Amanda Black

Evaluation of soil metal bioavailability estimates using two plant species (L. perenne and T. aestivum) grown in a range of agricultural soils treated with biosolids and metal salts

Few studies have quantified the accuracy of soil metal bioavailability assays using large datasets. A meta-analysis from experiments spanning 6 months to 13 years on 12 soil types, compared bioavailability estimate efficiencies for wheat and ryegrass. Treatments included biosolids ± metals, comparing total metal, Ca(NO₃)₂, EDTA, soil solution, DGT and free ion activity. The best correlations between soil metal bioavailability and shoot concentrations were for Ni using Ca(NO₃)₂ (r² = 0.72) which also provided the best estimate of Zn bioavailability (r² = 0.64). DGT provided the best estimate of Cd bioavailability, accounting for 49% of shoot Cd concentrations. There was no reliable descriptor of Cu bioavailability, with less than 35% of shoot Cu concentrations defined. Thus interpretation of data obtained from many soil metal bioavailability assays is unreliable and probably flawed, and there is little justification to look beyond Ca(NO₃)₂ for Ni and Zn, and DGT for Cd.

Influence of copper on expression of nirS, norB and nosZ and the transcription and activity of NIR, NOR and N2OR in the denitrifying soil bacteria Pseudomonas stutzeri

Reduction of the potent greenhouse gas nitrous oxide (N2O) occurs in soil environments by the action of denitrifying bacteria possessing nitrous oxide reductase (N2OR), a dimeric copper (Cu)‐dependent enzyme producing environmentally benign dinitrogen (N2). We examined the effects of increasing Cu concentrations on the transcription and activity of nitrite reductase (NIR), nitric oxide reductase (NOR) and N2OR in Pseudomonas stutzeri grown anaerobically in solution over a 10‐day period. Gas samples were taken on a daily basis and after 6 days, bacterial RNA was recovered to determine the expression of nirS, norB and nosZ encoding NIR, NOR and N2OR respectively. Results revealed that 0.05 mM Cu caused maximum conversion of N2O to N2 via bacterial reduction of N2O. As soluble Cu generally makes up less than 0.001% of total soil Cu, extrapolation of 0.05 mg l−l soluble Cu would require soils to have a total concentration of Cu in the range of, 150–200 μg g−1 to maximize the proportion of N2O reduced to N2. Given that many intensively farmed agricultural soils are deficient in Cu in terms of plant nutrition, providing a sufficient concentration of biologically accessible Cu could provide a potentially useful microbial‐based strategy of reducing agricultural N2O emissions.

Application of MicroResp™ for soil ecotoxicology.

MicroResp™ is a miniaturised method for measuring substrate induced respiration (SIR) in soil. We modified the MicroResp™ method to develop a rapid tool for quantifying the ecotoxicological impact of contaminants. The method is based on reduction in SIR across a gradient of contaminant, allowing for determination of dose-response curves EC-values. Contaminants are mixed into soil samples at a range of concentrations; each sample is then dispensed into a column of eight wells in 96 well format (deep) plates. Moisture and glucose are added to the samples at levels to provide maximum response. Released CO₂ from the soils is then measured using colorimetric gel-traps, following the standard MicroResp™ methodology. Examination revealed that this method works over a range of soil types and is insensitive to minor variations in assay length (2-7 h), alteration of moisture content (±20 μL from optimum), and soil storage conditions (4 °C versus fresh).

Effects of long-term fertiliser inputs on the quantities of organic carbon in a soil profile under irrigated grazed pasture

Abstract The long-term fertiliser field trial at Winchmore was used to investigate relationships between pasture production and soil organic carbon (C) storage. In 2009, soil samples to 1 m depth were taken from plots that had been subject to three levels of annual superphosphate fertiliser input for 57 years (nil, 188 kg ha−1 [188PA] and 376 kg ha−1 [376PA]). Although annual pasture production was 2.4–2.8 fold higher for the fertiliser treatments compared with nil P, concentrations and amounts of organic C were similar for the various treatments at most soil depths. Furthermore, differences in total quantities of organic C in the soil profile between the nil P (107 t ha−1), 188PA (101 t ha−1) and 376PA (114 t ha−1) treatments were not significant. The absence of any significant accumulation of soil organic C in response to increased production was attributed to accelerated decomposition of organic matter inputs linked to a combination of improved pasture quality and increased earthworm activity.

Metal bioavailability dynamics during a two-year trial using ryegrass (Lolium perenne L.) grown in soils treated with biosolids and metal salts

A 24-month field lysimeter experiment using ryegrass (Lolium perenne L.) grown in three soil types was used to investigate metal bioavailability dynamics following amendment with biosolids and metal salts (Cd, Cu, Ni, Zn). Common surrogates of soil metal bioavailability (total soil metal, EDTA, Ca(NO3)2, total dissolved, diffusive gradient in thin film, and modelled free ion activity) were determined on soil samples taken every 6 months. Ryegrass was also harvested every 6 months and analysed for metal concentrations. Across soils and treatments dissolved organic carbon (DOC) and pH decreased, whereas dissolved Ca and Mg increased with time. The free ion activity concentrations of each metal also increased over 24 months, whereas Ca(NO3)2-extracted metals were unchanged. Zinc presented the most changes in bioavailability status, with total Zn concentration decreasing over time, and EDTA-extractable and soil solution Zn increasing significantly by 1.82mgkg -1 (1.1%) and 1.52mgL -1 (29%), respectively. Shoot concentration of Zn increased by 1.32mgkg -1 (2.7%), whereas shoot Ni concentration decreased by 0.65mgkg -1 (4%). The findings of this study clearly demonstrated that over 24 months, soil metal bioavailability and shoot metal concentrations register only minor changes and appear to be unaffected by soil DOC and pH fluctuations.

Impacts of long-term plant biomass management on soil phosphorus under temperate grassland

AimsWe assessed and quantified the cumulative impact of 20 years of biomass management on the nature and bioavailability of soil phosphorus (P) accumulated from antecedent fertiliser inputs.MethodsSoil (0–2.5, 2.5–5, 5–10 cm) and plant samples were taken from replicate plots in a grassland field experiment maintained for 20 years under contrasting plant biomass regimen- biomass retained or removed after mowing. Analyses included dry matter production and P uptake, root biomass, total soil carbon (C), total nitrogen (N), total P, soil P fractionation, and 31P NMR spectroscopy.ResultsContemporary plant production and P uptake were over 2-fold higher for the biomass retained compared with the biomass removed regimes. Soil C, total P, soluble and labile forms of inorganic and organic soil P were significantly higher under biomass retention than removal.ConclusionsReserves of soluble and labile inorganic P in soil were significantly depleted in response to continued long-term removal of P in plant biomass compared to retention. However, this was only sufficient to sustain plant production at half the level observed for the biomass retention after 20 years, which was partly attributed to limited mobilisation of organic P in response to P removal.

Effects of long-term irrigation on soil phosphorus under temperate grazed pasture: Irrigation and soil phosphorus

G . B o i t t a , J . T i a n b,c, A . B l a c k d, S . A . W a k e l i n e & L . M . C o n d r o n a aDepartment of Soil Science, Faculty of Agriculture and Life Sciences, Lincoln University, PO Box 85084, Ellesmere Junction Road/Springs Road, Lincoln, 7647 Christchurch, New Zealand, bInstitute of Applied Ecology, Chinese Academy of Sciences, PO Box 417, Shenyang 110016, China, cUniversity of Chinese Academy of Sciences, Beijing 100049, China, dBio-Protection Research Centre, Lincoln University, PO Box 85084, Ellesmere Junction Road/Springs Road, Lincoln, 7647 Christchurch, New Zealand, and eDepartment of Forest Systems, Scion Research, PO Box 29237, Christchurch 8540, New Zealand

Indigenous biosecurity: Māori responses to kauri dieback and myrtle rust in Aotearoa New Zealand

It is widely acknowledged that Indigenous peoples have traditional knowledge relevant to modern environmental management. By asserting roles within associated science and policy networks, such Indigenous Knowledge (IK) can be seen as part of the resistance to colonisation that includes protest, treaty making, political and economic empowerment, legislation, cultural renaissance and regulatory influence. In New Zealand, these achievements inform attempts by Māori (the Indigenous people of New Zealand) to manage forest ecosystems and cultural keystone species. This chapter presents two case studies of how indigenous participation in modern biosecurity through the example of Māori asserting and contributing to forest management. While progress is often frustratingly slow for indigenous participants, significant gains in acceptance of Māori cultural frameworks have been achieved.

Indigenous bacteria enhance growth and modify essential oil content in Leptospermum scoparium (mānuka)

ABSTRACT Leptospermum scoparium J.R.Forst. et G.Forst. var. scoparium (Myrtaceae), or mānuka, is a New Zealand medicinal plant that yields essential oils with varying triketones concentrations. The effects of mānuka-associated bacteria, isolated from plants growing in five regions, on growth and essential oil composition of one regional variety, were investigated for the first time. Leaf essential oil compositions and yields were determined by microscale solvent extraction and GC-MS analyses. Erwinia sp. T4MS11P and Pseudomonas sp. M3R43 increased growth compared to control plants. Plants inoculated with Erwinia sp. T4MS11P had similar concentrations of triketone grandiflorone as control plants, whereas plants inoculated with Pseudomonas sp. M3R43 had lower grandiflorone concentrations. In contrast, inoculation with a bacterial consortium isolated from the West Coast did not increase plant growth, but gave higher grandiflorone concentrations (> 160%) compared to control plants. The different treatments showed some effects on qualitative oil composition, but these were not significantly different between regional chemotypes. Overall, the results demonstrated that bacteria increased the growth of mānuka and grandiflorone concentrations in leaves. These effects would be valuable in commercial essential oil production from plantation-grown mānuka.