Mycorrhizal Infection in Pennine Grassland. II. Effects of Mycorrhizal Infection on the Growth of Some Upland Grasses on γ-Irradiated Soils

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Abstract
The effects of mycorrhizal infection on the growth of 5 upland grass spp. [Anthoxanthum udoratum, Nardus stricta, Agrostis tenuis, Cynosurus cristatus, Festuca rubra] were assessed using 3 soils partially sterilized by .gamma.-irradiation. Glomus tenuis was the dominant endophyte in grasses that received a mixed mycorrhizal inoculum. Mycorrhizal infection did not significantly increase plant dry weight after 20 wk and frequently depressed it. Mycorrhizal infection increased plant dry weight and the shoot P percentage of grasses grown for 19 mo. on the soil with least available phosphate. Grasses inoculated with G. mosseae formed mycorrhizas on only 1 soil, and after 43 wk the infected plants were smaller than the controls but had higher shoot P percentages. The generally negative effects of mycorrhizas on grass growth can probably be attributed initially to the greater availability of nutrients in irradiated soil. The fine much-branched root system of grasses permits efficient uptake of phosphate, and mycorrhizal uptake is not significant until the soil is very severely depleted.