title: Carbon dioxide losses from terrestrial organic matter resulting from photodegradation and microbial respiration

authors: Rutledge-Jonker, Susanna

subjects: respiration

abstract: Losses of soil organic matter (SOM) can lead to a decrease in soil quality, cause an increase in CO₂ emissions, thereby contributing to a rise in atmospheric CO₂ concentration, which in turn can affect the global climate. Microbial decomposition of SOM to CO₂ is one of the main processes by which SOM is lost. Breakdown of organic matter (OM) by solar irradiance (called “photodegradation”) can also contribute to decomposition, especially in dry ecosystems. Photodegradation has been studied in the field by measuring the mass loss of litter, but its contribution to CO₂ losses has not previously been determined at spatial and temporal scales appropriate for ecosystems. The main aim of this research was to examine the magnitude and drivers of the CO₂ efflux from terrestrial organic matter resulting from both microbial decomposition and photodegradation. Carbon dioxide fluxes were measured at a bare peatland in New Zealand using eddy covariance (EC) and a closed chamber. The EC system measured the total CO₂ flux, whereas the chamber only measured the biological component of the CO₂ flux. The abiotic irradiance-induced component of the CO₂ flux was obtained by subtracting the chamber flux from the EC flux, and by comparing day-and night-time EC measurements made under similar temperature and moisture conditions. Analogous comparisons were made using field data from a grassland site in California during the dry summer period when plants had senesced. To confirm that solar irradiance contributed to CO₂ effluxes from terrestrial OM, short incubations of OM in a small transparent flow-through chamber system (referred to as the “container”) were conducted. The container was also used to study the controls of photodegradation including the effects of irradiance intensity, wavelength and substrate species. On hot summer days, irradiance-induced CO₂ fluxes accounted for up to 58% and 90% of the total mid-day CO₂ flux at the peatland and grassland, respectively. Annual CO₂ production at the peatland was estimated to be 269 g C m-², of which 20% was due to photodegradation. At the grassland during the dry season (~3 months), approximately 27 g C m-² was lost as CO₂, of which 60% was due to photodegradation. Irradiance-induced CO₂ fluxes measured both in the field and in the container showed a very strong relationship with the intensity of solar irradiance. Higher fluxes were observed at greater temperatures, but temperature effects could not be separated from irradiance effects. Field data suggested that the dose response coefficient (=moles of CO₂ produced per unit of energy of incoming solar irradiance) did not differ between wet and dry conditions at the peatland. Per unit of energy, peat produced more CO₂ than grass litter in both the field and the container. Container measurements indicated the irradiance in the UV wavelength band was responsible for 14 % of the total irradiance-induced CO₂ flux. Per unit of energy, approximately 5 times as much CO₂ was produced in the field compared to the container fluxes. The causes for this difference are not known, and this observation highlighted the importance of conducting ecosystem-scale field experiments in addition to small-scale controlled experiments. The rate of CO₂ loss at the peatland resulting from microbial respiration was primarily controlled by the position of the water table, which in turn determined the thickness of the aerated peat layer. Greatest losses were observed in summer, when the water table was low and peat temperatures relatively high. Simple models previously applied in northern hemisphere peatlands predicted up to 86% of the variation in the observed daily averaged CO₂ fluxes based on peat temperature and depth to water table. The models were less successful at explaining the within-day variation of the CO₂ flux. To explain the complex variation in CO₂ fluxes at the within-day time scale, or if modelling is intended to increase understanding of the underlying processes of soil respiration, mechanistic models describing both CO₂ production at various depths and diffusion of CO₂ to the peat surface might be more appropriate. Carbon dioxide losses due to abiotic processes like photodegradation have generally been ignored in ecosystem-scale carbon exchange studies and models. The results of this study strongly suggest that this process should not be ignored for a variety of ecosystems where OM is exposed to high levels of solar irradiance for extended periods of time. The role of photodegradation in assisting microbial decomposition of complex OM is also poorly understood. To obtain reliable estimates of carbon cycling component fluxes, the contribution of photodegradation to OM decomposition and CO₂ losses should be quantified across a wide range of other ecosystems and the process should be incorporated into global carbon cycling models.

text: Carbon dioxide losses from terrestrial organic matter resulting from photodegradation and microbial respiration Losses of soil organic matter (SOM) can lead to a decrease in soil quality, cause an increase in CO₂ emissions, thereby contributing to a rise in atmospheric CO₂ concentration, which in turn can affect the global climate. Microbial decomposition of SOM to CO₂ is one of the main processes by which SOM is lost. Breakdown of organic matter (OM) by solar irradiance (called “photodegradation”) can also contribute to decomposition, especially in dry ecosystems. Photodegradation has been studied in the field by measuring the mass loss of litter, but its contribution to CO₂ losses has not previously been determined at spatial and temporal scales appropriate for ecosystems. The main aim of this research was to examine the magnitude and drivers of the CO₂ efflux from terrestrial organic matter resulting from both microbial decomposition and photodegradation. Carbon dioxide fluxes were measured at a bare peatland in New Zealand using eddy covariance (EC) and a closed chamber. The EC system measured the total CO₂ flux, whereas the chamber only measured the biological component of the CO₂ flux. The abiotic irradiance-induced component of the CO₂ flux was obtained by subtracting the chamber flux from the EC flux, and by comparing day-and night-time EC measurements made under similar temperature and moisture conditions. Analogous comparisons were made using field data from a grassland site in California during the dry summer period when plants had senesced. To confirm that solar irradiance contributed to CO₂ effluxes from terrestrial OM, short incubations of OM in a small transparent flow-through chamber system (referred to as the “container”) were conducted. The container was also used to study the controls of photodegradation including the effects of irradiance intensity, wavelength and substrate species. On hot summer days, irradiance-induced CO₂ fluxes accounted for up to 58% and 90% of the total mid-day CO₂ flux at the peatland and grassland, respectively. Annual CO₂ production at the peatland was estimated to be 269 g C m-², of which 20% was due to photodegradation. At the grassland during the dry season (~3 months), approximately 27 g C m-² was lost as CO₂, of which 60% was due to photodegradation. Irradiance-induced CO₂ fluxes measured both in the field and in the container showed a very strong relationship with the intensity of solar irradiance. Higher fluxes were observed at greater temperatures, but temperature effects could not be separated from irradiance effects. Field data suggested that the dose response coefficient (=moles of CO₂ produced per unit of energy of incoming solar irradiance) did not differ between wet and dry conditions at the peatland. Per unit of energy, peat produced more CO₂ than grass litter in both the field and the container. Container measurements indicated the irradiance in the UV wavelength band was responsible for 14 % of the total irradiance-induced CO₂ flux. Per unit of energy, approximately 5 times as much CO₂ was produced in the field compared to the container fluxes. The causes for this difference are not known, and this observation highlighted the importance of conducting ecosystem-scale field experiments in addition to small-scale controlled experiments. The rate of CO₂ loss at the peatland resulting from microbial respiration was primarily controlled by the position of the water table, which in turn determined the thickness of the aerated peat layer. Greatest losses were observed in summer, when the water table was low and peat temperatures relatively high. Simple models previously applied in northern hemisphere peatlands predicted up to 86% of the variation in the observed daily averaged CO₂ fluxes based on peat temperature and depth to water table. The models were less successful at explaining the within-day variation of the CO₂ flux. To explain the complex variation in CO₂ fluxes at the within-day time scale, or if modelling is intended to increase understanding of the underlying processes of soil respiration, mechanistic models describing both CO₂ production at various depths and diffusion of CO₂ to the peat surface might be more appropriate. Carbon dioxide losses due to abiotic processes like photodegradation have generally been ignored in ecosystem-scale carbon exchange studies and models. The results of this study strongly suggest that this process should not be ignored for a variety of ecosystems where OM is exposed to high levels of solar irradiance for extended periods of time. The role of photodegradation in assisting microbial decomposition of complex OM is also poorly understood. To obtain reliable estimates of carbon cycling component fluxes, the contribution of photodegradation to OM decomposition and CO₂ losses should be quantified across a wide range of other ecosystems and the process should be incorporated into global carbon cycling models.

year: 2010

title: “High 5!” Strategies to enhance comprehension of expository text

authors: Dymock, Susan

subjects: education

abstract: This article reviews theoretical and research evidence to support the explicit and systematic teaching of five comprehension strategies that will help all students tackle expository texts with success. The article explains the “High 5!” strategies and how to teach them. An example of a lesson is included to show how the five strategies connect with students' background knowledge to enhance comprehension.

text: “High 5!” Strategies to enhance comprehension of expository text This article reviews theoretical and research evidence to support the explicit and systematic teaching of five comprehension strategies that will help all students tackle expository texts with success. The article explains the “High 5!” strategies and how to teach them. An example of a lesson is included to show how the five strategies connect with students' background knowledge to enhance comprehension.

year: 2010

title: "Ko au te whenua, ko te whenua ko au:" A Māori housing development process

authors: Fletcher, Marcus Anzac Kewene

subjects: Māori

abstract: Tangata whenua (People of the land/Indigenous people of Aotearoa) are being recognised as emerging property and land developers in Aotearoa New Zealand (hereafter, Aotearoa). Literature and practice demonstrates how Māori are developing housing in different ways than traditional developers, supporting the wellbeing of whānau (families), hapū (sub-tribes) and iwi (tribes), while contributing to addressing the national housing crisis. The distinctiveness of these approaches are important to understand if we want to deepen our knowledge of urban development and the modelling of housing markets in Aotearoa. This thesis aims to reveal, codify and examine Māori decision-making processes relating to how and why we develop housing in Aotearoa and the values and principles that inform these approaches. Utilising Kaupapa Māori Theory and taking an insider/whānaunga (relatives) approach to the research, four whakawhiti kōrero sessions with Waikato whānau and kaimahi (workers) were undertaken to better understand how and why Māori develop housing and the processes and rationalities at play. The thesis has three contributions for academia, environmental planning and the housing sector in Aotearoa: insights into the values and rationalities that influence Māori urban development; the introduction of a Māori housing development framework; and insights into how the framework may be utilised to contribute towards more accurate and sophisticated agent-based modelling (ABM) or urban growth modelling.  

The findings and discussion identified six prominent values that Māori utilise to develop housing: kaitiakitanga, manaakitanga, orangatanga, whānaungatanga, ūkaipōtanga and rangatiratanga. Being rooted in Māori knowledge and epistemology essentially demands differing rationalities for when Māori undertake housing development, which are placed within an overarching framework. The framework represents a new tool to disrupt the current understanding of ‘developers’ as a single entity with a defined pathway that influences all development behaviour. Moreover, it demonstrates how whānau, hapū and iwi draw on the established learning and guidance of our tūpuna (ancestors) and the strides taken to reclaim tino rangatiratanga (self-determination). The thesis argues that academics, environmental practitioners and the housing sector should re-examine their understanding of developers in Aotearoa to become more pluralistic, which may present new challenges and opportunities for ABM and urban growth modelling. This framework argues some aspects may have potential to be incorporated into these technical analyses, while other aspects should be considered in the context of Māori and Indigenous Data Sovereignty to protect the contributions and mana of the participants within this thesis, or resist the ability to be captured altogether.

text: "Ko au te whenua, ko te whenua ko au:" A Māori housing development process Tangata whenua (People of the land/Indigenous people of Aotearoa) are being recognised as emerging property and land developers in Aotearoa New Zealand (hereafter, Aotearoa). Literature and practice demonstrates how Māori are developing housing in different ways than traditional developers, supporting the wellbeing of whānau (families), hapū (sub-tribes) and iwi (tribes), while contributing to addressing the national housing crisis. The distinctiveness of these approaches are important to understand if we want to deepen our knowledge of urban development and the modelling of housing markets in Aotearoa. This thesis aims to reveal, codify and examine Māori decision-making processes relating to how and why we develop housing in Aotearoa and the values and principles that inform these approaches. Utilising Kaupapa Māori Theory and taking an insider/whānaunga (relatives) approach to the research, four whakawhiti kōrero sessions with Waikato whānau and kaimahi (workers) were undertaken to better understand how and why Māori develop housing and the processes and rationalities at play. The thesis has three contributions for academia, environmental planning and the housing sector in Aotearoa: insights into the values and rationalities that influence Māori urban development; the introduction of a Māori housing development framework; and insights into how the framework may be utilised to contribute towards more accurate and sophisticated agent-based modelling (ABM) or urban growth modelling.  

The findings and discussion identified six prominent values that Māori utilise to develop housing: kaitiakitanga, manaakitanga, orangatanga, whānaungatanga, ūkaipōtanga and rangatiratanga. Being rooted in Māori knowledge and epistemology essentially demands differing rationalities for when Māori undertake housing development, which are placed within an overarching framework. The framework represents a new tool to disrupt the current understanding of ‘developers’ as a single entity with a defined pathway that influences all development behaviour. Moreover, it demonstrates how whānau, hapū and iwi draw on the established learning and guidance of our tūpuna (ancestors) and the strides taken to reclaim tino rangatiratanga (self-determination). The thesis argues that academics, environmental practitioners and the housing sector should re-examine their understanding of developers in Aotearoa to become more pluralistic, which may present new challenges and opportunities for ABM and urban growth modelling. This framework argues some aspects may have potential to be incorporated into these technical analyses, while other aspects should be considered in the context of Māori and Indigenous Data Sovereignty to protect the contributions and mana of the participants within this thesis, or resist the ability to be captured altogether.

year: 2025