Growth, phosphorus uptake, and water relations of safflower and wheat infected with an arbuscular mycorrhizal fungus

Safflower (Carthamus tinctorius L. cv. S555) and spring wheat (Triticum aestivum L. cv. Anza) were grown with or without the arbuscular mycorrhizal fungus Glomus etunicatum Pecker & Gerd., under environmentally controlled conditions. Soil phosphate concentrations were adjusted before planting to produce mycorrhizal (M) and non-mycorrhizal (NM) plants that had similar leaf areas and root length densities at the same stage of development before initiating drought stress treatments. Drought did not affect the amount of mycorrhizal infection in safflower or wheat. Interactions between water stress treatments and mycorrhizal infection on plant growth and phosphorus uptake were limited and only occurred in wheat. NM wheat plants had 28 % greater shoot d. wt, slightly 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 were similar. Mycorrhizas did not affect stomatal behaviour during drought stress in either safflower or wheat, i.e., transpiration and stomatal conductance declined independently of infection as soil water was depleted and leaf water potentials declined. Therefore, mycorrhizal infection did not alter the intrinsic hydraulic properties of the plant/soil system. Whilst wheat maintained turgor of recently expanded leaves during severe drought and safflower did not, mycorrhizal infection had no effect on leaf turgor during drought in either plant species.