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Title: C4 grasses prosper as carbon dioxide eliminates desiccation in warmed semi-arid grasslands

Author
item Morgan, Jack
item Lecain, Daniel
item PENDALL, ELISE - University Of Wyoming
item Blumenthal, Dana
item Kimball, Bruce
item CARILLO, YOLIMA - University Of Wyoming
item WILLIAMS, DAVID - University Of Wyoming
item Heisler White, Jana
item DIJKSTRA, FEIKE - University Of Sydney
item West, Mark

Submitted to: Nature
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2011
Publication Date: 8/10/2011
Citation: Morgan, J.A., Lecain, D.R., Pendall, E., Blumenthal, D.M., Kimball, B.A., Carillo, Y., Williams, D., Heisler White, J.L., Dijkstra, F., West, M.S. 2011. C4 grasses prosper as carbon dioxide eliminates desiccation in warmed semi-arid grasslands. Nature. 476:202-205.

Interpretive Summary: Global climate change models suggest that predicted future warmer atmospheres and altered precipitation patterns will induce droughts in several world regions. This manuscript describes results from a field experiment conducted in native prairie in Wyoming in which ambient CO2 levels and temperature were both increased to simulate conditions expected in the second half of this century. The results indicate that while warming causes some desiccation, the increased water use efficiency plants experience at higher levels of CO2 essentially nullifies the potentially negative desiccating consequences of higher temperature on plant growth. As a result, plant production is unchanged in some years, and enhanced in one year under warmed, CO2-enriched conditions. While rising CO2 is unlikely to eliminate the severe and protracted droughts predicted for regions like southwestern North America or the Mediterranean where both substantive temperature increase and reduced precipitation are predicted, the results suggest that the desiccating effects of temperature rise alone may be less harmful for plant production in many semi-arid rangelands than previously expected.

Technical Abstract: Global warming is predicted to induce desiccation in many world regions through increases in evaporative demand. Rising CO2 may counter that trend by improving plant water use efficiency (WUE). However, it is not clear how important this CO2-enhanced WUE might be in off-setting warming-induced desiccation since higher CO2 also leads to higher plant biomass, and therefore greater transpirational surface. Further, while warming is predicted to favor warm-season, C4 grasses, rising CO2 should favor C3, or cool-season plants. Here we show in a semi-arid grassland that elevated CO2 can completely reverse the desiccating effects of moderate warming. While enrichment of air to 600 ppmv CO2 increased soil water content (SWC), 1.5/3.0 °C day/night warming resulted in desiccation, such that combined CO2 enrichment and warming had no effect on SWC relative to control plots. As predicted, elevated CO2 favored C3 grasses and enhanced stand productivity, while warming favored C4 grasses. Combined warming and CO2 enrichment stimulated aboveground growth of C4 grasses in two of three years when soil moisture most limited plant productivity. The results suggest that in a warmer, CO2-enriched world, both SWC and productivity in semi-arid grasslands may be higher than previously expected.