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- All Subjects: Soil Sciences
- All Subjects: carbon cycling
- All Subjects: Enzyme Activity
- Genre: Masters Thesis
- Creators: Davis, Kelsie
Description
As the global population continues to increase, so does the need for agriculture resulting in increased fertilizer use. Nanofertilizers and biochar have been proposed as alternatives to fertilizers currently in use to reduce negative environmental impacts. In this study, the effects of various nanofertilizers and biochar on the soil microbial community were investigated. Soils treated with graphene nanoplatelet (GNP), graphene oxide (GO), reduced graphene oxide (rGO), graphite nano-additive (GNA) and biochar (BC) at concentrations of 5 mg/kg and 1000 mg/kg were sampled before and after a 28-day incubation period. Quantitative PCR assays were carried out against the following target genes: 16S rRNA, nirK, nirS, nifH, amoA and nosZ. Overall, all treatments experienced a decrease in 16S rRNA abundance after the incubation period with an average decrease of 48% however, all treatments were higher in abundance than the control. The abundances of nitrogen (N) cycling functional genes were evaluated in terms of relative abundance as a percentage of 16S rRNA. There was an increase across all treatments in nirK relative abundance over time and when compared to the control. The most notable differences in abundance were in rGO (high) as well as BC. Both nirS and nosZ exhibited an increase over time but decreased compared to the control. A decrease in relative abundances of nifH in BC as well as GO (low) and rGO (high) was observed. Lastly, there was an increase in amoA relative abundance across all treatments after the incubation period. However, all treatments were significantly lower than the control. The increase of denitrifying genes (nirK, nirS and nosZ) and nitrifying genes (amoA) suggests the potential increase in denitrification which can result in increased N loss into the atmosphere and the potential decrease of nitrification resulting in reduced N loss into waterways, respectively. At the time of writing, this study is one of the first to investigate and provide observations on the effects of nanofertilizers on nifH, which is responsible for N-fixation. The results presented here suggest that rGO and BC impart similar effects on the microbial community, whereas GNP had the most significant impact overall.
ContributorsDavis, Kelsie (Author) / Penton, Christopher R (Thesis advisor) / Park, Yujin (Committee member) / Suzart de Albuquerque, Fabio (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