ARBUSCULAR MYCORRHIZAL ASSOCIATION IN SOME SELECTED DRY FOREST SPECIES AT BUNDALA NATIONAL PARK, SRI LANKA

Abstract

The vegetation of dry forests at Bundala National Park, Sri Lanka is under a threat due tothe invasion of alien exotic species and poor natural forest regeneration. Since it isimportant to understand the effects of soil microorganisms in sustainable forestmanagement, this study attempts to find out how the mycorrhizal infections would favourdry forest plant species for their growth and survival. Fine lateral roots of seven naturalforest species (Cassia auriculata, Drypetes sepiaria, Dichrostachys cineria, Securenigaleucopyros, Salvadora persica, Zyzyphus oenoplia, Manilkara hexandra) and twoinvasive species (Opuntia dillenii, Prosopis juliflora) were collected from BundalaNational Park and examined for mycorrhizal infection in two different times (wet anddry) of the year. Processing and staining of root samples were carried out using themodified Philips and Heyman (1970) method.

Muscular mycorrhizal infections were detected in fine lateral roots of all the studiedspecies except in Manilkara hexandra. Percentage infection of mycorrhizae in dry andwet periods was significantly different. There was an increased mycorrhizal infection inCassia auriculata, Drypetes septaria, Opuntia dillenii and Prosopis juliflora in the dryseason compared to the wet season and this would facilitate the absorption of water andphosphorus by these species and thereby help them to grow and compete with other plantspecies successfully. A non-cyst forming nematode has been identified in the xylem offine roots of Manilkara hexandra and this may be the reason for the die-back of matureindividuals of the species in the area during the drought periods.