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The effects of mycorrhizal soil inoculation by Glomus mosseae on the growth and photosynthesis of barley cv. Manitou were investigated in sand culture at 5 concentrations of calcium phosphate (50, 100, 200, 400 or 800 mg P/kg soil). Mycorrhizal infection was low and declined from 3.3% at 50 mg P/kg to 1.5% at the highest P concentration. In general, small differences in biomass between mycorrhizal (+M) and non-mycorrhizal (-M) barley were observed, but a significant reduction in dry mass of senesced leaves occurred in +M plants. Leaf P concentration increased with P application, but was not significantly different between +M and -M plants. Although no differences were observed in dry mass between +M and -M plants at 50 mg P/kg, +M plants exhibited higher rates of photosynthesis and greater P- and N-use efficiencies. The mycorrhizal enhancement of maximum photosynthetic rate at the lowest P concentration was associated with higher stomatal conductance, but was not related to increased leaf P or to changes in photon yield or the ratio of variable (Fv) to maximum (Fm) chlorophyll fluorescence.
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