Shifts in Soil Bacterial Communities as a Function of Carbon Source Used During Anaerobic Soil Disinfestation

Anaerobic soil disinfestation (ASD) is an organic amendment-based management practice for controlling soil-borne plant pathogens. Pathogen suppression appears to be carbon source-dependent and mediated by bacteria that proliferate and produce volatile organic compounds, as well as physico-chemical changes (i.e., elevated temperature, lowered redox potential and pH, release of metal ions) in soil. ASD is under study for adoption in tree crops as a replacement for chemical-fumigation, but its widespread use is limited by incomplete understanding of its suppression mechanisms and high economic costs. The carbon substrate is one component of the ASD process that can be optimized to enhance effectiveness and affordability. While rice bran is currently the standard carbon source used for ASD, we identified three alternative substrates (molasses, mustard seed meal, and tomato pomace) that are similar in efficacy to rice bran at generating and sustaining soil anoxia and reducing populations of introduced plant pathogens. Here, we used replicated ASD field trials to determine if rice bran and the alternative carbon substrates would elicit similar soil bacterial communities (characterized via amplicon sequencing of the 16S rRNA gene v4 region) and to assess if any observed community shifts were consistent across repeated trials. We found significant, but minimal differences in community composition between ASD carbon treatments (F4, 30 = 2.80, P < 0.001, R2 = 0.22) and trials (F1, 30 = 5.24, P < 0.001, R2 = 0.10). In both trials, the abundances of Bacteroidales, Clostridiales, Selenomonadales, and Enterobacteriales increased significantly (>5 log2 fold change) in all ASD treatments compared to untreated controls. A group of shared core genera belonging to the Clostridiales and Selenomonadales were identified in both trials and constituted 22.6 and 21.5% of the communities. Bacterial taxa that were most responsive to ASD treatments had the genomic potential for denitrification, nitrogen fixation, and fermentation reactions that produce organic acids (such as acetate and butyrate) known to inhibit in vitro growth of plant pathogens based on predicted metagenomes. Together, these results indicate that reproducible and effective implementation of ASD is achievable with alternative carbon substrates to rice bran

Is Fairtrade in commercial farms justifiable?: its impact on commercial and small-scale producers in South Africa

Fairtrade initially was limited to improving the lives of small-scale and peasant farmers, but later on it embraced commercial farmers, which attracted criticism. While there are a number of justifications for the Fairtrade organization's decision, there are authors who feel that meaningful “fair trade” cannot be achieved with the inclusion of commercial farms. This paper investigates the impact of Fairtrade on commercial farms and small-scale farmer cooperatives in South Africa. Fairtrade on South African commercial farms embraces a number of policy concerns related to land reform, BEE and sustainable development. The results of the study show that when commercial farms are included in the Fairtrade model, communities in which these farmers live benefit from developmental projects. In addition, in some instances, farm workers gain shares in the commercial farms, and benefit from the farm owners’ knowledge and capital

Meteorological Controls on Local and Regional Volcanic Ash Dispersal

Volcanic ash has the capacity to impact human health, livestock, crops and infrastructure, including international air traffic. For recent major eruptions, information on the volcanic ash plume has been combined with relatively coarse-resolution meteorological model output to provide simulations of regional ash dispersal, with reasonable success on the scale of hundreds of kilometres. However, to predict and mitigate these impacts locally, significant improvements in modelling capability are required. Here, we present results from a dynamic meteorological-ash-dispersion model configured with sufficient resolution to represent local topographic and convectively-forced flows. We focus on an archetypal volcanic setting, Soufrière, St Vincent, and use the exceptional historical records of the 1902 and 1979 eruptions to challenge our simulations. We find that the evolution and characteristics of ash deposition on St Vincent and nearby islands can be accurately simulated when the wind shear associated with the trade wind inversion and topographically-forced flows are represented. The wind shear plays a primary role and topographic flows a secondary role on ash distribution on local to regional scales. We propose a new explanation for the downwind ash deposition maxima, commonly observed in volcanic eruptions, as resulting from the detailed forcing of mesoscale meteorology on the ash plume

Adaptations to Submarine Hydrothermal Environments Exemplified by the Genome of Nautilia profundicola

Submarine hydrothermal vents are model systems for the Archaean Earth environment, and some sites maintain conditions that may have favored the formation and evolution of cellular life. Vents are typified by rapid fluctuations in temperature and redox potential that impose a strong selective pressure on resident microbial communities. Nautilia profundicola strain Am-H is a moderately thermophilic, deeply-branching Epsilonproteobacterium found free-living at hydrothermal vents and is a member of the microbial mass on the dorsal surface of vent polychaete, Alvinella pompejana. Analysis of the 1.7-Mbp genome of N. profundicola uncovered adaptations to the vent environment—some unique and some shared with other Epsilonproteobacterial genomes. The major findings included: (1) a diverse suite of hydrogenases coupled to a relatively simple electron transport chain, (2) numerous stress response systems, (3) a novel predicted nitrate assimilation pathway with hydroxylamine as a key intermediate, and (4) a gene (rgy) encoding the hallmark protein for hyperthermophilic growth, reverse gyrase. Additional experiments indicated that expression of rgy in strain Am-H was induced over 100-fold with a 20°C increase above the optimal growth temperature of this bacterium and that closely related rgy genes are present and expressed in bacterial communities residing in geographically distinct thermophilic environments. N. profundicola, therefore, is a model Epsilonproteobacterium that contains all the genes necessary for life in the extreme conditions widely believed to reflect those in the Archaean biosphere—anaerobic, sulfur, H2- and CO2-rich, with fluctuating redox potentials and temperatures. In addition, reverse gyrase appears to be an important and common adaptation for mesophiles and moderate thermophiles that inhabit ecological niches characterized by rapid and frequent temperature fluctuations and, as such, can no longer be considered a unique feature of hyperthermophiles

Modelling tephra dispersal and ash aggregation: application to the 26 April 1979 eruption of La Soufri\ue8re St. Vincent

On 26 April 1979, La Soufri\ue8re St. Vincent volcano (West Indies) erupted producing a tephra fallout that blanked the main island and neighbouring island of Bequia, located southwards. Using deposit measurements and available observations reported in Brazier et al. (1982), we reproduce the main features and processes of the eruption and estimate by best-fit the eruption source parameters such as the Mass Eruption Rate (MER), the Total Erupted Mass (TEM), and validate the Total Grain-Size Distribution (TGSD). Tephra transport and deposition is simulated using the 3D time-dependent Eulerian model FALL3D. The TGSD reconstructed by Brazier et al. (1982) showed a bi-modal pattern having a coarse mode around 0.5 mm and a fine mode around 0.06 mm. Because ash aggregation was significant during the eruption, we perform a comparative study by neglecting and accounting for aggre- gation using three different aggregation models. The models for ash aggregation in the plume assume wet conditions consistently with the eruptive phreatomagmatic features, considering both the effects of air moisture and magmatic water. The sensitivity to the driving meteoro- logical model (WRF-ARW) is also investigated considering model spatial resolutions of 5 and 1 km showing that, for this kind of eruptions, high-resolution meteorology is pivotal. The optimal best-fit results indicate a column height of ~13 km above the vent, a MER of ~7 7106 kg/s which, for an eruption duration of 370 seconds, gives a TEM of ~2.7 710^9 kg. The opti- mal aggregate mean diameter obtained is 1.5\u3a6 with a density of 520 kg/m3 contributing to ~28 % of the deposit loading