Classifying the fire‐response traits of plants: How reliable are species‐level classifications?

Plant species in fire‐prone environments possess specific traits which allow them to survive fire. Species are commonly classified according to whether they survive fire and resprout or whether they are killed by fire and regenerate from seed. However, different populations of the same species have been shown to vary in their responses. Therefore, the classification of a species into a single category based on fire‐response traits may not necessarily be representative of every population under every circumstance. This study examined the extent of within‐species variation in fire‐response traits of woody plants in south‐eastern Australia after the 2003 fires. Species were then classified using two approaches: (i) using data from a field survey of fire‐response traits, taking into account within‐species variation; and (ii) using species' fire responses listed in a pre‐existing fire‐response database compiled from a variety of primary sources. Field data showed that the majority of species in the study area resprouted after fire with around one in 10 species variable in their resprouting response. Almost half of all species varied from site to site according to whether they regenerated from seed, either solely or in addition to resprouting. The numbers of species classified as resprouters and seed regenerators varied according to the classification method used. Differences were also found between the classification method when calculating the mean proportion of resprouters and seed regenerators across sites. The fire‐response traits for some species from the database were found to differ from the observed field responses. This study demonstrated that the application of a fire‐response trait, reported in a trait database, to an entire species, may not adequately represent the actual fire responses of the populations of interest. Rather than considering the fire‐response traits of a species, accurate prediction may be better achieved by considering how different populations of plants will respond to fire.     

Changes in spring arrival of Nearctic-Neotropical migrants attributed to multiscalar climate

Climate-related changes associated with the California marine ecosystem have been documented; however, there are no studies assessing changes in terrestrial vertebrate phenology on the Pacific coast of western North America. We analyze the spring phenology of 21 Nearctic-Neotropical migratory songbird species in central and northern CA. Using observational and banding data at multiple sites, we evaluate evidence for a change in arrival timing being linked to either nonclimatic or multiscalar climatic explanations. Using correlation analysis, of the 13 species with a significant ( P <0.10) change in arrival, the arrival timing of 10 species (77%) is associated with both temperature and a large-scale climate oscillation index (El Niño Southern Oscillation, ENSO; North Atlantic Oscillation, NAO; and/or Pacific Decadal Oscillation, PDO) at least at one location. Eight of the 13 species (62%) are advancing their migratory timing. All species for which spring arrival is associated with climate at multiple locations are exhibiting changes ( n =5) and all species lacking evidence for association between migration phenology and climate ( n =3) exhibit no change. Migrants tend to arrive earlier in association with warmer temperatures, positive NAO indices, and stronger ENSO indices. Twelve species negatively correlate ( P ≤0.05) with local or regional temperature at least at one location; five species negatively correlate with ENSO. Eleven species' arrival is correlated ( P ≤0.05) with NAO; 10 are negatively associated. After an exhaustive literature search, this is apparently the first documentation of an association between NAO and migratory phenology in western North America.     

The changing ecosystem of a shallow, brackish lake, Hickling Broad, Norfolk, U.K. II. Long-term trends in water chemistry and ecology and their implications for restoration of the lake

• 1 Hickling Broad underwent major changes from a clear water, charophyte-dominated state in the decades previous to 1970 to a turbid, phytoplankton-dominated state by the mid 1970s. These changes were complexly linked with increasing eutrophication by black-headed gulls and increased salinity due to agricultural changes in the catchment.
• 2 At the turn of the 1970s, the lake began to change again and during the 1980s a submerged plant community, of tall, vigorously growing species (e.g. Myriophyllum spicatum, Patamogeton pectinatus) had recovered, despite a major reduction in the roosting gull population, no change in salinity, and only small reductions in phytoplankton biomass and total phosphorus concentration.
• 3 Recovery of the plants may be linked to grazing of periphyton on them by an increased population of a mysid Neomysis integer which had been suppressed by toxicity from an alga, Prymnesium parvum formerly stimulated by the ingress of gull guano.
• 4 A cladoceran community present in the clear-water phase has not recovered and may be suppressed by continued high salinities. Further restoration of the lake requires displacement of the large phytoplankton biomass and this might best be contemplated by land use changes leading to lowered salinity and predicted recovery of grazing Cladocera.
• 5 Models are given which summarize the likely workings of the system in the early twentieth century, the mid-twentieth century, the 1970s and the late 1980s.

     

An example of Holocene vegetation stability from Camerons Lagoon,a near treeline site on the Central Plateau,Tasmania

Abstract A discontinuous record of vegetation over the past 7500 years was obtained through pollen analysis of pond sediments from an extensive treeless plain on the relatively dry Central Plateau of Tasmania. The results demonstrate continuity of treeless conditions, which probably persisted from the Pleistocene throughout the Holocene, up to the present day. Some changes to the structure of the grassland were observed, especially over the past 200 years. Analysis of carbonized particles showed that fires had been infrequent over the period examined. It seems that this area, close to the altitudinal tree limit, has remained a natural grassland, and the hypothesis of Jackson (1973), that unreliable summer conditions may be a major factor in maintaining open conditions, is supported. Parts of the Central Plateau may thus preserve plant communities with some of the floristic elements and structure of widespread Bassian grasslands of the Late Pleistocene.     

Enzyme Distribution in Potato Mitochondria

Enzyme distribution in potato mitochondria was investigatedby selectively disrupting the outer and inner membranes withdigitonin. Antimycin-insensitive NADH-cytochrome c reductase,an outer membrane marker, was released at low digitonin concentrations(0.1 mg mg^–1 mitochondrial protein). Soluble matrix enzymes,fumarase and malate dehydrogenase were released at 0.3–0.4mg digitonin mg^–1 protein, as the inner membrane ruptured.Very little (about 10%) cytochrome oxidase activity was released,even at higher digitonin concentrations, in accord with thisenzyme being an integral inner membrane protein. By this criterionadenylate kinase is also firmly bound to the inner membrane.Evidence indicates that it faces the intermembrane space. Malic enzyme activity was released by the same digitonin concentrationthat released fumarase and malate dehydrogenase, indicatingthat malic enzyme is a soluble matrix enzyme. No activity wasreleased at low digitonin concentrations which selectively breakthe outer membrane, showing that malic enzyme is not presentin the intermembrane space. Considerable catalase activity (20—40 µmol O₂ min^–1mg^–1 protein) was associated with washed mitochondrialpreparations, but 95% of this was lost upon purification ofmitochondria. The remaining activity was firmly bound to themitochondrial membranes.     

Liquid-Tissue Mechanics in Amphibian Gastrulation: Germ-Layer Assembly in Rana Pipiens

During amphibian gastrulation, migrating subsurface germ layersmay flow past one another like immiscible viscous liquids inresponse to tissue surface tension forces. We describe heretwo physical tests for liquid-tissue morphogenesis in culturedaggregates of subsurface ectoderm (E), mesoderm (M) and endoderm(N) excised from mid-yolk-plug Rana pipiens gastrulae. (i) Liquidsare coherent substances in which subunits can slip past oneanother to relax internal shear stresses. We find, in cross-sectionsof cell aggregates fixed during compression, that cells withinflattened aggregates are intially deformed, but do, as predicted,gradually reassume their original, undistorted shapes, (ii)Surface tensions ('s) govern ordinary liquid-droplet spreading;e.g., if equal-sized droplets A and B fuse in medium O, B spreadsaround A when _{AO BO}. When pairs of subsurface aggregates arecultured together, N surrounds M and E, and M surrounds E. Tosee if _EO > _MO > _NO. we flatten aggregates with quartzfibers calibrated to measure the force of compression. As predicted,under the same flattening force, E aggregates are rounder thanM aggregates, which are rounder than N aggregates. Furthermore,a second surface tension relationship can account for the autonomousinvolution of M between E and N; and these surface tension relationshipscan also explain the inversion of E, M and N by coated ectodermto produce normal gastrular germ-layer arrangements. We concludethat, combined with active cell shape changes in solid-likesurface cell layers and also with autonomous elongation of dorsallip mesoderm, tissue surface tension control of liquid-tissueflow in subsurface germ layers is a key morphogenetic mechanismin amphibian gastrulation which might be regulated by changesin intercellular adhesiveness.     

Attachment of Rhizobium to Legume Roots as the Basis for Specific Interactions

Experiments were conducted to elucidate the basis of the observation that different strains of Rhizobium infect particular legumes. Rhizobia specific for a variety of legumes were grown with ¹³PO^2?₄ and exposed to pea roots (Pisum sativum L.), R. leguminosarum 128C53, which nodulates pea, did not attach to the roots in greater numbers than those strains of rhizobia incapable of infecting pea roots. A complex of R. leguminosarum 128C53 conjugated to a fluorochrome-labeled antibody exhibited a striking attachment to the tips of pea root hairs, where infection normally occurs, but this fluorescent complex also bound to the root hairs of Canavalia en siformis DC., Lupinus polyphyllus Lindl., Trifolium pratense L., and Medicago sativa L., which are not infected by this bacterium. A reproducible, quantitative technique developed for studying interactions between fluorochrome-labeled lectins and rhizobia revealed no relationship between lectin-Rhizobium interactions and the capacity to infect a plant. The data are interpreted as suggesting that simple attachment of Rhizobium to a legume root is not the basis of host-symbiont specificity in this system.     

Ullucus virus C, a newly recognised comovirus infecting Ullucus tuberosus (Basellaceae)

Ullucus virus C (UVC) is a comovirus prevalent in Ullucus tuberosus grown at high altitudes in the Bolivian and Peruvian Andes. It was transmitted mechanically to U. tuberosus (Basellaceae) and to five of 26 species from three of eight other families, infecting U. tuberosus symptomlessly but inducing conspicuous systemic infection in Chenopodium amaranticolor and C. quinoa. Sap from infected C. quinoa was usually infective after 10 min at 70 but not 75 °C, after dilution to 10^-7 but not 10^-8, and after 8 but not 16 wk at 20 °C. UVC was not transmitted by either of two aphid species (Aphis gossypii and Myzus persicae) or through seed of C. quinoa, but it was transmitted by leaf contact between infected and healthy plants. UVC has isometric particles which, in neutral phosphotungstate, are c. 28 nm in diameter. The particles sediment as three components (T, M and B) with sedimentation coefficients (s^?_{20, w}) of 51 S (T), 95 S (M) and 116 S (B). M component particles have a buoyant density (g cm^-3) in caesium chloride of 1.404, and B component particles separated into minor and major sub-components with densities of 1.409 and 1.463, respectively. T, M and B particles were serologically indistinguishable, and each contained similar relative amounts of two polypeptides of mol. wts 20 700 and 45 100. T particles contained only protein, but M particles also contained c. 30% ss-RNA of mol. wt 1–45 ×10⁶ and B particles c. 38% ss-RNA of mol. wt 2·2 × 10⁶. The virus is serologically distantly related to cowpea mosaic virus but, as it showed no relationship to any of 11 other similar viruses, it is probably a distinct member of the comovirus group.