Environmental factors affecting seed germination of gray birch (Betula populifolia) collected from abandoned anthracite coal mine spoils in northeast Pennsylvania

Germination of gray birch (Betula populifolia) seed collected from anthracite mine spoils in northeastern Pennsylvania was studied. Environmental conditions of the spoil banks are such that high mortality may occur at seed and germination stages because of low moisture availability and thermal stress. The mine spoil banks are harsh environments with respect to key seed germination factors: percent soil moisture as low as 1.8% and soil surface temperatures reaching 59°C. In the field, gray birch typically germinated in mid-April prior to severe environmental stress. Trends in germination success were inversely related to rising soil temperature and decreasing soil moisture availability. Although seeds were capable of survival and germination under laboratory conditions of constant temperatures in excess of 55°C, dramatic decline in germination was observed under fluctuating temperature regimes likely to be experienced in the field. No germinations occurred under fluctuating temperatures in excess of 30°C. Germinations in the field were seen to end after mid-June when substrate temperatures exceeded 30°C.     

Mapping the Microenvironment for Seed Germination in the Field

Gaps in the canopy have a major influence upon the microenvironmentfor seed germination in natural vegetation. Two methods formeasuring gaps in grasslands are described. The first uses afield-portable instrument for mapping R/IR ratios under thecanopy, and the second employs infrared photography and imageanalysis to measure gaps from above. The methods are illustratedwith results from an experiment in which grazing sheep are theprinciple influence upon the structure of the grass canopy.Results of both methods show that the effects of current andpast grazing regimes may be detected in the canopy structureof the grassland. Seeds of Geranium dissection sown into gapsof different sizes showed greater establishment in small gaps(1–2 cm²) than under a closed canopy Canopy gap, germination, grassland, grazing, Geranium dissectum     

Distribution of Fibronectin and Collagen during Mouse Limb and Palate Development

Indirect immunofluorescence has been used to study the distribution of fibronectin and collagen types I, II, and III in the developing primary and secondary palatal processes and forelimb buds of the Swiss Webster (NIH) mouse. In the palatal processes fibronectin and types I and III collagen are distributed throughout the mesenchyme. Fibronectin is present in the basement membrane, while types I and III collagen are localized in a linear, discontinuous fashion beneath the basement membrane. Fibronectin is not observed in the epithelium, including the presumptive fusion areas. In the forelimb bud these components show a similar distribution prior to chondrogenesis (early day 11). When chondrogenesis commences (late day 11 or early day 12) fibronectin and, to a lesser degree, types I and III collagen are apparently concentrated in the core mesenchyme, suggesting that fibronectin has a role in initiating chondrogenesis, perhaps by increasing cellular aggregation. Type II collagen is observed only in chondrogenic regions. The codistribution of fibronectin and types I and III collagen supports in vitro studies which indicate that cells use fibronectin to bind to collagen in the matrix. The developing chondrogenic regions appear to lose fibronectin gradually, concomitant with the appearance of type II collagen, suggesting that fibronectin is not involved in the maintenance of functional chondrocytes in their matrices.     

The Continuous Culture of Luminous Bacteria: a Luminostat

A method has been designed for the continuous culture of luminous bacteria. The control system for the culture uses a combination of luminescence and optical density as a light signal received by a photomultiplier. This combined signal operates pumps which exchange the growth medium. Using this method, a culture of brightly luminescing bacteria was maintained for periods up to 3 weeks.     

Skolithos pipe rock and associated ichnofabrics from the southern Rocky Mountains,Canada: colonization trends and environmental controls in an early Cambrian sand‐sheet complex

Desjardins, P.R., Mángano, M.G., Buatois, L.A. & Pratt, B.R. 2010: Skolithos pipe rock and associated ichnofabrics from the southern Rocky Mountains, Canada: colonization trends and environmental controls in an early Cambrian sand‐sheet complex. Lethaia, 10.1111/j.1502‐3931.2009.00214.x The Lower Cambrian Gog Group of the southern Rocky Mountains of western Canada offers an opportunity to explore animal–sediment relationships in a high‐energy setting, during the early phase of Phanerozoic diversification. Its strata record a sand‐sheet complex on the broad pericontinental shelf of West Laurentia. Six ichnofabrics are recognized: Skolithos IF‐1 characterized by Skolithos linearis in planar cross‐stratified sandstone; Skolithos IF‐2 with Skolithos linearis and accessory Diplocraterion parallelum in ripple cross‐laminated, and planar and trough cross‐stratified sandstone; Skolithos IF‐3 with S. linearis and Planolites montanus in wavy‐ and flaser‐bedded sandstone, interfingering with bioturbated mudstone exhibiting P. montanus and Teichichnus rectus; Skolithos IF‐4, characterized by abundant Skolithos linearis in planar and trough cross‐stratified sandstone; Rosselia IF‐1 consisting of Rosselia isp. in planar cross‐stratified sandstone; and Rosselia IF‐2 consisting of scattered small Rosselia isp. in hummocky, cross‐stratified sandstone. The presence of contrasting ichnofabrics within a single early Cambrian sand‐sheet complex illuminates how the colonization trends of suspension and detritus feeders were controlled by factors specific to the various sub‐environments. □Gog Group, Ichnofabric, Lower Cambrian, Pipe Rock, Rosselia, Skolithos.     

Excising stem samples underwater at native tension does not induce xylem cavitation

Xylem resistance to water stress‐induced cavitation is an important trait that is associated with drought tolerance of plants. The level of xylem cavitation experienced by a plant is often assessed as the percentage loss in conductivity (PLC) at different water potentials. Such measurements are constructed with samples that are excised underwater at native tensions. However, a recent study concluded that cutting conduits under significant tension induced cavitation, even when samples were held underwater during cutting. This resulted in artificially increased PLC because of what we have termed a ‘tension‐cutting artefact’. We tested the hypothesized tension‐cutting artefact on five species by measuring PLC at native tension compared with after xylem tensions had been relaxed. Our results did not support the tension‐cutting artefact hypothesis, as no differences were observed between native and relaxed samples in four of five species. In a fifth species (Laurus nobilis), differences between native and relaxed samples appear to be due to vessel refilling rather than a tension‐cutting effect. We avoided the tension‐cutting artefact by cutting samples to slightly longer than their measurement length and subsequent trimming of at least 0.5 cm of sample ends prior to measurement.     

Dieback and mortality of South African fynbos shrubs is likely driven by a novel pathogen and pathogen‐induced hydraulic failure

We examined whether extensive dry season dieback and mortality in a South African fynbos community were due to drought or pathogen attack. Plant dieback and mortality have been reported elsewhere in similar plant communities suggesting potential for a widespread climatic or biotic threat to this community. We collected tissue samples from Brunia noduliflora, the dominant plant in the community, and cultured them for potential plant pathogens. We also measured dry season predawn and midday water potentials of healthy and stressed plants and constructed pressure‐volume curves to assess turgor loss point. Plant stress and mortality were monitored over a 2‐year study period. Both healthy plants and plants that displayed moderate signs of stress had dry season predawn water potentials well above their turgor loss point suggesting plants were not water stressed. However, plants displaying >60% crown dieback had much lower water potentials (as low as ?12 MPa). A previously undescribed fungus (Pythium sp.) was isolated from the root vascular tissue of all stressed plants and was not present in healthy plants. The proximate cause of plant stress was likely pathogen‐induced, while the ultimate cause of plant death appears to be extreme water stress. The present study suggests that Brunia (Bruniceae), Leucadendron (Proteaceae) and Erica (Ericaceae), all emblematic and dominant genera within the diverse fynbos community, may be susceptible to Pythium infection. This may pose a serious threat to communities already threatened by climate change.     

Effect of Cercospora zeae-maydis infested maize residue on progress and spread of grey leaf spot of maize in central Uganda

The spread of grey leaf spot caused by Cercospora zeae‐maydis from infested maize residue on the soil surface and progress over time were studied under tropical conditions at two locations in central Uganda, Kabanyolo and Namulonge, using a susceptible local cultivar, LP16. Infested maize residue collected the previous season was used as the inoculum source in varying amounts; 80% coverage, 40% coverage and 0% soil coverage were used to simulate no tillage, minimum tillage and maximum tillage with complete burial of residues. In all the seasons, disease spread was adequately described by a power law model, whereas disease progress over time was equally well represented by both Gompertz and logistic models. The time factor was highly significant (P < 0.05) for disease development, indicating both increases in disease intensity over time and change in gradients with time. The amount of infested residue on the soil surface in the maize planting was highly significant (P < 0.05) for slope (b) and intercept (a) of the linearised disease gradient. The gradient parameter (b) based on the average for the four directions from the residue source ranged from ?0.96 to ?0.08 in the second cropping season of 1999, from ?2.16 to ?0.01 and from ?0.87 to ?0.03 in the first and second seasons of 2000, respectively. The distance from the infested residue significantly affected foliar disease, but the direction from the residue inoculum source did not, nor was the distance by direction interaction significant. However, interactions between amount of residue and distance were significant. Percentage leaf area affected by grey leaf spot, the areas under disease progress curves and disease intercepts decreased with distance at both locations, but rate of disease increase (r) was generally constant with distance from residue source at Kabanyolo, but not at Namulonge. The relationship between disease severity and amount of residue cover appeared to be affected by the level of background inoculum. At Kabanyolo, where little background inoculum was present, differences were detected in disease severity parameters between the no‐residue plots and residue plots, whereas at Namulonge, where high background levels existed, there was no effect of residue on disease.