Arbuscular mycorrhizal soil infectivity in a stand of the wetland tree Pterocarpus officinalis along a salinity gradient

Pterocarpus officinalis (Jacq.) is the dominant wetland legume tree species of the seasonally flooded swamp forests in Guadeloupe, Lesser Antilles. This tree is periodically exposed to saline and flooded soil conditions. We examined mycorrhizal soil infectivity (most probable number (MPN) values) and arbuscular mycorrhizal (AM) colonization of P. officinalis along the salinity gradient where the salt levels ranged from 26 to 2‰ and from 22 to 5‰ at the end of the dry and wet season, respectively. MPN values were higher in the dry season than in the wet season. They decreased when the salt levels increased whatever the season. AM colonization of P. officinalis was well developed (up to 50%) only within the low salinity levels (below 10‰) whatever the season. No spores were found in soil cores, suggesting that propagules were only mycelium pieces and/or root fragments of colonized Pterocarpus roots. These AM fungi may be adapted to salt stress and explain the maintenance of the high mycorrhizal inoculum potential in the P. officinalis swamp forest.