Responses of endomycorrhizal plants grown in a calcined montmorillonite clay to different levels of soluble phosphorus. I. Effect on growth and mycorrhizal development

Abstract

Greenhouse experiments were conducted to compare the growth of mycorrhizal and nonmycorrhizal plants in a calcined montmorillonite clay (Turface) supplied with nutrient solutions of different P concentrations. Apple (Malus pumila Mill., var. Beautiful Arcade), leek (Allium porrum L., var. American Flag), and marigold (Tagetes patulus L., var. Golden Boy) plants were inoculated with 1 g of fresh leek roots colonized singly with the following endomycorrhizal fungi: Glomus epigaeum Daniels & Trappe, Glomus monosporum Gerd. & Trappe, Glomus sp. 3, and Glomus sp. 5. Each experimental plant was inoculated with one of two fungal species at five levels of P. In addition, marigold was inoculated by one fungal species at eight levels of P. The results show that in all cases the inoculated plants grew better than the noninoculated ones, even at high P levels. However, in the first three experiments, the two fungal species used had similar effects on the plant growth. The root endomycorrhizal colonization (REC) indexes decreased when P levels increased, but very much less for leek than for apple and marigold plants. In the second experiment with marigold, starting with level V, the intramatrical structures were altered and the usual vesicular–arbuscular (VA) endomycorrhizal structures almost disappeared; however, the growth stimulation of marigold plants inoculated with G. epigaeum remained. The different fungi can apparently reach the same level of colonization provided the appropriate levels of soluble P are used. The authors suggest a thorough evaluation of the infectivity and the efficiency of a given endomycorrhizal fungus on a given host plant; experiments should be conducted with different levels of P.