Phosphorus efficiency of three cereals as related to indigenous mycorrhizal infection

The influence of indigenous vesicular-arbuscular mycorrhizal infection on the assessment of phosphorus (P) efficiency in wheat ( Triticum aestivum L. cv. Spear), barley (Hordeum vulgare L. cv. Galleon) and rye (Secale cereale L. cv. S.A. Commercial) was studied. P efficiency was defined in terms of uptake (mg P pot-1) or utilization (g dw mg-1 P). Experiments were set up with two soils which had low concentrations of plant available P and had been used in a previous study of P efficiency in cereals. Numbers of spores and infective propagules were significantly different in the two soils. In the soil with low propagule density, the extent of mycorrhizal infection of barley, wheat and rye increased with time. Twenty days after transplanting 3-day old seedlings, there was no difference in the percentage of root length infected (2.0%), but at 40 days, wheat (22.4%) and barley (19.3%) had significantly greater percentage of infected root than had rye (10.7%). At 30 days, wheat had a significantly higher percentage of root length infected than barley. In the soil with high propagule density, infection occurred more rapidly, so that the percentage of root length of wheat and barley infected was not significantly different at the three times of harvest. However, infection of rye significantly increased with time and was higher (31.8%) than that of barley (19.8%) at the final harvest. Mycorrhizal infection was positively correlated with efficiency of P uptake in barley, but not in wheat or rye. However, efficiency in utilization of P by barley and wheat was negatively correlated with infection. The colonization of cereals by the indigenous mycorrhizal fungi decreased with the addition of P to the soils. The results of these studies indicate the potential importance of mycorrhizal infection in assessment of P efficiency in cereals.