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 development and taste of fruit of gold kiwifruit (Actinidia chinensis Planch. Var. chinensis "Gold3")

authors: Le Lievre, Danielle Evelyn

abstract: The “Gold3” cultivar of kiwifruit (Actinidia chinensis Planch. var. chinensis “Gold3”) has proven to be capable of producing high yields, however, growers have also noted an increased risk of small fruit that have high acidity, low dry matter and poor flavour. This thesis investigated how fruit composition and flavour components develop in “Gold3” kiwifruit, and whether altering the carbohydrate supply using common orchard practises would influence the accumulation and partitioning of the flavour components (starch, sugars and acids) in fruit.
Fruit from a “Gold3” orchard were sampled fortnightly, from anthesis through to harvest, from canes receiving five treatment combinations of leaf or fruit thinning and girdling. These treatments increased or decreased carbohydrate supply, either early or late in fruit development. 
Overall, the “Gold3” fruit demonstrated similar patterns of starch, sugar and acid accumulation to other A. chinensis cultivars, in particular the gold kiwifruit cultivar “Hort16A”, with slight differences in timings and peak concentrations. An altered carbohydrate supply to developing fruit strongly influenced their composition in unique ways. As expected fresh weight growth and starch accumulation responded positively to a period of high carbohydrate supply. Regulation of organic acids were shown to be more complex, with the concentrations of some acids responding inversely to increased carbohydrate supply. At eating ripe the fruit from lower carbohydrate supply had altered sugar: acid ratios, with increased total acid concentrations, as well as decreased sugar concentrations. 
To identify how these compositional changes affected the taste of fruit at eating ripeness, a controlled consumer sensory experiment was carried out with 78 inexperienced consumers. Fruit from the different treatments were all perceived as having acceptable flavours, despite the fruit having significant differences in the standard flavour determinants (DM, rSSC and TA). Consumers were able to detect differences in sugar and acid concentrations between treatments. Low carbohydrate supply treatments had significantly higher TA, citric acid and quinic acid concentrations, combined with lower °Brix, DM and sucrose concentrations at eating ripe. Consumers more closely associated these fruit with being more acidic and having more sour and under-ripe flavours compared to the treatments that received increased carbohydrate supply.
Overall the results of the research support the hypothesis that “Gold3” kiwifruit are vulnerable to changes in composition due to changes in growing conditions, and that these changes influence flavour as perceived by consumers. These effects may be more pronounced in orchards where high crop loads, shading, or variation in leaf to fruit ratio between shoots create populations of even more carbon deficient fruit.

text: The development and taste of fruit of gold kiwifruit (Actinidia chinensis Planch. Var. chinensis "Gold3") The “Gold3” cultivar of kiwifruit (Actinidia chinensis Planch. var. chinensis “Gold3”) has proven to be capable of producing high yields, however, growers have also noted an increased risk of small fruit that have high acidity, low dry matter and poor flavour. This thesis investigated how fruit composition and flavour components develop in “Gold3” kiwifruit, and whether altering the carbohydrate supply using common orchard practises would influence the accumulation and partitioning of the flavour components (starch, sugars and acids) in fruit.
Fruit from a “Gold3” orchard were sampled fortnightly, from anthesis through to harvest, from canes receiving five treatment combinations of leaf or fruit thinning and girdling. These treatments increased or decreased carbohydrate supply, either early or late in fruit development. 
Overall, the “Gold3” fruit demonstrated similar patterns of starch, sugar and acid accumulation to other A. chinensis cultivars, in particular the gold kiwifruit cultivar “Hort16A”, with slight differences in timings and peak concentrations. An altered carbohydrate supply to developing fruit strongly influenced their composition in unique ways. As expected fresh weight growth and starch accumulation responded positively to a period of high carbohydrate supply. Regulation of organic acids were shown to be more complex, with the concentrations of some acids responding inversely to increased carbohydrate supply. At eating ripe the fruit from lower carbohydrate supply had altered sugar: acid ratios, with increased total acid concentrations, as well as decreased sugar concentrations. 
To identify how these compositional changes affected the taste of fruit at eating ripeness, a controlled consumer sensory experiment was carried out with 78 inexperienced consumers. Fruit from the different treatments were all perceived as having acceptable flavours, despite the fruit having significant differences in the standard flavour determinants (DM, rSSC and TA). Consumers were able to detect differences in sugar and acid concentrations between treatments. Low carbohydrate supply treatments had significantly higher TA, citric acid and quinic acid concentrations, combined with lower °Brix, DM and sucrose concentrations at eating ripe. Consumers more closely associated these fruit with being more acidic and having more sour and under-ripe flavours compared to the treatments that received increased carbohydrate supply.
Overall the results of the research support the hypothesis that “Gold3” kiwifruit are vulnerable to changes in composition due to changes in growing conditions, and that these changes influence flavour as perceived by consumers. These effects may be more pronounced in orchards where high crop loads, shading, or variation in leaf to fruit ratio between shoots create populations of even more carbon deficient fruit.

year: 2017

title: Researching the Process of Auahi Kore for Marae

authors: Masters-Awatere, Bridgette

abstract: • The current report is piece of a qualitative research exploring issues relating the development of Marae Auahi Kore. Such aspects as; factors that aid or impede the process, resources available or required by marae, and people's perceptions of the Auahi Kore brand were explored.

• Interviews were conducted with people from a variety of backgrounds. Research participants included: Marae Trustees, Public Health Workers, Runanga Staff as well as Kaumatua and Kuia. These people were identified as key informants for the current project. A total of 25 people were interviewed during March and April using an open interview schedule.

• Exploration into the Smokefree policies of marae was not pursued within the current project as this was not the focus nor the intent of the research. Project constraints such as time and budget meant there was a limit to what could be undertaken for the current piece of research.

text: Researching the Process of Auahi Kore for Marae • The current report is piece of a qualitative research exploring issues relating the development of Marae Auahi Kore. Such aspects as; factors that aid or impede the process, resources available or required by marae, and people's perceptions of the Auahi Kore brand were explored.

• Interviews were conducted with people from a variety of backgrounds. Research participants included: Marae Trustees, Public Health Workers, Runanga Staff as well as Kaumatua and Kuia. These people were identified as key informants for the current project. A total of 25 people were interviewed during March and April using an open interview schedule.

• Exploration into the Smokefree policies of marae was not pursued within the current project as this was not the focus nor the intent of the research. Project constraints such as time and budget meant there was a limit to what could be undertaken for the current piece of research.

year: 2000