Massey Documents by Type
Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294
Browse
6 results
Search Results
Item Redox-induced phosphorus release from critical source areas following rainfall events in New Zealand(Elsevier Ltd, United Kingdom, 2025-02) Palihakkara J; Burkitt L; Jeyakumar P; Attanayake CPCritical source areas (CSAs) can act as a source of phosphorus (P) during intermittent rainfall events and contribute to dissolved P loss via runoff. Dissolved forms of P are readily accessible for plant and algal uptake; hence it is a concern in terms of the eutrophication of freshwater bodies. The potential of CSAs to release dissolved P to surface runoff upon intermittent short-term submergence caused by different rainfall events has not been studied at a field-scale in New Zealand previously. A field study was conducted to investigate the potential of two different pastoral soil CSAs (Recent and Pallic soil) to release soil P over five rainfall events during winter and to explore the mechanisms of P release in these soils. Ten sampling stations were installed within each CSA in an area of 6 × 2 m2. Each sampling station had two porewater samplers installed at two depths (2 and 10 cm) below the soil surface. Two platinum half-cell electrodes were installed at the same two depths. Porewater and floodwater samples were collected following five rainfall events. Redox potentials were measured in-situ. Dissolved reactive phosphorus (DRP), pH, dissolved organic carbon, cations, anions, and alkalinity of the water samples were measured. Soil chemical P fractions were assessed at the beginning, middle and end of the experiment. Thermodynamic modelling was used to infer dissolution and formation of P and P-associated minerals. The average porewater DRP at the two depths during the rainfall events of the Recent and Pallic soils were 0.32-1.3 mg L-1 and 0.26-2.31 mg L-1, respectively. The average floodwater DRP concentrations of the Recent and Pallic soils were 35 and 43-fold higher than the target DRP concentration (0.01 mg L-1) for the Manawatū River. The study highlights the substantial risk of P loss from CSAs to surface water, driven primarily by the reductive dissolution of Fe and Mn oxy(hydr)oxides. The findings underscore the importance of targeted management strategies to mitigate dissolved P runoff, particularly in high-risk CSAs frequent submerged during rainfall events. This study developed an effective method for monitoring soil porewater P and redox conditions, offering valuable insights and practical tools for resource managers seeking to reduce P contamination.Item Requirement of digestible calcium at different dietary concentrations of digestible phosphorus for broiler chickens 3. Broiler finishers (d 25 to 35 post-hatch)(y Elsevier Inc (USA), on behalf of Poultry Science Association Inc, 2023-04) David LS; Abdollahi MR; Bedford MR; Ravindran VAn experiment was conducted to determine the digestible calcium (Ca) and digestible phosphorous (P) requirements of 25 to 35-day-old broiler chickens. Fifteen corn-soybean meal-based diets containing 2.0, 2.5, 3.0, 3.5, and 4.0 g/kg standardized ileal digestible (SID) Ca and 2.5, 3.5, and 4.5 g/kg SID P were fed to broilers from d 25 to 35 post-hatch. Each experimental diet was randomly allocated to 6 replicate cages (8 birds per cage). Body weight and feed intake were recorded, and the feed conversion ratio was calculated. On d 35, birds were euthanized to collect the ileal digesta, tibia, and carcass for the determination of ileal Ca, and P digestibility, concentrations of ash, Ca, and P in tibia and the retention of Ca and P in the carcass. Titanium dioxide (5.0 g/kg) was included in all diets as an indigestible indicator for the ileal digestibility measurement. Feed intake and total excreta output were measured during the last 4 d of the experimental period for the measurement of apparent total tract retention of Ca and P. Fixed effects of the experiment were dietary concentrations of SID Ca and SID P and their interaction. If the interaction or main effects were significant (P < 0.05), the parameter estimates for second-order response surface model (RSM) were determined using General Linear Model procedure of SAS. The maximum response was not predicted for most of the parameters (including growth performance and tibia) as the Ca effect was linear which indicated that the highest level of Ca employed in the study may have not been high enough. The requirement of dietary SID Ca for maximization of these parameters, therefore, depends on the dietary SID P concentration when the dietary SID Ca is within 2.0 to 4.0 g/kg. However, based on the factorial analysis, the highest weight gain was observed at 3.5 g/kg SID P and 3.5 g/kg SID Ca concentrations. Tibia ash was higher in birds fed 4.5 g/kg SID P and was unaffected by dietary SID Ca concentrations. However, based on overall findings, a combination of 3.5 g/kg SID P and 3.0-3.5 g/kg SID Ca may be recommended for the optimum tibia ash. The recommended SID Ca requirements (at 3.5 g/kg SID P) for weight gain (3.5 g/kg or 6.4 g/kg total Ca) and tibia ash (3.0-3.5 g/kg or 5.5-6.4 g/kg total Ca) are lower than the current Ca recommendations (7.8 g/kg total Ca equivalent to 4.25 g/kg SID Ca; Ross, 2019) for broiler finishers, suggesting possible excess of Ca in diets formulated based on the current recommendation.Item Requirement of digestible calcium at different dietary concentrations of digestible phosphorus for broiler chickens. 2. Broiler growers (d 11 to 24 post-hatch)(Elsevier Inc. on behalf of Poultry Science Association Inc., 2022-11) David LS; Abdollahi MR; Bedford MR; Ravindran VAn experiment was conducted to determine the digestible calcium (Ca) and digestible phosphorous (P) requirements of 11 to 24 d old broiler chickens. Eighteen corn-soybean meal-based diets containing 1.80, 2.35, 2.90, 3.45, 4.00, and 4.55 g/kg standardized ileal digestible (SID) Ca and 3.5, 4.5, and 5.5 g/kg SID P were fed to broilers from d 11 to 24. Each experimental diet was randomly allocated to six replicate cages (8 birds per cage). Body weight and feed amount were recorded at the start and end of the experiment and the feed conversion ratio was calculated. On d 24, birds were euthanized to collect ileal digesta, tibia, and carcass for the determination of digestible Ca and P, the concentration of ash, Ca and P in tibia and the retention of Ca and P in the carcass, respectively. Titanium dioxide (5 g/kg) was included in all diets as an indigestible indicator for apparent ileal digestibility measurement. Total excreta output was measured during the last 4 d of the experimental period for the measurement of apparent total tract retention of Ca and P. Fixed effects of the experiment were dietary concentrations of SID Ca and SID P and their interaction. If the interaction or main effect was significant (P < 0.05), the parameter estimate for second-order response surface model was determined using General Linear Model procedure of SAS. The weight gain of broiler growers was optimized at the SID P concentration of 3.5 g/kg and SID Ca concentrations between 2.35 and 4.00 g/kg. At 3.5 g/kg SID P concentration, the required SID Ca for maximum weight gain was determined to be 3.05 g/kg, which corresponded to SID Ca to SID P ratios of 0.87. The concentration of SID Ca that maximized tibia ash at 3.5 g/kg SID P was 3.69 g/kg, which corresponded to SID Ca to SID P ratio of 1.05. Maximizing bone ash requires more Ca than maximizing weight gain. Carcass Ca and P retention were reflective of total tract Ca and P retention values. The estimated SID Ca requirements (at 3.5 g/kg SID P) for both maximized weight gain (3.05 g/kg or 6.11 g/kg total Ca) and bone ash (3.69 g/kg or 7.28 g/kg total Ca) are lower than the current Ca recommendation (8.70 g/kg total Ca equivalent to 4.03 g/kg SID Ca; Ross, 2019) for broiler growers, indicating possible oversupply of Ca in diets formulated based on the current recommendation.Item Nutrient criteria to achieve New Zealand's riverine macroinvertebrate targets(PeerJ, Inc, 2021) Canning AD; Joy MK; Death RG; Brauns MWaterways worldwide are experiencing nutrient enrichment from population growth and intensive agriculture, and New Zealand is part of this global trend. Increasing fertilizer in New Zealand and intensive agriculture have driven substantial water quality declines over recent decades. A recent national directive has set environmental managers a range of riverine ecological targets, including three macroinvertebrate indicators, and requires nutrient criteria be set to support their achievement. To support these national aspirations, we use the minimization-of-mismatch analysis to derive potential nutrient criteria. Given that nutrient and macroinvertebrate monitoring often does not occur at the same sites, we compared nutrient criteria derived at sites where macroinvertebrates and nutrients are monitored concurrently with nutrient criteria derived at all macroinvertebrate monitoring sites and using modelled nutrients. To support all three macroinvertebrate targets, we suggest that suitable nutrient criteria would set median dissolved inorganic nitrogen concentrations at ~0.6 mg/L and median dissolved reactive phosphorus concentrations at ~0.02 mg/L. We recognize that deriving site-specific nutrient criteria requires the balancing of multiple values and consideration of multiple targets, and anticipate that criteria derived here will help and support these environmental goals.Item Effects of a novel consensus bacterial 6-phytase variant on the apparent ileal digestibility of amino acids, total tract phosphorus retention, and tibia ash in young broilers(Oxford University Press, 2022-02-01) Dersjant-Li Y; Abdollahi MR; Bello A; Waller K; Marchal L; Ravindran VThe effect of a novel consensus bacterial 6-phytase variant (PhyG) on apparent ileal digestibility (AID) of amino acids (AA) and phosphorus (P) utilization in young broilers when added to diets with high phytate-P (PP) content without added inorganic phosphate (Pi) and deficient in digestible (dig) AA and metabolizable energy (ME) was investigated. A total of 256 Ross 308 male broilers were assigned to 4 treatments (8 birds/cage, 8 cages/treatment) in a completely randomized design. Treatments comprised a positive control (PC, 2,975 kcal/kg ME, 3.7 g/kg dig P, 2.83 g/kg PP, 8.4 g/kg Ca, 10.6 g/kg dig lysine), a negative control (NC) without added Pi (ME −68 kcal/kg, crude protein −10 g/kg, dig AA −0.1 to −0.4 g/kg, Ca −2.0 g/kg, dig P −2.2 g/kg, Na −0.4 g/kg vs. PC), and NC plus 500 or 1,000 FTU/kg of PhyG. Test diets were corn/soy/rapeseed-meal/rice-bran-based and fed from 5 to 15 d of age. Ileal digesta and tibias were collected on day 15. Excreta was collected during days 12 to 15 to determine P retention. The NC (vs. PC) reduced (P < 0.05) P retention (−10.4% units), tibia ash (−14.3% units), weight gain (−109 g), feed intake (−82 g) and increased FCR (from 1.199 to 1.504), confirming that the NC was extremely deficient in nutrients and energy. Phytase addition to the NC linearly (P < 0.001) improved performance, but did not fully recover it to the level of the PC due to the severe nutrients/energy reduction in NC. Phytase linearly increased P retention (P < 0.001), tibia ash (P < 0.001), AID of dry matter (P < 0.05), nitrogen (P < 0.01), gross energy (P < 0.05), and all 17 individual AA (P < 0.01). At 1,000 FTU/kg, phytase increased (P < 0.05) P retention vs. PC and NC (+14.5 and +24.9% units, respectively) and increased tibia ash vs. NC (+13.8% units), equivalent to PC. The NC decreased AID of Cys, Gly, Thr, and Met vs. PC (P < 0.05). At 1,000 FTU/kg, phytase increased AID of all 17 AA vs. NC (P < 0.01), equivalent to PC. At 1,000 FTU/kg, AID AA responses (above NC) ranged from +4.5% (Met) to +15.0% (Cys), being maximal for essential Thr (+10.4%) and Val (+8.2%) and non-essential Cys (+15.0%) and Gly (+10.4%). The results highlight the efficacy of PhyG at a dose level of 500 to 1,000 FTU/kg in young broilers for improving the ileal digestibility of nitrogen, AA, and energy alongside P retention and tibia ash. The performance data emphasize the need to consider digestible nutrient intake as a response variable in exogenous enzyme studies.Item Environmental influences on polyphosphate accumulation in microalgae : an investigation into species differences and transcriptional responses : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering at Massey University, Manawatū, New Zealand(Massey University, 2022) Cliff, AlexanderMany species of microalgae can store phosphorus (P) as polyphosphate (polyP) granules during the process of ‘luxury uptake’, a term describing intracellular P accumulation above levels required for normal metabolism (0.2 – 1% P by dry weight). Environmental conditions can influence P luxury uptake but it is not known whether the effects of environmental conditions on luxury P uptake are the same for all microalgae or whether all microalgae can in fact store P as polyP. The broad aim of the work described in this thesis was to extend the current knowledge of polyphosphate (polyP) synthesis in microalgae, enabling improved exploitation of their ability to sequester P from water sources and enhance recovery of a vital nutrient. Specifically, the mechanisms by which environmental conditions influence luxury uptake and potential species differences need to be studied to better understand observations at the population level and make informed decisions in the design of treatment processes. The experimental work was therefore divided into two main objectives: Objective 1 sought to determine whether there were in fact differences in luxury uptake ‘abilities’ between species. In Chapter 3, this is explored through the use of genetic database searches, biochemical assays, and protein modelling. Objective 2 examined the effects of environmental factors known to influence luxury uptake. In Chapter 4, the responses of the microalgae Chlamydomonas reinhardtii and Chlorella vulgaris to P repletion were studied in a range of conditions to identify similarities and differences in environmental influences. Chapter 5 sought to determine whether the observed differences could be due to responses at the genetic level, by comparing the gene expression levels of P-related genes in C. reinhardtii under selected sets of conditions from the previous chapter. An additional experiment was conducted, to examine gene expression without inducing ‘noise’ through changes in growth conditions, and this is discussed in Chapter 6. Using protein sequence homology searches, phylogenetic tree generation, protein structure modelling, and biochemical assays (using the chlorophytes C. reinhardtii, C. vulgaris, Desmodesmus cf. armatus, Gonium pectorale, Pediastrum boryanum, and the cyanobacterium Microcystis aeruginosa), it was shown that the ability to store P as polyP is common among microalgae, as implied by the broad conservation of the polyP polymerase VTC4, but luxury uptake abilities vary between species. All six tested microalgae responded to P addition following a period of P depletion by accumulating P as granular polyP. Under the conditions tested, the total P assimilated over 24 hours was similar for five of the microalgae tested (2.6 – 3.6% P by dry weight) but C. vulgaris assimilated considerably less P (~1.2% P) than the others. The effects of environmental conditions on P uptake and polyP accumulation were assessed by triggering luxury uptake in C. vulgaris and C. reinhardtii in different conditions of light supply, temperature, and pH, with different P repletion doses following different P depletion times. P uptake and polyP accumulation were influenced by light supply, P depletion time, and P repletion dose in both microalgae but P dose had the strongest influence in C. reinhardtii versus light supply in C. vulgaris. PolyP was still accumulated by these two species in conditions suppressing growth and severely repressing metabolism (10 °C and darkness), evidencing that P uptake and polyP synthesis do not require light energy. The model alga C. reinhardtii was then used to evaluate, for the first time, whether the differences in P uptake and polyP accumulation observed with respect to differences in environmental conditions were associated with differences in gene expression. Although the genes assessed were downregulated (relative to controls) 24 hours after P repletion, as expected, in all experimental conditions, changing conditions at the start of the experiment also caused changes in gene expression in controls, making it hard to distinguish responses to P repletion from ‘global’ responses to changing conditions. Another experiment was therefore performed where temperature and light intensity were maintained constant before and after P repletion. The results confirmed that increased P repletion dose and P depletion time were associated with increased P uptake and polyP accumulation over 24 hours. The results evidenced the expected downregulation of PSR1, VTC4, VTCX, and PTB5 after 1 hour of P repletion, but this response was much more salient after 7 days of P depletion (compared to 3 days). Changes in gene expression were also associated with P repletion dose, but only after 7 days of P depletion. This showed that the response to P repletion is stronger after a longer P depletion time but the observed expression changes did not support the hypothesis that these changes were the reason for the higher observed P uptake and polyP accumulation. For the first time, it has been systematically shown that the ability to accumulate P as polyP is widespread among microalgae but that the kinetics of P accumulation vary between species and this species-dependence is influenced by environmental factors. These factors engender differences at the level of gene expression, involving both components of the VTC complex and phosphate transporters. However, the differences in P uptake and polyP accumulation may be better understood by investigating the structural differences and changes in activity of relevant proteins.