title: The effects of urban forest restoration and environmental heterogeneity on microbial diversity and ecosystem functioning

authors: Mitchell, Grace

subjects: Restoration

abstract: Increasing global urbanisation poses extensive environmental threats, including the loss of biodiversity and associated ecosystem functions. Ecosystem restoration interventions like native plantings can assist in halting and reversing the degradation of forest patches in urban settings, which is particularly relevant for the United Nations’ decade of ecosystem restoration. While the benefits of restoration plantings for aboveground communities have been well established, belowground community responses remain understudied. It is assumed that the soil microbiome will self-assemble to a pre-disturbance state following restoration. However, as microorganisms are rarely the target of restoration interventions themselves, various questions remain regarding the extent to which microbial communities will respond and recover with aboveground plantings, and how environmental variability might influence trajectories of microbial community reassembly. In this thesis, I contribute to this knowledge gap by investigating the impacts of forest age since restoration alongside a suite of environmental covariates on microbial community responses. My fieldwork took place in a New Zealand-wide chronosequence of restored urban forest sites. I analysed the diversity and taxonomic composition of bacterial, archaeal, fungal, and protist communities from these soil samples using metabarcoding data in chapter 2. Furthermore, I investigated changes in total microbial biomass, bacterial and fungal taxonomic group biomass via PLFA, total basal respiration, the spatial variability of microbial biomass and respiration, and carbon metabolism on substrates of varying recalcitrance using MicroResp™ in chapter 3. My synthesised findings show that environmental variability is typically more explanatory of microbial responses than forest age alone. Plant community factors in particular—such as native woody seedling density and tree species richness—were most often linked with enhanced microbial diversity and respiration, as well as driving increased local spatial variability. Specific phylum-level shifts from metabarcoding data indicated microbiome recovery on a trajectory towards mature forest soil communities, yet PLFA data showed that community composition does not yet reflect fungal dominance as would be expected in a mature or fully recovered forest soil. This thesis provides a holistic assessment of microbial community responses to urban forest restoration interventions, by assessing both diversity and microbial functions at multiple taxonomic resolutions. In conclusion, results from my thesis highlight the importance of taking into account the recovery of the soil microbiome and its associated ecosystem functioning to improve both aboveground and belowground success in future forest restoration projects.

text: The effects of urban forest restoration and environmental heterogeneity on microbial diversity and ecosystem functioning Increasing global urbanisation poses extensive environmental threats, including the loss of biodiversity and associated ecosystem functions. Ecosystem restoration interventions like native plantings can assist in halting and reversing the degradation of forest patches in urban settings, which is particularly relevant for the United Nations’ decade of ecosystem restoration. While the benefits of restoration plantings for aboveground communities have been well established, belowground community responses remain understudied. It is assumed that the soil microbiome will self-assemble to a pre-disturbance state following restoration. However, as microorganisms are rarely the target of restoration interventions themselves, various questions remain regarding the extent to which microbial communities will respond and recover with aboveground plantings, and how environmental variability might influence trajectories of microbial community reassembly. In this thesis, I contribute to this knowledge gap by investigating the impacts of forest age since restoration alongside a suite of environmental covariates on microbial community responses. My fieldwork took place in a New Zealand-wide chronosequence of restored urban forest sites. I analysed the diversity and taxonomic composition of bacterial, archaeal, fungal, and protist communities from these soil samples using metabarcoding data in chapter 2. Furthermore, I investigated changes in total microbial biomass, bacterial and fungal taxonomic group biomass via PLFA, total basal respiration, the spatial variability of microbial biomass and respiration, and carbon metabolism on substrates of varying recalcitrance using MicroResp™ in chapter 3. My synthesised findings show that environmental variability is typically more explanatory of microbial responses than forest age alone. Plant community factors in particular—such as native woody seedling density and tree species richness—were most often linked with enhanced microbial diversity and respiration, as well as driving increased local spatial variability. Specific phylum-level shifts from metabarcoding data indicated microbiome recovery on a trajectory towards mature forest soil communities, yet PLFA data showed that community composition does not yet reflect fungal dominance as would be expected in a mature or fully recovered forest soil. This thesis provides a holistic assessment of microbial community responses to urban forest restoration interventions, by assessing both diversity and microbial functions at multiple taxonomic resolutions. In conclusion, results from my thesis highlight the importance of taking into account the recovery of the soil microbiome and its associated ecosystem functioning to improve both aboveground and belowground success in future forest restoration projects.

year: 2022

title: Development of an Intraruminal Controlled-Release Device

authors: McLellan, Bradley John

subjects: gas-producing cell

abstract: Slow-release devices retained in the rumen, are a simple method for continuous administration of bioactives to ruminant animals.  To satisfy regulatory requirements and avoid waste of bioactive due to under- or over-dosing, it is advantageous to have a constant and predictable release rate.  Existing intraruminal controlled-release technologies cannot easily be adapted for different bioactives or rates of release and can be influenced by the variable physiological environment in the rumen.  Some existing commercial products use the pressure generated by a hydrogen gas-producing cell to extrude fluids from a syringe-like device.  This technology may provide advantages for ruminal controlled-release as the gas production rate is unaffected by environment in the rumen and can be easily adjusted using electrical resistance applied to the gas cell.  This technology was adapted for use in the rumen in these studies.
Initial experiments identified the need for greater understanding of the rate that hydrogen is produced by the gas cell and the rate that gas diffuses through the barrel walls.  Gas production rate was found to be inversely proportional to the resistance applied to the gas-producing cell.  Factors affecting gas diffusion rate from the device were studied and a polymer was identified that reduced hydrogen diffusion to 5% of that for the initial components used.  A relationship was developed to predict the release profile of a device.  Controlled-release devices were constructed from selected materials.  They released blank formulation at in vitro at a constant rate, which was within experimental variation of predicted values.  Release rates from the devices used in vivo were slightly higher than predicted.  The presence of rumen gases inside in vivo devices suggested that the difference may be due to inward diffusion of these gases; these may be eliminated by further study of barrel materials.  Recommendations on the redesign of this technology for use as a generic intraruminal delivery system are given.

text: Development of an Intraruminal Controlled-Release Device Slow-release devices retained in the rumen, are a simple method for continuous administration of bioactives to ruminant animals.  To satisfy regulatory requirements and avoid waste of bioactive due to under- or over-dosing, it is advantageous to have a constant and predictable release rate.  Existing intraruminal controlled-release technologies cannot easily be adapted for different bioactives or rates of release and can be influenced by the variable physiological environment in the rumen.  Some existing commercial products use the pressure generated by a hydrogen gas-producing cell to extrude fluids from a syringe-like device.  This technology may provide advantages for ruminal controlled-release as the gas production rate is unaffected by environment in the rumen and can be easily adjusted using electrical resistance applied to the gas cell.  This technology was adapted for use in the rumen in these studies.
Initial experiments identified the need for greater understanding of the rate that hydrogen is produced by the gas cell and the rate that gas diffuses through the barrel walls.  Gas production rate was found to be inversely proportional to the resistance applied to the gas-producing cell.  Factors affecting gas diffusion rate from the device were studied and a polymer was identified that reduced hydrogen diffusion to 5% of that for the initial components used.  A relationship was developed to predict the release profile of a device.  Controlled-release devices were constructed from selected materials.  They released blank formulation at in vitro at a constant rate, which was within experimental variation of predicted values.  Release rates from the devices used in vivo were slightly higher than predicted.  The presence of rumen gases inside in vivo devices suggested that the difference may be due to inward diffusion of these gases; these may be eliminated by further study of barrel materials.  Recommendations on the redesign of this technology for use as a generic intraruminal delivery system are given.

year: 2007

title: Review: Memoirs of Active Service

authors: Cheesman, Sue

subjects: Maaka Pepene

abstract: Ka maumahara tonu tatou ki a ratou - we will remember them…poignant last words…   bidding farewell to a generation of veterans moving on...leaving fragments  of memories and diaries for children/grandchildren to honour, celebrate and remember …black costumes billow, fold, swirl and wrap the dancers bodies…wide sweeping arm movements…jumps and turns…slides on all fours - provides the vehicle for five accomplished dancers to fill the space with fluidity and lyricism in this very moving finale, a lament set to Albinoni’s adagio - maybe old soldiers never die.

text: Review: Memoirs of Active Service Ka maumahara tonu tatou ki a ratou - we will remember them…poignant last words…   bidding farewell to a generation of veterans moving on...leaving fragments  of memories and diaries for children/grandchildren to honour, celebrate and remember …black costumes billow, fold, swirl and wrap the dancers bodies…wide sweeping arm movements…jumps and turns…slides on all fours - provides the vehicle for five accomplished dancers to fill the space with fluidity and lyricism in this very moving finale, a lament set to Albinoni’s adagio - maybe old soldiers never die.

year: 2007