Nitrous oxide emissions from soil in mango and banana fields: effects of nitrogen rate, fertiliser type, and ground cover practices

Globally, agricultural soils are the dominant source of the greenhouse gas, nitrous oxide (N₂O), and a growing body of evidence indicates that soils in tropical zones may emit disproportionately large amounts to the atmosphere. This is important as N₂O contributes approximately 6% of anthropogenically induced global warming and is also responsible for ozone depletion. These emissions primarily originate from microbial nitrification and denitrification processes in soil, which are driven by soil water content, temperature, available nitrogen (N), organic carbon (OC) and their interactions. This study investigated the effects of N fertiliser application rate and type, and ground cover, on N₂O emissions from soil in mango and banana fields in tropical northern Australia. The fertiliser types were conventional urea and two enhanced efficiency fertilisers (EEFs): urea treated with a nitrification inhibitor (3, 4-dimethylpyrazole phosphate, DMPP) and polymer sulphur-coated (PC) urea mixed with standard urea at a 40/60 ratio (in mangoes only). Ground cover treatments were bare ground versus vegetative ground cover in bananas, and bare ground versus hay mulch in mangoes. A manual chamber technique was used to measure gas emissions from three field experiments with factorial designs (randomised block, four replications of each treatment). The experiments were conducted in 1) a commercial mango orchard on a Yellow Chromosol soil at Mutchilba, 2) a commercial banana farm on a Red Ferrosol soil at East Palmerston, and 3) a banana research farm on a Brown Dermosol soil at South Johnstone. In banana fields (Chapter 3), soil mineral N content, water content, and time since fertiliser application were the primary drivers of N₂O emissions. Low N rate treatments (12 kg N ha⁻¹ mth⁻¹) had consistently lower N₂O emissions than high N rates (18 to 54 kg N ha⁻¹ mth⁻¹), however overall N₂O flux was highest in all treatments when fertiliser was applied during persistently wet conditions (>68% water-filled pore space, WFPS). Urea treated with DMPP had approximately half the N₂O emissions than untreated urea on the Brown Dermosol, but did not significantly reduce emissions on the Red Ferrosol. Vegetative ground cover reduced N₂O emissions compared to bare soil during wet conditions and with higher N rates, presumably due to N uptake by the ground cover decreasing soil mineral N concentrations. In the mango orchard (Chapter 2), N₂O emissions were lower than under bananas at the other sites. The mango site soil had less mineral N, lower water holding capacity and lower OC content. N₂O emissions were not lowered by using EEFs rather than urea at application rates <25 kg N ha⁻¹. However, at a higher fertiliser application rate of 42 kg N ha⁻¹, DMPP approximately halved N₂O emissions. Mulching also lowered N₂O emissions, however sufficient irrigation after fertiliser application to mulch is recommended to reduce potential ammonia volatilisation. Overall, the management factors examined influenced soil mineral N, water content, temperature and possibly OC, all of which played important roles in determining total N₂O emissions in both crops. In banana fields, using lower N rates and DMPP treated urea during wet conditions will reduce N₂O losses. However, vegetative ground covers do not appear to be a reliable or consistent method of N₂O mitigation, as any reduction may be offset by the potential additional N required to compensate for plant competition and to avoid yield decline. In mangoes the most benefit would be gained from mulching, due to the reduction in N₂O and an increase in yield. However, further research is required to substantiate the N₂O reduction of hay mulch over the longer term. There appeared to be little justification for N₂O mitigation measures with EEFs in mangoes, due to generally negotiable N₂O emissions in the Yellow Chromosol, and the additional cost of EEFs. On the whole, more research is required around the mechanisms reducing the efficacy of DMPP-treated urea in Red Ferrosols and during hot conditions (35– 45°C). Finally, the PC urea product in this study needs to be tested in more suitable conditions that favour denitrification (higher N rate and soil water content) in order to more appropriately assess its impact on N₂O production

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Direct and indirect effects of Basta®, a glufosinate-based herbicide, on banana plantation soil microbial diversity and function

Herbicide applications have doubled over the past 30 years to control weeds, but their use may influence soil microbial communities, which mediate important ecosystem services. Here, we characterised the direct effects of a single application of Basta® (glufosinate), at 1× and 2× the recommended rate (5 and 10 kg product ha−1), as well as the indirect effects of vegetation loss on the diversity and function of soil microbial communities within a banana plantation. A 10-month pre-experimental period using Basta® to remove additional vegetation from half of the experimental area created conditions for assessing the indirect herbicide effects. Direct assessments on soil microbial communities began when the Basta® herbicide treatments were applied to the areas with and without vegetation and continued over multiple time-points, for 56 days. Herbicide treatment had no significant direct impacts on basal, and substrate induced respiration rates, or the potential activities of microbial enzymes as inferred from fluorescein diacetate hydrolysis (FDA) and β-glucosidase assays. Similarly, phylogenetic marker gene sequencing indicated that Basta® application did not significantly influence the diversity of soil bacterial or fungal communities. Indirectly, Basta® had a greater influence on the soil microbial activity and functions by removing understory vegetation cover around banana plants. This suggested that continual use of herbicides to reduce soil vegetation cover under bananas had a greater impact on soil microbial communities than a single application of the herbicide. Furthermore, the presence or absence of vegetation cover, significantly altered the abundance of Fusarium oxysporum, plus an additional eight bacterial and ten fungal taxa. Our results indicated that a single application of glufosinate as Basta® at the recommended or double the recommended rate, did not adversely affect soil microbial communities or their activities in banana plantations directly. However, application of herbicides, such as Basta® in crops like banana, indirectly alters soil microbial communities and their activities through loss of vegetation cover and should only be used as a component of an integrated weed management system

Bananas and mangoes: fertiliser and ground cover management to benefit production, soil and the environment

Bananas are the number one selling item in Australia's supermarkets, and had a farm-gate value of $600 million in 2014. Mangoes, another important crop for domestic markets and for export, had a farm-gate value of$140 million in 2014. In both industries, fertiliser management, especially nitrogen, is critical for production, but there is little information on optimum rates and application practices. Furthermore, there are concerns that current management practices negatively impact on soil health and the Great Barrier Reef due to losses of nutrients to the environment.\ud \ud Here we report on current grower participatory field evaluations of new fertiliser and ground cover management practices and their effects on crop productivity, soil condition (physical, chemical and biological) and greenhouse gas emissions. For bananas, current farmer nutrient management is being compared with a reduced nitrogen rate, with and without the nitrification inhibitor ENTEC® (3,4-dimethylpyrazole phosphate). For mangoes, current farmer nutrient management is being compared with ENTEC®-treated and polymer-coated nitrogen fertiliser, all at the same rate. In all cases the nitrogen fertiliser is urea.The ground cover treatments compare the dominant current practice (bare soil) with added mulch in mangoes or living ground cover in bananas. In the first season of the trials, growth of bananas did not differ significantly between the fertiliser treatments, although reduced nitrogen rate led to a reduction in leaf chlorophyll at bunch emergence. Living mulch did not reduce banana growth. Under mangoes, added mulch influenced the soil water balance and greenhouse gas emissions (N2O and CO2)

Nitrogen and carbon management in Australian mango orchards to improve productivity and reduce greenhouse gas emissions

Australian mango orchards, particularly of the 'Kensington Pride' cultivar, are often characterized by low yields and irregular bearing. Improved nutrition management techniques which increase total soil carbon sequestration and reduce nitrogen losses (nitrous oxide) may improve productivity and also reduce greenhouse gas emissions. A factorial trial was established in a 'Kensington Pride' mango orchard at Mareeba, Australia to assess the benefits of applying organic hay mulch to tree rows in combination with three nitrogen fertiliser treatments including two controlled-release fertiliser products. Three years after the initiation of treatments it was found that mango tree growth and fruit productivity was significantly improved when mulching was used to increase soil organic matter. Mulched soils had improved soil water holding capacity, less temperature variability, increased root biomass in the top soil, greater canopy leaf area and higher plant tissue potassium levels. Average fruit weights were increased by 10% and mango fruit yields per tree increased by 11%. Fruit quality was not affected when standard fungicide management treatments were used, although disease levels were higher with no post-harvest fungicide treatment. The nitrogen fertiliser products investigated did not have a significant influence on mango growth or final productivity. Trial results suggest that the adoption of mulching practices in mango orchards is a management practice which can increase orchard productivity and the sequestration of soil organic carbon, without detrimental effects on fruit quality

Cu 2 + -induced modification of the kinetics of A�(1-42)channels

We found that the amyloid β peptide Aβ(1-42) is capable of interacting with membrane and forming heterogeneous ion channels in the absence of any added Cu2+ or biological redox agents that have been reported to mediate Aβ(1-42) toxicity. The Aβ(1-42)

Dispersal of suspended sediments and nutrients in the Great Barrier Reef lagoon during river-discharge events: conclusions from satellite remote sensing and concurrent flood-plume sampling

Intense wet-season rainfall in January 2005 caused rivers in the Mackay–Whitsunday region of Queensland, Australia, to produce large discharges to the Great Barrier Reef (GBR) lagoon. The regional land use is dominated by sugarcane cultivation, beef grazing and urban uses. The high nutrient (nitrogen and phosphorus) fluxes from these land uses via river runoff produced a massive phytoplankton bloom in the GBR lagoon, which, after 9 days, had spread 150 km offshore. The plume and algal bloom surrounded inner-shelf reefs of the GBR such as Brampton Island Reef and its spread was tracked with a variety of satellite sensors including MODIS, SeaWiFS and Landsat over the 9-day period. The ability to be able to access imagery from a large number of satellite sensors allowed almost daily estimates of the extent of plume to be made, despite periods of cloud. Analysis of water samples from the plume revealed elevated (2–50 times higher) concentrations of Chlorophyll a (and hence phytoplankton biomass), up to 50 times higher than in non-flood conditions, nutrients (2–100 times higher) and herbicide residues (10–100 times higher) compared with GBR lagoon waters in non-discharge conditions. The concentration data from the samples and estimated exposure periods from the satellite images allowed estimates of the exposure of GBR marine ecosystems (coral reefs, the pelagic community, seagrass beds and mangrove forests) to the terrestrial contaminants to be made

Copper Modulation of Ion Channels of PrP[106-126] Mutant Prion Peptide Fragments

We have shown previously that the protease-resistant and neurotoxic prion peptide fragment PrP[106-126] of human PrP incorporates into lipid bilayer membranes to form heterogeneous ion channels, one of which is a Cu2+-sensitive fast cation channel. To investigate the role of PrP[106-126]'s hydrophobic core, AGAAAAGA, on its ability to form ion channels and their regulation with Cu2+, we used the lipid-bilayer technique to examine membrane currents induced as a result of PrP[106-126] (AA/SS) and PrP[106-126] (VVAA/SSSS) interaction with lipid membranes and channel formation. Channel analysis of the mutant (VVAAA/SSS), which has a reduced hydrophobicity due to substitution of hydrophobic residues with the hydrophilic serine residue, showed a significant change in channel activity, which reflects a decrease in the β-sheet structure, as shown by CD spectroscopy. One of the channels formed by the PrP[106-126] mutant has fast kinetics with three modes: burst, open and spike. The biophysical properties of this channel are similar to those of channels formed with other aggregation-prone amyloids, indicating their ability to form the common β sheet-based channel structure. The current-voltage (I-V) relationship of the fast cation channel, which had a reversal potential, Erev, between -40 and -10 mV, close to the equilibrium potential for K+ (EK = -35 mV), exhibited a sigmoidal shape. The value of the maximal slope conductance (gmax) was 58 pS at positive potentials between 0 and 140 mV. Cu2+ shifted the kinetics of the channel from being in the open and "burst" states to the spike mode. Cu2+ reduced the probability of the channel being open (Po) and the mean open time (To) and increased the channel's opening frequency (Fo) and the mean closed time (Tc) at a membrane potential (Vm) between +20 and +140 mV. The fact that Cu2+ induced changes in the kinetics of this channel with no changes in its conductance, indicates that Cu2+ binds at the mouth of the channel via a fast channel block mechanism. The Cu2+-induced changes in the kinetic parameters of this channel suggest that the hydrophobic core is not a ligand Cu2+ site, and they are in agreement with the suggestion that the Cu2+-binding site is located at M109 and H111 of this prion fragment. Although the data indicate that the hydrophobic core sequence plays a role in PrP[106-126] channel formation, it is not a binding site for Cu2+. We suggest that the role of the hydrophobic region in modulating PrP toxicity is to influence PrP assembly into neurotoxic channel conformations. Such conformations may underlie toxicity observed in prion diseases. We further suggest that the conversions of the normal cellular isoform of prion protein (PrPc) to abnormal scrapie isoform (PrPSc) and intermediates represent conversions to protease-resistant neurotoxic channel conformations

Herbicides: A new threat to the Great Barrier Reef

The runoff of pesticides (insecticides, herbicides and fungicides) from agricultural lands is a key concern for the health of the iconic Great Barrier Reef, Australia. Relatively low levels of herbicide residues can reduce the productivity of marine plants and corals. However, the risk of these residues to Great Barrier Reef ecosystems has been poorly quantified due to a lack of large-scale datasets. Here we present results of a study tracing pesticide residues from rivers and creeks in three catchment regions to the adjacent marine environment. Several pesticides (mainly herbicides) were detected in both freshwater and coastal marine waters and were attributed to specific land uses in the catchment. Elevated herbicide concentrations were particularly associated with sugar cane cultivation in the adjacent catchment. We demonstrate that herbicides reach the Great Barrier Reef lagoon and may disturb sensitive marine ecosystems already affected by other pressures such as climate change. Herbicide residues have been detected in Great Barrier Reef catchment waterways and river water plumes which may affect marine ecosystems