ARBUSCULAR MYCORRHIZAE IN A TROPICAL SAND DUNE ECOSYSTEM ON THE GULF-OF-MEXICO .2. EFFECTS OF ARBUSCULAR MYCORRHIZAL FUNGI ON THE GROWTH OFSPECIES DISTRIBUTED IN DIFFERENT EARLY SUCCESSIONAL STAGES

The effects of arbuscular mycorrhizal fungi on the growth of seven pla nt species established during the first stages of colonization in diff erent areas of a tropical sand dune system on the Gulf of Mexico were investigated by comparing several growth parameters in 21- and 63-day- old mycorrhizal and non-mycorrhizal plants. There were no significant differences between mycorrhizal and non-mycorrhizal plants in root, st em and leaf biomass after 21 days, but after 63 days, mycorrhizal resp onsiveness was evident. Ipomoea pes-caprae, Sporobolus virginicus and Canavalia rosea, stoloniferous pioneer species of the beach, embryo du nes and foredunes, were less responsive to the mycorrhizal treatment, following the trend predicted for early seral species. However, large increases in total dry weight, leaf area and relative growth rate of C hamaecuista chamaecristoides, Palafoxia lindenii and Trachypogon gouin ii (plants from the beach, embryo dunes and foredunes as well as mobil e dunes) suggest that mycorrhizal infection is also crucial for the gr owth of early successional species. Most species allocated the same or more biomass to shoots than to roots. With the exception of T. gouini i, this pattern of biomass allocation was not altered by the mycorrhiz al treatment. C. rosea and S. virginicus showed a higher allocation to the roots in the non-mycorrhizal plants. The possible relationship be tween mycorrhizae and succession in this tropical sand dune ecosystem is discussed.