Oral Paper

         Ecology

Investigating the function of the awn and its role in invasion success of Microstegium vimineum (stiltgrass)

Presenting Author
Lauren Kosslow
Description
Invasive species pose a threat to biodiversity, yet factors that determine why some species become invasive and others do not remains poorly understood. This research focuses on a specific trait, the awn, and its role in invasion success of Microstegium vimineum (stiltgrass), an invasive grass species in the US. The invasive range of M. vimineum is expanding northward and westward in the US, resulting in further habitat degradation and complicating conservation efforts. Along with climate change, a possible explanation for northern expansion is the geographic distribution of awn types across the invasive range. Awns are bristle-like extensions from the floret that respond to changes in moisture and are a hallmark of many grass species. Awns coil when dry then straighten when wet and have been shown to increase burial and germination under certain conditions in some grass species. Microstegium vimineum has multiple awn forms (awned, awnless, and intermediate-awned) with a distinct awned-awnless distribution from north-south in the native and invasive ranges, the only grass for which this geographic pattern of awn type has been documented. This north-south distribution of awn types suggests awns may be favored by natural selection in some environments, but the extent of awn function in M. vimineum remains largely unknown. We hypothesize awns allow florets to bury in the soil, which protects the seeds from freezing temperatures at high latitudes, leading to a selective advantage of awns in the north and increasing northern range expansion. Our goal is to determine the function of the awn and identify its role in invasion success through reciprocal transplant experiments of all awn types across various latitudes, elevations, and soil freezing conditions over three years. These experiments will provide evidence of awn function by examining the effects of awn type on germination and survival at each location. These experiments are being conducted at four locations including Erie, PA (northern), Clemson, SC (southern), Morgantown, WV (low elevation, mid-latitude), and Davis, WV (high elevation, mid-latitude). Five replicates of three awn types were used at each site, including the awned-type, awnless-type, and an awn-removed treatment to account for differences due to awned-type traits other than the awn itself. Results from year one show the awned-type had the greatest germination/survival at high latitude, suggesting greater survival of the awned-type at high soil freezing conditions. The awnless-type had the greatest mortality at high latitude and elevation, further supporting a survival advantage of the awned-type at high soil freezing. The awn-removed type had the greatest germination/survival at high elevation, which may suggest another associated trait of the awned-type, rather than the awn itself, confers a survival advantage in northern climates. Year two of the experiment will further investigate the function of the awn in survival by studying how awn type affects survival over multiple winters in the seedbank. The outcomes of this research will allow for elucidation of M. vimineum awn function, essential to explaining the geographic awn type distribution observed in the US, determining the likelihood of invasion success, and predicting future range expansion.