Effects of ectomycorrhizal and vesicular-arbuscular mycorrhizal fungi on drought tolerance of four leguminous woody seedlings

Seedlings ofAcacia auriculiformis A. Cunn. ex. Benth.,Albizia lebbeck (L.) Benth.,Gliricidia sepium (Jac.) Walp andLeucaena leucocephala (Lam.) de Wit. were inoculated with an ectomycorrhizal (Boletus suillus (l. ex. Fr.) or indigenous vesicular-arbuscular mycorrhizal (VAM) fungi in a low P soil. The plants were subjected to unstressed (well-watered) and drought-stressed (water-stressed) conditions. InGliricidia andLeucaena, both mycorrhizal inoculations stimulated greater plant growth, P and N uptake compared to their non-mycorrhizal (NM) plants under both watering regimes. However, inAcacia andAlbizia, these parameters were only stimulated by either ectomycorrhiza (Acacia) or VA mycorrhiza (Albizia). Growth reduction occurred as a result of inoculation with the other type of mycorrhiza. This was attributed to competition for carbon betweenAcacia and VA mycorrhizas and parasitic association betweenAlbizia and ectomycorrhiza. Drought-stressed mycorrhizal and NMLeucaena, and drought-stressed mycorrhizalAcacia tolerated lower xylem pressure potentials and larger water losses than the drought-stressed mycorrhizal and NMAlbizia andGliricidia. These latter plants avoided drought by maintaining higher xylem pressure potentials and leaf relative water content (RWC). All the four leguminous plants were mycorrhizal dependent. The higher the mycorrhizal dependency (MD), the lower the drought tolerance expressed in terms of drought response index (DRI). The DRI may be a useful determinant of MD, as they are inversely related.