Environmental controls on CH4 emission from polygonal tundra on the microsite scale in the Lena river delta,Siberia

The carbon budgets of the atmosphere and terrestrial ecosystems are closely coupled by vertical gas exchange fluxes. Uncertainties remain with respect to high latitude ecosystems and the processes driving their temporally and spatially highly variable methane (CH₄) exchange. Problems associated with scaling plot measurements to larger areas in heterogeneous environments are addressed based on intensive field studies on two nested spatial scales in Northern Siberia. CH₄ fluxes on the microsite scale (0.1–100 m²) were measured in the Lena River Delta from July through September 2006 by closed chambers and were compared with simultaneous ecosystem scale (10⁴–10⁶ m²) flux measurements by the eddy covariance (EC) method. Closed chamber measurements were conducted almost daily on 15 plots in four differently developed polygon centers and on a polygon rim. Controls on CH₄ emission were identified by stepwise multiple regression. In contrast to relatively low ecosystem‐scale fluxes controlled mainly by near‐surface turbulence, fluxes on the microsite scale were almost an order of magnitude higher at the wet polygon centers and near zero at the drier polygon rim and high‐center polygon. Microsite scale CH₄ fluxes varied strongly even within the same microsites. The only statistically significant control on chamber‐based fluxes was surface temperature calculated using the Stefan–Boltzmann equation in the wet polygon centers, whereas no significant control was found for the low emissions from the dry sites. The comparison with the EC measurements reveals differences in controls and the seasonal dynamics between the two measurement scales, which may have consequences for scaling and process‐based models. Despite those differences, closed chamber measurements from within the EC footprint could be scaled by an area‐weighting approach of landcover classes based on high‐resolution imagery to match the total ecosystem‐scale emission. Our nested sampling design allowed for checking scaling results against measurements and to identify potentially missed sources or sinks.     

MtPM25 is an atypical hydrophobic late embryogenesis‐abundant protein that dissociates cold and desiccation‐aggregated proteins

Late embryogenesis‐abundant (LEA) proteins are one of the components involved in desiccation tolerance (DT) by maintaining cellular structures in the dry state. Among them, MtPM25, a member of the group 5 is specifically associated with DT in Medicago truncatula seeds. Its function is unknown and its classification as a LEA protein remains elusive. Here, evidence is provided that MtPM25 is a hydrophobic, intrinsically disordered protein that shares the characteristics of canonical LEA proteins. Screening protective activities by testing various substrates against freezing, heating and drying indicates that MtPM25 is unable to protect membranes but able to prevent aggregation of proteins during stress. Prevention of aggregation was also found for the water soluble proteome of desiccation‐sensitive radicles. This inhibition was significantly higher than that of MtEM6, one of the most hydrophilic LEA protein associated with DT. Moreover, when added after the stress treatment, MtPM25 is able to rapidly dissolve aggregates in a non‐specific manner. Sorption isotherms show that when it is unstructured, MtPM25 absorbs up to threefold more water than MtEM6. MtPM25 is likely to act as a protective molecule during drying and plays an additional role as a repair mechanism compared with other LEA proteins.     

Interaction between two synthetic pyrethroids and the spread of two non-persistent viruses in cowpea

The effectiveness of the synthetic pyrethroids deltamethrin and lambda-cyhal-othrin in preventing (i) aphid colonisation of four cowpea cultivars with different levels of aphid resistance and (ii) the introduction and subsequent spread of cowpea aphid-borne mosaic virus and cucumber mosaic virus was investigated under tropical field conditions. Sprays of these pyrethroids eight days apart prevent aphid colonisation and within crop spread of virus by the colonising Aphis craccivora. However, neither deltamethrin nor lambda-cyhalothrin prevented the initial introduction of virus into the cowpea crop and, when incoming alate incidence was high, virus incidence was higher in the sprayed than in the unsprayed plots. In addition, the degree of aphid resistance of each cultivar affected secondary virus spread within the crop, with greatest spread in the most resistant cultivar.     

Cell Expansion and Wall pH in the Fern Regnellidium diphyllum, A Plant Lacking Acidinduced Growth

Petioles of the semi-aquatic fern Regnellidium diphyllum donot show acid growth but low wall pH is a necessary conditionfor maximum rates of IAA-induced cell expansion. Measurementsof wall pH by two indirect methods indicate an unusually lowvalue, in the range pH 4 to 5. This is one to two pH units belowthat estimated for petioles of the semi-aquatic dicotyledonNymphoides peltata, a species in which IAA aand ethylene causegrowth responses very similar to those in Regnellidium but whereacid growth occurs. Having shown previously that fusicoccinenhances proton secretion in both Regnellidium and Nymphoides,we now show that although it causes a reduction in the estimatedapoplast pH to below 4·0 in Regnellidium, cell expansionis not promoted. The FC-induced reduction in pH in Nymphoidesis less and occurs more slowly, but growth is promoted significantly;when IAA and fusicoccin are present together, growth promotionis approximately additive for Nymphoides A model is proposed for Regnellidium in which equilibrium wallpH is maintained at a low value that is optimal for acid growth,the availability of acid-labile sites in the wall being thechief limitation to cell extension. We suggest that this controlmechanism may be widespread for organs without a cuticle, includingroots and the gametophytes of lower plants growing in acidicconditions. Key words: Acid growth, wall pH, fusicoccin, Regnellidium diphyllum, Nymphoides peltata     

Modelling habitat selection of Common Cranes Grus grus wintering in Portugal using multiple logistic regression

Predictive models of habitat suitability for the Common Crane Grus grus in a wintering area of southern Portugal were derived using logistic multiple regression and Geographic Information Systems. The study area was characterized by landscape variables and surveyed uniformly for the presence of cranes. The most important variables were distance to roosts, to open Holm Oak woods and to villages, and the occurrence of unpaved roads, shrubby vegetation, slope and orchards. Two models were built, the second having one variable fewer than the first. The selection of the best model was based on statistical and biological criteria. Crane distribution was negatively related to: distance to open Holm Oak Quercus rotundifolia woods and roosts. Additionally, unsuitable vegetation and orchard areas are avoided. In these areas movement is difficult, food availability is reduced and the risk of predation increased. We also found that villages and roads were avoided; disturbance is a significant factor for this species. Some management guidelines are proposed for the area: (1) maintenance of open Holm Oak woodlands, (2) incentives to avoid the abandonment of traditional agriculture and pastoral use of the area, which would lead to an increase of shrubby vegetation areas, (3) preservation of suitable roosting places and (4) management of new patches of forest and orchards.     

The relationship between invertebrate assemblages and available food at forest and pasture sites in three southeastern Australian streams

1. Levels of ash-free dry matter (AFDM) and chlorophyll a in epilithon, benthic participate organic matter (BPOM), invertebrate assemblage composition, and biomass of functional feeding groups were compared in winter and summer at forest and pasture sites in three Victorian streams. 2. Chlorophyll a concentrations of epilithon were significantly higher at pasture than forest sites in winter but not in summer while BPOM was not significantly greater at forest sites in either season. Epilithic biomass as AFDM did not show consistent differences between land uses or seasons. 3. Total biomass of invertebrates did not differ between forest and pasture sites but the biomass of shredders was significantly higher, and that of grazers significantly lower, at forest than pasture sites. A site shaded with an artificial canopy behaved as a forest site for grazers but as a pasture site for shredders. 4. Cluster analyses of invertebrate assemblages grouped pasture sites with forest sites on the same stream at the same season, indicating that assemblage composition was less influenced by land-use differences than by between-stream and seasonal differences. 5. Biomass of functional feeding groups appeared to be a more sensitive indicator of invertebrate assemblage response to land-use alteration than either species diversity/ richness measures, or multivariate assemblage composition measures.     

Immune response to nylon filaments in two damselfly species that differ in their resistance to ectoparasitic mites

1. Insects commonly resist parasites using melanotic encapsulation. Many studies measuring immune response use the amount of melanin deposited on an artificial object that has been inserted into the animal as a proxy of the amount of resistance that the host is capable of mounting to natural parasites. 2. The relevance of this methodology to immune response in natural insect populations needs further study. Here, we examined two temperate damselfly species to elucidate the relationships among damselfly size, natural resistance to mites, and the immune response mounted by the same damselflies against nylon filaments. 3. The damselfly species that had high rates of melanotic encapsulation of mites in nature deposited more melanin on the nylon inserts than the species with low rates of natural resistance. 4. In females of this species, those that had resisted mites naturally melanised the nylon filament more aggressively than those that did not resist mites. 5. Our results show some support for the use of nylon filaments to assess natural patterns of immune response in these damselflies, but also suggest that caution should be used in interpreting the responses.