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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Rangeland Resources & Systems Research » Research » Publications at this Location » Publication #322926
Title: Impacts of warming and elevated CO2 on a semi-arid grassland are non-additive, shift with precipitation, and reverse over time

Author
item Mueller, Kevin
item Blumenthal, Dana
item PENDALL, ELISE - Western Sydney University
item CARRILLO, YOLIMA - Western Sydney University
item DIJKSTRA, FEIKE - University Of Sydney
item WILLIAMS, DAVID - University Of Wyoming
item FOLLETT, RON - Retired ARS Employee
item MORGAN, JACK - Retired ARS Employee

Submitted to: Ecology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2016
Publication Date: 6/27/2016
Citation: Mueller, K.E., Blumenthal, D.M., Pendall, E., Carrillo, Y., Dijkstra, F., Williams, D., Follett, R., Morgan, J. 2016. Impacts of warming and elevated CO2 on a semi-arid grassland are non-additive, shift with precipitation, and reverse over time. Ecology Letters. 19:956-966. doi:10.1111/ele.12634.

Interpretive Summary: The effects of rising air temperatures and atmospheric carbon dioxide concentrations were studied in an intact, mixed-grass prairie in Wyoming. The mediating roles of yearly weather variability and experiment duration were evaluated by statistically characterizing the temporal patterns apparent over the 7-year experiment. Temperature and carbon dioxide concentrations were maintained at levels expected in the future due to ongoing climate change, using techniques that maximize the realism of the experimental conditions. Plant productivity was stimulated above and belowground by elevated carbon dioxide, but the extent of this stimulation in each year was dependent upon how much precipitation occurred in the growing-season. In ‘wet’ growing-seasons, the effect of carbon dioxide was smaller for aboveground plant biomass but larger for root biomass, perhaps because nitrogen was more limiting to plant growth in wet growing-seasons. By statistically accounting for the role of precipitation, it was also clear that the effects of warming and elevated carbon dioxide shifted from the beginning to the end of the experiment. Early in the experiment, the combination of warming and elevated carbon dioxide favored grasses with a particular type of photosynthesis (C4). However, over time, grasses and sedges with a different photosynthetic pathway (C3) progressively became more abundant at the expense of the C4 grasses. This shift in plant community composition over time occurred as warming and elevated carbon dioxide had increasingly positive effects on the amount of nitrogen in soil. Other herbaceous plants, particularly the common sub-shrub fringed sagebrush (or prairie sagewort), were negatively impacted by warming, and increasingly so over time (regardless of the carbon dioxide concentration in the air). Thus, the mixed-grass prairie in Wyoming appears to be poised for substantial changes in productivity and community composition due to climatic changes that are anticipated in the future. These potential shifts in plant productivity and community composition will likely impact the production of other ecosystem services by rangelands, such as cattle production. Long-term experiments are necessary to reveal the most likely impacts of climatic changes on grassland ecosystems.

Technical Abstract: The impacts of environmental change are temporally dynamic and better revealed in long-term studies. Rising air temperatures and atmospheric carbon dioxide concentrations [CO2] are the most pervasive of environmental changes on land, yet multi-year, factorial studies of warming and elevated CO2 (eCO2) in intact ecosystems are exceedingly rare. Here, we evaluate the temporal dynamics of warming and CO2 effects on a North American, mixed-grass prairie; this perennial-dominated ecosystem is the most widespread grassland type in North America. Across 7 years, precipitation regulated the responses of plant productivity, forage quality, and soil resources to warming and CO2. In ‘wet’ growing-seasons with higher apparent nitrogen-limitation, eCO2 had less positive effects on aboveground biomass, more positive effects on root biomass, and less negative effects on plant nitrogen concentrations. After accounting for weather, the magnitude and direction of warming and CO2 effects changed over time for several ecosystem attributes. The abundance of C3 graminoids increased progressively at the expense of C4 grasses due to the combination of eCO2 and warming, while this treatment had increasingly positive effects on nitrogen-availability and increasingly negative effects on soil moisture. These results suggest future climatic conditions will substantially alter the provision of ecosystem services in semiarid grasslands.