INTERSPECIFIC DIFFERENCES IN THE RESPONSE OF ARBUSCULAR MYCORRHIZAL FUNGI TO ARTEMISIA-TRIDENTATA GROWN UNDER ELEVATED ATMOSPHERIC CO2

Arbuscular mycorrhizal (AM) fungi form mutualistic symbioses with the root systems of most plant species. These mutualisms regulate nutrient exchange in the plant-soil interface and might influence the way in w hich plants respond to increasing atmospheric CO2. In other experiment s, mycorrhizal responses to elevated CO2 have been variable, so in thi s study we test the hypothesis that different genera of AM fungi diffe r in their response, and in turn alter the plant's response, to elevat ed CO2. Four species from three genera of AM fungi were tested. Artemi sia tridentata Nutt. seedlings were inoculated with either Glomus intr aradices Schenck & Smith, Glomus etunicatum Becker & Gerdemann, Acaulo spora sp. or Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders and grown at either ambient CO2 (350 ppm) or elevated CO2 (700 ppm). Several significant inter-specific responses were detected. Elevated C O2 caused percent arbuscular and hyphal colonization to increase for t he two Glomus species, but not for Acaulospora sp. or S. calospora. Ve sicular colonization was not affected by elevated CO2 for any fungal s pecies. In the extra-radical phase, the two Glomus species produced a significantly higher number of spores in response to elevated CO2, whe reas Acaulospora sp. and S. calospora developed significantly higher h yphal lengths. These data show that AM fungal taxa differ in their gro wth allocation strategies and in their responses to elevated CO2, and that mycorrhizal diversity should not be overlooked in global change r esearch.