title: 'Hass' avocado tree water use and the effects of water stress on fruit development

authors: Kaneko, Teruko

subjects: Hass

abstract: ‘Hass’ avocado tree water use and the effects of water deficits on fruit development were assessed in New Zealand from 2017 to 2019. 
Avocado tree water use was quantified by sap flow measurement and the soil water balance method at three sites in the main avocado growing regions of the Bay of Plenty, Whangarei, and the Far North, New Zealand, with consideration of local differences in climate and soil type, and variation in tree fruit load, leaf area, crown size and orchard shaded area. The results showed that all three sites had similar patterns of tree water use relative to reference evapotranspiration (ETₒ), regardless of differences in soil type, showing the highest tree water use in January at 2.7 mm d⁻¹ and the lowest in June at 1.2 to 1.4 mm d⁻¹. Crop coefficients (Kc) were provided for each site, and the three sites had similar Kc values throughout the year, as all three orchards were considered mature, with >75% orchard shaded area. However, fruit load influenced tree water use. At all three sites, the Kc values increased from light to heavy fruit load, therefore, Kc values should be adjusted for variation in fruit load. The relationship between orchard shaded area and Kc was also considered, to provide a method for estimating Kc for orchards differing in tree size and spacing. 
Irrigation requirements were assessed in more detail at the avocado orchard in the Bay of Plenty, investigating the effects of any water deficits resulting from a lack of irrigation on tree physiology and fruit growth. Rainfall at the study site was variable over the three years, but each summer there was a dry period without any rainfall for more than two weeks that resulted in a significant decrease in soil water content if avocado trees were not irrigated. Tree fruit load was highly variable between years and trees within years, and increasing fruit load caused decreasing individual fruit weight and dry matter content. However, in the year with the highest average fruit load, a dry period occurred during early fruit development, causing fruit weight at harvest in the non irrigated treatment to decrease by 26.4 g per fruit, independently of the effects of fruit load on fruit weight. The trees responded to dry conditions by reducing stomatal conductance (gₛ) by 20%, resulting in a constant leaf water potential (Ψₗₑₐբ) above  0.25 MPa. This finding suggests that irrigation is important for New Zealand avocado production because photosynthetic activity and fruit growth can be reduced by even mild water stress during a dry period. In the Bay of Plenty with allophanic soil, irrigation of avocado trees is recommended when soil water content decreases below 0.40 m³ m⁻³ (-30 kPa of soil tension) at a depth of 30 cm. Adverse effects on gs and fruit growth caused by water stress may appear when soil water content decreases below 0.35 m³ m⁻³ (-50 kPa of soil tension). 
To gain a better understanding of how water stress affects fruit development, an experiment was conducted on potted avocado trees in a glasshouse over the summer of 2018-19. Vascular water flows were monitored in the shoot stems and fruit pedicels with external sap flow gauges, while fruit growth was monitored continuously using linear transducers (LTs). The fruit water balance was modelled as the sum of fruit transpiration and inward and outward vascular flows, and compared with actual fruit diameter growth over time while a period of water stress followed by re-watering was imposed. The results showed that water flows in one direction through shoot stems from the parent stem to leaves, while flow occurred in both directions at different times of day through the fruit pedicels. Fruit size fluctuated in a response to water movement, but overall, avocado fruit increased in size by 1.4 (±0.09 S.E.) cm³ d⁻¹ under well watered conditions. However, under water-stressed conditions, the plants showed a clear response to water stress with a reduction in gₛ, photosynthetic net assimilation (A), and sap flow within shoot stems of 60-70%. Fruit water inflow was also decreased by 31% and the outflow from fruit to the parent stem was increased by 65% under water stressed conditions. As a result, the fruit growth rate decreased to 0.4 (±0.06) cm³ d⁻¹
. After the period of water stress was ended by re-watering, the fruit growth rate of the water-stressed treatment recovered quickly, and vascular flows and fruit volume growth exceeded that of the non-stressed treatment. Final fruit size did not differ between the two treatments in this experiment. Avocado fruit growth is sensitive to water stress because of direct effects of stress on vascular flows of water to the developing fruit, and potentially indirect effects of stress on photosynthesis and phloem flows, mediated by an isohydric stomatal response to water potential. Further research to investigate the interacting contributions of phloem and xylem flows to fruit growth in avocado is recommended.

text: 'Hass' avocado tree water use and the effects of water stress on fruit development ‘Hass’ avocado tree water use and the effects of water deficits on fruit development were assessed in New Zealand from 2017 to 2019. 
Avocado tree water use was quantified by sap flow measurement and the soil water balance method at three sites in the main avocado growing regions of the Bay of Plenty, Whangarei, and the Far North, New Zealand, with consideration of local differences in climate and soil type, and variation in tree fruit load, leaf area, crown size and orchard shaded area. The results showed that all three sites had similar patterns of tree water use relative to reference evapotranspiration (ETₒ), regardless of differences in soil type, showing the highest tree water use in January at 2.7 mm d⁻¹ and the lowest in June at 1.2 to 1.4 mm d⁻¹. Crop coefficients (Kc) were provided for each site, and the three sites had similar Kc values throughout the year, as all three orchards were considered mature, with >75% orchard shaded area. However, fruit load influenced tree water use. At all three sites, the Kc values increased from light to heavy fruit load, therefore, Kc values should be adjusted for variation in fruit load. The relationship between orchard shaded area and Kc was also considered, to provide a method for estimating Kc for orchards differing in tree size and spacing. 
Irrigation requirements were assessed in more detail at the avocado orchard in the Bay of Plenty, investigating the effects of any water deficits resulting from a lack of irrigation on tree physiology and fruit growth. Rainfall at the study site was variable over the three years, but each summer there was a dry period without any rainfall for more than two weeks that resulted in a significant decrease in soil water content if avocado trees were not irrigated. Tree fruit load was highly variable between years and trees within years, and increasing fruit load caused decreasing individual fruit weight and dry matter content. However, in the year with the highest average fruit load, a dry period occurred during early fruit development, causing fruit weight at harvest in the non irrigated treatment to decrease by 26.4 g per fruit, independently of the effects of fruit load on fruit weight. The trees responded to dry conditions by reducing stomatal conductance (gₛ) by 20%, resulting in a constant leaf water potential (Ψₗₑₐբ) above  0.25 MPa. This finding suggests that irrigation is important for New Zealand avocado production because photosynthetic activity and fruit growth can be reduced by even mild water stress during a dry period. In the Bay of Plenty with allophanic soil, irrigation of avocado trees is recommended when soil water content decreases below 0.40 m³ m⁻³ (-30 kPa of soil tension) at a depth of 30 cm. Adverse effects on gs and fruit growth caused by water stress may appear when soil water content decreases below 0.35 m³ m⁻³ (-50 kPa of soil tension). 
To gain a better understanding of how water stress affects fruit development, an experiment was conducted on potted avocado trees in a glasshouse over the summer of 2018-19. Vascular water flows were monitored in the shoot stems and fruit pedicels with external sap flow gauges, while fruit growth was monitored continuously using linear transducers (LTs). The fruit water balance was modelled as the sum of fruit transpiration and inward and outward vascular flows, and compared with actual fruit diameter growth over time while a period of water stress followed by re-watering was imposed. The results showed that water flows in one direction through shoot stems from the parent stem to leaves, while flow occurred in both directions at different times of day through the fruit pedicels. Fruit size fluctuated in a response to water movement, but overall, avocado fruit increased in size by 1.4 (±0.09 S.E.) cm³ d⁻¹ under well watered conditions. However, under water-stressed conditions, the plants showed a clear response to water stress with a reduction in gₛ, photosynthetic net assimilation (A), and sap flow within shoot stems of 60-70%. Fruit water inflow was also decreased by 31% and the outflow from fruit to the parent stem was increased by 65% under water stressed conditions. As a result, the fruit growth rate decreased to 0.4 (±0.06) cm³ d⁻¹
. After the period of water stress was ended by re-watering, the fruit growth rate of the water-stressed treatment recovered quickly, and vascular flows and fruit volume growth exceeded that of the non-stressed treatment. Final fruit size did not differ between the two treatments in this experiment. Avocado fruit growth is sensitive to water stress because of direct effects of stress on vascular flows of water to the developing fruit, and potentially indirect effects of stress on photosynthesis and phloem flows, mediated by an isohydric stomatal response to water potential. Further research to investigate the interacting contributions of phloem and xylem flows to fruit growth in avocado is recommended.

year: 2020

title: Sick of social media scrolling?  A behavioural intervention to reduce problematic social media use via smartphone device

authors: Moffat, Zaida

subjects: concurrent multiple baseline design

abstract: Excessive social media use can be problematic, with risks for individuals including compromised health and wellbeing and disruptions to work and personal relationships. Currently there is a lack of empirically supported treatments for reducing problematic social media use. Stinson and Dallery (2023) recently demonstrated the success of a behavioural intervention in reducing social media use with nine university students in Florida. I aimed to conduct an approximate replication of their intervention with university students in New Zealand. I initially administered a modified Internet Addiction Test to 148 participants. Of these, 38 qualified and three completed the behavioural intervention study. Social media use was tracked through the screen time function of each participant’s smartphone. Once a stable baseline was established, participants began an intervention phase. The intervention was contingency management with automated notifications and the selection of three alternative activities. Results of this intervention indicate success in the reduction of social media use for two of three participants. However, a lack of evidence to suggest any increase in the duration of time spent in chosen alternative activities replaced social media use. These results raise further questions regarding the effects of environmental changes on the strength of contingency management reinforcement for participants during this intervention. Identifying key variables in the reinforcement of contingency management that successfully reduces social media use for participants could be beneficial to many groups, particularly students who may use social media to escape academic demands.

text: Sick of social media scrolling?  A behavioural intervention to reduce problematic social media use via smartphone device Excessive social media use can be problematic, with risks for individuals including compromised health and wellbeing and disruptions to work and personal relationships. Currently there is a lack of empirically supported treatments for reducing problematic social media use. Stinson and Dallery (2023) recently demonstrated the success of a behavioural intervention in reducing social media use with nine university students in Florida. I aimed to conduct an approximate replication of their intervention with university students in New Zealand. I initially administered a modified Internet Addiction Test to 148 participants. Of these, 38 qualified and three completed the behavioural intervention study. Social media use was tracked through the screen time function of each participant’s smartphone. Once a stable baseline was established, participants began an intervention phase. The intervention was contingency management with automated notifications and the selection of three alternative activities. Results of this intervention indicate success in the reduction of social media use for two of three participants. However, a lack of evidence to suggest any increase in the duration of time spent in chosen alternative activities replaced social media use. These results raise further questions regarding the effects of environmental changes on the strength of contingency management reinforcement for participants during this intervention. Identifying key variables in the reinforcement of contingency management that successfully reduces social media use for participants could be beneficial to many groups, particularly students who may use social media to escape academic demands.

year: 2025

title: Upoko Tapu, Upoko Whakakapowai, Upoko Hokona

authors: Gabel, Robert Rutene Whakaangi

subjects: Ngāpuhi

abstract: Ngāpuhi, a confederation of Māori iwi (tribes) from Te Tai Tokerau, the northern region of Aotearoa, is the largest iwi of New Zealand. They were one of the first iwi to come into contact with Europeans in the early 19th century. During this period of contact, particularly between the years 1820 – 1831, Ngāpuhi had a devastating impact on the history of Māori, as they amassed a fighting force of some two thousand warriors and acquired the use of European firearms. Ngāpuhi then circumnavigated the North Island, waging war on coastal and inland tribes with the purpose of avenging past defeats and losses suffered at the hands of their traditional enemies. This objective was ultimately achieved, but this period of war also saw the emergence of another key event in Māori history, the beginning of the trade in what we now call toi moko, which were used to trade with Europeans for muskets. 

Given that Māori have always regarded the head as the most tapu part of the human anatomy, this thesis investigates and explores what effect or influence tikanga and tapu had on this trade. It further studies some of the rationales which allowed Ngāpuhi to override that sacred tradition and move into the trade of toi moko. This thesis argues that Ngāpuhi did not desecrate tapu in the selling and trading of toi moko but took advantage of another long-standing tradition that the tapu of the vanquished ceased to exist upon his death. Lastly, it argues that the trade in toi moko was necessary to ensure the safety and continuity of the Ngāpuhi iwi.

text: Upoko Tapu, Upoko Whakakapowai, Upoko Hokona Ngāpuhi, a confederation of Māori iwi (tribes) from Te Tai Tokerau, the northern region of Aotearoa, is the largest iwi of New Zealand. They were one of the first iwi to come into contact with Europeans in the early 19th century. During this period of contact, particularly between the years 1820 – 1831, Ngāpuhi had a devastating impact on the history of Māori, as they amassed a fighting force of some two thousand warriors and acquired the use of European firearms. Ngāpuhi then circumnavigated the North Island, waging war on coastal and inland tribes with the purpose of avenging past defeats and losses suffered at the hands of their traditional enemies. This objective was ultimately achieved, but this period of war also saw the emergence of another key event in Māori history, the beginning of the trade in what we now call toi moko, which were used to trade with Europeans for muskets. 

Given that Māori have always regarded the head as the most tapu part of the human anatomy, this thesis investigates and explores what effect or influence tikanga and tapu had on this trade. It further studies some of the rationales which allowed Ngāpuhi to override that sacred tradition and move into the trade of toi moko. This thesis argues that Ngāpuhi did not desecrate tapu in the selling and trading of toi moko but took advantage of another long-standing tradition that the tapu of the vanquished ceased to exist upon his death. Lastly, it argues that the trade in toi moko was necessary to ensure the safety and continuity of the Ngāpuhi iwi.

year: 2012