Protective Effects Against Erwinia amylovora Induced by hrp Mutants in the Whole Plant are Only Partially Mimicked in Cultivated Cells

A virulent strain of Erwinia amylovora, the causal agent of fire blight of Maloideae, and two of its non-virulent hrp mutants (a secretory and a regulatory mutant) were inoculated into apple cell suspensions either alone or in mixed inoculations. In single inoculations, death of 4- to 5-day-old apple cells occurred only when the concentration of the virulent strain of E. amylovora reached a threshold inoculum concentration of 10⁴CFUml^–1, while high concentrations of the hrp mutants were unable to kill apple cells. When mixed inoculated with the virulent parental strain, both hrp mutants protected apple cells from death caused by the virulent strain. The protective effect was associated with a decrease in the population level of the virulent strain and it was dependent on the non-virulent to virulent inoculum concentration suggesting a competition between the non-virulent mutant and the virulent strain. However, no differential protective ability between the two types of mutants could be noticed, contrary to previous results obtained with apple seedlings or apple flowers in which the regulatory mutant was significantly more effective than the secretory mutant. In conclusion, inoculation of apple cell cultures with E. amylovora does not seem to be a model suitable for investigating mechanisms leading to protection.     

Effects of high and low inspired fractions of oxygen on horse erythrocyte membrane properties, blood viscosity and muscle oxygenation during anaesthesia

ObjectivesTo evaluate whether a period of hyperoxia or after a period of hypoxia produced changes attributable to reactive oxygen species in anaesthetized horses.Study designProspective randomized experimental study.AnimalsSix healthy (ASA I) geldings, aged 4.5–9.5 years and weighing 510–640 kg^?1.MethodsAfter 30 minutes breathing air as carrier gas for isoflurane, horses were assigned randomly to breathe air as carrier gas (CG0.21) or oxygen as carrier gas (CG1.00) for a further 90 minutes. After an interval of 1 month each horse was re-anaesthetized with the other carrier gas for the 90 minute test period. Ventilation was controlled throughout anaesthesia. Arterial blood was sampled to measure gas tensions, lactate, cholesterol, vitamin E, 4-hydroxy-alkenals, 8-epi-PGF_2α, half haemolysis time, half erythrolysis time, and erythrocyte membrane fluidity. Muscle blood flow and oxygenation were evaluated by near infrared spectroscopy and coloured Doppler.ResultsAfter the first 30 minutes horses were hypoxemic. Subsequently the CG1.00 group became hyperoxaemic (PaO₂～240 mmHg) whereas the CG0.21 group remained hypoxaemic (PaO₂～60 mmHg) and had increased lactate concentration. No significant changes in vitamin E, 4-hydroxy-alkenals, or 8-epi-PGF_2α concentrations were detected. During the 90 minute test period the CG0.21 group had increased resistance to free-radical-mediated lysis in erythrocytes, whereas the CG1.00 group had slightly decreased resistance of whole blood to haemolysis. CG0.21 induced a progressive muscle deoxygenation whereas CG1.00 induced an increase in muscle oxygen saturation followed by progressive deoxygenation towards baseline.Conclusions and clinical relevanceDuring isoflurane anaesthesia in horses, the hyperoxia induced by changing from air to oxygen induced minimal damage from reactive oxygen species. Using air as the carrier gas decreased skeletal muscle oxygenation compared with using oxygen.     

Butterfly dispersal in farmland: a replicated landscape genetics study on the meadow brown butterfly (<Emphasis Type="Italic">Maniola jurtina</Emphasis>)

Context

Anthropogenic activities readily result in the fragmentation of habitats such that species persistence increasingly depends on their ability to disperse. However, landscape features that enhance or limit individual dispersal are often poorly understood. Landscape genetics has recently provided innovative solutions to evaluate landscape resistance to dispersal.

Objectives

We studied the dispersal of the common meadow brown butterfly, Maniola jurtina, in agricultural landscapes, using a replicated study design and rigorous statistical analyses. Based on existing behavioral and life history research, we hypothesized that the meadow brown would preferentially disperse through its preferred grassy habitats (meadows and road verges) and avoid dispersing through woodlands and the agricultural matrix.

Methods

Samples were collected in 18 study landscapes of 5 × 5 km in three contrasting agricultural French regions. Using circuit theory, least cost path and transect-based methods, we analyzed the effect of the landscape on gene flow separately for each sex.

Results

Analysis of 1681 samples with 6 microsatellites loci revealed that landscape features weakly influence meadow brown butterfly gene flow. Gene flow in both sexes appeared to be weakly limited by forests and arable lands, whereas grasslands and grassy linear elements (road verges) were more likely to enhance gene flow.

Conclusion

Our results are consistent with the hypothesis of greater dispersal through landscape elements that are most similar to suitable habitat. Our spatially replicated landscape genetics study allowed us to detect subtle landscape effects on butterfly gene flow, and these findings were reinforced by consistent results across analytical methods.

     

Has global change induced divergent trends in radial growth of Pinus sylvestris and Pinus halepensis at their bioclimatic limit? The example of the Sainte-Baume forest (south-east France)

? It is agreed that climate (precipitation and temperature) influences the distribution of plant species. Near the margins of a species’ natural range, climate becomes limiting to physiological processes. There, climate change may be expected to have a significant impact on tree growth and the species’ ranges may be altered.

? In order to assess what influence climate change could exert on the distribution of pine species at their margin, radial growth trends in ring-width chronologies over the last century were analysed. In the French Mediterranean area where climate change is characterized by increased temperature, forest plots were selected along an altitudinal transect on the north-facing slope of the Sainte-Baume mountain (Bouches-du-Rhône, France) where the ranges of Pinus sylvestris and Pinus halepensis overlap.

? Two growth patterns were identified. For P. halepensis, radial growth has increased at all altitudes indicating that climate change has improved growth conditions of this species near the margin of its ecological range. For P. sylvestris, radial growth has increased only at low altitudes and even decreased at high altitudes.

? It must be deduced that the growth changes observed cannot be generalised either at the species level or at the geographical level and must be interpreted with great caution.

     

A new bioclimatic model calibrated with vegetation for Mediterranean forest areas

? Water availability is one of the main factors explaining flora composition and growth in Mediterranean regions, where it may decline with climate change.

? Our goal was to develop a model for forest site assessment in Mediterranean environments, focusing on water availability to assess potential vegetation composition and productivity in any places, whatever their level of disturbance.

? We designed a statistical model, using global climatic and geographic variables, as well as detailed local topographic and edaphic variables, to compute a bioclimatic index for Mediterranean forest environments. This model was calibrated in France with a flora index from 325 old forests. The model explained 80.3% of the flora index variance. The method fills a gap in existing models, bridging scales from the region to forest sites.

? Beyond its theoretical aspect, it was designed to allow practical tools to be derived from it for decision-making and management, such as the assessment of climate change impact on vegetation, and of forest productivity. Its development and adaptation is possible in other Mediterranean regions, and in any region where water is one of the main limiting factors.

     

Impact of Macrotermes termitaria as a source of heterogeneity on tree diversity and structure in a Sudanian savannah under controlled grazing and annual prescribed fire (Burkina Faso)

Macrotermes termitaria are conspicuous features of savannah ecosystems in the Sudanian and Sahelian zones of West Africa. The mounds, alive or abandoned, are a major source of heterogeneity in the landscape. The purpose of the present study was to assess the impact of termitaria on tree community in a state forest of the Sudanian regional centre (Tiogo forest, Burkina Faso), under controlled burning and grazing experiments. A comparative inventory was carried out in a split-plot experiment (16 subplots of 2500 m²): 8 subplots where fire regime and grazing were controlled and 8 subplots exposed to grazing and with annual prescribed fire since 1992. All tree individuals (≥1.5 m) were recorded, both on termitaria and outside and their basal area at stump level was measured. A total of 61 observed (or 65.7 ± 2.4 estimated) tree species were recorded on 28 Macrotermes subhyalinus mounds (54 observed species or 60.8 ± 3.3 estimated), the immediate surroundings (44 observed and 59.0 ± 0.0 estimated species) and the rest of subplots (56 observed and 63.6 ± 0.0 estimated). Specific density was higher on mounds in comparison with the surroundings (P < 0.05). Results showed that termitaria played a key role in maintaining higher species diversity as compared to their surroundings (P < 0.05). Differences in species diversity between termitaria and immediate surroundings appeared more pronounced in disturbed plots (submitted to both fire and grazing). Some species, such as Tamarindus indica, Boscia senegalensis, Cadaba farinosa, Capparis sepiaria and Maerua angolensis are found solely on termitaria. Besides, the density of trees was significantly higher on termitaria compared to the surrounding (P < 0.05), as well as total basal area per unit of 100 m² area (P < 0.05). We concluded that Macrotermes termitaria play an important role as a source of heterogeneity in this Sudanian savannah woodland ecosystem. This role is particularly important in ecosystems under stresses. Termitaria acted as refuge for tree vegetation. The density and dynamics of M. subhyalinus termitaria should, therefore, be taken into account in the global strategy of the forest resources management and conservation.     

Effect of increasing densities of Urochloa brizantha cv. Marandu on Eucalyptus urograndis initial development in silvopastoral system

In silvopasture system, the coexistence of eucalyptus seedlings with other species may result in growth reduction, especially during eucalyptus early development.Therefore, studies elucidating how forage species affect the eucalyptus growth can provide important information for their rational management aiming to obtain the maximum gain of the system. The aim of this work was to evaluate the effect of increasing densities of Urochloa brizantha cv.Marandu in the early development of Eucalyptus urograndis. An experiment was conducted in 20 L pots, in an open and semi-controlled area, during 90 days after planting of eucalyptus. A completely randomized design with four replications was used, in a 6 9 7 factorial system, meaning six evaluation periods and seven densities of U. brizantha: 0(control), 22, 33, 44, 67, 89 and111 plants m^-2. Fortnightly, eucalyptus height, stem diameter and chlorophyll fluorescence(Fv/Fm) were evaluated. At the end of experimental period, the net assimilation rate, stomatal conductance and transpiration rate of eucalyptus plants were determined, in addition to the dry matter of eucalyptus(leaves and stem) and U. brizantha (leaves). In coexistence with 111 plants m^-2, eucalyptus had reduction of 63.9% on total dry matter and 72.7% on leaf area, compared to the control. From the density of22 plants m^-2, U. brizantha negatively interfere significantly the growth of E. urograndis. Up to 8 plants m^-2 there are no reductions greater than 5% in eucalyptus height and stem diameter.     

Smallholder Agroforestry in Rwanda: A SWOT-AHP Analysis

The perception of Rwandan government officials, NGOs, and extension specialists about smallholder agroforestry adoption as a strategy for smallholder farmers in Rwanda was investigated using a strengths, weaknesses, opportunities, and threats analysis framework combined with the analytical hierarchy process. Results indicate that smallholder agroforestry is viewed positively as a suitable strategy for Rwandan smallholder farmers. The most important positive features were the potential for increased agricultural output from agroforestry and a favorable policy environment in Rwanda supporting sustainable agriculture. Results also indicate that there needs to be better coordination of various efforts to promote agroforestry and stronger extension services for smallholder farmers. Carbon offset markets and other environmental service markets were seen as a potential opportunity for smallholder agroforestry. However, the results also indicate that there is substantial uncertainty and skepticism concerning how such markets would benefit smallholder farmers who adopted agroforestry.     

Variations of plant and soil 87Sr/86Sr along the slope of a tropical inselberg

? From the summit downslope a granitic inselberg in French Guiana, soils and vegetation evolve from bare granite covered by cyanobacteria, to a savannah-type vegetation on thin patchy sandy accumulations, then to a low forest on shallow young soils and to a high forest on deep highly weathered ultisols.

? We have used element budgets and Sr isotopic variations in soils and plants to investigate the mineral nutrient supply sources of the different plant communities.

? Granite and atmospheric deposition have ⁸⁷Sr/⁸⁶Sr ratios of 1.3 and 0.71, respectively. The ⁸⁷Sr/⁸⁶Sr ratio of cyanobacteria (0.72) suggests granite weathering by cyanobacteria crusts. The ⁸⁷Sr/⁸⁶Sr ratio of the savannah-type vegetation is 0.73 and varies between 0.75 and 0.76 in the low and high forest leaf litter regardless of soil depth, age and degree of impoverishment.

? These almost constant ratio suggest that forest Sr comes from rainwater and from the summit of this inselberg, where it is released and redistributed along the slope, by surface flow, lateral redistribution of litter, and mineral particles. However, because of its very low content in the rock and soils, Ca is supplied to plants by atmospheric deposition.

     

Influence of plantation site and wastewater sludge fertilization on the performance and foliar nutrient status of two willow species grown under SRIC in southern Quebec (Canada)

Salix discolor Mühl. (Sd) and Salix viminalis L. (Sv) were planted under short-rotation intensive culture (SRIC) on three unirrigated abandoned farmland sites with different drainage conditions, one well-drained (S₁) and the other two poorly-drained (S₂, S₃). One dose of dried and granulated sludge equivalent to 150 (T₁) kg of “available” N ha⁻¹ was applied to some plots in the spring of the second season while others were left unfertilized (T₀). The aims of the experiment were (i) to investigate plant response (growth and productivity) to plantation site conditions and sludge application; (ii) study nutrient status by foliar analysis. Over three seasons, growth in height and aboveground biomass were greater for S. viminalis than for S. discolor on all sites. S. viminalis planted on poorly-drained site 2 had the highest biomass yield (45.28 t ha⁻¹). Both species showed best height and diameter growth on poorly-drained sites. For both species, best performances were obtained on wastewater sludge fertilized plots. Comparative foliar analysis suggested that unfertilized sandy soil (S₁) and low foliar nitrogen concentration and content were limiting factors in the performance of the two species. Soil nitrate concentration increased as a result of sludge application. Heavy metal accumulation from sludge does not represent a risk to the environment. It was concluded that S. viminalis had the best productivity on clay sites, and that a moderate dose of dried and pelleted sludge (150 kg of “available” N ha⁻¹) may be a good fertilizer during the establishment of willows in SRIC, and may reduce nitrate leaching.