Effects of ectomycorrhizal and vesculararbuscular mycorrhizal fungi on drought tolerance of four leguminous woody seedlings

Seedlings of Acacia auriculiformis A. Cunn. ex. Benth., Albizia lebbeck (L.) Benth., Gliricidia sepium (Jac.) Walp and Leucaena 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. In Gliricidia and Leucaena , both mycorrhizal inoculations stimulated greater plant growth, P and N uptake compared to their non-mycorrhizal (NM) plants under both watering regimes. However, in Acacia and Albizia , 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 between Acacia and VA mycorrhizas and parasitic association between Albizia and ectomycorrhiza. Drought-stressed mycorrhizal and NM Leucaena , and drought-stressed mycorrhizal Acacia tolerated lower xylem pressure potentials and larger water losses than the drought-stressed mycorrhizal and NM Albizia and Gliricidia . 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