title: Measuring the temperature response of soil respiration from two distinct carbon pools in soil.

authors: Robinson, Jasmine May

subjects: Soil respiration

abstract: As soils contain a large store of terrestrial carbon, understanding the dynamics and stability of this important carbon reserve and how it may change with regards to future changes in temperature is of global interest. It is primarily understood that carbon exists in different pools within soil, but there is considerable debate around the number, size and contents of these pools. Despite this debate, when modelling carbon cycling, it can be erroneously assumed that the decomposition of carbon pools will behave the in the same way with regards to temperature and varying management practices. 

The first objective of this research was to develop and test a new protocol allowing the measurement of the temperature response of two distinct carbon pools in soil. A Horotiu silt loam was mixed with a ¹³C labelled rye-grass clover litter, and incubated for 5 and 20 hours at 30 discrete temperatures (~2 – 50 °C). Resulting CO₂ was separated into litter and soil organic carbon (SOC) sourced respiration rates using a mixing model, and then fit with macromolecular rate theory (MMRT). Litter-derived respiration had a lower temperature optimum (Tₒₚₜ) than SOC-derived respiration. It was suggested that decomposition of highly available labile litter is rate-limited by enzyme kinetics, which displays a clear temperature optimum. In contrast, decomposition of stable SOC is more limited by desorption processes and diffusion of carbon to microbes, prior to decomposition, and so exhibits Arrhenius behaviour as temperature increases. 

The second objective was to use the developed protocol to measure temperature response of respiration was measured for ¹³C-labelled new photosynthate carbon inputs and bulk SOC, partitioned from soils labelled under seasonal irrigated and dryland conditions. Additionally, mass litter inputs of both root and shoot material were incubated with unlabelled soil. Root and shoot litter inputs showed a similar response to temperature with a well-defined MMRT-like response (Tₒₚₜ of 45  °C and 38 °C respectively). In contrast to this, respiration from new photosynthate carbon and SOC had the same Arrhenius-like temperature response (Tₒₚₜ of 50 °C for dryland and 62 °C for irrigated soils). It was suggested that the new carbon inputs deposited through roots were rapidly incorporated into the soil and thus had a similar availability and temperature response as SOC. Consequently, carbon inputs through roots appear to be more stabilised than litter inputs (as either root or above ground fragments). Respiration from dryland soils had lower a Topt than respiration from irrigated soils, which diminished with the application of autumnal rainfall, most likely due to an increase in short-term turnover of carbon under irrigation. 

In a similar experiment, soils were labelled under constant conditions prior to the imposition of seasonal irrigation or dryland treatments. Again, there was no difference between the temperature response of new photosynthate carbon and SOC. Increases in short term carbon cycling caused greater respiration under irrigation compared to dryland soils. However, this increased respiration did not contribute to a noticeable change in temperature response. 

Overall this research demonstrated a reliable protocol for measuring the temperature response of two distinct carbon pools in soil. This approach can be used to examine the stability of new carbon inputs from different sources to soil. Future research using the developed methodology with different forms of 13C labelled carbon will expand knowledge on the temperature response of distinctive pools of carbon in soil, allowing continued improvement on carbon cycling modelling.

text: Measuring the temperature response of soil respiration from two distinct carbon pools in soil. As soils contain a large store of terrestrial carbon, understanding the dynamics and stability of this important carbon reserve and how it may change with regards to future changes in temperature is of global interest. It is primarily understood that carbon exists in different pools within soil, but there is considerable debate around the number, size and contents of these pools. Despite this debate, when modelling carbon cycling, it can be erroneously assumed that the decomposition of carbon pools will behave the in the same way with regards to temperature and varying management practices. 

The first objective of this research was to develop and test a new protocol allowing the measurement of the temperature response of two distinct carbon pools in soil. A Horotiu silt loam was mixed with a ¹³C labelled rye-grass clover litter, and incubated for 5 and 20 hours at 30 discrete temperatures (~2 – 50 °C). Resulting CO₂ was separated into litter and soil organic carbon (SOC) sourced respiration rates using a mixing model, and then fit with macromolecular rate theory (MMRT). Litter-derived respiration had a lower temperature optimum (Tₒₚₜ) than SOC-derived respiration. It was suggested that decomposition of highly available labile litter is rate-limited by enzyme kinetics, which displays a clear temperature optimum. In contrast, decomposition of stable SOC is more limited by desorption processes and diffusion of carbon to microbes, prior to decomposition, and so exhibits Arrhenius behaviour as temperature increases. 

The second objective was to use the developed protocol to measure temperature response of respiration was measured for ¹³C-labelled new photosynthate carbon inputs and bulk SOC, partitioned from soils labelled under seasonal irrigated and dryland conditions. Additionally, mass litter inputs of both root and shoot material were incubated with unlabelled soil. Root and shoot litter inputs showed a similar response to temperature with a well-defined MMRT-like response (Tₒₚₜ of 45  °C and 38 °C respectively). In contrast to this, respiration from new photosynthate carbon and SOC had the same Arrhenius-like temperature response (Tₒₚₜ of 50 °C for dryland and 62 °C for irrigated soils). It was suggested that the new carbon inputs deposited through roots were rapidly incorporated into the soil and thus had a similar availability and temperature response as SOC. Consequently, carbon inputs through roots appear to be more stabilised than litter inputs (as either root or above ground fragments). Respiration from dryland soils had lower a Topt than respiration from irrigated soils, which diminished with the application of autumnal rainfall, most likely due to an increase in short-term turnover of carbon under irrigation. 

In a similar experiment, soils were labelled under constant conditions prior to the imposition of seasonal irrigation or dryland treatments. Again, there was no difference between the temperature response of new photosynthate carbon and SOC. Increases in short term carbon cycling caused greater respiration under irrigation compared to dryland soils. However, this increased respiration did not contribute to a noticeable change in temperature response. 

Overall this research demonstrated a reliable protocol for measuring the temperature response of two distinct carbon pools in soil. This approach can be used to examine the stability of new carbon inputs from different sources to soil. Future research using the developed methodology with different forms of 13C labelled carbon will expand knowledge on the temperature response of distinctive pools of carbon in soil, allowing continued improvement on carbon cycling modelling.

year: 2020

title: The lithospheric geodynamics of plate boundary transpression in New Zealand: Initiating and emplacing subduction along the Hikurangi margin, and the tectonic evolution of the Alpine Fault system

authors: Furlong, Kevin P.

subjects: plate tectonics of New Zealand

abstract: In contrast to the normal ‘Wilson cycle’ sequence of subduction leading to continental collision and associated mountain building, the evolution of the New Zealand plate boundary in the Neogene reflects the converse—initially a period of continental convergence that is followed by the emplacement of subduction. Plate reconstructions allow us to place limits on the location and timing of the continental convergence and subduction zones and the migration of the transition between the two plate boundary regimes. Relative plate motions and reconstructions since the Early to Mid-Miocene require significant continental convergence in advance of the emplacement of the southward migrating Hikurangi subduction—a sequence of tectonism seen in the present plate boundary geography of Hikurangi subduction beneath North Island and convergence in the Southern Alps along the Alpine Fault. In contrast to a transition from subduction to continental convergence where the leading edge of the upper plate is relatively thin and deformable, the transition from a continental convergent regime, with its associated crustal and lithospheric thickening, to subduction of oceanic lithosphere requires substantial thinning (removal) of upper plate continental lithosphere to make room for the slab. The simple structure of the Wadati–Benioff zone seen in the present-day geometry of the subducting Pacific plate beneath North Island indicates that this lithospheric adjustment occurs quickly. Associated with this rapid lithospheric thinning is the development of a series of ephemeral basins, younging to the south, that straddle the migrating slab edge. Based on this association between localized vertical tectonics and slab emplacement, the tectonic history of these basins records the effects of lithospheric delamination driven by the southward migrating leading edge of the subducting Pacific slab. Although the New Zealand plate boundary is often described as simply two subduction zones linked by the transpressive Alpine Fault, in actuality the present is merely a snapshot view of an ongoing and complex evolution from convergence to subduction.

text: The lithospheric geodynamics of plate boundary transpression in New Zealand: Initiating and emplacing subduction along the Hikurangi margin, and the tectonic evolution of the Alpine Fault system In contrast to the normal ‘Wilson cycle’ sequence of subduction leading to continental collision and associated mountain building, the evolution of the New Zealand plate boundary in the Neogene reflects the converse—initially a period of continental convergence that is followed by the emplacement of subduction. Plate reconstructions allow us to place limits on the location and timing of the continental convergence and subduction zones and the migration of the transition between the two plate boundary regimes. Relative plate motions and reconstructions since the Early to Mid-Miocene require significant continental convergence in advance of the emplacement of the southward migrating Hikurangi subduction—a sequence of tectonism seen in the present plate boundary geography of Hikurangi subduction beneath North Island and convergence in the Southern Alps along the Alpine Fault. In contrast to a transition from subduction to continental convergence where the leading edge of the upper plate is relatively thin and deformable, the transition from a continental convergent regime, with its associated crustal and lithospheric thickening, to subduction of oceanic lithosphere requires substantial thinning (removal) of upper plate continental lithosphere to make room for the slab. The simple structure of the Wadati–Benioff zone seen in the present-day geometry of the subducting Pacific plate beneath North Island indicates that this lithospheric adjustment occurs quickly. Associated with this rapid lithospheric thinning is the development of a series of ephemeral basins, younging to the south, that straddle the migrating slab edge. Based on this association between localized vertical tectonics and slab emplacement, the tectonic history of these basins records the effects of lithospheric delamination driven by the southward migrating leading edge of the subducting Pacific slab. Although the New Zealand plate boundary is often described as simply two subduction zones linked by the transpressive Alpine Fault, in actuality the present is merely a snapshot view of an ongoing and complex evolution from convergence to subduction.

year: 2009

title: Co-opting or valuing the indigenous voice through translation? A decision for research teams

authors: Kidd, Jacquie

subjects: Māori

abstract: Although te reo Māori is an official language of Aotearoa New Zealand, translation of research material such as information sheets, consent forms and questionnaires into te reo Māori remains highly variable. Translation tends to occur in research projects where Māori lead the work and that exclusively focus on Māori communities and topics. Translations are not offered or undertaken as a matter of course for all research. As a team of Māori and Indigenous researchers working within the health sector, we believe that there are important questions that need to be explored around the practice of using Indigenous languages, rich in similes and metaphors, to convey English/Western concepts/constructs/ideologies. In this paper, we draw on the story of one project to deconstruct and challenge the hegemonic terms through which translation of research material occurs. We explore the messages that translated material sends to potential research participants.
We contend that the choice about whether to translate research material into te reo Māori is one that should be undertaken within a robust decision-making framework that considers the reasons for a translation and its impact on the participants. Translation should not be undertaken primarily to attract Māori participants, but should reliably signal that the research is being undertaken in a way that honours a Māori worldview.

text: Co-opting or valuing the indigenous voice through translation? A decision for research teams Although te reo Māori is an official language of Aotearoa New Zealand, translation of research material such as information sheets, consent forms and questionnaires into te reo Māori remains highly variable. Translation tends to occur in research projects where Māori lead the work and that exclusively focus on Māori communities and topics. Translations are not offered or undertaken as a matter of course for all research. As a team of Māori and Indigenous researchers working within the health sector, we believe that there are important questions that need to be explored around the practice of using Indigenous languages, rich in similes and metaphors, to convey English/Western concepts/constructs/ideologies. In this paper, we draw on the story of one project to deconstruct and challenge the hegemonic terms through which translation of research material occurs. We explore the messages that translated material sends to potential research participants.
We contend that the choice about whether to translate research material into te reo Māori is one that should be undertaken within a robust decision-making framework that considers the reasons for a translation and its impact on the participants. Translation should not be undertaken primarily to attract Māori participants, but should reliably signal that the research is being undertaken in a way that honours a Māori worldview.

year: 2019