Intraspecific variation in Elymus elymoides root traits and its influence on competitive outcomes

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Understanding how root traits vary within and among species, and how they respond to heterogeneous environments, can provide important insight into functional plant attributes that influence plant survival in competitive environments. Selecting plant material with root traits that will support its survival in competitive environments may help improve the outcomes of ecological restoration, yet root traits are rarely incorporated into restoration sourcing decisions. Specifically, the impacts of population-level variation in root traits of restoration material are often overlooked. For these reasons, seven root traits of seedlings from twelve populations of Elymus elymoides spp. elymoides were quantified using agar as a growth medium. Elymus elymoides is a native perennial bunchgrass frequently used in restoration in the Colorado Plateau that has been shown to exhibit significant among-population variation in many above- and below-ground traits. The root growth of all E. elymoides populations was compared to growth in seedlings of Bromus tectorum, an annual invasive grass found on the Colorado Plateau with a dense fibrous root system that proficiently captures soil water and outcompetes most native plants. Results showed significant variation among E. elymoides populations in seedling root length (ANOVA, p<0.001) and lateral root number (GLM, p<0.001). Two E. elymoides populations were chosen for use in a greenhouse study imposing competition from cheatgrass and a water stress gradient. One population (Ashley National Forest, UT, USA collection), whose seedlings had a similar number of lateral roots as cheatgrass, represents direct spatial overlap of soil resources with cheatgrass, and thus has access to similar resources. The second population (Fishlake National Forest, UT, USA collection), whose seedlings had fewer lateral roots than cheatgrass, represents indirect soil resource overlap with cheatgrass. While all seedlings were competitively excluded under cheatgrass competition, a time of death analysis showed that the Ashley population persisted longer (p=0.029, R2 = 0.028) than the Fishlake population suggesting that seedling traits such as a more robust root system positively influences seedling survival. The water stress gradient revealed differing allocation strategies and plastic responses to water stress in each population: the Ashley population had higher root length ratio (RLR) and root mass fraction (RMF) and had a stronger plastic response to water stress while the Fishlake population allocated more biomass to aboveground growth (including seed production). These results suggest that populations that allocate more growth to belowground traits (as in the Ashley population) will perform better in restorations where competition from species like cheatgrass is present. However, this presents a practical challenge when trying to produce seeds for restoration because plants that invest more in root growth tend to have lower seed production, as only the Fishlake population produced seeds during the study period.

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  • 11/08/2023
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