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: Making Sense of the Census: Classifying and Counting Ethnicity in Oceania, 1965-2011

authors: Broman, Patrick David

subjects: Ethnicity

abstract: As the flagship government effort to count and classify its population, censuses are a key site for rendering and making visible group boundaries. Despite claims to objective rationality, however, census taking is a political and inherently subjective exercise. Censuses help shape the very categories they claim to capture: censuses do more than reflect social reality, they also participate in the social construction of this reality (Kertzer and Arel, 2002b, p. 2). While ethnicity – as a social construct – is imagined, its effects are far from imaginary, and census categorisations may have significant material consequences for the lives of citizens.

Although an increasing number of studies have examined how and why governments in particular times or places count their populations by ethnicity, studies that are both cross-national and longitudinal are rare. Attempting to in part bridge this gap, this thesis studies census questionnaires from 1965 to 2011 for 24 countries in Oceania. In doing so, it explores three general questions: 1) how ethnicity is conceptualised and categorised in Oceanic censuses over time; 2) the relationship between ethnic counting in territories to that of their metropoles; and 3) Oceanic approaches towards multiple ethnic identities. Spread over an area of thirty million square kilometres of the Pacific Ocean, Oceania provides an interesting context to study ethnic counting. The countries and territories which make up the region present an enormous diversity in physical geography and culture, languages and social organization, size and resource endowment. As the last region in the world to decolonise, Oceania includes a mix of dependencies and sovereign states.

The study finds that engagement with ethnic classification and counting is near-ubiquitous across the time period, with most countries having done so in all five cross-sectional census rounds. In general terms, in ethnic census questions ‘racial’ terminology of race and ancestry has been displaced over the focal period by ‘ethnic’ terminology of ethnicity and ethnic origin. Overall, the concept of ethnic origins predominates, although interestingly it is paired with race in the US territories, reflecting the ongoing social and political salience of race in the metropole. With respect to ethnic categories provided on census forms (and thus imbued with the legitimacy of explicit state recognition) the study finds a shift away from the imagined and flawed Melanesian/Micronesian/ Polynesian racial typology and other colonial impositions to more localised and self-identified Pacific identities. It is theorised that these shifts are emblematic of broader global changes in the impetuses for ethnic counting, from colonially-influenced ‘top down’ counting serving exclusionary ends to more inclusive, ‘bottom up’ approaches motivated by concerns for minority rights and inclusive policy-making.

text: Making Sense of the Census: Classifying and Counting Ethnicity in Oceania, 1965-2011 As the flagship government effort to count and classify its population, censuses are a key site for rendering and making visible group boundaries. Despite claims to objective rationality, however, census taking is a political and inherently subjective exercise. Censuses help shape the very categories they claim to capture: censuses do more than reflect social reality, they also participate in the social construction of this reality (Kertzer and Arel, 2002b, p. 2). While ethnicity – as a social construct – is imagined, its effects are far from imaginary, and census categorisations may have significant material consequences for the lives of citizens.

Although an increasing number of studies have examined how and why governments in particular times or places count their populations by ethnicity, studies that are both cross-national and longitudinal are rare. Attempting to in part bridge this gap, this thesis studies census questionnaires from 1965 to 2011 for 24 countries in Oceania. In doing so, it explores three general questions: 1) how ethnicity is conceptualised and categorised in Oceanic censuses over time; 2) the relationship between ethnic counting in territories to that of their metropoles; and 3) Oceanic approaches towards multiple ethnic identities. Spread over an area of thirty million square kilometres of the Pacific Ocean, Oceania provides an interesting context to study ethnic counting. The countries and territories which make up the region present an enormous diversity in physical geography and culture, languages and social organization, size and resource endowment. As the last region in the world to decolonise, Oceania includes a mix of dependencies and sovereign states.

The study finds that engagement with ethnic classification and counting is near-ubiquitous across the time period, with most countries having done so in all five cross-sectional census rounds. In general terms, in ethnic census questions ‘racial’ terminology of race and ancestry has been displaced over the focal period by ‘ethnic’ terminology of ethnicity and ethnic origin. Overall, the concept of ethnic origins predominates, although interestingly it is paired with race in the US territories, reflecting the ongoing social and political salience of race in the metropole. With respect to ethnic categories provided on census forms (and thus imbued with the legitimacy of explicit state recognition) the study finds a shift away from the imagined and flawed Melanesian/Micronesian/ Polynesian racial typology and other colonial impositions to more localised and self-identified Pacific identities. It is theorised that these shifts are emblematic of broader global changes in the impetuses for ethnic counting, from colonially-influenced ‘top down’ counting serving exclusionary ends to more inclusive, ‘bottom up’ approaches motivated by concerns for minority rights and inclusive policy-making.

year: 2013

title: Iwi sex ratios in the New Zealand population census: Why are women so dominant?

authors: Kukutai, Tahu

abstract: Recent census-based studies of iwi (tribal) population growth have revealed a high degree of volatility that cannot be explained by demographic factors alone. Although focused on a small number of iwi, these studies have shown that changing patterns of identification are an important driver of iwi population growth, and that the propensity to identify with an iwi appears to be much stronger among Māori women than men. Thus, the vast majority of iwi in the census have far more females than males, and female domination has increased over time. This paper describes the key features of female-favoured iwi sex ratios in the census and explores possible explanations. Focusing on sex ratios for the ten largest iwi, we find that female domination is highest in the 25–44 age group, and that this pattern is consistent over time. Further analysis shows that Māori women aged 25–34 years are more likely than their male counterparts to know detailed aspects of their pepeha (tribal identity), to explore whakapapa (genealogy) and to speak te reo Māori. Our results underscore the importance of Māori women as cultural connectors within their whānau, as well as in a broader iwi context.

text: Iwi sex ratios in the New Zealand population census: Why are women so dominant? Recent census-based studies of iwi (tribal) population growth have revealed a high degree of volatility that cannot be explained by demographic factors alone. Although focused on a small number of iwi, these studies have shown that changing patterns of identification are an important driver of iwi population growth, and that the propensity to identify with an iwi appears to be much stronger among Māori women than men. Thus, the vast majority of iwi in the census have far more females than males, and female domination has increased over time. This paper describes the key features of female-favoured iwi sex ratios in the census and explores possible explanations. Focusing on sex ratios for the ten largest iwi, we find that female domination is highest in the 25–44 age group, and that this pattern is consistent over time. Further analysis shows that Māori women aged 25–34 years are more likely than their male counterparts to know detailed aspects of their pepeha (tribal identity), to explore whakapapa (genealogy) and to speak te reo Māori. Our results underscore the importance of Māori women as cultural connectors within their whānau, as well as in a broader iwi context.

year: 2017