GROWTH AND GAS-EXCHANGE RESPONSES OF HEVEA-BRASILIENSIS SEEDLINGS TO INOCULATION WITH GLOMUS-MOSSEAE

The beneficial effect of arbuscular mycorrhizal (AM) fungi on plant gr owth is well known, but the physiological processes involved are still discussed. The purpose of this study was to determine if Glomus mosse ae affects the growth of Hevea brasiliensis seedlings and, if it is th e case, if it could be associated with variations in leaf CO2 and H2O gas exchange. H. brasiliensis rubber trees were,grown for 9 months in a medium containing either propagules of G. mosseae or sterilized inoc ulum. Plant size, root collar diameter and leaf area, as well as net C O2 assimilation, stomatal conductance (g(s)) and water-use efficiency of photosynthesis were evaluated during the first 5 stages of growth. At stage 2, a growth depression occurred in the mycorrhizal seedlings coincident with the first AM infections. Then, at stage 5, Glomus moss eae-inoculated plants had moderate colonization (47% of root length) a nd were taller than control plants with a larger root collar diameter and an enhanced leaf organogenesis. This enhanced growth was accompani ed by increased photosynthesis, transpiration, and stomatal conductanc e. After 9 months, dry weights of shoots and roots of inoculated plant s were greater than those of controls by 27 and 17%, respectively.