South Island Sites Research Articles

Modeling GIC in the Southern South Island of Aotearoa New Zealand Using Magnetotelluric Data

AbstractMagnetotelluric (MT) impedances from 62 sites in southern South Island of Aotearoa New Zealand have been used to model geomagnetically induced currents (GIC) in four transformers during two solar storms. Induced electric fields during the storms are calculated from the MT impedances using the magnetic fields measured at the Eyrewell (EYR) geomagnetic observatory, approximately 200 km north of the study area. Calculated GIC during the sudden storm commencements (SSC) give a generally good match to GIC measured by the network operator, Transpower New Zealand. Long period GIC (periods longer than about 10,000 s) are less well modeled. Calculations based on thin‐sheet modeling, which has restrictions on the shortest period of variation which can be modeled, perform less well for the GIC associated with SSC, but are equally good, if not better, at modeling longer period GIC. Consistent underestimation of large GIC at one transformer (HWBT4) near Dunedin are likely to be the result of uncertainty in the assumed values of line, transformer, and earthing resistances. The assumption of a spatially uniform magnetic field across the study area, which is implied by use of the magnetic field measured at EYR as a basis for calculation, may also lead to incorrect calculation of GIC. For one storm use of magnetic field data from a magnetometer within the study area leads to much improved modeling of the observed GIC. This study compares modeled and measured GIC using specifically measured MT impedance data.

Influence of Tectonic and Geological Structure on GIC in Southern South Island, New Zealand

AbstractAs part of a 5‐year project to assess the risk posed by geomagnetically induced currents (GIC) to the New Zealand electrical transmission network, long‐period magnetotelluric (MT) measurements have been made at 62 sites in southern South Island of New Zealand, a region where there was an absence of previous MT data. The data are largely 3‐dimensional in character, but show distinct features that can be related to the known tectonic and geological structure. In this work we focus on how the measured MT impedance tensors, and a simple interpretation of conductivity structure, can be used to assess the influence of tectonic and geological structure on GIC. We use the impedance tensors to calculate the magnitudes and orientations of induced electric fields in response to various orientations of inducing magnetic field. The electric fields so calculated are then used in a simplified model of the transmission network to calculate GIC at grounded substations. Our results confirm that tectonic/geological structure in the lower South Island and the resulting electrical conductivity variations have important impacts on the GIC magnitude. In the south‐west, smaller induced electric fields, associated with the higher conductivity in that region, lead to much reduced GIC at a substation in that area. In contrast, higher electric fields occurring in a NW‐SE band across the center of the region, contribute to much larger GIC in Dunedin city. Our results thus help explain the observed GIC reported at transformers in the region.

Coastal Diptera species and communities and their geographic distribution in Aotearoa|New Zealand

ABSTRACT The coast provides an important habitat for insects throughout the world. Some insect taxa are entirely dependent on this continuous but narrow strip of habitat between the land and sea, despite the challenging environmental conditions. In Aotearoa|New Zealand (hereafter Aotearoa), the coastal environment is extensive and varies enormously. Aotearoa is also home to a diverse and predominantly endemic Diptera fauna of roughly 5500 species, and a small but significant proportion of these are found along the coast. Here we provide the first extensive survey of Aotearoa’s coastal flies, and describe how the diversity, richness, and abundance of specialised wrack-inhabiting communities vary. Overall, we recorded 257 different species collected from 109 sites from around Aotearoa’s three main islands, with highest abundance, species richness and diversity all found at South Island sites. Our surveys are estimated to have captured over 80% of the species occupying the seashore, and 100% of the wrack specialist community, for which we identified a country-wide baseline community. This study has provided new and interesting insights into the distribution and diversity of flies in Aotearoa. It also highlights the importance of carrying out broad community surveys to capture and improve our understanding of our local fauna.

Climate influences the value of a plant structural defence against browsing

Abstract The circumstances that select for plant anti‐herbivore defences are not well understood. In New Zealand, the ‘divaricate’ cage‐like architecture of many woody plants may have arisen as a defence against avian browsing; it also has some ability to deter browsing by introduced deer. Its prominence on alluvial soils in frosty and droughty areas led us to hypothesize that structural defences are of most value where fertile soils coincide with climatic constraints that prevent plants from quickly growing out of the browse zone. We tested this hypothesis by growing seedlings of three divaricate species and their broadleaved congeners on fenced and unfenced plots beneath tree‐fall gaps at three humid frost‐free sites in the North Island of New Zealand, and at three colder and drier sites in the South Island. Soil total phosphorus levels were moderate to high at all sites (344–961 ppm), and pellet counts indicated similar average deer densities at North and South Island sites, enabling us to attribute variation in seedling growth and survival primarily to climatic differences between our sites. On fenced plots, average relative height growth rates in the North Island exceeded those on the southern sites by 64%, and growth of broadleaved species averaged 132% and 99% greater than that of divaricate congeners at North and South Island sites, respectively. On the northern sites, broadleaved species also held a large (137%) net height growth advantage over divaricates even on unfenced plots. In contrast, exposure to browsing on the coldest sites resulted in complete loss of the broadleaved net height growth advantage. Synthesis. Even in the presence of deer, divaricate plants were overgrown on humid frost‐free sites, but not on colder and drier sites, where browsing neutralized the superior growth potential of broadleaved species. The cost of structural defences therefore paid off only on sites where climatic adversity reduces the ability of plants lacking such defences to grow quickly out of the browse zone, in agreement with our hypothesis.

Characterizing spatial and temporal variation in 18O and 2H content of New Zealand river water for better understanding of hydrologic processes

AbstractTime series of hydrogen and oxygen stable isotope ratios (δ2H and δ18O) in rivers can be used to quantify groundwater contributions to streamflow, and timescales of catchment storage. However, these isotope hydrology techniques rely on distinct spatial or temporal patterns of δ2H and δ18O within the hydrologic cycle. In New Zealand, lack of understanding of spatial and temporal patterns of δ2H and δ18O of river water hinders development of regional and national‐scale hydrological models. We measured δ2H and δ18O monthly, together with river flow rates at 58 locations across New Zealand over a two‐year period. Results show: (a) general patterns of decreasing δ2H and δ18O with increasing latitude were altered by New Zealand's major mountain ranges; δ2H and δ18O were distinctly lower in rivers fed from higher elevation catchments, and in eastern rain‐shadow areas of both islands; (b) river water δ2H and δ18O values were partly controlled by local catchment characteristics (catchment slope, PET, catchment elevation, and upstream lake area) that influence evaporation processes; (c) regional differences in evaporation caused the slope of the river water line (i.e., the relationship between δ2H and δ18O in river water) for the (warmer) North Island to be lower than that of the (cooler, mountain‐dominated) South Island; (d) δ2H seasonal offsets (i.e., the difference between seasonal peak and mean values) for individual sites ranged from 0.50‰ to 5.07‰. Peak values of δ18O and δ2H were in late summer, but values peaked 1 month later at the South Island sites, likely due to greater snow‐melt contributions to streamflow. Strong spatial differences in river water δ2H and δ18O caused by orographic rainfall effects and evaporation may inform studies of water mixing across landscapes. Generally distinct seasonal isotope cycles, despite the large catchment sizes of rivers studied, are encouraging for transit time analysis applications.

Gymnocoronis spilanthoides

Gymnocoronis spilanthoides

Aquatic nitrogen-fixing cyanobacteria associated with blooms of Didymosphenia geminata: insights from a field study

The nuisance diatom Didymosphenia geminata has recently increased in abundance worldwide and has spread through oligotrophic rivers in the South Island of New Zealand. However, it remains absent from the North Island. Its proliferation in oligotrophic environments has prompted work on phosphorus acquisition, but potential nitrogen acquisition pathways have received little attention. We partially sequenced the nifD gene, encoding a component of nitrogenase, from South Island samples containing D. geminata and compared its diversity with that of North Island sites independently ranked as high, medium and low risk for infestation. Godleyacean cyanobacteria were present in all four South Island provinces investigated, and also in three North Island sites rated medium or high risk. Most high-risk sites were dominated by Nostoc sequences, as were some infested South Island sites. Monte Carlo simulations and the weighted UniFrac metric showed that nifD diversity in low-risk North Island sites differed significantly from sites rated medium and high risk, and from infested South Island sites; however, random resampling showed that the data were insufficient to separate didymo-infested and high-risk sites from medium-risk sites. The relationships we discovered suggest that success of D. geminata in New Zealand could be mediated by indigenous nitrogen-fixing cyanobacteria.

Spatial covariation of local abundance among different parasite species: the effect of shared hosts.

Within any parasite species, abundance varies spatially, reaching higher values in certain localities than in others, presumably reflecting the local availability of host resources or the local suitability of habitat characteristics for free-living stages. In the absence of strong interactions between two species of helminths with complex life cycles, we might predict that the degree to which their abundances covary spatially is determined by their common resource requirements, i.e. how many host species they share throughout their life cycles. We test this prediction using five trematode species, all with a typical three-host cycle, from multiple lake sampling sites in New Zealand's South Island: Stegodexamene anguillae, Telogaster opisthorchis, Coitocaecum parvum, Maritrema poulini, and an Apatemon sp. Pairs of species from this set of five share the same host species at either one, two, or all three life cycle stages. Our results show that when two trematode species share the same host species at all three life stages, they show positive spatial covariation in abundance (of metacercarial and adult stages) across localities. When they share hosts at two life stages, they show positive spatial covariation in abundance in some cases but not others. Finally, if two trematode species share only one host species, at a single life stage, their abundances do not covary spatially. These findings indicate that the extent of resource sharing between parasite species can drive the spatial match-mismatch between their abundances, and thus influence their coevolutionary dynamics and the degree to which host populations suffer from additive or synergistic effects of multiple infections.

Geochemical sourcing of obsidians from the Pūrākaunui site, South Island, New Zealand

AbstractWe report the first well‐documented case of a South Island site where Mayor Island obsidian is not the dominant source represented. At the Pūrākaunui site (I44/21), located in coastal Otago, we find that most obsidians come from the Taupo Volcanic Zone, including sources near Lake Taupo (52%) and Rotorua (27.7 %). A small proportion of the collection comes from Mayor Island (10.8%) and the Coromandel Peninsula (9.5%) obsidian. The results point to early effects of regionalisation in source exploitation on the South Island.

Incidence of cereal and pasture viruses in New Zealand's native grasses

This study provides evidence for frequent and multiple invasions of New Zealand's native grasses by exotic cereal and pasture viruses. Fifteen native and three exotic grasses from 29 North Island and six South Island sites were surveyed for the presence of viruses using enzyme‐linked immunosorbent assay (ELISA). Barley yellow dwarf virus and Cereal yellow dwarf virus (BYDV, CYDV: Luteoviridae) and Cocksfoot mottle virus (CoMV, Sobemovirus) are widespread throughout New Zealand. CoMV, previously considered to have a natural host range restricted to Dactylis and Triticum, was detected in Poa anceps, P. cita, Festuca novae‐zelandiae, and Chionochloa rubra. New virus host reports include BYDV‐PAV in Microlaena stipoides and Dichelachne crinita; BYDV‐MAV in P. cita, F. novae‐zelandiae and Hierochloe redolens; and CYDV‐RPV in P. cita and M. stipoides. Nominal logistic regression analyses showed a correlation between the presence of exotic grass species and virus incidence. Host range experiments for BYDV‐PAV and CoMV were performed with selected native and exotic grasses, and the results are discussed in context of the field‐survey findings.

Evolution and biogeography of New Zealand's longjaw galaxiids (Osmeriformes: Galaxiidae): the genetic effects of glaciation and mountain building

Summary1. The biological impact of glaciation in Southern Hemisphere freshwaters is poorly understood. Several large rivers of eastern South Island, New Zealand, represent a mosaic of glaciated and non‐glaciated regions, and are thus well‐suited for studies of post‐glacial recolonization.2. We conducted mtDNA analyses of South Island's endemic non‐migratory longjaw galaxiids Galaxias prognathus and G. cobitinis (Osmeriformes: Galaxiidae) to test hypotheses of post‐glacial recolonization, and to assess the vicariant effects of Pleistocene mountain building.3. We analysed the phylogeography of longjaw cytochrome b sequences from 38 sites in central South Island (n = 83). On the basis of our sampling it seems that G. prognathus and G. cobitinis have a parapatric distribution in the Waitaki River system, their disjunction broadly coinciding with three large post‐glacial lakes. Waitaki clades of both species are deeply divergent relative to conspecific taxa in drainages to the north and south.4. Tests for recent population growth – predicted under post‐glacial expansion of G. prognathus– do not refute recent recolonization of streams above glaciated lakes in the Waitaki River drainage. The apparent absence of potential ‘source’ populations from non‐glaciated regions suggests a post‐glacial population decline for G. prognathus below the Waitaki lakes.5. Molecular clock calibrations based on several freshwater vicariant events elsewhere in New Zealand supported the geologically‐derived hypothesis of Waitaki–Canterbury drainage isolation approximately 300 ka.

An inference model for mean summer air temperatures in the Southern Alps, New Zealand, using subfossil chironomids

Quantitative paleoclimate reconstructions from Southern Hemisphere mid-latitude sites are critical for identifying spatial and temporal patterns of abrupt climate change and for testing hypotheses about possible causal mechanisms. The analysis of chironomid distributions and environmental variables from 61 lakes was undertaken to develop a robust inference model for quantitative temperature reconstruction from sites in South Island, New Zealand. Detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) indicated that mean summer air temperature (SmT), chlorophyll a, conductivity, organic content of sediment as determined by loss-on-ignition, and mean annual precipitation account for a significant portion of variance in chironomid taxa distribution. SmT was the dominant variable. The strongest performing inference model, based on weighted averaging-partial least squares (WA-PLS), was developed from 60 lakes for SmT, having a root mean square error of prediction (RMSEP jack) of 1.27 °C and a coefficient of determination of 0.80 ( r 2 jack). These results confirm that New Zealand chironomids may be used to provide robust estimates of mean summer air temperature and are a reliable method for quantitative paleoenvironmental reconstruction.

Holocene vegetational and climatic history, Sponge Swamp, Haast, south-western New Zealand

Palynological studies from most of the drier eastern and southern parts of the South Island, New Zealand, suggest that the climate regime switched from prevailing northerly airflows to dominant south-westerly airflows during the mid to late Holocene. To substantiate the tenet, a South Westland mire site with little historic disturbance was selected for vegetation reconstruction and comparison with the regional environmental history. Pollen concentrations were dated to provide better age control. Lowland podocarp/hardwood forest persisted under a warm and moist climate from about 7700 BP after the formation of the fen. The climate became slightly warmer and drier around 6800 BP, which was responsible for the loss of mire flora, the suppression of Dacrydium cupressinum and a subsequent large increase of Ascarina lucida. From ca. 6800 BP, a substantial cool interval started with a sudden decline in stands of A. lucida in conjunction with expansion or establishment of some cold tolerant taxa, in particular Nothofagus menziesii. This period lasted nearly 3000 years and was most pronounced at ca. 3500 BP. A significant dry episode from ca. 3700 BP was shown by gradual replacement of tree ferns and swamp forest taxa with forest taxa which are tolerant of drought. The reduction of rainfall is also supported by evidence from the substantial positive excursion of δ 13C values around 3230 BP in coastal northwest South Island sites. Vegetation and climate history reconstructed from this site coincided well with the regional vegetation and climate history. The climate trend derived from this site, e.g. from warm and moist to cold and dry conditions, is most likely to be caused by the reduction of the humid northerlies and intensification of the cold and dry south-westerlies.

Douglas fir provenance susceptibility to Swiss needle cast in New Zealand

Swiss needle cast caused by the needle-infecting ascomycete Phaeocryptopus gaeumannii is responsible for substantial growth loss in many New Zealand Douglas fir plantations. Data were collected in a provenance trial at age 13 years, when the introduced pathogen was extending its range throughout the country, in order to investigate variation in disease resistance or tolerance among a selection of the more vigorous Douglas fir seedlots. Infection was high and did not vary in incidence between seven provenances sampled at four North Island sites and one South Island site, but was still only negligible or absent at two other South Island sites. Foliage retention varied significantly between provenances and between sites, but there was no significant site x provenance interaction. Retention was less at the North Island sites, but showed more variation between provenances than at the South Island sites. However, South Island provenance rankings appeared to follow those in the infected North Island stands, implying that infection may act by accentuating natural differences in needle retention among host populations. Comparison with provenance growth data suggests that although foliage retention does not appear to relate directly to vigour, it is still a useful secondary character when selecting superior Douglas fir seed for regions subject to high infection.

Effect of plant density and depth of harvest on the production and quality of licorice (Glycyrrhiza glabra) root harvested over 3 years

Licorice (Glycyrrhiza glabra) root production was investigated in Central Otago, Canterbury, and Waikato regions of New Zealand over 4 years. Increasing plant populations at establishment had a large effect on production. Maximum root and rhizome production was achieved with plant populations above 24 000 plants/ha. Low plant densities favoured rhizome production and high densities favoured root production. Sampling roots and rhizomes to 900 mm showed that the majority of production was in the top 300 mm. Roots harvested from below 300 mm contained less glycyrrhizin than surface roots. Glycyrrhizin concentration increased each year and surpassed the minimum international standard of 4% in the first harvest in the Waikato but not until the third harvest at South Island sites. By the third harvest both Waikato and Canterbury grown licorice contained similar amounts of glycyrrhizin but with 90% of the glycyrrhizin content in roots in the 0–300 mm soil layer in the Waikato and in the 0–600 mm soil layer in Canterbury. These trials show that licorice can be grown in New Zealand with fresh root and rhizome yields of 17–28 t/ha in the second and third years of production and with a glycyrrhizin content above the minimum international standard.

Motion and rigidity of the Pacific Plate and implications for plate boundary deformation

Using up to 11 years of data from a global network of Global Positioning System (GPS) stations, including 12 stations well distributed across the Pacific Plate, we derive present‐day Euler vectors for the Pacific Plate more precisely than has previously been possible from space geodetic data. After rejecting on statistical grounds the velocity of one station on each of the Pacific and North American plates, we find that the quality of fit of the horizontal velocities of 11 Pacific Plate (PA) stations to the best fitting PA Euler vector is similar to the fit of 11 Australian Plate (AU) velocities to the AU Euler vector and ∼20% better than the fit of nine North American Plate (NA) velocities to the NA Euler vector. The velocities of stations on the Pacific and Australian Plates each fit a rigid plate model with an RMS residual of 0.4 mm/yr, while the North American velocities fit a rigid plate model with an RMS velocity of 0.6 mm/yr. Our best fitting PA/AU relative Euler vector is located ∼170 km southeast of the NUVEL‐1A pole but is not significantly different at the 95% confidence level. It is also close (<70 km in position and <3% in rate) to a pole derived from transform faults identified from satellite altimetry, suggesting that the vector has not changed significantly over the past 3 Myr. Our relative Euler vector is also consistent with all known geological and geodetic evidence concerning the AU/PA plate boundary through New Zealand. The GPS sites offshore of southern California are presently moving 4–5 ± 1 mm/yr relative to predicted Pacific velocity, with their residual velocities in approximately the opposite direction to PA/NA relative motion. Likewise, the easternmost sites in South Island, New Zealand, are moving ∼3 ± 1 mm/yr relative to predicted Pacific velocity, with the residuals in approximately the opposite direction to PA/AU relative motion. These velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern California and New Zealand, implying that the plate boundary zones in both regions are wider than previously believed.

Optical dating of quartz sediments and accelerator mass spectrometry 14C dating of bone gelatin and moa eggshell: A comparison of age estimates for non‐archaeological deposits in New Zealand

A consensus has not been reached on the validity of “old” (pre‐Polynesian settlement) 14C ages for Pacific rat bones from New Zealand. As an independent test of their validity, we have applied optical dating techniques to fossiliferous sediments at three non‐archaeological sites in the North and South Islands. In this paper, we report the optical ages obtained from quartz grains and compare them with a suite of accelerator mass spectrometry (AMS) 14C ages obtained from the bone gelatin of Pacific rats (Rattus exulans) and five species of bird (four herbivores and one omnivore). An AMS 14C age is also reported for one sample of moa (Aves: Dinornithiformes) eggshell. All dated fossil remains were collected from known stratigraphic positions. Additional chronological control is provided by two known‐age volcanic tephras at the Hukanui sites in the North Island. At the South Island site (Earthquakes #1), an infilled burrow provides independent age control, in that fossils inside the burrow should yield younger ages than the sediments and fossils outside the burrow. Bone preservation is uniformly good at all sites, as shown by surface detail, nitrogen content, and C:N ratios. In addition, amino acid profiles are consistent with those of collagen from modern Pacific rats and the laboratory rat collagen standard. Single‐aliquot optical dating protocols were employed to avoid age overestimation due to incomplete bleaching of sediments before burial and to permit the identification of any post‐depositional disturbance. At the Hukanui sites, 14C ages on bird bone and eggshell agree with the optical ages for the enclosing sediments, and both chronologies are consistent with the accepted ages for the overlying Taupo Ignimbrite (c. 1850 yr BP) and the underlying Waimihia Tephra (c. 3300 yr BP). Two 14C ages from Finsch's duck (Chenonettafinschi) bones excavated from within the Taupo Ignimbrite agree with the accepted age of the ignimbrite. In addition, a gelatin sample from a Pacific rat bone reportedly excavated from beneath the Taupo Ignimbrite has a similar amino acid profile to that of modern collagen. This measure of good bone preservation provides confidence in the 14C age for this sample (1775 ± 93 yr BP), which accords with its position beneath the ignimbrite. At Earthquakes #1, five 14C determinations were made: three on Pacific rat, one on New Zealand pigeon (Hemiphaga novaeseelandiae), and one on South Island kokako (Callaeas cinerea). All five ages are consistent with the stratigraphic locations of the fossils, and with the optical ages for the enclosing sediments. We conclude that the early arrival of rats in New Zealand is supported by the array of chronological evidence presented here: the concordance of 14C and optical ages at each of the sites; the agreement between 14C ages on different materials and for a range of species; and the consistency of the 14C and optical ages with stratigraphic and other chronological markers. The Pacific rat was present in both the North and South Islands of New Zealand at least 800 years before permanent Polynesian settlement.

No evidence for establishment of the wasp parasitoid, Sphecophaga vesparum burra (Cresson) (Hymenoptera: Ichneumonidae) at two sites in New Zealand

Sphecophaga vesparum burra (Cresson) (Hymenoptera: Ichneumonidae) has been released at seven sites in New Zealand as a biological control agent for wasps (Vespula spp.). Between 1996 and 1998, more than 35 000 overwintering cocoons were released nationwide, more than half of them at two South Island sites: Binser Track in Arthur's Pass National Park (13 200 cocoons) and Tennyson Inlet in the Marlborough Sounds (13 660 cocoons). Monitoring at these two climatically and altitudinally disparate sites revealed that over 5000 adult parasitoids emerged at each site over the 4 years. More than 300 wasp nests were dug and inspected for attack by S. v. burra, but there was no evidence of establishment.

Effects of grassland afforestation on exchangeable soil and soil solution aluminium

The impact of land use change from grassland to conifer forest on the aluminium (Al) concentrations in soils and soil solutions was examined. Soils from grassland were compared with those from adjoining 15–19-year old forest stands at 3 contrasting pairs of sites in South Island, New Zealand. The site pairs were on a terrace [Pinus nigra/P. ponderosa, and grassland (CP)], and a hill slope [Pseudotsuga menziesii and grassland (CF)] in the Craigieburn range, Canterbury, and a hill slope in the Lammerlaw Range, Otago [P. radiata and grassland (LP)]. The sites had never been cultivated or fertilised, and for each pair the forest and grassland were similar in terms of soil and topography. The 1 M KCl exchangeable and 0.02 M CaCl 2 extractable Al levels at 0–10 cm were higher in forest than in grassland topsoil at CP and LP (P < 0.01). In soil solutions there was a trend for both ‘reactive Al’ and Al bound in labile organic complexes to be higher in forest soil at all sites, but site-pair differences were only significant at LP, and only for ‘reactive Al’. The increase in ‘reactive Al’ at this site was linked to the low pH and low base saturation. The ratios of exchangeable and soil solution Ca 2+ and Mg 2+ to ‘reactive Al’ were substantially lower in forest than grassland soils at all sites. Aluminium complexation capacity (Al-CC) values at all sites were higher in forest soil solutions than in grassland soil solutions. For the grassland and forest sites at LP, the Al-CC correlated strongly with the amount of soluble fulvic and humic matter present, as estimated from soil solution UV absorbance at 250 nm. In soils with the lowest percentage base saturation and buffering capacity (LP), afforestation of pastoral grassland with Pinus radiata significantly reduced soil pH and base cation levels, while increasing both soil and soil solution Al concentrations. Under such conditions (base saturation <20%), the increase in ‘reactive Al’ concentrations in soil solutions under fast growing conifer tree species may be sufficient to affect Mg uptake.

Cocksfoot mottle virus spreads to the South Island of New Zealand

In previous surveys of New Zealand cocksfoot (Dactylis glomerata L.) pastures, Cocksfoot mottle virus (CoMV) was detected at only one site near Taupo on the North Island. However, we have recently found CoMV at two sites near Dunedin on the South Island. Isolates from these sites, associated with mild and severe symptoms in cocksfoot (CoMV-Wa and CoMV-Ok, respectively), were partially characterised. In agarose gels, the virions of the two isolates had slightly different mobilities when subjected to an electric field, indicating a difference in net surface charge. However, both isolates produced similar leaf mottle symptoms in wheat, their capsid proteins had similar molecular weights (Mr = ca. 31 kDa) as determined by SDS-polyacrylamide gel electrophoresis and they were serologically indistinguishable in double-diffusion tests using 17 antisera to 10 sobemoviruses. CoMV-Ok and CoMV-Wa were serologically related to Lucerne transient streak virus but not to eight other sobemoviruses. Further surveys using DAS-ELISA showed variable incidences of CoMV (range 0–80%) at nine South Island sites. The beetle vectors of CoMV have not been introduced into New Zealand. At two sites where CoMV was found, we observed severe feeding damage from armyworms (Persectania aversa Walker). However, in growth-cabinet experiments this species failed to transmit the virus. Incidences were significantly higher at mown sites (39%) than at unmown sites (11%), suggesting that mechanical transmission is responsible for spread. In view of the increased use of cocksfoot on New Zealand farms, the impact of CoMV on cocksfoot productivity now needs to be assessed and current levels of resistance to CoMV in commercial cultivars need to be evaluated.