last update October 14, 1999
In a complete 2 X 2 factorial greenhouse experiment we examined the responses of arbuscular mycorrhizal (AM) and non-mycorrhizal fungi to Gutierrezia sarothrae shrubs grown in elevated atmospheric carbon dioxide (750 mul l-1) and fertilized with N. AM percent infection did not change significantly with elevated CO2, but arbuscular infection increased 14-fold in the low-N treatment. Extraradical hyphal length increased on an absolute basis in elevated CO2, and also per infected root length. In the high-N treatments, increasing CO2 caused a decrease in hyphal length per infected root length, and an increase in vesicular infection. There was a significant positive response of AM infection intensity to increasing CO2 for the high N treatment, and a similar trend in the low N treatment. Infection intensity was positively correlated with arbuscular infection and with vesicular infection. Nonmycorrhizal fungi did not respond to any of the treatment combinations, as measured by percent root infection and external hyphal length. Our results indicate that C allocation to the AM fungi was increased in elevated CO2, and that the mycobiont in turn increased C allocation to external hyphae.