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Terrestrial particulate nutrients transported during flood events are known to indirectly fuel phytoplankton blooms in rivers, lakes and coastal waters, although the mechanisms are poorly understood. Quantifying the response of phytoplankton to nutrients in sediments eroded from catchments is fundamental to prioritizing areas for erosion control. This study developed a novel bioassay technique for rapidly assessing the effects of nutrients released from suspended sediments on the growth of marine and freshwater phytoplankton communities. A range of sediment slurries were placed in bioassay bottles within dialysis tubing in the presence of phytoplankton and their photosynthetic efficiency (F v /F m ) was measured over 72 h. This allowed an assessment of the effects of dissolved nutrients released from sediments without the confounding effects of suspended sediments. Chlorophyll a concentrations were also measured for comparison with F v /F m . Our study showed F v /F m was an effective method for measuring phytoplankton responses to sediment slurries. Photosynthetic efficiency was a more sensitive response metric than chlorophyll a . Applying the method to a range of suspended sediments from two tropical catchments in Australia that drain into Great Barrier Reef coastal waters, we identified a subset of sediment types (~40%) that increased F v /F m under the bioassay conditions. These sediments have the potential to stimulate marine and freshwater phytoplankton growth under the loads simulated in this study. The bioassay has the advantage of being a rapid and relatively simple method where a large number of sediments can be simultaneously tested for a phytoplankton response. To our knowledge this is the first time F v /F m has been used to assess phytoplankton responses to sediments in a bioassay. This approach advances the use of F v /F m as a sensitive indicator of phytoplankton responses to nutrients and could be used to develop indices of the relative risk various sediments pose, hence support decision making for erosion control measures. [ABSTRACT FROM AUTHOR]

Agriculture contributes more than a third of anthropogenic nitrous oxide (N 2 O) emissions globally. In New Zealand, land application of dairy shed effluent contributes to the 90% of N 2 O emitted from agricultural soils. Novel strategies are urgently required to mitigate N 2 O production to ensure New Zealand’s dairy-based economy is environmentally sustainable. Species of Myrtaceae, including Kunzea spp. (kānuka, white tea-tree) have previously been shown to produce antimicrobial compounds which extend to the soil. It is possible that these may inhibit the microbes involved in biological nitrification and denitrification which could thereby suppress N 2 O production. Therefore, in this work we aimed to test whether irrigation of effluents to stands of Kunzea spp. could minimize resulting N 2 O emissions. This study investigated soil inorganic N and N 2 O emissions following the application of dairy shed effluent to soil beneath 5-yr-old K. robusta compared with bare soil. Following effluent application, N 2 O emissions beneath K. robusta were reduced by 80% relative to bare soil, but nitrate-N was five-fold higher than bare soil, sufficiently available for denitrification. The drier, more aerated soil associated with K. robusta may have constrained denitrification. Application of DSE (50 kg N ha −1 ) to K. robusta produced 0.133 kg N 2 O–N ha −1 during the experimental period; equivalent to the lower range of emissions measured following comparable applications to grazed dairy pastures in New Zealand (0.13-1.08 kg N ha −1 ). The environmental benefits of reduced N 2 O emissions warrant further investigation on the effect of Myrtaceae on the soil N cycle worldwide. [ABSTRACT FROM AUTHOR]

Restoring woody vegetation to riparian zones helps to protect waterways from excessive sediment and nutrient inputs. However, the associated leaf litter can be a major source of dissolved organic matter (DOM) leached into surface waters. DOM can lead to the formation of disinfection by-products (DBPs) during drinking water treatment. This study investigated the DBPs formed during chlorination of DOM leached from leaf litter and assessed the potential toxicity of DBPs generated. We compared the leachate of two native Australian riparian trees, Casuarina cunninghamiana and Eucalyptus tereticornis , and a reservoir water source from a catchment dominated by Eucalyptus species. Leachates were diluted to dissolved organic carbon concentrations equivalent to the reservoir (~9 mg L−1). E. tereticornis leachates produced more trihalomethanes (THMs), haloacetic acids (HAAs), and haloketones after chlorination, while C. cunninghamiana produced more chloral hydrate and haloacetonitriles. Leachate from both species produced less THMs and more HAAs per mole of carbon than reservoir water. This may be because reservoir water had more aromatic, humic characteristics while leaf leachates had relatively more protein-like components. Using in vitro bioassays to test the mixture effects of all chemicals, chlorinated E. tereticornis leachate induced oxidative stress in HepG2 liver cells and bacterial toxicity more frequently and at lower concentrations than C. cunninghamiana and reservoir water. Overall, this study has shown that the DOM leached from litter of these species has the potential to generate DBPs and each species has a unique DBP profile with differing bioassay responses. E. tereticornis may pose a relatively greater risk to drinking water than C. cunninghamiana as it showed greater toxicity in bioassays. This implies tree species should be considered when planning riparian zones to ensure the benefits of vegetation to waterways are not offset by unintended increased DBP production and associated toxicity following chlorination at downstream drinking water intakes. [Display omitted] • Leachate of Eucalyptus and Casuarina sp. litter had constating DOM composition. • Litter DOM formed more haloacetic acids than water from a vegetated reservoir. • Organic nitrogen and protein-like content drove differences in DBP formation. • Eucalyptus induced greater oxidative stress in in vitro bioassays than Casuarina. [ABSTRACT FROM AUTHOR]

• Astrocytes and microglia key fulfil homeostatic and immune functions in the CNS. • Dysfunction of these cell types is implicated in neurodegenerative diseases. • Understanding cellular autonomy and early pathogenic changes is a key goal. • New human iPSC models will inform on disease mechanisms and therapy development. Both astrocytes and microglia fulfil homeostatic and immune functions in the healthy CNS. Dysfunction of these cell types have been implicated in the pathomechanisms of several neurodegenerative diseases. Understanding the cellular autonomy and early pathological changes in these cell types may inform drug screening and therapy development. While animal models and post-mortem tissue have been invaluable in understanding disease processes, the advent of human in vitro models provides a unique insight into disease biology as a manipulable model system obtained directly from patients. Here, we discuss the different human in vitro models of astrocytes and microglia and outline the phenotypes that have been recapitulated in these systems. [ABSTRACT FROM AUTHOR]

• Leaf litter source affected the load and composition of leached DOM. • Over 90% of DOC leached from litter was retained by soil in simulated heavy rainfall. • Leaf leachate DOM profile determined the loads and composition leaching from soil. • Casuarina litter primed DON retention in soil, while Eucalyptus enhanced losses. • NMR fingerprinting quantified sugars, amino and fatty acids leaching to waterways. Wetting of leaf litter accumulated in riparian zones during rainfall events provides pulses of dissolved organic matter (DOM) to rivers. Restoring riparian vegetation aims to reduce sediment and nutrient transport into rivers, however DOM from leaf litter can stimulate phytoplankton growth and interfere with water treatment processes. Improved understanding of the loads and chemical composition of DOM leached from leaf litter of different plant species, and how subsequent leaching through soils affects DOM retention or transformation, is needed to predict the outcomes of riparian revegetation. To investigate this, we simulated rapid leaching of rainfall through the leaf litter of two riparian tree species with and without subsequent leaching through soil, comparing dissolved organic carbon (DOC) and nitrogen (DON) loads, and DOM chemical composition (via spectroscopic and novel NMR-fingerprinting techniques). Plant source affected the load and composition of DOM leaching, with Eucalyptus tereticornis leaching more DOC than Casuarina cunninghamiana. Additionally, E. tereticornis DOM had a higher sugar, myo-inositol, benzoic acid, flavonoid and oxygenated aromatic content. More than 90% of leaf litter DOM was retained in the soil under simulated repeated heavy rainfall. The DOM chemistry of these species determined the total loads and changes in DOM composition leaching through soil. Less E. tereticornis DOM was retained by the soil than C. cunninghamiana DOM, with sugars, myo-inositol and amino acids being poorly retained compared to fatty acids and aromatic compounds. It also appears that DOM from E. tereticornis litter primed the soil, resulting in more DON being leached compared with bare soil. In comparison, C. cunninghamiana litter resulted in greater retention of DON, oxygenated aromatic compounds and the amino acid tryptophan. This study provides new information on how a range of DOM sources and transformations affect the DOM ultimately leached into waterways, key to developing improved models of DOM transformations in catchments. [ABSTRACT FROM AUTHOR]

Sediments delivered to freshwater and marine environments can make important contributions to the aquatic bioavailable nutrient pool. In the Great Barrier Reef (GBR) catchments, particulate nutrients comprise an important fraction of the end of catchment loads; however, their contribution to the bioavailable nutrient pool is not well understood. This research determined which particulate nutrient parameters are the best indicators of the potential effect of fine sediment (<10 μm) on phytoplankton growth. Surface and subsurface sediments were lab-generated to cover a wide spectrum of particulate nutrient bioavailability from key soil types, land uses and erosion processes (hillslope and gully) in a wet and a dry tropics catchment of the GBR. Phytoplankton bioassays were used to assess freshwater and marine phytoplankton responses to sediments. The best indicators were selected by regressing measurements of phytoplankton growth against nutrient bioavailability parameters measured on the sediments. The selected indicator equations included organic carbon (C) pools for both fresh and marine water, highlighting the role of bacteria in mediating nutrient availability for phytoplankton. The equations also included various fractions of particulate nitrogen (N) (differentiating the adsorbed ammonium-N from the particulate organic N), and the ratios of C to N, which indicate the lability of the organic matter present in the sediment. Dissolved reactive phosphorus was also an important indicator in freshwater. The indicators performed better in assessing bioavailability potential than traditional methods to monitor particulate nutrients, e.g., particulate N and particulate phosphorus. Phytoplankton bioassays indicated that nutrients in sediment can promote phytoplankton growth, with nutrient bioavailability depending not only on sediment load, but also sediment characteristics associated with its parent soil. These characteristics vary with soil type, land use and erosion process. Findings will help prioritize erosion control to catchment areas which are most likely to contribute large amounts of bioavailable particulate nutrients to the GBR. [ABSTRACT FROM AUTHOR]

Cyanobacteria species are sensitive to many plant allelochemicals, such as pyrogallol. However, little attention has been paid to the relative effects of these xenobiotics on co-occurring toxigenic and non-toxigenic cyanobacterial strains, despite their co-existence in blooms. Hence, the responses of one toxigenic (TS2) and two non-toxigenic (NS1, NS2) Microcystis aeruginosa strains to pyrogallol were tested under three conditions: mono-culture and co-cultured either directly or separately by dialysis membrane. The study showed that the inhibitory effects of pyrogallol on the growth and photosynthetic yield (Fv/Fm) of either toxigenic or non-toxigenic M. aeruginosa strains were lower in direct and dialysis co-culture conditions than those in mono-culture conditions. This result indicated that chemical-mediated reciprocal effects occur between the co-existing toxigenic and non-toxigenic strains. The toxigenic M. aeruginosa strain was more sensitive to pyrogallol than the non-toxigenic strains in both mono- and co-culture systems, though whether this outcome is due to the former's toxigenic status is unclear. Intracellular microcystin-LR (MC-LR) concentrations of the toxigenic strain decreased after pyrogallol addition in both mono- and co-culture systems, whereas extracellular MC-LR concentrations increased. This finding may reflect the cell damage of M. aeruginosa because of the pyrogallol. At the same initial number of cells, the extracellular MC-LR concentration released from the same amount of TS2 cells in mono-culture was slightly higher than that in dialysis co-culture conditions. Overall, this study shows that plant allelochemicals may have the potential to reduce bloom toxicity by reducing the proportion of toxigenic cyanobacterial strains, and the effects of co-existing strains must be considered when assessing the effects of plant allelochemicals on target strains. • Lower pyrogallol toxicity to co-existing M. aeruginosa than mono-strains. • Chemical-mediated reciprocal interaction of co-existing strains existed. • Toxigenic M. aeruginosa was more sensitive to pyrogallol than non-toxigenic strain. • Less intracellular microcystin-LR of toxigenic M. aeruginosa exposed to pyrogallol. • More extracellular microcystin-LR of toxigenic M. aeruginosa exposed to pyrogallol. [ABSTRACT FROM AUTHOR]