GROWTH-RESPONSES TO VESICULAR-ARBUSCULAR MYCORRHIZAE AND ELEVATED CO2IN SEEDLINGS OF A TROPICAL TREE, BEILSCHMIEDIA-PENDULA

1. Vesicular-arbuscular (VA) mycorrhizae increased relative growth rat es (RGR) of the shade-tolerant tropical tree species Beilschmiedia pen dula at both ambient and doubled CO2 concentrations. 2. RGR was correl ated with the net assimilation rate (NAR) of plants. Within this gener al correlation, in plants with similar RGR, NAR was decreased in VA-my corrhizal plants compared with non-mycorrhizal plants. As RGR is the p roduct of NAR and the leaf area ratio (LAR, the ratio of leaf area to plant mass), increases in RGR in VA-mycorrhizal plants were the result s of increased LAR. Thus, VA-mycorrhizae increased growth rates of B. pendula by altering the morphology of the seedlings. 3. Under elevated CO2 the amount of fungus within roots increased in VA-mycorrhizal pla nts compared with those grown under ambient CO2 and this was associate d with a greater post-inoculation depression in leaf growth. Post-inoc ulation depressions in leaf growth and the lower NAR (in plants with s imilar RGR) of VA-mycorrhizal plants indicate there is increased carbo n transfer to soils under elevated CO2.