Illuminating the presence and role of dark septate endophytes in Populus fremontii and Tamarix spp

Alexandra Schuessler and Ron Deckert, Biological Sciences, Northern Arizona University, Flagstaff, AZ, Catherine Gehring, Merriam Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ

Background/Question/Methods
Root associated fungi are highly diverse and have important ecological functions, yet most studies focus on mycorrhizal or pathogenic fungi. The more poorly understood dark septate endophytes (DSE) are widespread, abundant and appear equally likely to colonize the roots of native and non-native host plants. While DSE can improve plant soil resource uptake, provide defense against pests, and produce plant growth regulators, it is unclear if these fungi differentially affect native and invasive plants. We surveyed the root endophyte community of both a foundation native riparian tree species, Populus fremontii (Fremont Cottonwood), and its invasive competitor, Tamarix spp. (tamarisk) and assessed how three common DSE influenced cottonwood and tamarisk growth and functional traits using greenhouse experiments.
Results/Conclusions
We found cottonwoods hosted twice as many DSE isolates than found on tamarisk, but both plant species had diverse DSE communities. We isolated a total of 33 different DSE genera from the trees, with 22 genera found on cottonwood roots and 17 genera on tamarisk roots, only 6 of which were shared. However, the fungal genera shared by the two plant species were the most common and DSE community composition did not differ significantly between the species. Inoculation with the DSE Phialophora sp., Phomopsis sp. and Pleosporales sp. affected the growth and biomass allocation of both cottonwoods and tamarisk relative to sterile-inoculated controls. In both plant species, inoculation with DSE decreased root biomass. However, DSE increased specific root length and root surface area in tamarisk, while having the opposite effect in cottonwoods. For aboveground traits, only Phialophora sp increased leaf dry mass in tamarisk and while all DSE species increased leaf mass in cottonwoods. These results demonstrate that taxa of DSE colonize the roots of native and invasive riparian plants similarly. However, the fungi differed in how they affected the functional traits of the two plant species, which could have implications for their growth, survival, and competitive dynamics.