Plant life span and response to inoculation with vesicular-arbuscular mycorrhizal fungi

Abstract

To determine if annual and perennial species from weakly mycotrophic families exhibit the same differential patterns of responsiveness to vesicular-arbuscular mycorrhizae (VAM) as do members of the strongly mycotrophic grass family (Poaceae), this study examined the responses of congeneric, sympatric annual and perennials species from the Caryophyllaceae and Solanaceae to inoculation with the VAM fungus Glomus intraradices. The perennial Solanum carolinense responded as positively to G. intraradices as did perennial grasses. The other perennials examined, Solanum dulcamara and Silene nivea, were both relatively unresponsive to VAM inoculation and had mean responsiveness values below the typical level for annuals from strongly mycotrophic families. The annual Solanum nigrum exhibited a small positive response to inoculation, and was as responsive as many annuals from more mycotrophic families, especially at low P supply rates. The annual Silene noctiflora was strongly inhibited by inoculation. Mortality over 8 weeks was fivefold higher in VAM-inoculated Silene noctiflora than in uninoculated plants. Among the four herbaceous species examined, the species which persists longest in old-field succession in eastern North America was also the most responsive to VAM inoculation. Mechanisms are proposed for successional persistence and replacement based on VAM responsiveness and soil nutrient pool sizes.