GROWTH, PHOSPHORUS UPTAKE, AND WATER RELATIONS OF SAFFLOWER AND WHEATINFECTED WITH AN ARBUSCULAR MYCORRHIZAL FUNGUS

Safflower (Carthamus tinctorius L. cv. S555) and spring wheat (Triticu m aestivum L. cv. Anza) were grown with or without the arbuscular myco rrhizal fungus Glomus etunicatum Pecker & Gerd., under environmentally controlled conditions. Soil phosphate concentrations were adjusted be fore planting to produce mycorrhizal (M) and non-mycorrhizal (NM) plan ts that had similar leaf areas and root length densities at the same s tage of development before initiating drought stress treatments. Droug ht did not affect the amount of mycorrhizal infection in safflower or wheat. Interactions between water stress treatments and mycorrhizal in fection on plant growth and phosphorus uptake were limited and only oc curred in wheat. NM wheat plants had 28 % greater shoot d. wt, slightl y greater root length densities, and 39 % greater P acquisition than M plants when grown under well watered conditions, but under droughted conditions plant size and tissue P contents of M and NM wheat plants w ere similar. Mycorrhizas did not affect stomatal behaviour during drou ght stress in either safflower or wheat, i.e., transpiration and stoma tal conductance declined independently of infection as soil water was depleted and leaf water potentials declined. Therefore, mycorrhizal in fection did not alter the intrinsic hydraulic properties of the plant/ soil system. Whilst wheat maintained turgor of recently expanded leave s during severe drought and safflower did not, mycorrhizal infection h ad no effect on leaf turgor during drought in either plant species.