SOIL FUNGAL-ARTHROPOD RESPONSES TO POPULUS-TREMULOIDES GROWN UNDER ENRICHED ATMOSPHERIC CO2 UNDER FIELD CONDITIONS

We investigated the influence of elevated CO2 and soil N availability on the growth of arbuscular mycorrhizal and non-mycorrhizal fungi, and on the number of mycophagous soil microarthropods associated with the roots of Populus tremuloides. CO2 concentration did not significantly affect percentage infection of Populus roots by mycorrhizal or non-my corrhizal fungi. However, the extra-radical hyphal network was altered both qualitatively and quantitatively, and there was a strong interac tion between CO2 and soil N availability. Under N-poor soil. condition s, elevated CO2 stimulated hyphal length by arbuscular mycorrhizal fun gi, but depressed growth by non-mycorrhizal fungi. There was no CO2 ef fect at high N availability. High N availability stimulated growth by opportunistic saprobic/pathogenic fungi. Soil mites were not affected by any treatment, but collembolan numbers were positively correlated w ith the increase in non-mycorrhizal fungi. Results indicate a strong i nteraction between CO2 concentration and soil N availability on mycorr hizal functioning and on fungal-based soil food webs.