SEASONAL AND EDAPHIC VARIATION IN VESICULAR-ARBUSCULAR MYCORRHIZAL INFECTION OF GRASSES BY GLOMUS-TENUIS

Seasonal differences in percentage length of gramineous host root infected with Glomus tennis were measured in three field sites in Pennsylvania, U.S.A. Highest G. tennis infection levels were generally found in the spring in very phosphorus‐deficient soils low in moisture. In roots sampled from soils with a high spring soil‐moisture content, fine endophyte infection increased to a maximum later in the growing season. A higher percentage frequency of fine endophyte infection on fine grass feeder roots in spring is taken as evidence for the hypothesis that G. tenuis is a vesicular–arbuscular mycorrhizal fungus particularly adapted to penetrating host roots during brief seasonal fluxes of phosphorus availability. The implications of these data are discussed in relation to mechanisms in grasses which adapt them to nutrient stress. Copyright © 1979, Wiley Blackwell. All rights reserved