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dc.contributor.advisorSchipper, Louis A.
dc.contributor.authorvan de Laar, Allycia
dc.date.accessioned2021-10-08T01:36:07Z
dc.date.available2021-10-08T01:36:07Z
dc.date.issued2021
dc.identifier.citationvan de Laar, A. (2021). Limited changes in microbial respiration along a geothermal gradient (Thesis, Master of Science (Research) (MSc(Research))). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/14591en
dc.identifier.urihttps://hdl.handle.net/10289/14591
dc.description.abstractSoil carbon is the largest terrestrial stock of carbon (C) globally. This C stock has the potential to be negatively impacted by global warming through the acceleration of microbial respiration via positive feedback loops. Microbial respiration is a temperature dependent process that releases carbon dioxide (CO₂). Thermal adaptation of microbial respiration may partially offset positive feedback loops, alleviating accelerated responses. The first aim of this thesis was to determine the temperature response of microbial respiration (of labile C and soil organic matter (SOM)) in soil and evaluate the potential for thermal adaptation using a geothermal gradient as a proxy for soil warming. Here, the geothermal gradient, located in Rotorua, New Zealand, spanned average soil temperatures of 18-36 °C, encompassing a range of temperatures experienced in temperate and tropical ecosystems. Soil from along this gradient was sampled and incubated in a laboratory temperature block at 40 different temperatures (~1.8-53 °C) for five hours. For the experiments, 40 control (soil + distilled water) and 40 treatment (soil + glucose solution) tubes were used to separate the SOM and labile C respiration temperature responses. CO₂ concentrations were measured on an Infrared Gas Analyser (IRGA) after five hours. The second aim of the thesis was to determine the temperature response of priming along the geothermal gradient. Soil priming occurs when added labile C substrates in soil promote the acceleration or deceleration of SOM decomposition. This aim was also completed using the temperature block and IRGA for CO₂ measurements, but instead using a δ ¹³C labelled glucose solution to separate the temperature response of priming. These samples were also run on an Off Axis Integrated Cavity Output Spectroscopy (OA-ICOS) instrument to measure the isotopic fraction. A mixing model allowed the separation of SOM, glucose and priming temperature responses. This thesis used a temperature model called Macromolecular rate theory (MMRT) to characterise the temperature responses in terms of temperature optimum (Tₒₚₜ) and temperature inflection point (Tᵢₙ𝒻). Changes in these parameters gave insight into potential responses to warming temperatures. The results of this thesis found evidence for modest thermal adaptation occurring for the Tₒₚₜ of labile C respiration and the Tᵢₙ𝒻 of SOM respiration in response to soil warming. However, these changes were small with changes no larger than 0.198 °C per °C change in environmental temperature (°C °C⁻¹) and 0.263 °C °C⁻¹, respectively. There was no evidence that the Tᵢₙ𝒻 of labile C respiration and the Tₒₚₜ of SOM respiration changed with increasing environmental temperature. The priming results suggested that the temperature response of priming remains constant at different environmental temperatures but differs largely with soil properties. The degree of priming decreased with increasing incubation temperatures (particularly above 40 °C). Overall, the results suggested that thermal adaptation may occur in response to global warming, however, this adaptation is likely minor. This means that feedback loops may be alleviated in response to climate change. However, the modesty of the observed changes may indicate that thermal adaptation may not occur or may not be enough to offset feedback loops. Additionally, the negative relationship of priming with increasing temperature may dampen feedback loops with climate change. Overall, further work is required to fully understand the implications of soil warming on microbial responses.
dc.format.mimetypeapplication/pdf
dc.language.isoen
dc.publisherThe University of Waikato
dc.rightsAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.
dc.subjectSoil respiration
dc.subjectTemperature response
dc.subjectSoil carbon
dc.subjectGeothermal gradient
dc.subjectSoil priming
dc.subjectThermal adaptation
dc.subjectMacromolecular rate theory
dc.subject.lcshMicrobial respiration
dc.subject.lcshGeothermal resources -- New Zealand -- Rotorua
dc.subject.lcshEarth temperature -- New Zealand -- Rotorua
dc.subject.lcshTerrestrial heat flow -- New Zealand -- Rotorua
dc.subject.lcshSoil temperature -- New Zealand -- Rotorua -- Measurement
dc.subject.lcshSoil respiration -- New Zealand -- Rotorua -- Measurement
dc.subject.lcshThermal adaptation -- New Zealand -- Rotorua
dc.titleLimited changes in microbial respiration along a geothermal gradient
dc.typeThesis
thesis.degree.grantorThe University of Waikato
thesis.degree.levelMasters
thesis.degree.nameMaster of Science (Research) (MSc(Research))
dc.date.updated2021-10-06T01:45:35Z
pubs.place-of-publicationHamilton, New Zealanden_NZ


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