Browsing by Author "Smith, Melinda, advisor"
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Item Open Access Constraints in the compensatory response of a tallgrass prairie plant community to the loss of a dominant species(Colorado State University. Libraries, 2020) Chaves RodrÃguez, Francis Andrea, author; Smith, Melinda, advisor; Knapp, Alan, committee member; Ocheltree, Troy, committee member; Sala, Osvaldo, committee member; Webb, Colleen, committee memberBiodiversity loss is one of the major consequences of global change driven by human activities. The loss of a dominant species is expected to have profound consequences on ecosystem processes (e.g. aboveground productivity) given their highest relative abundance and proportionally large contribution to community biomass production. However, through competitive release, the newly available resources following its lost, are expected to be utilized by the remaining species in the community to increase in abundance and compensate for the function lost. Complete functional compensation does not occur in every ecological community following the loss of dominant species or entire functional groups, and 1) limited resource availability, 2) absence of functionally redundant species, and 3) lack of functional traits that promote compensation have been proposed as possible constraints on compensation. In this dissertation, I evaluate the effect of removing these constraints on the biomass compensation response of a tallgrass prairie plant community following the loss of the dominant species, the C4 tallgrass, Andropogon gerardii Vitman. I experimentally removed the dominant species from a native intact tallgrass prairie plant community at Konza Prairie Biological Station, Kansas, where I selected two contrasting sites, one with functionally redundant species Panicum virgatum L. and Sorghastrum nutans (L.) Nash in low abundances, and a second site where those functionally redundant were codominants with A. gerardii. The first site was irrigated to alleviate water limitation during four growing seasons and fertilized with nitrogen during the final season of the experiment. The second site did not exhibit water limitation and was fertilized during the second growing season of the two-year experiment. My results show that in the short-term removing resource limitation promoted aboveground primary productivity but not enough to produce full biomass compensation. The presence of functionally redundant species, also C4 tall grasses with similar functional effect traits as A. gerardii, did increase aboveground biomass production, but did not promote full biomass compensation, not even when they were present in high abundance. I hypothesize that additional to the constraints proposed, compensation is limited by response traits in the remaining species that limit their demographic response to the increased available space, light, water and soil resources following the loss of the dominant species. Overall, my results show the compensation approach is important to evaluate not only the effect of species loss on ecosystem processes, but also the response of the remaining species and their ability to compensate for the function lost. They also suggest the existence of additional mechanisms in play that need to be identified and tested in order to improve the understanding of how communities recover in the face of biodiversity loss.Item Open Access Defining, describing, and assessing growth determinacy as a mechanism of plant species codominance(Colorado State University. Libraries, 2022) Gray, Jesse Edward, author; Smith, Melinda, advisor; Knapp, Alan, committee member; Ocheltree, Troy, committee member; Blumenthal, Dana, committee memberTo view the abstract, please see the full text of the document.Item Open Access Evaluating Bouteloua gracilis cultivars' performance after drought; The role of the soil microbiome(Colorado State University. Libraries, 2024) Donne, Carina, author; Smith, Melinda, advisor; Havrilla, Caroline, committee member; Trivedi, Pankaj, committee member; Metcalf, Jessica, committee memberDrought has affected the Great Plains throughout history, most notably during the Dust Bowl of the 1930's. While most drought events are not as severe as the Dust Bowl, they still cause significant agricultural losses every year. As research has begun to uncover the mechanisms and responses of drought, there are still unanswered questions. For instance, the mechanisms of ecosystem recovery after drought ends remain relatively unexplored. It is possible that intervention methods such as reseeding will need to be done to help restore ecosystem structure and function after drought. After the Dust Bowl, it was a common practice to reseed native grasses, such as Blue Grama (Bouteloua gracilis), in sites severely impacted by the drought. Given forecasts of droughts on par or even more severe than the Dust Bowl, reseeding may need to be employed more frequently in the future to enhance post-drought recovery. However, with reseeding efforts, it is imperative to understand the adaptability of cultivars to the environmental conditions in which they are planted. One aspect of environmental conditions that has rarely been examined the soil microbiome. Here, I used a common garden experiment that included two cultivars of B. gracilis that were planted with soil microbial inocula extracted from either previously droughted or non-droughted soils. These soils were collected from a recently ended four-year drought experiment in the shortgrass steppe of northeastern Colorado, which caused the widespread loss of B. gracilis. The goal of the greenhouse experiment I conducted was to examine whether the post-drought legacy of altered soil microbial communities affected the growth and performance of two common cultivars of B. gracilis. I assessed plant performance by measuring weekly height to estimate relative growth rate and at the end of the experiment, I measured plant above- and belowground biomass. I found no significant differences in relative growth rate or plant biomass, and minimal differences in the bacterial community composition between the two cultivars. These results suggest that the post-drought legacy of altered soil bacterial communities did not differentially affect growth and performance of the two common B. gracilis cultivars evaluated in this study, and that the growth of these cultivars did not differ in their effects on the soil bacterial communities found under ambient vs. previously droughted conditions. Overall, both cultivars may be suitable for reseeding in the shortgrass steppe grassland after extreme drought, yet further studies are needed to examine a broader range of B. gracilis cultivars and whether soil bacterial communities previously exposed to extreme drought would allow for improved growth and performance of different cultivars to future drought conditions.