THE RESPONSE OF MYCORRHIZAL COLONIZATION TO ELEVATED CO2 AND CLIMATE-CHANGE IN PASCOPYRUM-SMITHII AND BOUTELOUA-GRACILIS

Large intact soil cores of nearly pure stands of Pascopyrum smithii (w estern wheatgrass, C-3) and Bouteloua gracilis (blue grama, C-4) were extracted from the Central Plains Experimental Range in northeastern C olorado, USA and transferred to controlled environment chambers. Cores were exposed to a variety of water, temperature and CO2 regimes for a total of four annual growth cycles. Root subsamples were harvested af ter the completion of the second and fourth growth cycles at a time co rresponding to late winter, and were examined microscopically for the presence of mycorrhizae. After two growth cycles in the growth chamber s, 54% of the root length was colonized in P smithii, compared to 35% in blue grama. Field control plants had significantly lower colonizati on. Elevation of CO2 increased mycorrhizal colonization in B. gracilis by 46% but had no effect in P. smithii. Temperatures 4 degrees C high er than normal decreased colonization in P. smithii by 15%. Increased annual precipitation decreased colonization in both species. Simulated climate change conditions of elevated CO2, elevated temperature and l owered precipitation decreased colonization in P. smithii but had less effect on B. gracilis. After four growth cycles in P. smithii, trends of treatments remained similar, but overall colonization rate decreas ed.