Arbuscular mycorrhizae in a tropical sand dune ecosystem on the Gulf of Mexico .1. Mycorrhizal status and inoculum potential along a successional gradient

Root samples of 37 species distributed on the beach and along a successional gradient (from mobile to stabilized areas) in a tropical sand dune system on the Gulf of Mexico showed that 97% of the species were mycorrhizal. The mycorrhizal inoculum potential of the sand from several dune areas was compared using two different bioassays. Firstly, the field rate of colonization by arbuscular mycorrhizal fungi of Chamaecrista chamaecristoides seedlings transplanted to random plots in the foredunes and in the mobile area was measured. The seedlings were harvested at intervals during 3 weeks to record mycorrhizal structures. In the mobile area, no mycorrhizal colonization was observed during the experiment. In the foredunes, hyphae and external mycelium were present in 40% of the seedlings as early as 8 days after transplanting. After 15 days, arbuscules and vesicles were observed in 60 and 20% of the seedlings, respectively, and after 21 days, 100, 46 and 20% of the seedlings showed hyphae, arbuscules and vesicles, respectively. Secondly, maize seedlings were transplanted to pots previously filled with sand from the foredunes, mobile dunes, grassland and a Dyphisa robinoides shrub area. After 1 month, the lowest mycorrhizal inoculum potential was recorded for the mobile dunes and the highest for the shrub area. As expected, mycorrhizal inoculum potential increased with dune stabilization.