Date of Award
Master of Science (MS) in Biology
Invasive winter annual grasses, IWAGs, have degraded extensive ecosystems around the world and continue to invade new ones yearly. IWAGs readily form large monocultures or near monocultures, thus management and restoration goals largely focus on maintaining or increasing plant diversity in impacted ecosystems. Unfortunately, common management methods also reduce native plant diversity and harm the soil microbiome. These effects require additional measures to be taken, like reseeding, and plant diversity is still usually well below remnant targets. Early season short-term nutrient reduction to manage IWAGs is largely unexplored and would potentially decrease IWAG abundance, active earlier than most plants, but impact later season species less. Low rates of labile carbon, as sucrose, were applied to soils in a Pacific Northwest semi-arid grassland in early spring to stimulate microbial growth and temporarily reduce nutrient availability to the IWAG Ventenata dubia. Inorganic nitrogen was tracked throughout the experiment and plant and soil microbial community changes were determined at the end of the growing season. Labile carbon application reduced nitrogen at the beginning of the year, but effects did not persist to mid may when most plants were still active and soil moisture was not limiting. Treatments reduced V.dubia cover, per area seed production, and seed mass with no corresponding impact on perennial or other annual plants, except at the highest application rate when annual cover was reduced by 2%. The soil microbial community, determined via PLFA and NLFA analysis, was largely unchanged at the end of the season with slightly higher bacterial biomass and, importantly, no reduction in AMF abundance. These results suggest that this method has few negative impacts on the plant and soil community aside from a reduction in V.dubia cover and possibly its seed bank. This short-term nutrient reduction method has the potential to not only target IWAGs, active early, but also any non-native plants targeted for management that are active earlier or later than the native plant community.
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Lamm, Jaren F., "Targeted short-term nutrient reduction to manage Ventenata dubia an invasive winter annual grass: soil and plant responses" (2019). EWU Masters Thesis Collection. 567.