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 which plants respond to increasing atmospheric CO₂. In other experiments, mycorrhizal responses to elevated CO₂ 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 CO₂. Four species from three genera of AM fungi were tested. Artemisia tridentata Nutt. seedlings were inoculated with either Glomus intraradices Schenck & Smith, Glomus etunicatum Becker & Gerdemann, Acaulospora 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 CO₂ 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 CO₂ for any fungal species. In the extra-radical phase, the two Glomus species produced a significantly higher number of spores in response to elevated CO₂, 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 CO₂, and that mycorrhizal diversity should not be overlooked in global change research.