during 2012. This higher soil respiration rate in both years was not directly caused by significant differences among treatments in soil temperature or soil moisture, but was likely an indirect result of increased carbon substrate availability in the warmed relative to the control treatment.