Autolysis of chlamydospores of Fusarium solani f. sp. cucurbitae in chitin and laminarin amended soils

Lysis of chlamydospores of Fusarium solani f. sp. cucurbitae is enhanced both in chitin and in laminarin amended soils. In soil amended with both chitin and laminarin, lysis of chlamydospores resembles that in control soil. Addition of chitin and laminarin to soil stimulates the growth of both bacteria and actinomycetes. In soils amended with chitin and with both chitin and laminarin, a chitinolytic microflora is stimulated. Penetration of chlamydospore cells by soil microorganisms has not been observed using the electron microscope. The mechanism of lysis of chlamydospores in soil is discussed.     

Effect of Extraction Temperature on Pressurized Liquid Extraction of Bioactive Compounds from Fucus vesiculosus

This study was aimed at investigating the effect of low polarity water (LPW) on the extraction of bioactive compounds from Fucus vesiculosus and to examine the influence of temperature on the extraction yield, total phenolic content, crude alginate, fucoidan content, and antioxidant activity. The extractions were performed at the temperature range of 120–200 °C with 10 °C increments, and the extraction yield increased linearly with the increasing extraction temperature, with the highest yields at 170–200 °C and with the maximum extraction yield (25.99 ± 2.22%) at 190 °C. The total phenolic content also increased with increasing temperature. The extracts showed a high antioxidant activity, measured with DPPH (2,2-Diphenyl-1-picrylhydrazyl) radicals scavenging and metal-chelating activities of 0.14 mg/mL and 1.39 mg/mL, respectively. The highest yield of alginate and crude fucoidan were found at 140 °C and 160 °C, respectively. The alginate and crude fucoidan contents of the extract were 2.13% and 22.3%, respectively. This study showed that the extraction of bioactive compounds from seaweed could be selectively maximized by controlling the polarity of an environmentally friendly solvent.     

High yield and rapid growth of Neoparamoeba pemaquidensis in co-culture with a rainbow trout gill-derived cell line RTgill-W1

Neoparamoeba pemaquidensis is an ubiquitous amphizoic marine protozoan and has been implicated as the causative agent for several diseases in marine organisms, most notably amoebic gill disease (AGD) in Atlantic salmon. Despite several reports on the pathology of AGD, relatively little is known about the protozoan and its relationship to host cells. In this study, an in vitro approach using monolayers of a rainbow trout gill cell line (RTgill-W1, ATCC CRL-2523) was used to rapidly grow large numbers of N. pemaquidensis (ATCC 50172) and investigate cell-pathogen interactions. Established cell lines derived from other tissues of rainbow trout and other fish species were also evaluated for amoeba growth support. The amoebae showed preference and highest yield when grown with RTgill-W1 over nine other tested fish cell lines. Amoeba yields could reach as high as 5 x 10(5) cells mL(-1) within 3 days of growth on the gill cell monolayers. The amoebae caused visible focal lesions in RTgill-W1 monolayers within 24 h of exposure and rapidly proliferated and spread with cytopathic effects destroying the neighbouring pavement-like cells within 48-72 h after initial exposure in media above 700 mOsm kg(-1). Disruption of the integrity of the gill cell monolayers could be noted within 30 min of exposure to the amoeba suspensions by changes in transepithelial resistance (TER) compared with control cell monolayers maintained in the exposure media. This was significantly different by 2 h (P < 0.05) compared with control cells and remained significantly different (P < 0.01) for the remaining 72 h that the TER was monitored. The RTgill-W1 cell line is thus a convenient model for growing N. pemaquidensis and for studying host-pathogen interactions in AGD.     

Some Limiting Factors in Superintensive Production of Juvenile Pacific White Shrimp,Litopenaeus vannamei,in No‐water‐exchange,Biofloc‐dominated Systems

Superintensive shrimp culture in zero‐exchange, biofloc‐dominated production systems is more biosecure and sustainable than traditional shrimp farming practices. However, successful application of this technology depends upon optimizing dietary formulations, controlling Vibrio outbreaks, and managing accumulative changes in water quality and composition. A 49‐d study investigated the effect of two commercial feeds of differing protein content and an indoor limited‐exchange, biofloc‐dominated culture environment on Litopenaeus vannamei performance and tissue composition, water quality and ionic composition, and Vibrio dynamics. Juveniles (5.3 g) were stocked at 457/m³ into four 40 m³ shallow raceways containing biofloc‐dominated water and fed one of two commercial feeds with differing protein content, 35 or 40%. Shrimp performance, Vibrio populations, and changes in shrimp and culture water composition were monitored. There were no significant differences (P > 0.05) in shrimp performance (survival, weight, growth, specific growth rate, total biomass, yield, feed conversion ratio, and protein efficiency ratio) or proximate composition between feed types. The 40% protein feed resulted in higher culture water nitrate and phosphate concentrations, alkalinity consumption and bicarbonate use, and higher phytoplankton density. The presence of Vibrio, specifically Vibrio parahaemolyticus, reduced shrimp survival. This survival decrease corresponded with increased culture water Vibrio concentrations. Culture water K⁺ and Mg²⁺ increased significantly (P < 0.05), and Sr²⁺, Br^?, and Cl^? decreased significantly (P < 0.05) over time. While Cu²⁺ and Zn²⁺ did increase in shrimp tissue, no heavy metals accumulated to problematic levels in culture water or shrimp tissue. These results demonstrate the importance of monitoring Vibrio populations and ionic composition in limited‐exchange shrimp culture systems.     

Effects of cover crop quality and quantity on nematode-based soil food webs and nutrient cycling

Soil food webs cycle nutrients and regulate parasites and pathogens, services essential for both agricultural productivity and ecosystem health. Nematodes provide useful indicators of soil food web dynamics. This study was conducted to determine if nematode soil food web indicators and crop yield can be enhanced by combinations of cover crops in a conservation tillage system. The effects of three cover crop treatments (vetch/pea, oat/wheat and oat/wheat/pea/vetch) with low, medium and high C:N and a bare fallow control were investigated in Davis, CA. Nematode fauna, soil properties and plant productivity were measured. Soil food web indices, including the Enrichment Index (EI), Structure Index (SI), Basal Index (BI), and Channel Index (CI), based on the composition of nematode assemblages, were calculated to infer soil food web condition. Cover cropped tomato/corn rotations had twice the number of enrichment opportunist bacterial feeding nematodes, active participants in nitrogen mineralization, than fallowed tomato/corn rotations (opportunist bacterial feeders = 163 versus 98). In winter fallowed plots food webs were basal, common in disturbed, nutrient-poor conditions (BI = 37). Total number of enrichment opportunist nematodes, soil NH₄-N levels, and inferred nitrogen mineralization, were higher in cover crop treatments with low to mid C:N ratios. Omnivore and predator nematodes were scarce, averaging less than 6 nematodes 100 g^?1 in all treatments. In year one, plant productivity was highest after fallow. In contrast, in year two productivity was highest after cover crops with high nitrogen content and productivity significantly correlated with the structure of the soil fauna. Monitoring the abundance of enrichment opportunists may provide managers with a new tool to evaluate soil food web nitrogen mineralization and plant productivity.     

Determining soil organic carbon for agricultural soils: a comparison between the Walkley & Black and the dry combustion methods (north Belgium)

Mapping soil organic carbon (SOC) and establishing any change over time are important because of CO₂ fluxes between soil and atmosphere and cropland decreases in SOC. The latter is one of the main causes of soil fertility decline and increased erodibility. As most analytical methods underestimate total SOC content, correction factors are needed to avoid methodological bias when comparing SOC data from sampling campaigns using different analytical procedures. The traditional method for SOC analysis used to be, and in most cases still is wet oxidation in potassium dichromate, better known as the Walkley & Black method. In this study, we aim to estimate correction factors for the classic and modified version of the Walkley & Black method for different land use and soil type combinations for agricultural soils in north Belgium. General correction factors of 1.47 for the classic Walkley & Black method and 1.20 for the modified Walkley & Black method are proposed. The results show that sandy grassland soils are characterised by lower recoveries than silt loam grassland soils. Furthermore, the correction factor appears to increase with soil wetness.     

Chronology of plaggic deposits; palynology,radiocarbon and optically stimulated luminescence dating of the Posteles (NE-Netherlands)

Plaggic agriculture was the dominant land use system on Pleistocene sandy soils in Northwest Europe before the introduction of chemical fertilizers. In the today's landscape plaggic deposits are still recognizable as characteristic soils and landforms, related to this historical land use system. They are also important constituents of the soil archives in Northwest Europe. In preliminary studies of plaggic anthrosols, the reconstruction of the development of the plaggic deposits was based on palynological and historical data and radiocarbon dates. Disagreement appeared between palaeopedological and historical explanation of the evolution of plaggic anthrosols. Application of OSL dating improves the knowledge of chronology of plaggic deposits. The soil organic matrix, including pollen grains, consists of a complex mix of compounds of different ages and sources. Pollen diagrams of plaggic anthrosols show a palynological registration of the Late Holocene landscape evolution, but the palynological signal is not consequently correlated with the age of the plaggic sediments. An older soil organic matrix is suspended in the voids of a younger mineral soil skeleton.     

Parsimoniously modelling perennial vegetation suitability and identifying priority areas to support China's re-vegetation program in the Loess Plateau: Matching model complexity to data availability

The Chinese Central government's policy to re-vegetate large areas of the Loess Plateau is currently being rapidly implemented at the provincial, prefecture, county, township, and village levels of government. Managers at these five levels of government need access to information to assist them to plan the land use change prior to performing on-ground activities. To this end, the suitability of 38 predominately native species in the 113,000 km² Coarse Sandy Hilly Catchments (CSHC) has been mapped at a 100 m resolution. In this data-sparse region, this was achieved by using a five-variable spatial overlay approach as we were able to readily access the required environmental variables and rule-set defining the species’ requirements (or tolerances). As the rules did not consider optimal growth they were possibly ‘too inclusive’, so the spatial extent of areas suggested for re-planting was refined by defining ‘target areas’ for trees, shrubs and grasses based on precipitation, aspect, landform, and slope. In the land-use planning criteria developed here we suggest that hill-slopes and gullies with slopes greater than or equal to 15° (defined from a 100 m resolution DEM) be left for natural succession. Due to lateral flow of water, sediment and nutrients from these steep slope and gullies, further prioritising re-vegetation target areas to the zone adjacent to and down slope from these steep portions of the landscape reduces sediment entering the river network with a minimal decrease of regional stream flow. These two functions (mapping species suitability and locating where priority and target re-vegetation activities should be undertaken) are available at a 100 m resolution for the entire CSHC by accessing a bilingual decision support tool called ReVegIH (Re-Vegetation Impacts on Hydrology). Finally, an ecohydrological model was used to simulate changes in average annual stream flow originating from the CSHC based on implementing the ‘target’ and ‘priority’ area re-vegetation activities within the constraints of two land limits.