Long-term persistence of prairie dog towns: insights for designing networks of prairie reserves

We studied the persistence of 281 towns of the black-tailed prairie dog (Cynomys ludovicianus) from surveys conducted in Oklahoma in 1966 and 1967 and again in 1988 and 1989. Town size during initial surveys tended to increase along a northwesterly gradient toward the panhandle of the State, and larger towns tended to occur in clusters while small towns occurred as isolates. Persistence of prairie dog towns from 1967 to 1989 increased significantly with town size and decreased with town isolation, with higher persistence for towns that occurred in landscapes with greater coverage of other towns. Comparisons to our studies of persistence of towns mapped in 1989 and resurveyed in 1997 [Journal of Mammalogy, 82 (2001) 937] indicate that the latter part of this pattern was reversed, with persistence highest for the most isolated towns. The reversal in persistence patterns may be attributed to an outbreak of plague (Yersinia pestis) during the early 1990s, favoring isolated towns. We recommend adaptive management and a mixed strategy for the development of prairie reserves which should include networks (clusters) of relatively large reserves, along with large but isolated reserves across the species’ native range.     

Terrestrial vertebrate communities at black-tailed prairie dog (Cynomys ludovicianus) towns

We capitalized on a regional-scale, anthropogenic experiment—the reduction of black-tailed prairie dog (Cynomys ludovicianus) towns across the Great Plains of North America—to test the hypothesis that decline of this species has led to declines in diversity of native grassland vertebrates of this region. We compared species richness and species composition of non-volant mammals, reptiles and amphibians at 36 prairie dog towns and 36 paired sites in the Panhandle Region of Oklahoma during the summers and falls of 1997, 1998 and 1999. We detected 30 species of mammals, 18 species of reptiles and seven species of amphibians. Comparisons between communities at prairie dog towns and paired sites in the adjacent landscape indicated that while richness per se was not necessarily higher in towns, they did harbor significantly more rare and imperiled species. Species that were positively associated with prairie dog towns during one or both seasons (summer and fall) included badgers (Taxidea taxus), eastern cottontails (Sylvilagus floridanus), coyotes (Canis latrans), grasshopper mice (Onychomys leucogaster), swift fox (Vulpes velox), pronghorn antelopes (Antilocapra americana), striped skunks (Mephitis mephitis), white-tailed deer (Odocoileus virginianus), cattle, thirteen-lined ground squirrels (Spermophilus tridecemlineatus), black-tailed jackrabbits (Lepus califonicus), barred tiger salamanders (Ambystoma tigrinum), plains spadefoot toads (Scaphiopus bombifrons), Great Plains toad (Bufo cognatus), Woodhouse's toad (Bufo woodhousii), prairie rattlesnakes (Crotalis viridis), western plains garter snakes (Thamnophis radix), Texas horned lizards (Phrynosoma cornutum), and ornate box turtles (Terrapene ornata).     

Autumn swarming behaviour of Natterer’s bats in the UK: Population size, catchment area and dispersal

Many species of temperate bats visit underground sites in autumn, prior to hibernation, and chase each other in and around the entrances in an event known as autumn swarming. It has been suggested that swarming is a mating event that facilitates gene flow between bats from otherwise isolated summer colonies. We describe swarming behaviour at a cluster of four caves in the North of England and provide direct evidence for seasonal migration of Natterer’s bats (Myotis nattereri ) between these caves and many summer nursery roosts in a catchment area of at least 60 km radius. Mark-recapture analysis suggests that an estimated 2000-6000 Natterer’s bats use the three best-studied caves, together with smaller numbers of four other species: M. daubentonii, M. brandtii, M. mystacinus and Plecotus auritus. Recaptures also show that there is a small interchange of bats between these three caves, which are 0.6-1.5 km apart. Capture rates, automatic logging and video recordings at one cave suggest that an average 310-400 bats visit the cave each night. Mating at swarming sites would be particularly important for gene flow if a species showed no other dispersal pattern. We provide evidence for natal philopatry, with little or no dispersal, in both sexes of Natterer’s bats. The protection of swarming sites is discussed in light of our findings.     

Insect visitation and pollen deposition in an invaded prairie plant community

Invasive plants with large flowering displays have been shown to compete with native plants for pollinator services, often to the detriment of native plant fitness. In this study, we compare the pollinator communities and pollen deposited on stigmas of native plant species within and away from stands of the invasive alien plant, leafy spurge (Euphorbia esula) at a large natural area in North Dakota, USA. Specifically, we ask if infestation influences (1) visitation rates and taxonomic composition of visitors to native flowers, and (2) the amount of conspecific pollen, number of pollen species, and proportion of heterospecific pollen on stigmas of native plants. We observed visits to selected native species during May and June 2000 and 2001. Stigmas were collected from a subsample of the flowers within these plots, squashed, and the pollen identified and counted under a light microscope. Visitation varied between years and among species of native plants: infestation had mixed effects in 2000 but visitation, especially by halictids was always lower within infestations in 2001. Despite differences in visitation between years, we found significantly less conspecific pollen on stigmas from infested plots in six of eight cases; we never found significantly more conspecific pollen on stigmas from within infestations. Our results emphasize the temporal variability in plant-pollinator relations and the added complexity imposed by an invasive species that will always make prediction of effects difficult. Nonetheless, the consistently lower conspecific pollen counts on native stigmas within infestations, regardless of visitation, suggest the likelihood of negative effects.     

Surface water and ground-water thresholds for maintaining Populus-Salix forests, San Pedro River, Arizona

Ground-water and surface flow depletions are altering riparian ecosystems throughout the southwestern United States, and have contributed to the decline of forests of the pioneer trees Populus fremontii (Fremont cottonwood) and Salix gooddingii (Goodding willow). On some rivers, these forests have been replaced by shrublands of Tamarix ramosissima (tamarisk), a drought-tolerant species from Eurasia. The physiological response of these three riparian plant species to decreases in water availability is well studied, but little attention has been given to shifts in community and population structure in response to declines in surface flow and ground-water levels. Based on study of 17 sites spanning a hydrologic gradient, this research identified hydrologic thresholds above which P. fremontii-S. gooddingii maintain tall dense stands with diverse age classes, and above which they are more abundant than T. ramosissima stands along the San Pedro River in Arizona. Surface flow permanence was the hydrologic variable that explained most of the variance in species abundance and relative importance, with inter-annual ground-water fluctuation and depth to ground water also contributing. P. fremontii and S. gooddingii were dominant over T. ramosissima at sites where surface flow was present more than 76% of the time, inter-annual ground-water fluctuation was less than 0.5 m, and average maximum depth to ground water was less than 2.6 m, during a two-year period of data collection. Because T. ramosissima is a shrub species with smaller leaves and lower canopy heights than P. fremontii and S. gooddingii, these shifts in species composition corresponded to decreases in maximum canopy height and upper stratum (above 8 m) vegetation volume as site water availability declined. As well, sites with deeper water tables and more intermittent flows had greater areal coverage of shrublands and less of woodlands. The altered vegetation structure along dewatered rivers may lower wildlife habitat quality. This study provides river managers with quantitative hydrologic guidelines for conserving tall dense P. fremontii-S. gooddingii stands and emphasizes the importance of maintaining long-term hydrologic conditions that are favorable to these species. The study also has implications for riparian restoration and invasive species management by suggesting that desired outcomes may be achieved through restoration of physical processes.     

Control of one invasive plant species allows exotic grasses to become dominant in northern Great Plains grasslands

Decline of leafy spurge (Euphorbia esula) in the northern Great Plains of the US is generally viewed as a success story for biological control, but quality of the vegetation that survived the infestation is key to recovery of ecosystem function. In addition, effects of other invasive species, notably cool-season exotic grasses, must be taken into account. Objectives of this study were (1) to evaluate direction and significance of changes in biomass of native and exotic grasses, forbs, and leafy spurge and in plant species composition following control of leafy spurge by flea beetles and (2) to evaluate the relative effects of leafy spurge and exotic grasses on biomass of native grasses, biomass of forbs, and richness of native species. We monitored species composition (1998-2003 and 2008) and biomass (2000, 2002, 2003 and 2008) of these groups on spurge-infested and noninfested permanent plots at three sites with unbroken prairie sod in North Dakota, USA. We found little evidence, in terms of species richness or biomass of native grasses or forbs, that leafy spurge was being replaced by desirable native species, although desirable as well as weedy and exotic species were characteristic of 2008 vegetation at all three sites. Structural equation models revealed that leafy spurge had temporally intermittent negative effects on forb biomass and species richness, but no effects on native grasses. In contrast, exotic grass had consistently strong, negative effects on native grass biomass, as well as stronger negative effects than leafy spurge on native species richness. Although substantial native plant diversity remains at these sites, exotic grasses pose an important threat to these crucial building blocks of native prairie ecosystems.     

Persistence of toxins and cells of Bacillus thuringiensis subsp. kurstaki introduced in sprays to Sardinia soils

Sprays of commercial insecticidal preparations of the bacterium, Bacillus thuringiensis subsp. kurstaki (Btk), usually a mixture of cells, spores and parasporal crystals, have been used for the last 10 yr in Sardinia (Italy) to protect cork oak forests against the gypsy moth (Lymantria dispar L.). Until now, the protective antilepidopteran efficacies of each of the various spray treatments rather than their effects on the environment have been evaluated. Consequently, the persistence of Btk and its toxin, released in sprays (FORAY 48B^®), in soils of cork oak stands, located in Orotelli, Tempio Pausania and Calangianus (Sardinia), were investigated. In the Calangianus soil, the numbers of Btk remained essentially constant for 28 months (the longest time studied) after spraying, indicating that Btk was able to compete with the indigenous microbial community; the toxin was detected 28 months after spraying by immunological assay, but at a reduced concentration; and the larvicidal activity decreased essentially linearly to 14 months and then decreased markedly between 14 and 28 months. In the Tempio Pausania and Orotelli soils, cells of Btk were detected, whereas the toxin was not detected by immunological and larvicidal assays, 52 and 88 months (the longest times studied) after spraying, respectively. The numbers of Btk cells detected were probably too low to account for the presence of the toxin in all of the soils studied, as there was no correlation between numbers of Btk and toxin detected by immunological assays (correlation coefficient of −0.66) in the Calangianus soil. Our results indicated that Btk and its toxin introduced into soils in sprays can persist for long periods (at least 88 months for Btk and at least 28 months for its toxin).     

Effects of grazing practices and fossorial rodents on a winter avian community in Chihuahua, Mexico

Chihuahuan Desert grasslands are important wintering grounds for grassland and shrub-adapted birds. Many species belonging to these assemblages are currently exhibiting population declines. One area recognized for its importance to biological diversity, including grassland birds, is the Janos-Nuevo Casas Grandes black-tailed prairie dog (Cynomys ludovicianus) complex in northwestern Chihuahua, Mexico, an area containing 58 colonies with 30,000 ha of prairie dogs. This is one of the largest remaining prairie dog complexes and the only intact complex in the Chihuahuan Desert. In its current condition, a large percentage of this complex is of reduced value to wildlife. Overgrazing on communal (ejido) lands has resulted in areas being comprised of annual grasses and forbs. The density of active prairie dog burrows and banner-tailed kangaroo rat (Dipodomys spectabilis) mounds as well as avian diversity and abundance were lower on ejido lands than an adjacent private ranchland with and without prairie dogs. Few avian species used overgrazed portions of the prairie dog colony. Community similarity among plot types was low due to different management practices and differences on and off colony. To retain, and in many instances restore the biological diversity of this important region it is essential to work with local ejidos on grazing management.     

Using habitat models to determine conservation priorities for pond-breeding amphibians in a privately-owned landscape of northern Idaho, USA

As rural landscapes experience increasing levels of residential development, the persistence of species that rely on them will depend on informed planning and management decisions. An understanding of habitat requirements is essential for setting priorities and developing landscape-level plans for the survival of these species. In many temperate rural landscapes, artificially created ponds may be the only wetlands available for aquatic reproduction by amphibians. The introduction of non-native fish into these ponds reduces survival and prohibits successful reproduction of many native pond-breeding amphibians. We surveyed 105 randomly selected wetlands in a primarily privately-owned, rural landscape in north Idaho, USA, for pond-breeding amphibian larvae in 2004 and 2005. We used an information theoretic multimodel inference and an algorithmic (random forests) approach to model habitat for each species based on local and landscape characteristics. We also used a mail survey to quantify how landowners value fish in their wetlands and their plans for future wetland development and fish stocking. Sixty-seven percent of pond owners reported that fishing in their pond was at least slightly important to them and 36% of owners indicated that they were at least 50% likely to add fish to their ponds in the next 5-10 years. Landscape change predictions for this area indicate that forests will become more open due to thinning; habitat models indicated that this is likely to be detrimental to long-toed salamanders and beneficial to Pacific treefrogs. Habitat models also indicate that Columbia spotted frog breeding sites consist of wetlands on flat ground with high solar insolation and that this species is sensitive to nearby development, indicating that as this landscape becomes further developed, this species may require habitat protection for persistence.     

Inferring extinction from biological records: Were we too quick to write off Miss Waldron’s Red Colobus Monkey (Piliocolobus badius waldronae)?

We are now entering a time of immense environmental upheaval where experts are increasingly required to provide conservation assessments. Quantitative assessment of trends in species’ range and abundance is costly, requiring extensive field studies over a long period of time. For many species in dense habitats, it may be very difficult to establish reliable and sensitive survey and monitoring techniques, which are able to warn of potentially catastrophic population declines. Unfortunately many other species are only known through a few ‘chance’ sightings or a handful of museum specimens and therefore extinction may be even harder to ascertain. In 2000 Miss Waldron’s Red Colobus, Piliocolobus badius waldronae, was reported as extinct, but since then (in 2001) a single specimen has been collected. Four probabilistic methods were used to infer extinction based on a record of sightings of the subspecies. Based on the date when the extinction statement of Miss Waldron’s Red Colobus was made, all four methods returned probability values >0.05, suggesting that the subspecies is extant, but is extremely rare. If we cannot successfully monitor populations of critically endangered taxa, it becomes almost impossible to predict their extinction with any certainty and we can expect increasing numbers of false alarms in future years, which may undermine the potential for conservation action and, more worryingly, public support for conservation.     

The abundance and efficacy of Rhizobium leguminosarum bv. viciae in cultivated soils of the eastern Canadian prairie

For optimum production, the use of commercial rhizobial inoculant on pea (Pisum sativum L.) at seeding is necessary in the absence of compatible rhizobial strains or when rhizobial soil populations are low or symbiotically ineffective. Multiple site experiments were conducted to characterize the abundance and effectiveness of resident populations of Rhizobium leguminosarum bv. viciae (Rlv) in eastern Canadian prairie soils. A survey of 20 sites across a broad geographical range of southern Manitoba was carried out in 1998 and was followed by more intensive study of five of the sites in 1999 and 2000. Appreciable nodulation of uninoculated pea was observed at all sites which had previously grown inoculated pea. However, uninoculated pea grown at two sites, which had not previously grown pea, had negligible nodulation. Likewise, wild Lathyrus sp. and Vicia sp. plants collected from uncultivated areas adjacent to agricultural sites were poorly nodulated. In the more intensively studied sites, there was a tendency towards higher nodulation in pea plants receiving commercial inoculant containing Rlv strain PBC108 across all site-years (e.g., 4.7% in nodulation and 22% in nodule mass), but the effect was significant at only 2 of 10 site-years. Despite a relatively high range of soil pH (6-8), regression analysis indicated that decreasing soil pH resulted in lower nodulation rates. Likewise, electrical conductivity (EC) was correlated to nodulation levels, however the effect of EC was likely more indicative of the influence of soil texture and organic matter than salinity. As with nodulation, commercial inoculation tended to increase above-ground dry matter (DM) and fixed-N (estimated by the difference method) at the early pod-filling stage, but again the effects were significant at only 2 of 10 site-years. Specifically, above-ground DM and fixed-N levels were up to 29 and 51% greater, respectively, in inoculated compared to non-inoculated treatments at these sites. Addition of N-fertilizer at a rate of 100 kg N ha⁻¹ decreased nodulation at almost all site-years (by as much as 70% at one site), but rarely resulted in increases in above-ground DM compared to inoculated plots. The study indicates for the first time that populations of infective, and generally effective strains of Rlv occur broadly in agricultural soils across the eastern Canadian prairie, but that there is a tendency for increased symbiotic efficiency with the use of commercial inoculant.     

The genetic diversity of Rhizobium leguminosarum bv. viciae in cultivated soils of the eastern Canadian prairie

Soil populations of Rhizobium leguminosarum bv. viciae (Rlv) that are infective and symbiotically effective on pea (Pisum sativum L.) have recently been shown to be quite widespread in agricultural soils of the eastern Canadian prairie. Here we report on studies carried out to assess the genetic diversity amongst these endemic Rlv strains and to attempt to determine if the endemic strains arose from previously used commercial rhizobial inoculants. Isolates of Rlv were collected from nodules of uninoculated pea plants from 20 sites across southern Manitoba and analyzed by plasmid profiling and PCR-RFLP of the 16S-23S rDNA internally transcribed spacer (ITS) region. Of 214 field isolates analyzed, 67 different plasmid profiles were identified, indicating a relatively high degree of variability among the isolates. Plasmid profiling of isolates from proximal nodules (near the base of the stem) and distal nodules (on lateral roots further from the root crown) from individual plants from one site suggested that the endemic strains were quite competitive relative to a commercial inoculant, occupying 78% of the proximal nodules and 96% of the distal nodules. PCR-RFLP of the 16S-23S rDNA ITS also suggested a relatively high degree of genetic variability among the field isolates. Analysis of the PCR-RFLP patterns of 15 selected isolates by UPGMA indicated two clusters of three field isolates each, with simple matching coefficients (SMCs) ≥0.95. However, to group all field isolates together, the SMC has to be reduced to 0.70. Regarding the origin of the endemic Rlv strains, there were few occurrences of the plasmid profiles of field isolates being identical to the profiles of inoculant Rlv strains commonly used in the region. Likewise, the plasmid profiles of isolates from nodules of wild Lathyrus plants located near some of the sites were all different from those of the field isolates. However, comparison of PCR-RFLP patterns suggested an influence of some inoculant strains on the chromosomal composition of some of the field isolates with SMCs of ≥0.92. Overall, plasmid profiles and PCR-RFLP patterns of the isolates from endemic Rlv populations from across southern Manitoba indicate a relatively high degree of genetic diversity among both plasmid and chromosomal components of endemic strains, but also suggest some influence of chromosomal information from previously used inoculant strains on the endemic soil strains.     

Protecting more than the wetland: The importance of biased sex ratios and habitat segregation for conservation of the Hine’s emerald dragonfly, Somatochlora hineana Williamson

Within species habitat use may depend on age, season or sex of an individual. The distribution of males and females may vary both temporally and spatially due to differences in the costs of reproduction and the distribution of critical resources. Conservation of a species requires knowledge of the habitat use of both sexes in order to predict the population size and protect all habitats that a species requires. Adult dragonfly populations often have highly male-biased sex ratios at the breeding habitat. This bias has been attributed to females using alternative habitats to avoid male harassment, or to high female mortality. We monitored adult Hine’s emerald dragonfly (Somatochlora hineana Williamson) populations, in breeding and non-breeding habitats in Door County, Wisconsin and found significant differences in habitat use between males and females. Males primarily used wetland habitats, while females primarily used dry meadows and marginal breeding habitats, only coming into wetlands to lay-eggs or find mates. We assessed food resources in the different habitats and found that high quality insect prey (primarily adult Diptera) were more available in the wetland habitat, indicating that these areas were likely a more productive foraging area for adult dragonflies. The fact that females appear to avoid the wetland habitat is consistent with the hypothesis that male harassment alters female distribution patterns. Consideration of the patterns of habitat use by S. hineana indicates the need to develop a broader understanding of the importance of non-wetland areas in the conservation of wetland species.     

Population decline of northern dusky salamanders at Acadia National Park, Maine, USA

We investigated and reviewed the current and historic distribution of northern dusky salamanders (Desmognathus fuscus fuscus) in Acadia National Park (ANP), Maine, USA during 1938-2003. Historical data indicate that northern dusky salamanders were once widespread and common in ANP. We conducted intensive surveys for stream salamanders during 2000-2003 and observed only two adult northern dusky salamanders on one stream. No eggs or larvae were observed. Although the cause of the observed population decline is unknown, we identify multiple potential stressors including stocking of predatory fishes, fungal pathogens, substrate embeddedness, and widespread pollution (i.e., from atmospheric pollutants) of surface waters at ANP. Our data suggest that ANP streams may no longer be suitable for northern dusky salamanders. This investigation is the first to document the decline of a stream dwelling amphibian species in a national park (i.e., areas that are not subject to obvious habitat loss or major changes in land use) with widespread mercury contamination of its surface waters.     

Relationship between total nodulation and nodulation at the root crown of peanut, soybean and common bean plants

The objective of this study was to simplify the procedure for evaluation of legume nodulation, by examining if there is a relationship between the nodulation of the whole root system and at the crown region. Roots of peanut, soybean and common bean plants growing in soils were split in two parts (crown and bottom) and assessed for nodulation (nodule number and dry weight). In general, most nodules were concentrated at the crown, and crown nodulation was generally positively correlated with total nodulation of all three legume crops. The results are highly applicable in studies such as strain selection for inoculants and assessment of inoculation technologies, among others, and is an important contribution to help reduce the time and labor required for the evaluation of nodulation parameters.     

Multiple spatial scale logistic and autologistic habitat selection models for northern pygmy owls, along the eastern slopes of Alberta’s Rocky Mountains

Little is known about the distribution and habitat use of northern pygmy owls (Glaucidium gnoma), in Alberta or throughout their range. In Alberta they are ranked as ‘sensitive’, meaning they are not believed to be at immediate risk of extirpation or extinction but may require special attention or protection to prevent them from becoming at risk.Diurnal broadcast surveys were conducted to determine distribution and habitat selection throughout a 28,500 km² study area situated along the eastern slopes of the Alberta Rocky Mountains. Surveys lasted for eight weeks in 2001, during which time 1532 site visits were made. Forty-eight responses were recorded at 42 sites representing 40 individual northern pygmy owls. Predictive models of habitat selection were developed using stepwise logistic and autologistic regression. Autologistic models accounted for observed spatial dependencies and as a result, produced better fitting models that more accurately reflect the role of predictor variables in influencing species occurrence. All models considered biophysical variable selection at two spatial scales, the minimum (75 ha) and maximum (300 ha) home range size. Northern pygmy owls showed a preference for older, structurally diverse mixedwood habitats, with line-of-sight enhanced by increased edge and terrain roughness.The use of habitat selection models resulting from this project and Geographic Information Systems as a tool, will enable managers to identify key habitat features, focus future survey efforts, set habitat goals and evaluate the effects of management decisions on current and future habitat availability.     

Distribution and environmental limitations of an amphibian pathogen in the Rocky Mountains, USA

Amphibian populations continue to be imperiled by the chytrid fungus (Batrachochytrium dendrobatidis). Understanding where B. dendrobatidis (Bd) occurs and how it may be limited by environmental factors is critical to our ability to effectively conserve the amphibians affected by Bd. We sampled 1247 amphibians (boreal toads and surrogates) at 261 boreal toad (Bufo boreas) breeding sites (97 clusters) along an 11° latitudinal gradient in the Rocky Mountains to determine the distribution of B. dendrobatidis and examine environmental factors, such as temperature and elevation, that might affect its distribution. The fungus was detected at 64% of all clusters and occurred across a range of elevations (1030-3550 m) and latitudes (37.6-48.6°) but we detected it in only 42% of clusters in the south (site elevations higher), compared to 84% of clusters in the north (site elevations lower). Maximum ambient temperature (daily high) explained much of the variation in Bd occurrence in boreal toad populations and thus perhaps limits the occurrence of the pathogen in the Rocky Mountains to areas where climatic conditions facilitate optimal growth of the fungus. This information has implications in global climate change scenarios where warming temperatures may facilitate the spread of disease into previously un- or little-affected areas (i.e., higher elevations). This study provides the first regional-level, field-based effort to examine the relationship of environmental and geographic factors to the distribution of B. dendrobatidis in North America and will assist managers to focus on at-risk populations as determined by the local temperature regimes, latitude and elevation.     

Natural N abundances in a tallgrass prairie ecosystem exposed to 8-y of elevated atmospheric CO2

After 8-y of elevated CO₂, we previously detected greater amounts of total soil nitrogen, suggesting that rates of ecosystem N flux into or out of tallgrass prairie had been altered. Denitrification and associative N fixation rates are the two primary biological processes that are known to control N loss and accumulation in tallgrass prairie soil. Therefore, our objective was to assess the natural abundance of plant and soil ¹⁵N isotopes as a cumulative index of potential change in efflux or influx of N into and out of the tallgrass prairie after 8-y of exposure to elevated CO₂. Aboveground plant delta ¹⁵N values of Andropogon gerardii were close to zero and more positive as a result of elevated CO₂, but whole-soil values at the 5-30 cm depth were significantly reduced (6.8 vs 7.3; P<0.05) under elevated CO₂-chamber (EC) relative to ambient CO₂- chamber (AC). Total, aboveground plant biomass, root-in-growth, extractable N, microbial biomass N, and soil pools collectively exhibited a range of delta ¹⁵N values from −2.8 to 7.3. Measurements of surface soil ¹⁵N indicate that a change in N inputs and outputs has occurred as a result of elevated atmospheric CO₂. In addition to possible changes in denitrification and N₂ fixation, other sources of N such as the re-translocation of N to the surface from deeper soil layers are needed to explain how soil N accrues in surface soils as a consequence of elevated CO₂. Our results support the notion that C accrual may promote N accrual, possibly driven by high plant and microbial N demand amplified by soil N limitation.     

Genetic and demographic responses of fragmented Acacia dealbata (Mimosaceae) populations in southeastern Australia

Genetic and demographic studies of fragmented populations of common plant species often reveal negative impacts that are likely to constrain persistence. Examining species that are broadly representative of functional groups within fragmented landscapes is one approach to providing a better understanding of how these processes will influence vegetation persistence. Acacias are a significant component of the Australian flora, with Acacia dealbata being a common and representative species of fragmented landscapes across New South Wales. Previous reproductive assessments of fragmented A. dealbata populations indicated significant constraints for small populations through low reproductive output mediated by fertilisation success. This study examined genetic diversity, mating system, and progeny growth parameters of the seed crops produced by these populations to assess whether further constraints to persistence could be detected. Spatially explicit simulation studies were also conducted to assess the persistence likelihood of fragmented populations. Landscape parameters such as population size and plant density were useful predictors for some of the genetic and demographic responses, but a poor response signal was generally observed. Strong evidence for a self-incompatibility mechanism was observed in A. dealbata and is likely to be the major driver of population persistence. Self-incompatibility in small populations limits mate availability and eliminates inbred progeny early in the reproductive cycle leading to poor reproductive output. The simulation data provides further evidence that mate limitation in smaller populations (<200 plants and 40 S alleles) constrains reproductive output and persistence. These data indicate that introducing new germplasm to smaller populations can dramatically improve their persistence likelihood.     

Effects of physicochemical interactions and microbial activity on the persistence of Cry1Aa Bt (Bacillus thuringiensis) toxin in soil

Genetically modified crops, that produce Cry insecticidal crystal proteins (Cry) from Bacillus thuringiensis (Bt), release these toxins into soils through root exudates and upon decomposition of residues. The fate of these toxins in soil has not yet been clearly elucidated. Persistence can be influenced by biotic (degradation by microorganisms) and abiotic factors (physicochemical interactions with soil components, especially adsorption). The aim of this study was to follow the fate of Cry1Aa Bt toxin in contrasting soils subjected to different treatments to enhance or inhibit microbial activity, in order to establish the importance of biotic and abiotic processes for the fate of Bt toxin. The toxin was efficiently extracted from each soil using an alkaline buffer containing a protein, bovine serum albumin, and a nonionic surfactant, Tween 20. The marked decline of extractable toxin after incubation of weeks to months was soil-dependent. The decrease of extractable toxin with incubation time was not related to microbial degradation but mainly to physicochemical interactions with the surfaces that may decrease immunochemical detectability or enhance protein fixation. Hydrophobic interactions may play an important role in determining the interaction of the toxin with surfaces.