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- Genre: Masters Thesis
Description
Dissolved organic matter (DOM) is an important part of aquatic foodwebs because it contains carbon, nitrogen, and other elements required by heterotrophic organisms. It has many sources that determine its molecular composition, nutrient content, and biological lability and in turn, influence whether it is retained and processed in the stream reach or exported downstream. I examined the composition of DOM from vascular wetland plants, filamentous algae, and riparian tree leaf litter in Sonoran Desert streams and its decomposition by stream microbes. I used a combination of field observations, in-situ experiments, and a manipulative laboratory incubation to test (1) how dominant primary producers influence DOM chemical composition and ecosystem metabolism at the reach scale and (2) how DOM composition and nitrogen (N) content control microbial decomposition and stream uptake of DOM. I found that differences in streamwater DOM composition between two distinct reaches of Sycamore Creek did not affect in-situ stream respiration and gross primary production rates. Stream sediment microbial respiration rates did not differ significantly when incubated in the laboratory with DOM from wetland plants, algae, and leaf litter, thus all sources were similarly labile. However, whole-stream uptake of DOM increased from leaf to algal to wetland plant leachate. Desert streams have the potential to process DOM from leaf, wetland, and algal sources, though algal and wetland DOM, due to their more labile composition, can be more readily retained and mineralized.
ContributorsKemmitt, Kathrine (Author) / Grimm, Nancy (Thesis advisor) / Hartnett, Hilairy (Committee member) / Throop, Heather (Committee member) / Arizona State University (Publisher)
Created2018
Description
Soil organic carbon (SOC) is a critical component of the global carbon (C) cycle, accounting for more C than the biotic and atmospheric pools combined. Microbes play an important role in soil C cycling, with abiotic conditions such as soil moisture and temperature governing microbial activity and subsequent soil C processes. Predictions for future climate include warmer temperatures and altered precipitation regimes, suggesting impacts on future soil C cycling. However, it is uncertain how soil microbial communities and subsequent soil organic carbon pools will respond to these changes, particularly in dryland ecosystems. A knowledge gap exists in soil microbial community responses to short- versus long-term precipitation alteration in dryland systems. Assessing soil C cycle processes and microbial community responses under current and altered precipitation patterns will aid in understanding how C pools and cycling might be altered by climate change. This study investigates how soil microbial communities are influenced by established climate regimes and extreme changes in short-term precipitation patterns across a 1000 m elevation gradient in northern Arizona, where precipitation increases with elevation. Precipitation was manipulated (50% addition and 50% exclusion of ambient rainfall) for two summer rainy seasons at five sites across the elevation gradient. In situ and ex situ soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were measured in precipitation treatments in all sites. Soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were highest at the three highest elevation sites compared to the two lowest elevation sites. Within sites, precipitation treatments did not change microbial biomass C, extracellular enzyme activity, and SOC. Soil CO2 flux was greater under precipitation addition treatments than exclusion treatments at both the highest elevation site and second lowest elevation site. Ex situ respiration differed among the precipitation treatments only at the lowest elevation site, where respiration was enhanced in the precipitation addition plots. These results suggest soil C cycling will respond to long-term changes in precipitation, but pools and fluxes of carbon will likely show site-specific sensitivities to short-term precipitation patterns that are also expected with climate change.
ContributorsMonus, Brittney (Author) / Throop, Heather L (Thesis advisor) / Ball, Becky A (Committee member) / Hultine, Kevin R (Committee member) / Munson, Seth M (Committee member) / Arizona State University (Publisher)
Created2019
Description
Dioecious plants often display sexual segregation in habitat preference and trait expression due to contrasts in reproductive costs. Females may be maladapted to environments with limited available resources, or habitats where resources are diminishing due to climate change. Reduced fitness in female individuals compared to males could lead to skewed sex ratios and reduce population fitness of dioecious species, including one of the most widely distributed dioecious tree species in North America, Acer negundo. The goal of this study was to evaluate how climate warming and drought may enhance sexual segregation in productivity and physiological stress in A. negundo. To address this goal, I measured radial growth and carbon isotope ratios (δ13C) in tree-ring cellulose of 22-year male and female A. negundo trees growing in a common garden in Salt Lake City, UT. The trees were originally transplanted as one-year old cuttings from a nearby site that was 6.5 °C cooler that the common garden. I hypothesized that 1) δ13C would be lower (more negative) in late growth that is formed during the hottest months of the growing season in males than in females, and during years with no supplemental watering, indicating lower stress from heat and drought in males than in females. And 2) radial growth would be greater in males under warm, well-watered conditions and the addition of drought will exacerbate the difference between males and females. To test these hypotheses, cores were extracted from the main stem of nine male and nine female trees with an increment borer. Annual growth was measured on each core and cellulose was extracted to measure annual δ13C ratios. Males had a 0.63‰ lower mean δ13C than females in years after supplemental water had ceased (p = 0.03) and a 4.12 mm wider radial growth compared to females while irrigated (p = 0.02). Although these data did not support my hypotheses per se, results nevertheless indicate that females are more likely to be maladapted to climate warming and drought to a greater extent than males. If so, a combination of drought and heat stress may have deleterious impacts on the population fitness of Acer negundo and other similar dioecious tree species.
ContributorsChisholm, Mary (Author) / Hultine, Kevin R (Thesis advisor) / Throop, Heather (Thesis advisor) / Morino, Kiyomi (Committee member) / Arizona State University (Publisher)
Created2023