Responses of litter arthropods to major natural or artificial ecological disturbances in mountain ash forest

Pitfall trapping was used in commercial Mountain Ash (Eucalyptus regnans) regrowth forest to study the effects on epigeal arthropods of high-intensity wildfire plus salvage logging, and of harvesting by clearfelling plus slash burning, followed by fire-induced natural or artificially established regeneration respectively. The study, the first of its kind in the Victorian Central Highlands, 60 km east of Melbourne, was based on 146 922 specimens of 30 ordinal or lower level taxa collected over a 3-year period. The abrupt replacement of the ecologically complex regrowth forest by ecologically much simpler even-aged regeneration caused appreciable instability among the litter-frequenting arthropods. An immediate decline in diversity occurred due to short-term boosts in activity of some common ‘major’ taxa (notably a species of seed-harvesting ant) and the suppression of other taxa. A broad mix of functionally diverse taxa reappeared within two years of regeneration, and all but three rarely trapped ‘minor’ taxa present in undisturbed 43–46 year old regrowth (‘control’) forest had returned within 5 years. Epigeal arthropods therefore appeared to be affected only over a short period relative to the nominal 80–150 year rotation of the E. regnans ecosystem. Research is needed at the species level to achieve a more precise assessment of arthropod responses to major ecological disturbances.     

On the chlorophyll a fluorescence yield in chloroplasts upon excitation with twin turnover flashes (TTF) and high frequency flash trains

Chlorophyll fluorescence is routinely taken as a quantifiable measure of the redox state of the primary quinone acceptor Q_A of PSII. The variable fluorescence in thylakoids increases in a single turnover flash (STF) from its low dark level F _o towards a maximum F _m^STF when Q_A becomes reduced. We found, using twin single turnover flashes (TTFs) that the fluorescence increase induced by the first twin-partner is followed by a 20–30% increase when the second partner is applied within 20–100 μs after the first one. The amplitude of the twin response shows a period-of-four oscillation associated with the 4-step oxidation of water in the Kok cycle (S states) and originates from two different trapped states with a life time of 0.2–0.4 and 2–5 ms, respectively. The oscillation is supplemented with a binary oscillation associated with the two-electron gate mechanism at the PSII acceptor side. The F(t) response in high frequency flash trains (1–4 kHz) shows (i) in the first 3–4 flashes a transient overshoot 20–30% above the F _m^STF = 3*F _o level reached in the 1st flash with a partial decline towards a dip D in the next 2–3 ms, independent of the flash frequency, and (ii) a frequency independent rise to F _m = 5*F _o in the 3–60 ms time range. The initial overshoot is interpreted to be due to electron trapping in the S₀ fraction with Q_B-nonreducing centers and the dip to the subsequent recovery accompanying the reoxidation of the double reduced acceptor pair in these RCs after trapping. The rise after the overshoot is, in agreement with earlier findings, interpreted to indicate a photo-electrochemical control of the chlorophyll fluorescence yield of PSII. It is anticipated that the double exciton and electron trapping property of PSII is advantageous for the plant. It serves to alleviate the depression of electron transport in single reduced Q_B-nonreducing RCs, associated with electrochemically coupled proton transport, by an increased electron trapping efficiency in these centers.     

Isolation and Structure of a New Victoxinine Derivative Produced by Helminthosporium victoriae

The structures of alkyl radicals generated in several methyl esters of fatty acids by irradiation with UV light were studied by the spin trapping technique. A spin trap, deuterated nitrosodurene, traps alkyl radicals in both saturated and unsaturated esters at the ambient temperature. The trapped radicals and their hyperfine splitting constants from several esters were as follows: pentadienyl radicals (a_N= 13.8 ~ 14.0 G, a_H = 5.9 ~ 6.0 G) from methyl linoleate, linolenate and docosahexaenoate; allyl radicals (a_N = 13.9 G, a_H = 6.8 G) and α-carbon radicals (a_N = 13.3 G, a_H = 10.0 G) from methyl oleate and elaidate; α-carbon radicals (a_N = 13.3 ~ 13.4 G, a_H = 9.6 ~ 10.0 G) and secondary alkyl radicals (a_N = 13.9 G, a_H = 6.8 ~ 7.2 G) from saturated esters.     

Cryopreservation of African violet (Saintpaulia ionantha Wendl.) shoot tips

Summary Cryopreservation of African violet via encapsulation-dehydration, vitrification, and encapsulation-vitrification of shoot tips was evaluated. Encapsulation-dehydration, pretreatment of shoot tips with 0.3 M sucrose for 2 d followed by air dehydration for 2 and 4 h resulted in complete survival and 75% regrowth, respectively. Dehydration of encapsulated shoot tips with silica gel for 1 h resulted in 80% survival but only 30% regrowth. Higher viability of shoot tips was obtained when using a step-wise dehydration of the material rather than direct exposure to 100% plant vitrification solution (PVS2). Complete survival and 90% regrowth were achieved with a four-step dehydration with PVS2 at 25°C for 20 min prior to freezing. The use of 2M glycerol plus 0.4M sucrose or 10% dimethyl sulfoxide (DMSO) plus 0.5M sucrose as a cryoprotectant resulted in 55% survival of shoots. The greatest survival (80–100%) and regrowth (80%) was obtained when shoot tips were cryoprotected with 10% DMSO plus 0.5M sucrose or 5% DMSO plus 0.75M sucrose followed by dehydration with 100% PVS2. Shoot tips cryoprotected with 2M glycerol plus 0.4M sucrose for 20 min exhibited complete survival (100%) and the highest regrowth (55%). In encapsulation-vitrification, dehydration of encapsulated and cryoprotected shoot tips with 100% PVS2 at 25°C for 5 min resulted in 85% survival and 80% regrowth.     

CO2 uptake patterns depend on water current velocity and shoot morphology in submerged stream macrophytes

1. The influence of current velocity on the pattern of photosynthetic CO₂ uptake in three species of submerged stream macrophytes was described by analysing the grain density in autoradiographs of leaves exposed to ¹⁴CO₂. 2. In Elodea canadensis, the CO₂ uptake was approximately two‐fold higher near the leaf periphery compared with the midrib section at high current velocity, whereas at low current velocity the area of relatively high CO₂ uptake expanded from the leaf periphery towards the midrib and basal sections of the leaves. 3. In Potamogeton crispus and Callitriche stagnalis the CO₂ uptake was uniform throughout the leaves at low current velocity, whereas at high current velocity the CO₂ uptake appeared to increase randomly in some areas of the leaves. 4. The relationship between the photosynthetic CO₂ uptake pattern and the dynamics of flow surrounding submerged shoots at low and high current velocity is discussed in relation to shoot morphology. In E. canadensis, thick diffusive boundary layers may develop between leaves because of screening effects at high current velocity. Increased diffusion path for CO₂ may contribute to inhibitory effects on photosynthesis in this species.     

Inheritance of bipyridyl herbicide resistance in Arctotheca calendula and Hordeum leporinum

The mode of inheritance of resistance to bipyridyl herbicides in bipyridyl-resistant biotypes of Arctotheca calendula and of Hordeum leporinum was investigated. F₁ plants from reciprocal crosses between diquat-resistant and -susceptible plants of A. calendula showed an intermediate response to diquat application that was nuclearly inherited. Treatment of F₂ plants with 100 g ai ha^-1 of diquat or 800 g ai ha^-1 of paraquat killed all homozygous-susceptible plants, caused severe injury to heterozygous plants but only slight or no injury to homozygous-resistant plants. Back crosses of F₁ to susceptible plants exhibited intermediate and susceptible phenotypes. The observed segregation ratios in F₂ and test-cross populations fitted predicted segregation ratios, 1:2:1 (R:I:S) and 1:1 (I:S) respectively, showing that bipyridyl resistance is conferred by a single incompletely-dominant gene. Biotypes of paraquat-resistant and -susceptible H. leporinum were crossed reciprocally. F₁ plants from reciprocal crosses showed an intermediate response to paraquat application. The F₂ progeny showed segregation ratios that fitted the predicted segregation ratio of 1:2:1 (R:I:S) forinheritance of resistance being governed by a single partially-dominant gene.     

Effect of salt on the stability of the pH 4.2 rA8 double helix in a series of organic/aqueous mixed solvents: A test of oligoelectrolyte theory

Temperature-dependent uv absorption spectroscopy has been used to investigate the salt dependence of the order–disorder transition for the pH 4.2 rA₈ double helix in 100% aqueous buffer and in a series of organic/aqueous mixed solvents. Melting temperature, T_m, data were obtained for the transitions in the different solvents by analysis of the uv melting curves. For the pure aqueous buffer solvent, the melting temperature was found to exhibit a reduced salt dependence (?t_m/? log Na⁺) when compared to the corresponding polymer. This reduction is explained in terms of end effects and is shown to be consistent with the theoretical treatments of oligoelectrolyte transitions developed by Record and Lohman [Biopolymers, 17 , 159–166 (1978)]. In the mixed solvents, the salt dependence of the melting temperature (?t_m/? log Na⁺) is shown to exhibit a linear dependence on the bulk dielectric constant of the medium for all of the hydroxyl-containing solvents studied. Significantly, N,N-dimethylformamide demonstrated different behavior.     

Effects of aquatic macrophytes on organic matter deposition,resuspension and phosphorus entrainment in a lowland river

1. Although macrophytes play a key role in the structure and functioning of lowland rivers, most of the basic plant, hydrodynamic and sediment‐water interactions have only been described qualitatively. We therefore studied quantitatively, the seasonal dynamics of matter deposition and mobilisation inside and outside (free path) a representative patch of arrowhead, Sagittaria sagittifolia, in the lowland River Spree, NE Germany, in August 2006. Our in situ study combined resuspension experiments, a hydrodynamically calibrated erosion chamber and concurrent measurements of the prevailing flow characteristics and bed load. 2. Increasing entrainment rates (E) of particles (E_SPM) and total P (E_TP), with increments of shear velocity (U_*) from 0.53 to 2.42 cm s^?1, were significantly higher inside the plant patch than outside. Indeed, E_SPM and E_TP at the lowest U_* were 8‐ and 12‐fold higher inside than outside the patch, reflecting the resuspension potential of the upper nutrient‐enriched layer and the extent of pulsed P inputs even at small increases in U_*. 3. Vertical distribution of velocity (u) revealed a flow pattern of a mixing layer inside the S. sagittifolia patch, and that of a boundary layer in the free path. The highest gradient of u in the mixing layer was located in the water column at about 0.5 m depth, whereas the highest gradient of u for the boundary layer was found near the riverbed. The maximum of U_* (1.65 cm s^?1) was only 4 mm above the sediment. 4. A plant mosaic provides a low‐energetic environment promoting extensive particle trapping and the accumulation of a fine‐grained, nutrient‐enriched sediment, and forming a large resuspension potential. Consequently, after plant decay and the concomitant increase of U_* this material is preferentially entrained at higher rates. Hence, the key role of submerged macrophytes in lowland rivers is more directly related to modifying the dynamic equilibria between vegetation trapping and resuspension, than to the retention of nutrients, particularly P, and the reduction of P loads downstream to other waters.     

Influence of base-pair changes and cooperativity parameters on the melting curves of short DNAs

Theoretical melting curves were calculated for four DNA restriction fragments, 157–257 base pairs (bp), and a series of hypothetical block DNAs with sequences d(C_2xA_xC_2x). d(C_2xT_xG_2x), 5 ? x ? 40. These DNAs provided a mixture of A·T/G·C sequence distributions with which to investigate the effects of parameters and base-pair changes on the melting of short DNAs. The sensitivity of DNA melting curves to changes in internal loop melting parameters σ and κ was examined. As Expected, theoretical melting curves of short DNAs with a quasirandom base-pair sequence vary little with changes in internal loop parameters. End melting dominates the transition behaviour of these moleucles. This was also observed for the block DNAs up to x = 22. Beyond this length, melting curves are highly sensitive to the internal loop parameters. Sensitivity is also predicted for a 157-bp fragment with a block distribution of A·T and G·C pairs. These results indicate that accurate evaluation of internal loop parameters is possible with short DNAs (100–200 bp) containing a G·C/A·T/G·C block distribution with at least 22 bp in each block. Duplex-to-single-strands dissociation parameters were reevaluated form experimental melting curve data of eight DNA fragments using a least squares fit approach. This analysis confirmed parameter values previously found with a simplified dissociation model. A Priori predictions are made on the effects of base-pair changes on the melting curves of three characterized DNA restriction fragments. Single base-pair changes are predicted to induce small but measurable changes in the melting curves. The characteristics of the altered melting curves depend on the location of the base-pair change.     

Herbivory,current velocity and algal regrowth: how does periphyton grow when the grazers have gone?

1. An experiment conducted in streamside channels was used to document the regrowth of grazed periphyton. Our objective was to determine the relative importance of current velocity, grazing duration, and grazer type in shaping the trajectory of algal and periphytic regrowth. 2. The grazing mayflies Baetis bicaudatus and Epeorus longimanus were used alone and in combination to create three grazing treatments at slow, medium and fast current (2–5, 15–20 and 30–40 cm s^?1, respectively). Duration treatments consisted of 2, 4, 6, 8, 10 days of grazing. Chlorophyll a and ash‐free dry mass (AFDM) accumulation on grazed tiles was measured (as periphytic AFDM and chlorophyll a, respectively) at 2, 4, 6, 8 and 10 days following the removal of grazers. 3. Chlorophyll a and AFDM was best predicted by interactions between current velocity, grazing duration and regrowth time. 4. The two grazer species did not differ in their effect on Chlorophyll a and AFDM during the period of periphytic regrowth that followed grazing. 5. Longer grazing duration reduced periphytic biomass, but also accelerated algal regrowth, and this growth enhancement was more pronounced at slower current velocities. 6. Data from this study suggest that herbivory can have important historical effects on periphytic accrual.     

Effect of Milling on DSC Thermogram of Excipient Adipic Acid

The purpose of this research was to investigate why and how mechanical milling results in an unexpected shift in differential scanning calorimetry (DSC) measured fusion enthalpy (∆_fus H) and melting point (T _m) of adipic acid, a pharmaceutical excipient. Hyper differential scanning calorimetry (hyper-DSC) was used to characterize adipic acid before and after ball-milling. An experimental study was conducted to evaluate previous postulations such as electrostatic charging using the Faraday cage method, crystallinity loss using powder X-ray diffraction (PXRD), thermal annealing using DSC, impurities removal using thermal gravimetric analysis (TGA) and Karl Fischer titration. DSC thermograms showed that after milling, the values of ∆_fus H and T _m were increased by approximately 9% and 5 K, respectively. Previous suggestions of increased electrostatic attraction, change in particle size distribution, and thermal annealing during measurements did not explain the differences. Instead, theoretical analysis and experimental findings suggested that the residual solvent (water) plays a key role. Water entrapped as inclusions inside adipic acid during solution crystallization was partially evaporated by localized heating at the cleaved surfaces during milling. The correlation between the removal of water and melting properties measured was shown via drying and crystallization experiments. These findings show that milling can reduce residual solvent content and causes a shift in DSC results.     

Investigation into Stability of Poly(Vinyl Alcohol)-Based Opadry® II Films

Poly(vinyl alcohol) (PVA)-based formulations are used for pharmaceutical tablet coating with numerous advantages. Our objective is to study the stability of PVA-based coating films in the presence of acidic additives, alkaline additives, and various common impurities typically found in tablet formulations. Opadry® II 85F was used as the model PVA-based coating formulation. The additives and impurities were incorporated into the polymer suspension prior to film casting. Control and test films were analyzed before and after exposure to 40°C/75% relative humidity. Tests included film disintegration, size-exclusion chromatography, thermal analysis, and microscopy. Under stressed conditions, acidic additives (hydrochloric acid (HCl) and ammonium bisulfate (NH₄HSO₄)) negatively impacted Opadry® II 85F film disintegration while NaOH, formaldehyde, and peroxide did not. Absence of PVA species from the disintegration media corresponded to an increase in crystallinity of PVA for reacted films containing HCl. Films with NH₄HSO₄ exhibited slower rate of reactivity and less elevation in melting temperature with no clear change in melting enthalpy. Acidic additives posed greater risk of compromise in disintegration of PVA-based coatings than alkaline or common impurities. The mechanism of acid-induced reactivity due to the presence of acidic salts (HCl vs. NH₄HSO₄) may be different.     

Home range,range overlap,and site fidelity of introduced Siberian chipmunks in a suburban French forest

Home range size, range overlap, and multiyear site fidelity were investigated for introduced Siberian chipmunks (Tamias sibiricus) in a French suburban forest from bimonthly trapping sessions for 4 years (2004–2007). Annual home range sizes (100% minimum convex polygon, ±SE) were estimated from 39 trapping histories of 28 different adult residents. Males (N = 13, 1.86 ± 0.32 ha) had a home range 2.5 times larger than females (N = 26, 0.71 ± 0.08 ha); a male home range included significantly more trapping centers (arithmetic mean of capture locations) of females (5.5 ± 0.7) than of males (2.3 ± 0.5). Chipmunks exhibited strong multiyear site fidelity: mean distance between annual trapping centers of individuals trapped over two successive years was small (N = 82, 26 ± 2 m) compared to the largest home range length (ranging from 36 to 281 m); overlap between annual home range sizes of residents was 84 ± 5% (N = 11). These results improve our understanding of the space occupation of this unknown species in a novel environment.     

Blockage of apoplastic bypass-flow of water in rice roots by insoluble salt precipitates analogous to a Pfeffer cell

Precipitates of insoluble inorganic salts were used to clog apoplastic pores in cell walls of the outer part of rice roots (OPR) in two rice cultivars (lowland cv. IR64 and upland cv. Azucena). Aerenchyma of two different root zones (20–50 and 50–100 mm from the apex) was perfused with 1 m m potassium ferrocyanide (K₄[Fe(CN)₆]) while the whole root segments were bathed in 0.5 m m copper sulphate (CuSO₄) medium. In another experiment, salts were applied on opposite sides of the OPR. The copper-ferrocyanide precipitation technique resembles the famous osmotic experiments of the German botanist Wilhelm Pfeffer, in which he used them with clay diaphragms. Precipitates were observed on the side where ferrocyanide was applied, suggesting that Cu²⁺ and SO₄^2– were passing the barrier including the Casparian bands of the exodermis much faster than ferrocyanide. There was a patchiness in the formation of precipitates, correlated with the maturation of the exodermis. The intensity of copper ferrocyanide staining decreased along developing rice roots. No precipitates were observed in mature parts beyond 70–80 mm from the root apex, except for sites around the emergence of secondary roots, which were fairly leaky to both water and ions. Blockage of the apoplastic pores with precipitates caused a three- to four-fold reduction of hydraulic conductivity of the OPR (Lp_OPR). The reflection coefficient of the OPR (σ_sOPR) increased in response to the blockage with precipitates. The osmotic versus diffusive water permeability ratios of the OPR (P_fOPR/P_dOPR) were around 600 for immature and 1200 for mature root segments. Treatment significantly affected the bulk rather than the diffusive water flow and caused a three- to five-fold reduction of the P_fOPR/P_dOPR ratios. Results indicated that despite the existence of an exodermis with Casparian bands, most of the water moved around cells rather than using the cell-to-cell passage.     

Trapping a translocating protein within the anthrax toxin channel: implications for the secondary structure of permeating proteins

Anthrax toxin consists of three proteins: lethal factor (LF), edema factor (EF), and protective antigen (PA). This last forms a heptameric channel, (PA₆₃)₇, in the host cell’s endosomal membrane, allowing the former two (which are enzymes) to be translocated into the cytosol. (PA₆₃)₇ incorporated into planar bilayer membranes forms a channel that translocates LF and EF, with the N terminus leading the way. The channel is mushroom-shaped with a cap containing the binding sites for EF and LF, and an ∼100 Å–long, 15 Å–wide stem. For proteins to pass through the stem they clearly must unfold, but is secondary structure preserved? To answer this question, we developed a method of trapping the polypeptide chain of a translocating protein within the channel and determined the minimum number of residues that could traverse it. We attached a biotin to the N terminus of LF_N (the 263-residue N-terminal portion of LF) and a molecular stopper elsewhere. If the distance from the N terminus to the stopper was long enough to traverse the channel, streptavidin added to the trans side bound the N-terminal biotin, trapping the protein within the channel; if this distance was not long enough, streptavidin did not bind the N-terminal biotin and the protein was not trapped. The trapping rate was dependent on the driving force (voltage), the length of time it was applied, and the number of residues between the N terminus and the stopper. By varying the position of the stopper, we determined the minimum number of residues required to span the channel. We conclude that LF_N adopts an extended-chain configuration as it translocates; i.e., the channel unfolds the secondary structure of the protein. We also show that the channel not only can translocate LF_N in the normal direction but also can, at least partially, translocate LF_N in the opposite direction.     

Photodegradation in Encapsulated Silole‐Based Polymer: PCBM Solar Cells Investigated using Transient Absorption Spectroscopy and Charge Extraction Measurements

Light induced degradation has been observed in the performance of organic solar cells in the absence of oxygen and a detailed analysis of the effect of this photodegradation on optical and electrical features has been accomplished. This photodegradation study has been performed on encapsulated photovoltaic blend devices comprised of the silole‐based donor–acceptor polymer KP115 blended with [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM). Photodegradation induces an almost 20% decrease in power conversion efficiency, primarily as a result of a reduction in short circuit current, J_SC. The initial burn‐in phase of the photodegradation has been examined using a combination of transient absorption spectroscopy and charge extraction measurements, including photo‐CELIV (charge extraction by linearly increasing voltage) and time‐resolved charge extraction using a nanosecond switch. These measurements reveal a bimodal KP115 polaron population, comprised of both delocalised and localised/trapped charge carriers. The photodegradation results are consistent with an alteration of this bimodal KP115 polaron population, with the polarons becoming trapped in a broader, deeper density of localised states. Under laser illumination and at open circuit conditions, this enhanced trapping after light soaking inhibits charges from undergoing bimolecular recombination, leading to higher extracted charge densities at long times. At the lower charge densities operating at short circuit conditions and under continuous white light illumination, where bimolecular recombination is much less significant, the J_SC decreases after light soaking due to a reduction in the efficiency of trapped charge carrier extraction.     

Trapping efficiency of three carnivorous Pinguicula species

Summary In situ trapping efficiencies of Pinguicula alpina L., P. villosa L., and P. vulgaris L. were compared with each other and with those of artificial traps at a subarctic site in northern Sweden. P. vulgaris had the highest trapping efficiency i.e., 21–37 g prey trapped cm^-2 day^-1 and apparently has some means of attracting prey. The other two species trapped about 14–18 g cm^-2 day^-1, a value similar to that of paper traps mimicing plant leaves. By weight, Nematocera and Collembola were the dominant groups trapped by P. alpina. P. villosa trapped mainly Collembola, while small Nematocera dominated the prey caught by P. vulgaris. Mites (Acarina) were caught in high numbers but contributed only a small part of the total captured biomass owing to their low weight.     

Three carnivorous plant species (Drosera spp.) in European Russia: peaceful coexistence?

In spite of the recent improvements in the understanding of carnivorous plants’ biology, some questions have remained unanswered. In this study, the segregation of food niches (i.e. specialization on different categories of prey) for three sympatric carnivorous temperate Drosera species with different shapes of trapping leaves is tested. Potentially available prey was also taken into account, by using artificial traps. Almost all the prey trapped by the three Drosera species and by passive traps belonged to four insect orders: Diptera, Hymenoptera, Coleoptera, Homoptera, as well as Araneae. Diptera specimens were the main prey for all the species. This study demonstrates that arthropods caught by the three temperate sympatric sundew species (D. rotundifolia, D. obovata and D. anglica), belong to the same orders. The proportions of prey from different orders, caught by different sundew species did not differ significantly. The result does not necessarily imply the absence of interspecific competition for prey: arthropods were identified only to order, and competition may have resulted in specialization on prey taxa of lower rank.     

Equilibrium conditions in polysomic inheritance for a panmictic population

A general model of a large 2m-ploid breeding population, withr loci ands _h alleles at the _h ^th locus is considered. It is assumed that the population is bisexual, non-overlapping and breeds by random mating. The genotypic structure of the population is presented as a bilinear form in the gametic output vectors where the genotype distribution is in the matrix form. Using the concept of the segregation distribution, the genotype proportions in the (n+1)^st generation are given. An equilibrium condition for random chromosome segregation is obtained in terms of gene frequencies.