Interactions between Tamarix ramosissima (Saltcedar), Populus fremontii (Cottonwood), and Mycorrhizal Fungi: Effects on Seedling Growth and Plant Species Coexistence

Little is known about the composition and function of the mycorrhizal fungal community in riparian areas, or its importance in competitive interactions between Populus fremontii, a dominant tree in southwestern United States riparian forests which forms arbuscular and ectomycorrhizas, and Tamarix ramosissima, an introduced tree species that has spread into riparian areas. The objectives of this study were to determine the mycorrhizal status of Tamarixand to evaluate the effect of mycorrhizal fungal inoculation on Tamarix growth and on the coexistence between Tamarix and Populus.Arbuscular mycorrhizal fungal colonization of Tamarix was very low in both field and greenhouse grown roots, but levels of colonization by dark septate endophytes were high. Fungal inoculation had little effect on Tamarix seedling growth in monoculture. When Populus and Tamarix were grown together in a greenhouse pot experiment, fungal inoculation reduced the height and biomass of Tamarix but had no effect on Populus. Fungal inoculation shifted coexistence ratios. When Tamarix and Populuswere grown together, Tamarixplants averaged 20 of pot biomass in the uninoculated control but only 5 of pot biomass in the inoculated treatment. These results indicate that Tamarix is non-mycotrophic and that in this greenhouse experiment inoculation altered patterns of coexistence between Populus and Tamarix.