title: Limited changes in microbial respiration along a geothermal gradient

authors: van de Laar, Allycia

subjects: Soil respiration

abstract: Soil 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.

text: Limited changes in microbial respiration along a geothermal gradient Soil 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.

year: 2021

title: Promoting engagement and learning in first year university studies: The role of personalisation

authors: Stanley, Peter

subjects: university studies

abstract: Student engagement in higher education can be conceptualised as involving three components: students’ social needs and circumstances, the cognitive characteristics of academic studies, and the prevailing institutional ethos or philosophy that specifies the relationships that students have with learning and knowledge. This paper reports on an investigation into student engagement in a first-year human development course at the University of Waikato at Tauranga, New Zealand where the teaching staff has a commitment to relating learning to individual experiences. Information from an end-of-course survey indicates that a philosophy of personalisation promotes learning engagement. Students reported that they were required to think a lot or a great deal, that they put time into the course assessments, and that they valued the human development course itself.

text: Promoting engagement and learning in first year university studies: The role of personalisation Student engagement in higher education can be conceptualised as involving three components: students’ social needs and circumstances, the cognitive characteristics of academic studies, and the prevailing institutional ethos or philosophy that specifies the relationships that students have with learning and knowledge. This paper reports on an investigation into student engagement in a first-year human development course at the University of Waikato at Tauranga, New Zealand where the teaching staff has a commitment to relating learning to individual experiences. Information from an end-of-course survey indicates that a philosophy of personalisation promotes learning engagement. Students reported that they were required to think a lot or a great deal, that they put time into the course assessments, and that they valued the human development course itself.

year: 2011

title: Testing a suicidal ideation-to-action framework among Queer and Takatāpui people in Aotearoa New Zealand: An examination of the three-step theory

authors: Schimanski, Irie

abstract: The three-step theory (3ST) of suicide is well-established in the general population and shows promise for explaining suicidal ideation among Queer samples. This study examined the applicability of the 3ST using data from 250 Queer (n = 213) and Takatāpui (n = 37) people aged 18-74 living in Aotearoa New Zealand. The analytic approach entailed hierarchical multiple regression, ANOVA, t-tests, and logistic regression. Step-one was partially supported, with discrimination and hopelessness independently associated with suicidal ideation, but not their interaction. Step-two was fully supported, showing social support associated with lower suicidal ideation when social support exceeded discrimination, compared with the inverse. Full support for step-three was observed, finding higher self-harm among participants with histories of attempted suicide than those who had never attempted. An adapted version of the 3ST for Queer and Takatāpui people is presented, offering novel approaches to testing the ideation-to-action framework with these communities.

text: Testing a suicidal ideation-to-action framework among Queer and Takatāpui people in Aotearoa New Zealand: An examination of the three-step theory The three-step theory (3ST) of suicide is well-established in the general population and shows promise for explaining suicidal ideation among Queer samples. This study examined the applicability of the 3ST using data from 250 Queer (n = 213) and Takatāpui (n = 37) people aged 18-74 living in Aotearoa New Zealand. The analytic approach entailed hierarchical multiple regression, ANOVA, t-tests, and logistic regression. Step-one was partially supported, with discrimination and hopelessness independently associated with suicidal ideation, but not their interaction. Step-two was fully supported, showing social support associated with lower suicidal ideation when social support exceeded discrimination, compared with the inverse. Full support for step-three was observed, finding higher self-harm among participants with histories of attempted suicide than those who had never attempted. An adapted version of the 3ST for Queer and Takatāpui people is presented, offering novel approaches to testing the ideation-to-action framework with these communities.

year: 2025-08-01