What Effects Do Beneficial Fungi and Tamarisk Legacy Have on the Rooting Structure of Fremont Cottonwood in the Southwestern US Riparian Systems?
Alexandra Cole*1, Julia Hull2, Thomas Whitham2,3, Gery Allan2,3, and Catherine Gehring2,3
1 Northern Arizona University, School of Earth & Sustainability, Flagstaff, Arizona, United States, aec397@nau.edu
2 Northern Arizona University, Department of Biological Sciences, Flagstaff, Arizona, United States
3 Merriam Powell Research Center, Flagstaff, Arizona, United States
We explored the hypothesis that tamarisk legacy, climate change, and addition of beneficial root-associated fungi affect root traits of Fremont cottonwood (Populus fremontii). Tamarisk (Tamarix spp.) and climate change are ecological threats to Fremont cottonwood, a foundation species in the riparian systems in the American southwest. Tamarisk alters chemical soil properties and reduces the abundance and diversity of beneficial fungi, upon which cottonwoods depend. These negative effects of tamarisk remain even after they are removed. We used a fully factorial greenhouse experiment to examine the effects of warming temperatures, tamarisk legacy and mycorrhizal fungi on the rooting structure of cottonwoods. We predicted the addition of beneficial fungi and growth in tamarisk legacy would result in greater root investment by cottonwoods. Three patterns emerged: 1) Cottonwoods from populations with co-occurring tamarisk invested more in their fine roots than cottonwoods from populations without co-occurring tamarisk. 2) Inoculation with beneficial root-associated fungi increased root mass and altered root architecture. 3) Cottonwoods grown in tamarisk legacy soil and in heated conditions had lower specific root length (SRL) than cottonwoods grown under other conditions; low SRL suggests greater investment in root structure than high SRL. We conclude that beneficial root fungi help cottonwoods compete with tamarisk. Because cottonwoods are a foundation species, improved cottonwood health will have cascading effects on other ecological communities and maintain, or potentially increase, biodiversity in riparian habitats. We suggest that the addition of beneficial root fungi should be used in the restoration and conservation of southwestern US riparian systems following tamarisk removal.