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- Genre: Masters Thesis
Description
Dryland ecosystems are integral to the global agricultural system and play an important role in soil carbon (C) storage. Despite their importance, drylands are currently facing many challenges including climate-change induced rainfall variability and soil degradation. These challenges are predicted to have effects on the soil microbial communities in drylands. Compost, an organic soil amendment, is a land management strategy that has been proposed to increase soil C storage as well as improve soil conditions in drylands, specifically in restoration and agricultural sites where degradation has affected soil properties like microbial biomass and respiration. Compost additions and rainfall variability may interact to affect soil moisture, an important catalyst for microbial activity. Assessing microbial activity responses under compost applications and variable moisture will aid in understanding how land management strategies will be affected by climate change in the future. This study investigates how soil microbial activity from a degraded dryland restoration site is affected by different compost applications amounts and variable soil moistures. A laboratory incubation study was conducted in a controlled environmental chamber for 60 days. Soils were amended with different treatments of compost (0, 0.35, and 0.70 g cm -2) and water pulses (5, 10, and 15 mm) in a full factorial design. Each treatment received the same cumulative amount of water throughout the incubation, but pulses were administered in different frequencies (every 5, 10, and 15 days). Soil respiration and soil water content were measured daily, and microbial biomass was measured at the end of the incubation to assess treatment effects on microbial activity. Microbial respiration and soil water content increased with increasing compost additions and water pulse sizes. Microbial biomass did not have consistent increases with compost additions or water pulse size. Cumulative microbial respiration was highest with the large-infrequent pulse size and smallest with the small-frequent pulse size. These results suggest that microbial activity and carbon dynamics in soils where compost amendments are used will respond to future changes in precipitation variability. The results of this study can aid in understanding how microbial activity is influenced by compost applications, which will be critical in making informed management decisions in the context of climate change.
ContributorsAmari, Katherine Nicole (Author) / Throop, Heather L (Thesis advisor) / Ball, Becky A (Committee member) / Blankinship, Joseph C (Committee member) / Gherardi, Laureano A (Committee member) / Cueva Rodriguez, Alejandro H (Committee member) / Arizona State University (Publisher)
Created2021
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