Theses and Dissertations at Montana State University (MSU)
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Item Pest management challenges and climate change in water limited winter wheat agroecosystems in southwestern Montana(Montana State University - Bozeman, College of Agriculture, 2020) Nixon, Madison Grace; Chairperson, Graduate Committee: Fabian D. MenalledDryland winter wheat production is influenced by many environmental factors including climate, disease, and resource availability. In Montana, Bromus tectorum (cheatgrass) and Fusarium pseudograminearum (a fungus causing root crown rot) are major winter wheat pests; reducing yield and grain quality. However, little is known how climate change and resource availability impact winter wheat, B. tectorum, and F. pseudograminearum individually as well as their multi-trophic interactions. Thus, this research aimed to 1) Determine the susceptibility of B. tectorum to F. pseudograminearum and assess how CO 2 and nitrogen impact their growth, and 2) Evaluate how elevated temperature, reduced precipitation, and plant competition impact winter wheat and B. tectorum growth and reproduction. Utilizing growth chambers, high and low nitrogen treatments, fungal inoculated and uninoculated treatments, and ambient and elevated CO 2 treatments, Bromus tectorum was found to be a host of F. pseudograminearum, and the fungus significantly reduced root, shoot and total biomass, as well as primary physiological processes of B. tectorum. Fusarium pseudograminearum infection was not impacted by nitrogen or CO 2 level. Low nitrogen increased emergence and root production early on, while high nitrogen increased shoot production at later growth stages. Low nitrogen also improved stomatal conductance and transpiration rate. High CO 2 increased B. tectorum root, shoot, and biomass production, as well as intercellular CO 2. An interaction between ambient CO 2 and low nitrogen resulted in the greatest shoot relative growth rate between the first and second harvest. Field tests, using three climate treatments (ambient, increased temperature, reduced precipitation with increased temperature) and three plant competition levels (monoculture winter wheat, monoculture B. tectorum, and biculture of the two), found that for both winter wheat and B. tectorum monocultures, ambient and warmer climates produced similar yields and biomass, respectively, whereas the drier with warmer treatment reduced these factors. Additionally, B. tectorum presence increased winter wheat grain protein. A quadratic interaction model of winter wheat yield as a function of B. tectorum biomass by climate treatment suggests that at low to moderate B. tectorum biomass levels, winter wheat yield was negatively impacted by the warmer and drier treatment, whereas ambient and warmer treatment results were similar.Item Effect of permafrost thaw on methane and carbon dioxide exchange in two western Alaska peatlands(Montana State University - Bozeman, College of Agriculture, 2013) Johnston, Carmel Eliise; Chairperson, Graduate Committee: Stephanie A. Ewing; Stephanie A. Ewing, Jennifer W. Harden, Paul C. Stoy, Ruth K. Varner, Kimberly P. Wickland, Joshua Koch, Christopher Fuller and Mark T. Jorgenson were co-authors of the article, '2.0 effect of permafrost thaw on CO 2 and CH 4 exchange in a western Alaska peatland chronosequence' submitted to the journal 'Environmental research letters' which is contained within this thesis.; Stephanie A. Ewing, Merritt R. Turetsky, Jennifer W. Harden, A. David McGuire and Miriam Jones were co-authors of the article, '3.0 effect of recent permafrost thaw on the spatial distribution of CO 2 and CH 4 exchange in a western Alaska peatland' submitted to the journal 'Environmental research letters' which is contained within this thesis.Methane (CH 4) causes about 20% of greenhouse gas radiative forcing despite its relatively short lifetime (~10 y) and low concentration (1800 ppb) in the atmosphere. Wetlands are the largest natural source of CH 4, amounting to 22% of CH 4 production globally, with emission of CH 4-C by both diffusion and ebullition pathways. Permafrost peatlands store about 10% of permafrost C and 5% of global belowground C; hence CH 4- C emission with peatland permafrost thaw is of concern. We quantified temporal and spatial aspects of CH 4 and CO 2 emissions from northern peatlands using two approaches: (1) a ~1000 y thaw chronosequence in remote western Alaska (Innoko Flats Wildlife Refuge; May-September, 2011), and (2) lateral transects in intermediate age (~20-500 y) collapse-scar bog features at a well-instrumented site near Fairbanks, Alaska (Alaska Peatland Experiment (APEX)/Bonanza Creek Long Term Experimental Research site; June-September, 2012). At Innoko Flats, peak CH 4 production was observed in features aged 30-590 y since thaw, which had warmer soils than younger sites and shallower water tables than older sites. Average surface flux at these 30-590 y sites (+2.52 ± 0.98 mg CH 4-C m -2 hr -1) was greater than estimated ebullition flux (0.13 ± 0.05 mg CH 4-C m -2 hr -1) based on an observed rate of 0.78 ± 0.33 mL m -2 hr -1. Net ecosystem exchange of CO 2-C (NEE) did not differ among chronosequence features, and offset CH 4-C emissions by a factor of 2 to 400 when considered as 100-y global warming potential. At APEX, bogs reflecting <100 y since most recent thaw showed high variability in CH 4 exchange, but rates were generally consistent with levels at the Innoko 30-590 y sites (mean of 5.42 ± 1.16 mg CH 4-C m -2 hr -1). APEX bogs showed greater balance between CH 4-C efflux and CO 2-C influx, with CH 4-C fluxes offsetting 80-140% of NEE during the growing season when considered as 100-y global warming potential. We argue that CH 4 contributes most significantly to post-thaw C loss over timescales of decades to centuries in these northern peatlands.Item Hydrologic-carbon cycle linkages in a subalpine catchment(Montana State University - Bozeman, College of Agriculture, 2008) Riveros-Iregui, Diego Andres; Chairperson, Graduate Committee: Brian L. McGlynn.The feedbacks between the water and the carbon cycles are of critical importance to global carbon balances. Forests and forest soils in northern latitudes are important carbon pools because of their potential as sinks for atmospheric carbon. However there are significant unknowns related to the effects of hydrologic variability, mountainous terrain, and landscape heterogeneity in controlling soil carbon dioxide (CO 2) efflux. Mountainous terrain imposes large spatial heterogeneity in the biophysical controls of soil CO 2 production and efflux, including soil temperature, soil water content, vegetation, substrate, and soil physical properties. Strong spatial and temporal variability in biophysical controls can lead to large heterogeneity in the magnitude of soil CO 2 efflux. This dissertation research investigates the relationships between these biophysical controls and the resultant CO 2 efflux across the soil-atmosphere interface in a 393-ha subalpine catchment of the Northern Rocky Mountains. This study incorporates knowledge gained through field observations (2 growing seasons) at multiple locations distributed across the watershed, and a range of empirical analytical techniques including a modeling approach to estimate point to catchment scale soil CO 2 efflux. Variability in soil CO 2 efflux was strongly related to topography and landscape structure. Riparian meadows were found to have the highest rates of cumulative soil CO 2 efflux across the entire watershed, likely due to more accumulation of soil water than upland sites, leading to enhanced plant and microbial respiration in riparian meadows. Landscape context and appreciation of organized heterogeneity are critical to estimation and interpretation of watershed-scale rates of soil CO 2 efflux and for up-scaling plot or point measurements of soil CO 2 efflux to larger spatial scales. This dissertation provides examples and suggestions for corroboration and integration of soil and canopy level CO 2 fluxes and for process understanding of spatiotemporal variability of biogeochemical processes driven by the hydrologic cycle.Item Variability in soil CO2 production and surface CO2 efflux across riparian-hillslope transitions(Montana State University - Bozeman, College of Agriculture, 2007) Pacific, Vincent Jerald; Chairperson, Graduate Committee: Bryan L. McGlynn.The spatial and temporal controls on soil CO2 production and surface CO2 efflux have been identified as an outstanding gap in our understanding of carbon cycling. I investigated both the spatial and temporal variability of soil CO2 concentrations and surface CO2 efflux across eight topographically distinct riparian-hillslope transitions in the ~300 ha subalpine upper-Stringer Creek Watershed in the Little Belt Mountains, Montana. Riparian-hillslope transitions provide ideal locations for investigating the spatial and temporal controls on soil CO2 concentrations and surface CO2 efflux due to strong gradients in respiration driving factors, including soil water content, soil temperature, and soil organic matter. I collected high frequency measurements of soil temperature, soil water content, soil air CO2 concentrations (20 cm and 50 cm), surface CO2 efflux, and soil C and N concentrations (once) at 32 locations along four transects. Soil CO2 concentrations were more variable in riparian landscape positions, as compared to hillslope positions, as well as along transects with greater upslope accumulated area. This can be attributed to a greater range of soil water content and higher soil organic matter availability.Item Biological and physical controls of CO 2 flux through snow in a forested ecosystem(Montana State University - Bozeman, College of Agriculture, 2013) Rains, Fredrick Aaron; Chairperson, Graduate Committee: Paul C. Stoy; Cliff Montagne (co-chair)Soil CO 2 efflux is the dominant component of carbon loss in many temperate forests. Wintertime respiration accounts for a significant contribution of the annual carbon loss to the atmosphere from terrestrial ecosystems, but the magnitude of this flux and physical transport mechanisms through snow are unclear. This research examines wintertime CO 2 flux in a lodgepole pine forest in the Upper Stringer Creek catchment at the Tenderfoot Creek Experimental Forest, Montana, USA. I hypothesized that: CO 2 production and efflux during the winter contributes a significant amount (10-20%)of CO 2 efflux to the atmosphere in the Tenderfoot Creek Experimental Forest; 2) Snow properties, i.e. depth and density, and thereby porosity and tortuosity vary during the winter via snow metamorphosis, thus changing the impediment to flux through the snow medium and CO 2 production increases when the snowpack becomes isothermal during melt due to increased soil moisture and soil temperature. A micrometeorological stations was installed to measure soil water content, soil temperature, incoming and outgoing radiation, albedo, snow depth, snow/soil interface CO 2 concentration, atmospheric CO 2 concentration, three-dimensional wind speed, and above snow/sub-canopy CO 2 flux on a half-hourly basis. In addition, throughout the winters of 2010/2011 and 2011/2012 snow pit analyses was performed in triplicate approximately once monthly and snow depth, density, and temperature were measured in 10-centimeter increments. Three methodological approaches were used to analyze CO 2 flux through the snow pack: Chamber on snow, two-point Fick's law based diffusivity modeling, and snow-surface/subcanopy eddy covariance. The results of the comparison show a significant difference in measured and estimated flux between methodologies during early and late winter, while demonstrating the Fick's based model is can accurately estimate up 75% of measured flux during mid-winter. Observations are consistent with advection, in addition to diffusion, as a mechanism of CO 2 transport through snow such that observation strategies that do not account for advection may underestimate wintertime efflux. Furthermore, all three methodologies indicate that wintertime respiration is a major contributor to the annual carbon budget when mean flux rates are compared to growing season flux rates.