Subtropical Southeast Queensland Research Articles

Decay of Cryptosporidium parvum DNA in cowpats in subtropical environments determined using qPCR

Cryptosporidium oocysts pose a significant threat to public health due to its ability to contaminate environmental waters, leading to outbreaks of waterborne diseases and emphasizing the crucial need for effective water treatment and monitoring systems. This study aimed to investigate the decay of Cryptosporidium oocyst DNA in cow fecal matter under different environmental conditions prevalent in sub-tropical Southeast Queensland (SEQ) during summer and winter seasons. The effects of ambient sunlight and shaded conditions on the decay rates of C. parvum DNA in cow fecal samples were evaluated. The results showed that measurable levels of C. parvum DNA were observed for up to 60 days during the summer experiments, with a slower decay rate on the surface (k = −0.029) and sub-surface (k = −0.043) of the cowpat under shaded conditions than those on the surface (k = −0.064) and sub-surface (k = −0.079) under sunlight conditions. The decay rates of C. parvum DNA on the surface and sub-surface of the cowpat under shaded conditions were significantly slower (p = 0.004; p = 0.004) than those on the surface and sub-surface under sunlight conditions during summer experiments. During the winter treatments, measurable levels of C. parvum DNA were observed for up to 90 days, and the decay rates were slower on the surface (k = −0.036) and sub-surface (k = −0.034) of the cowpat under shaded conditions than those under sunlight conditions (k = −0.067 for surface and k = −0.057 for sub-surface). The decay rates of C. parvum DNA on the surface and sub-surface of the cowpat under shaded conditions were significantly slower than those on the surface (p = 0.009) and sub-surface (p = 0.041) under sunlight conditions during winter experiments. Moreover, the decay rate in the summer sunlight surface treatment (k = −0.064) was significantly faster from those in the winter shaded surface (k = −0.036; p = 0.018) and sub-surface (k = −0.034; p = 0.011) treatments. Similar results were also observed for summer sunlight sub-surface (k = −0.079), which was significantly faster than winter shaded surface (k = −0.036; p = 0.0008) and sub-surface (k = −0.034; p = 0.0005) treatments. Overall, these findings are important to enhance our understanding on the degradation of C. parvum DNA in cow fecal matter in SEQ, particularly in relation to seasonal variations and environmental conditions.

‘Red Rhapsody’ Strawberry

Queensland’s winter strawberry (Fragaria ×ananassa Duch.) industry would benefit by having an early ripening, more profitable cultivar to replace current cultivars. ‘Strawberry Festival’ (Chandler et al., 2000) and, more recently, ‘Florida Radiance’ (Chandler et al., 2009) were introduced to Queensland and rapidly became major early-season cultivars with fruit and plant attributes desirable to growers. ‘Florida Radiance’ is marketed in Australia as ‘Florida Fortuna’. The average fruit size of ‘Strawberry Festival’ is less than ‘Florida Radiance’, but the latter is more difficult to establish in the field. Numerous plant losses sometimes occur, especially when demand for early supply of runners results in premature digging and lower quality runners. The commercial desirability of strawberry cultivars for producers, distributors, retailers, and consumers depends on many traits. Supply volumes influence market prices and profitability to the producer. Producer profitability is a key need for a stable production system. Herrington et al., (2012) analyzed the production and marketing system in Queensland in relation to the effect of changes in plant traits on the notional profitability of production. When this information was combined with genetic parameters, they found (Herrington et al., 2014) the key drivers of greater profitability compared with the current profitability in subtropical Southeast Queensland were having a greater proportion of yield early in the season and having a larger fruit size. In the development of ‘Red Rhapsody’ (Fig. 1), we focused on selecting for these traits while maintaining levels of other traits at or above commercially acceptable threshold levels.

Can’t touch this

Australia’s laid-back, sun-drenched beach lifestyle has been a celebrated and prominent part of its official popular culture for nigh on a century, and the images and motifs associated with this culture have become hallmarks of the country’s collective identity. Though these representations tend towards stereotype, for many Australians the idea of a summer holiday at the beach is one that is intensely personal and romanticised – its image is not at all urbanised. As Douglas Booth observed, for Australians the beach has become a ‘sanctuary at which to abandon cares – a place to let down one’s hair, remove one’s clothes […] a paradise where one could laze in peace, free from guilt, drifting between the hot sand and the warm sea, and seek romance’.1 Beach holidays became popular in the interwar years of the twentieth century, but the most intense burst of activity – both in touristic promotion and in the development of tourism infrastructure – accompanied the postwar economic boom, when family incomes were able to meet the cost of a car and, increasingly, a cheap block of land by the beach upon which a holiday home could be erected with thrift and haste. In subtropical southeast Queensland, the postwar beach holiday became the hallmark of the state’s burgeoning tourism industry; the state’s southeast coastline in particular benefiting from its warm climate and proximity to the capital, Brisbane. It was here – along the evocatively named Gold Coast (to Brisbane’s south) and Sunshine Coast (to its north) [1] – that many families experienced their first taste of what is now widely celebrated as the beach lifestyle [2]. As one reflection has it: In the era before motels and resorts, a holiday at the Gold and Sunshine coasts usually meant either pitching a tent and camping by the beach or staying in a simple cottage owned by family or friends […] Simplicity, informality, individuality […] were the hallmarks of these humble places.2

Cryptic diversity within the Scytonema complex: Characterization of the paralytic shellfish toxin producer Heterosyctonema crispum, and the establishment of the family Heteroscytonemataceae (Cyanobacteria/Nostocales)

Strains of the freshwater filamentous, benthic cyanobacterium Scytonema crispum Agardh isolated from six sites in subtropical south-east Queensland were characterised using a combination of phenotypic and genetic traits. Morphologically, the strains were consistent with the description of Scytonemataceae sensu stricto, and the description of Scytonema crispum. However, phylogenetic analysis of the 16S rRNA gene, the 16S-23S rRNA operon, and the nifH gene revealed that these strains and three others from outside Australia formed a monophyletic clade distinct from Scytonema and other species in the Scytonemataceae. Collectively, this data suggests this group is sufficiently evolutionarily distinct to be placed in a new family, Heteroscytonemataceae fam. nov. Accordingly, the taxon previously known as S. crispum has been transferred to a new genus Heteroscytonema gen nov., as H. crispum. Some strains of H. crispum exhibited facultative production of paralytic shellfish toxins (PSTs). The concentration of PSTs produced by individual strains varied widely, from 2.7 μg g−1 to 171.3 μg g−1, and included C toxins, decarbamoyl saxitoxin (dcSTX), gonyautoxins (GTX2, GTX3 and GTX5), saxitoxin (STX) and uncharacterised PSTs. The majority of the Australian strains produced dcSTX as the dominant saxitoxin analogue, a significant finding given that dcSTX has approximately half the relative toxicity of STX. The PST profile varied within and between Australian strains of H. crispum and in strains collected from New Zealand and the United States. The sxtA gene, one of the determinants for the production of PSTs, was present in all strains in which PSTs were detected. The discovery of PST-producing H. crispum in the headwaters of a major drinking water reservoir presents a serious risk for potential human and animal exposure to these neurotoxic compounds and further highlights the importance of monitoring benthic cyanobacteria populations for potentially toxigenic species.

Climatically-Controlled River Terraces in Eastern Australia

In the tectonically stable rivers of eastern Australia, changes in response to sediment supply and flow regime are likely driven by both regional climatic (allogenic) factors and intrinsic (autogenic) geomorphic controls. Contentious debate has ensued as to which is the dominant factor in the evolution of valley floors and the formation of late Quaternary terraces preserved along many coastal streams. Preliminary chronostratigraphic data from river terraces along four streams in subtropical Southeast Queensland (SEQ), Australia, indicate regionally synchronous terrace abandonment between 7.5–10.8 ka. All optically stimulated luminescence ages are within 1σ error and yield a mean age of incision at 9.24 ± 0.93 ka. Limited samples of the upper parts of the inset floodplains from three of the four streams yield near-surface ages of 600–500 years. Terrace sediments consist of vertically accreted fine sandy silts to cohesive clays, while top stratum of the floodplains are comprised of clay loams to fine-medium sands. The inundation frequency of these alluvial surfaces depends on their specific valley setting. In narrow valley settings, where floodplains comprise <5% of the valley floor, terraces are inundated between the 20 and 50-year annual exceedance probability (AEP) flood, while in wide settings (floodplains >20%), the terraces are no longer inundated. Floodplain inundation frequencies also vary between these settings by an order of magnitude between 5- to 50-year AEP, respectively. The correlation of terrace abandonment within SEQ with fluvial and palaeoenvironmental records elsewhere in the subtropics, and more broadly across eastern Australia, are an indication that terrace abandonment has primarily been driven by climatic forcing. Contemporaneous channel incision in the early Holocene may have been driven by an increasingly warmer and wetter environment in SEQ, with a climate commensurate with the delivery of more extreme weather events. Following channel incision, many streams in SEQ have been largely confined to their entrenched “macrochannel” form that remains preserved within the valley floor.

Anomalous ring identification in two Australian subtropical Araucariaceae species permits annual ring dating and growth-climate relationship development

Almost all Australian tropical and subtropical regions lack annually-resolved long-term (multi-decadal to centennial scale) instrumental climate records. Reconstructing climate in these regions requires the use of sparse climate proxy records such as tree rings. Tree rings often archive annually-resolved centennial-scale climate information. However, many tropical and subtropical species have short life-spans, the timbers are poorly preserved, and there is a belief that the proxy records of these species are often compromised by ring anomalies. Additionally, for many species the relationship between climate (e.g. temperature and/or rainfall) and tree growth has not been established. These factors have led to tree-ring data being underutilized in the Australian subtropics. Trees in the Araucariaceae family, a common family in northern and eastern Australia, are both longer lived than many species in the Australian subtropics, present growth rings that are annual in nature, and their growth is known to vary with climate. In this study we examine two subtropical Araucariaceae species, Araucaria cunninghamii and Araucaria bidwillii, and quantify the relationship between their radial growth and climate variability. Ring anomalies including false, faint, locally absent, and pinching rings, are found to be present in these species, however, bomb-pulse radiocarbon dating of A. cunninghamii samples together with a whole tree approach helped to identify annual growth patterns despite such anomalous ring boundaries. Additionally, to determine which climate variables most influence growth in these species, dendrometers were installed at two locations in subtropical Southeast Queensland, Australia. We found that rainfall variability drives annual ring growth, while temperature constrains the onset and conclusion of the growth season each year. Our results demonstrate that through the use of A. cunninghamii and A. bidwillii trees which demonstrate annual growth in relation to climate variables there is potential to develop centennial scale climate reconstructions from the Australian subtropics. We provide recommendations on how to best identify ring anomalies in these species to help in the future development of long-term chronologies and climate reconstructions.

A new method for dating tree-rings in trees with faint, indeterminate ring boundaries using the Itrax core scanner

Eastern Australia is known to experience multi-decadal periods of flood and drought. Subtropical Southeast Queensland is one region where these devastating extreme events occur regularly yet a full understanding of their frequency and magnitude cannot be determined from the short duration (<100 years) climate data available for the region. Tree-rings are a potential source of long-term (>100 years) proxy rainfall information but locating suitable forest stands is difficult due to extensive land clearing by European settlers. Another factor deterring the use of trees as proxy data sources is that longer-lived species frequently contain anomalous rings, particularly faint rings, hindering their use for paleoclimate study. Here we present a method which overcomes the problems of identifying faint ring boundaries in trees by using X-radiographs and density patterns developed on the Itrax core scanner. We analysed 39 tree cores from 20 trees at a site in D'Aguilar National Park located just north of Brisbane city in Queensland, Australia. Each core had a 2 mm lath cut perpendicular to its rings which was then passed through an Itrax core scanner. The tree-ring boundaries were identified on the image by both the visual features in the radiograph and the change in density observed between rings. From this information we developed a tree-ring chronology. The chronology was checked using bomb-pulse radiocarbon dating on five trees to confirm the annual nature of the rings, and to correct dating errors in the chronology due to false rings which are common in this species. Climate response function analysis showed Austral annual rainfall (June–May) was the dominant environmental variable driving tree growth. Finally, a 69-year statistically significant reconstruction of Brisbane precipitation was produced showing that this non-destructive Itrax ring identification technique together with age validation by bomb-pulse radiocarbon dating is useful for dendroclimatological studies of trees with faint ring boundaries.

Breeding objective for strawberry in subtropical southeast Queensland

An 'aggregate economic' value (H), which is a combination of genetic control and relative economic value of traits, for all traits in the breeding objective was developed to aid in multitrait selection of strawberry cultivars in the subtropical southeast Queensland program. A profitability index for 12 traits was calculated from the effect of unit changes in each trait on changes in production costs and profitability. The index was applied to the breeding values of 3008 genotypes to produce estimates of H. H was validated by its high correlation (R2=0.77) with year of selection (1945-1998) for commercial cultivars. H values for 3008 genotypes ranged from -0.36 to +0.28, when the zero value was set to the value of the cultivar 'Festival', which is the main cultivar grown in southeast Queensland. Modelling indicated that the gross margins were highly linearly related (R2>0.98) to H values where the genotype occupied less than 50% of total area planted in the industry, but this relationship became quadratic when the genotype occupied higher percentages of the total area planted to strawberries, and variation in gross margin increased as H values increased. H is efficient in identifying economically superior genotypes, but, when deploying new genotypes with high H, impacts on farm gross margin due to high adoption rates should also be considered.

Can changes in ant diversity along elevational gradients in tropical and subtropical Australian rainforests be used to detect a signal of past lowland biotic attrition?

Increasing temperatures are predicted to have profound effects on montane ecosystems. In tropical forests, biotic attrition may reduce lowland diversity if losses of species due to upslope range shifts are not matched by influxes of warmer-adapted species, either because there are none or their dispersal is impeded. Australian rainforests consist of a north-south chain of patches, broken by dry corridors that are barriers to the dispersal of rainforest species. These rainforests have repeatedly contracted and expanded during Quaternary glacial cycles. Many lowland rainforests are expansions since the Last Glacial Maximum and may, therefore, show a signal of historical biotic attrition. We surveyed ants from replicated sites along three rainforest elevational transects in eastern Australia spanning 200 to 1200m a.s.l. and nearly 14 degrees of latitude. We examined elevational patterns of ant diversity and if there was possible evidence of lowland biotic attrition. Each transect was in a different biogeographic region; the Australian Wet Tropics (16.3 degrees S), the central Queensland coast (21.1 degrees S) and subtropical south-eastern Queensland (28.1 degrees S). We calculated ant species density (mean species per site) and species richness (estimated number of species by incorporating site-to-site species turnover) within elevational bands. Ant species density showed no signal of lowland attrition and was high at low and mid-elevations and declined only at high elevations at all transects. Similarly, estimated species richness showed no evidence of lowland attrition in the Wet Tropics and subtropical south-east Queensland; species richness peaked at low elevations and declined monotonically with increasing elevation. Persistence of lowland rainforest refugia in the Wet Tropics during the Last Glacial Maximum and latitudinal range shifts of ants in subtropical rainforests during the Holocene climatic optimum may have counteracted lowland biotic attrition. In central Queensland, however, estimated richness was similar in the lowlands and mid-elevations, and few ant species were indicative of lower elevations. This may reflect historical biotic attrition due perhaps to a lack of lowland glacial refugia and the isolation of this region by a dry forest barrier to the north.

Reassessing the risk of microbial contamination from roosting cormorants in source water supply reservoirs

A previous water quality risk assessment of source water supply reservoirs in subtropical southeast Queensland (Australia) evaluated little black cormorants (Phalocrocorax sulcirostris) roosting on intake infrastructure as potentially posing an extreme risk of microbial contamination through direct deposition of fecal matter to the aquatic environment. To evaluate this risk rating, we assessed populations of little black cormorants occupying 3 intake structures across 2 reservoirs, enumerated Escherichia coli (E. coli) levels collected from fecal matter, and estimated a daily E. coli load to the reservoir for each population. Concurrently, we supplemented the existing routine monthly water quality monitoring program with targeted water sampling to measure E. coli concentrations in water at the 3 water intake points and at 2 sites without extant cormorant populations. Up to 3.9 × 1014 E. coli organisms were estimated to be produced per day by the largest population surveyed. Cormorants were present at intake sites and absent from reference sites; however, concentrations of E. coli were not significantly higher in water at intake sites compared with reference sites (p = 0.793 vs. p = 0.1069, respectively), and there was no significant relationship (p = 0.9671) between cormorant numbers and water column concentrations of E. coli. The inability to quantify significant differences in microbial concentrations among sites suggests a more intensive sampling regime is required to clarify the relative contribution of contamination sources. Populations of roosting cormorants in our study reservoirs are unlikely to pose an extreme risk to source water quality when compared to other catchment-based inputs that dominate microbial pollution.

Testing the Gippsland Basin zonation in northern Australia: palynostratigraphical analysis of a 23 Ma 40Ar/39Ar dated claystone from Toowoomba, southeast Queensland

The spore-pollen zonation developed for the Gippsland Basin, southeast Australia, is widely used to date Paleogene–Neogene terrestrial sediments elsewhere in Australia. Microfloras preserved in an argon-40 (40Ar)/argon-39 (39Ar) dated 23 Ma claystone on the summit of the Great Dividing Range at Toowoomba in subtropical southeast Queensland indicate the Gippsland zonation, and the parallel schemata developed for the epicontinental Murray Basin in southeastern Australia provide only a general guide to the age of Late Paleogene–Neogene sediments as far north as Queensland. The finding reiterates the need to develop regional spore-pollen palynostratigraphies for Queensland (and northern Australia) centred on Cenozoic microfloras whose geologic age can be independently verified by other dating techniques. The same microfloras, however, are reliable evidence of past vegetation and climates, in this instance that a form of Nothofagus-gymnosperm temperate rainforest was colonising basaltic soils at Toowoomba during the Oligo-Miocene transition when southeast Queensland was located c. 15° south of its present latitudial position.

Diversity and abundance of fungivorous thrips (Thysanoptera) associated with leaf-litter and bark across forest types and two tree genera in subtropical Australia

Leaf-litter thrips were much more common and diverse in dry sclerophyll forest than in wetter forest types in subtropical southeast Queensland, Australia. In dry sclerophyll forest, the species composition of thrips in leaf-litter was strongly differentiated from the thrips fauna associated with bark of the trees Eucalyptus major and Acacia melanoxylon (4 of 34 species in common). The species composition of bark-dwelling thrips was similar across the two tree species and also across two eucalypts with different bark types, Eucalyptus major (flaky) and Eucalyptus siderophloia (rough). The diversity of thrips from the leaf-litter was not differentiated across all of these tree species. Virtually all thrips collected were Phlaeothripidae, subfamilies Idolothripinae and Phlaeothripinae. Idolothripinae were associated almost exclusively with leaf-litter, but Phlaeothripinae were in leaf-litter and bark. The association of fungal-feeding thrips with dry sclerophyll forest raises questions about their ecological requirements and the role they play in nutrient cycling.

Bacterially mediated iron cycling and associated biogeochemical processes in a subtropical shallow coastal aquifer: implications for groundwater quality

Bacterially mediated iron redox cycling exerts a strong influence on groundwater geochemistry, but few studies have investigated iron biogeochemical processes in coastal alluvial aquifers from a microbiological viewpoint. The shallow alluvial aquifer located adjacent to Poona estuary on the subtropical Southeast Queensland coast represents a redox-stratified system where iron biogeochemical cycling potentially affects water quality. Using a 300 m transect of monitoring wells perpendicular to the estuary, we examined groundwater physico-chemical conditions and the occurrence of cultivable bacterial populations involved in iron (and manganese, sulfur) redox reactions in this aquifer. Results showed slightly acidic and near-neutral pH, suboxic conditions and an abundance of dissolved iron consisting primarily of iron(II) in the majority of wells. The highest level of dissolved iron(III) was found in a well proximal to the estuary most likely a result of iron curtain effects due to tidal intrusion. A number of cultivable, (an)aerobic bacterial populations capable of diverse carbon, iron, or sulfur metabolism coexisted in groundwater redox transition zones. Our findings indicated aerobic, heterotrophic respiration and bacterially mediated iron/sulfur redox reactions were integral to carbon cycling in the aquifer. High abundances of dissolved iron and cultivable iron and sulfur bacterial populations in estuary-adjacent aquifers have implications for iron transport to marine waters. This study demonstrated bacterially mediated iron redox cycling and associated biogeochemical processes in subtropical coastal groundwaters using culture-based methods.

Gully erosion in sub-tropical south-east Queensland, Australia

Analysis of aerial photographs shows that gully erosion in three catchments in south-east Queensland, Australia, was initiated by post-European settlement. Analysis of historical rainfall and runoff showed that for two of the catchments, gully initiation occurred during wet decadal periods. Historical descriptions of the settlement of south-east Queensland and Moreton Bay detail significant changes in landuse and clearing of vegetation for grazing of domestic animals and urban development since 1842. Historical gully erosion rates varied from 14 to 1826m2yr−1 and erosion rates are positively correlated with catchment area multiplied by slope. Analysis of gully erosion rates showed a linear increase in planemetric area over time. Together, these data show gully initiation in the three catchments is associated with post-European settlement land use practices and above average rainfall and runoff. Initiation of gullying across the region is similar to the previous studies in south-east Australia and highlights the sensitivity of the landscape to vegetation clearing and alternating periods of above average rainfall and drought.

Performance evaluation of eight contemporary passive solar homes in subtropical Australia

Subtropical south-east Queensland’s expanding population is expected to lead to a demand for an additional 754,000 dwellings by 2031. A legacy of poor housing design, minimal building regulations, an absence of building performance evaluation and various social and market factors has lead to a high and growing penetration of, and reliance on, air-conditioners to provide comfort in this relatively benign climate. This reliance impacts on policy goals to adapt to and mitigate against global warming, electricity infrastructure investment and household resilience. Based on the concept of bioclimatic design, this field study scrutinizes eight non-air conditioned homes to develop a deeper understanding of the role of contemporary passive solar architecture in the delivery of thermally comfortable and resilient homes in the subtropics. These homes were found to provide inhabitants with an acceptable level of thermal comfort (18–28°C) for 77–97% of the year. Family expectations and experiences of comfort, and the various design strategies utilized were compared against the measured performance outcomes. This comparison revealed issues that limited quantification and implementation of design intent and highlighted factors that constrained system optimisation.

Spatio-temporal variation in soil derived nitrous oxide emissions under sugarcane

Nitrous oxide (N 2O) is a significant greenhouse gas with a global warming potential that is 300 times than that of carbon dioxide. Soil derived N 2O emissions usually display a high degree of spatial and temporal variability because of their dependence on soil chemical and physical properties, and climate dependent environmental factors. However, there is little research that incorporates spatial dependence in the estimation of N 2O emissions allowing for environmental factors in the same model. This study aims to examine the impact of two environmental factors (soil temperature and soil moisture) on N 2O emissions and explore the spatial structure of N 2O in the sub-tropical South East Queensland region of Australia. The replicated data on N 2O emissions and soil properties were collected at a typical sugarcane land site covering 25 uniform grid points across 3600 m 2 between October 2007 and September 2008. A Bayesian conditional autoregressive (CAR) model was used to model spatial dependence. Results showed that soil moisture and soil temperature appeared to have substantially different effects on N 2O emissions after taking spatial dependence into account in the four seasons. There was a substantial variation in the spatial distribution of N 2O emission in the different seasons. The high N 2O emission regions were accompanied by high uncertainty and changed in varying seasons in this study site. Spatial CAR models might be more plausible to elucidate and account for the uncertainty arising from unclear variables and spatial variability in the assessment of N 2O emissions in soils, and more accurately identify relationships with key environmental factors and help to reduce the uncertainty of the soil parameters.

Evaluation of quantitative real-time PCR to characterise spatial and temporal variations in cyanobacteria, Cylindrospermopsis raciborskii (Woloszynska) Seenaya et Subba Raju and cylindrospermopsin concentrations in three subtropical Australian reservoirs

Three drinking water storage reservoirs in subtropical southeast Queensland, Australia have regular blooms of the toxic cyanobacterium Cylindrospermopsis raciborskii that can produce cylindrospermopsins. We tested water samples from 16 sites in 3 reservoirs on 2 sampling occasions during a bloom of C. raciborskii in the austral summer and autumn of 2007. Using a range of parameters including quantitative real-time PCR, microscope cell counts and HPLC–MS/MS we correlated the 16S ribosomal RNA gene with total cyanobacteria, the rpoC1 gene with C. raciborskii cell concentrations, and the cyrC gene with cylindrospermopsin concentrations to assess spatial and temporal variability within and between reservoirs. While the correlation between cyrC and cylindrospermopsin cell quotas was good (mean r 2 = 0.61 for February samples and 0.75 for March samples), the correlation between total cyanobacteria and the 16S ribosomal RNA gene, and between C. raciborskii and the rpoC1 gene were poor indicating that further work is needed to develop these novel molecular methods. Spatial and temporal analysis of the distribution of rpoC1, cylindrospermopsin cell quotas, and a range of physical and chemical water quality parameters showed the greatest variation occurred between reservoirs, and within the largest and most spatially diverse reservoir. This suggests that populations of C. raciborskii strains with inherently different cylindrospermopsin cell quotas may be an important driver of toxicity in these reservoirs. An outcome of this study was the observation that deoxycylindrospermopsin always exceeded the cylindrospermopsin cell quota by up to 5-fold, and that a peak cell quota of 60 fg (cylindrospermopsin + deoxycylindrospermopsin) cell −1 was measured.

Comparative productivity of irrigated short-term ryegrass (Lolium multiflorum) pasture receiving nitrogen, grown alone or in a mixture with white (Trifolium repens) and Persian (T. resupinatum) clovers

Dairy farms in subtropical Australia use irrigated, annually sown short-term ryegrass (Lolium multiflorum) or mixtures of short-term ryegrass and white (Trifolium repens) and Persian (shaftal) (T. resupinatum) clover during the winter–spring period in all-year-round milk production systems. A series of small plot cutting experiments was conducted in 3 dairying regions (tropical upland, north Queensland, and subtropical southeast Queensland and northern New South Wales) to determine the most effective rate and frequency of application of nitrogen (N) fertiliser. The experiments were not grazed, nor was harvested material returned to the plots, after sampling. Rates up to 100 kg N/ha.month (as urea or calcium ammonium nitrate) and up to 200 kg N/ha every 2 months (as urea) were applied to pure stands of ryegrass in 1991. In 1993 and 1994, urea, at rates up to 150 kg N/ha.month and to 200 kg N/ha every 2 months, was applied to pure stands of ryegrass; urea, at rates up to 50 kg N/ha.month, was also applied to ryegrass–clover mixtures. The results indicate that applications of 50–85 kg N/ha.month can be recommended for short-term ryegrass pastures throughout the subtropics and tropical uplands of eastern Australia, irrespective of soil type. At this rate, dry matter yields will reach about 90% of their potential, forage nitrogen concentration will be increased, there is minimal risk to stock from nitrate poisoning and there will be no substantial increase in soil N. The rate of N for ryegrass–clover pastures is slightly higher than for pure ryegrass but, at these rates, the clover component will be suppressed. However, increased ryegrass yields and higher forage nitrogen concentrations will compensate for the reduced clover component. At application rates up to 100 kg N/ha.month, build-up of NO3–-N and NH4+-N in soil was generally restricted to the surface layers (0–20 cm) of the soil, but there was a substantial increase throughout the soil profile at 150 kg N/ha.month. The build-up of NO3–-N and NH4+-N was greater and was found at lower rates on the lighter soil compared with heavy clays. Generally, most of the soil N was in the NO3–-N form and most was in the top 20 cm.

Trophic shifts in three subtropical Australian halfbeaks (Teleostei:Hemiramphidae)

To elucidate the trophic status of hemiramphids, the diets of three species from subtropical south-east Queensland were investigated. All undergo a marked ontogenetic trophic shift from an animal to plant diet, which occurred between 50 and 70 mm standard length (Ls) for Arrhamphus sclerolepis krefftii (freshwater) and between 80 and 110 mm Ls for both Hyporhamphus regularis ardelio and H. quoyi (both marine). After the ontogenetic shift, the diet of A. sclerolepis krefftii is dominated by filamentous algae, whereas the diet of the two marine species is dominated by Zostera capricorni. The two marine species feed mainly during the day, with gut fullness dropping markedly after dusk. Neither showed evidence of a diel trophic shift between herbivory and carnivory that has been reported for other hemiramphids. The lack of diel trophic switching in these subtropical hemiramphids may suggest that latitudinal effects on daylength and/or water temperature may influence the extent to which hemiramphids switch periodically to animal prey from an otherwise essentially herbivorous diet in order to balance their nutrient requirements.

Population dynamics and economic threshold of the nematodes Radopholus similis and Pratylenchus goodeyi on banana in Australia

To help banana growers to decide when to apply nematicide, economic thresholds were determined for tropical north Queensland, subtropical south-east Queensland and northern New South Wales, Australia. This was done by monitoring nematode populations, root damage and growth parameters of bunching pseudostems in several commercial crops for several years. There was no significant consistent change in the disease index in consecutive years in any of the regions, although there was great variation between crops. However, on two crops in the tropics, the disease index of roots increased. To reduce the risk of not applying nematicide when required, the economic threshold was adjusted down to allow for this increase on some crops. In the tropics with a crop value of $25 000 ha−1 year−1, the economic threshold occurred at a root disease index = 9.2-15.6. In the subtropics with a crop value of $10 000-15 000, the economic threshold occurred at a root disease index = 20.5-35.5. In the subtropics, Radopholus similis (burrowing nematode) was as pathogenic as Pratylenchus goodeyi (lesion nematode) as measured by root necrosis. However, both nematodes were less pathogenic in the subtropics than was R. similis in the tropics. In the subtropics, R. similis tended to be more numerous in warmer months and P. goodeyi in cooler months.