Interspecific differences in the response of arbuscular mycorrhizal fungi to <i>Artemisia tridentata</i> 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 which plants respond to increasing atmospheric CO 2 . In other experiments, mycorrhizal responses to elevated CO 2 have been variable, so in this study we test the hypothesis that different genera of AM fungi differ in their response, and in turn alter the plant's response, to elevated CO 2 . Four species from three genera of AM fungi were tested. Artemisia tridentata Nutt. seedlings were inoculated with either Glomus intraradices Schenck &amp; Smith, Glomus etunicatum Becker &amp; Gerdemann, Acaulospora sp. or Scutellospora calospora (Nicol. &amp; Gerd.) Walker &amp; Sanders and grown at either ambient CO 2 (350 ppm) or elevated CO 2 (700 ppm). Several significant inter‐specific responses were detected. Elevated CO 2 caused percent arbuscular and hyphal colonization to increase for the two Glomus species, but not for Acaulospora sp. or S. calospora . Vesicular colonization was not affected by elevated CO 2 for any fungal species. In the extra‐radical phase, the two Glomus species produced a significantly higher number of spores in response to elevated CO 2 , whereas Acaulospora sp. and S. calospora developed significantly higher hyphal lengths. These data show that AM fungal taxa differ in their growth allocation strategies and in their responses to elevated CO 2 , and that mycorrhizal diversity should not be overlooked in global change research.