Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake

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Abstract
Bethlenfalvay, G. J., Brown, M. S., Ames, R. N. and Thomas, R. S. 1988. Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake. ‐ Physiol. Plant. 72: 565–571.Soybean [Glycine max (L.) Merr.] plants were grown in pot cultures and inoculated with the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe or provided with P fertilizer (non‐VAM plants). After an initial growth period (21 days), plants were exposed to cycles of severe, moderate or no drought stress over a subsequent 28‐day period by rewatering at soil water potentials of ‐1.0, ‐0.3 or ‐0.05 MPa. Dry weights of VAM plants were greater at severe stress and smaller at no stress than those of non‐VAM plants. Phosphorus fertilization was applied to produce VAM and non‐VAM plants of the same size at moderate stress. Root and leaf P concentrations were higher in non‐VAM plants at all stress levels. All plants were stressed to permanent wilting prior to harvest. VAM plants had lower soil moisture content at harvest than non‐VAM plants. Colonization of roots by G. mosseae did not vary with stress, but the biomass and length of the extraradical mycelium was greater in severely stressed than in non‐stressed plants. Growth enhancement of VAM plants relative to P‐fertilized non‐VAM plants under severe stress was attributed to increased uptake of water as well as to more efficient P uptake. The ability of VAM plants to deplete soil water to a greater extent than non‐VAM plants suggests lower permanent wilting potentials for the former.