Dominant sources of dietary carbon and nitrogen for shrimp reared in extensive rice-shrimp ponds

Stable isotope analysis was used to determine the sources of dietary nitrogen (N) and carbon (C) for shrimp during the rearing phase in extensive rice‐shrimp ponds in My Xuyen and Gia Rai districts, Vietnam. Farm‐made feed was added as a food source in shrimp ponds in My Xuyen district, and based on stable isotope analyses, was generally a poor dietary source. The commercial formulated feed used in Gia Rai also appeared to contribute little directly to the nutritional needs of the shrimp. In contrast, the natural biota in all ponds appeared to contribute substantially. In particular, biota from beam trawls and benthic organic matter were the most likely sources of nutrition in My Xuyen ponds, while benthic organic matter was the main source in Gia Rai ponds. δ¹⁵N ratios in the natural biota in My Xuyen farms decreased over the growing season, suggesting increased N fixation in the case of the benthic organic matter reaching values as low as 1‰. This suggests N‐limitation in the ponds and that natural biota become increasingly dependent on N fixed by algae and/or other microorganisms. There is the potential to promote the growth of the plankton and hence, the other natural biota, by the judicious addition of fertilizer.     

Proximal sensor-enhanced soil mapping in complex soil-landscape areas of Brazil

Portable X-ray fluorescence (pXRF) spectrometry and magnetic susceptibility (MS) via magnetometer have been increasingly used with terrain variables for digital soil mapping. However, this methodology is still emerging in many countries with tropical soils. The objective of this study was to use proximal soil sensor data associated with terrain variables at varying spatial resolutions to predict soil classes using the Random Forest (RF) algorithm. The study was conducted on a 316-ha area featuring highly variable soil classes and complex soil-landscape relationships in Minas Gerais State, Brazil. The overall accuracy and Kappa index were evaluated using soils that were classified at 118 sites, with 90 being used for modeling and 28 for validation. Digital elevation models (DEMs) were created at 5-, 10-, 20-, and 30-m resolutions using contour lines from two sources. The resulting DEMs were processed to generate 12 terrain variables. Total Fe, Ti, and SiO₂ contents were obtained using pXRF, with MS determined via a magnetometer. Soil class prediction was performed using the RF algorithm. The quality of the soil maps improved when using only the five most important covariates and combining proximal sensor data with terrain variables at different spatial resolutions. The finest spatial resolution did not always provide the most accurate maps. The high soil complexity in the area prevented highly accurate predictions. The most important variables influencing the soil mapping were MS, Fe, and Ti. Proximal sensor data associated with terrain information were successfully used to map Brazilian soils at variable spatial resolutions.     

Soil chemical and biochemical properties of a salt-marsh alluvial Spanish area after long-term reclamation

Marisma, one of the largest salt-marsh alluvial areas in SW Spain, has been reclaimed since 1970 by artificial drainage and amendment with phosphogypsum (PG) so as to reduce Na⁺ saturation. Within the reclaimed area, two 250- × 20-m plots were treated as follows: (1) amendment with 25 Mg/ha of PG every 2 to 3 years between 1979 and 2003 (plot PY); (2) like PY but PG treatment stopped after 1997 (plot DR). A contiguous virgin Marisma salt-marsh plot (MV), neither drained nor amended, was the control. In MV, soil microbial biomass C, most enzyme activities and total organic C content were much greater than in PY and DR soils, despite the salinity stress. The decrease in soil organic matter content in PY and DR soils was likely due to cotton-cropping practices, which favoured the organic C mineralisation and nutrients removal by crops. Microbial activity of MV soil, probably stimulated by the rhizodepositions of the natural vegetation, did not suffer from the osmotic effect due to the raising of soil solution ionic strength. Microbial quotient could be ranked as MV > PY > DR, whereas the metabolic quotient had an opposite trend. Thus, both quotients suggested that the interruption of PG amendment was not favouring microbial activity. Principal component analysis clearly identified the chemical and biochemical soil properties mostly affected by the reclamation and also indicated the longer PG amendment in PY plot. Stepwise discriminant analysis identified two physiologically different types of soil microflora, one less active present in the MV virgin soil and another more active present in the reclaimed PY and DR soils.     

Contribution of the natural biota associated with substrates to the nutritional requirements of the post-larval shrimp, Penaeus esculentus (Haswell), inhigh-density rearing systems

The contribution of epiphytes associated with physical substrates to the nutritional requirements of post‐larval shrimp, Penaeus esculentus Haswell, was determined in high‐density rearing systems (3000, 6000 and 11 000 m^?3). Stable isotope signatures of epiphytes on polyethylene mesh substrate, AquaMats? and tank walls were compared with shrimp signatures. Two methods were used: the determination of carbon and nitrogen natural abundance ratios; and ¹⁵N‐nitrogen enrichment ratios after the addition of ¹⁵N‐ammonium to tanks. Using the natural abundance technique and a simple mixing model, epiphytes were found to contribute substantially to the carbon requirements of post‐larval shrimp (39–53%). This was despite the addition of formulated feed at satiation levels. There was no indication of a reduced contribution of carbon from epiphytes to shrimp nutrition at higher shrimp densities. The lack of a difference in the ¹⁵N/¹⁴N ratios of the two food sources meant that mixing models could not be used to calculate the contribution of nitrogen from epiphytes vs. artificial feed to shrimp nutrition. Using the ¹⁵N‐nitrogenenrichment method, the amount of nitrogen contributed by epiphytes to shrimp nutrition over 24 h could be determined. This method showed that nitrogen from epiphytes was assimilated by shrimp. ¹⁵N‐enrichment methods provided a more accurate alternative to natural abundance techniques, particularly when the stable isotope signals ofthe food sources are similar. This experiment hasshown the benefits in providing substrates for P.esculentus in high‐density rearing systems to provide an additional food source for shrimp.     

Effect of Beauveria bassiana and Metarhizium anisopliae on the Trialeurodes vaporariorum-Encarsia formosa system

The virulence of three strains of Beauveria bassiana and one of Metarhizium anisopliae was tested against Trialeurodes vaporariorum and its parasitoid Encarsia formosa in laboratory assays. These strains were previously selected for their virulence against Galleria mellonella and Tenebrio molitor. The commercial B. bassiana strain ATCC 74040, both as pure fungal culture and formulated myco-insecticide (Naturalis), was included in the assays as positive control. First, the entomopathogenic fungal strains were tested for their virulence against T. vaporariorum nymphs on tomato leaf disks. Then, the E. formosa development was evaluated under treatment with the entomopathogenic fungal strains at five different time points from the parasitization of T. vaporariorum nymphs. The virulence of our entomopathogenic fungal strains was superior to that of ATCC 74040, although not significantly, resulting in a cumulative mortality (CM) of T. vaporariorum nymphs 7 days after inoculation (DAI) greater than 86 %. Our M. anisopliae strain CIST8 was the most effective (96.6 % CM 7 DAI), even superior to the myco-insecticide Naturalis (94.2 %), which was more effective than the ATCC 74040 pure strain (85.6 %). The entomopathogenic fungal strains, and especially Naturalis, negatively affected E. formosa development and its parasitization activity of T. vaporariorum nymphs. This effect was more pronounced when the fungal strains were applied before parasitization. Results suggest that the application of entomopathogenic fungi is incompatible with E. formosa release on crops.     

Integrated pest management of Tuta absoluta: practical implementations across different world regions

Journal of Pest Science - The South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), has invaded most Afro-Eurasian countries and is threatening worldwide tomato...     

Progress and challenges in freshwater conservation planning

• 1. Freshwater ecosystems and their associated biota are among the most endangered in the world. This, combined with escalating human pressure on water resources, demands that urgent measures be taken to conserve freshwater ecosystems and the services they provide. Systematic conservation planning provides a strategic and scientifically defensible framework for doing this.
• 2. Pioneered in the terrestrial realm, there has been some scepticism associated with the applicability of systematic approaches to freshwater conservation planning. Recent studies, however, indicate that it is possible to apply overarching systematic conservation planning goals to the freshwater realm although the specific methods for achieving these will differ, particularly in relation to the strong connectivity inherent to most freshwater systems.
• 3. Progress has been made in establishing surrogates that depict freshwater biodiversity and ecological integrity, developing complementarity‐based algorithms that incorporate directional connectivity, and designing freshwater conservation area networks that take cognizance of both connectivity and implementation practicalities.
• 4. Key research priorities include increased impetus on planning for non‐riverine freshwater systems; evaluating the effectiveness of freshwater biodiversity surrogates; establishing scientifically defensible conservation targets; developing complementarity‐based algorithms that simultaneously consider connectivity issues for both lentic and lotic water bodies; developing integrated conservation plans across freshwater, terrestrial and marine realms; incorporating uncertainty and dynamic threats into freshwater conservation planning; collection and collation of scale‐appropriate primary data; and building an evidence‐base to support improved implementation of freshwater conservation plans.

Copyright © 2008 John Wiley & Sons, Ltd.     

Covariation between plant biodiversity and soil systems in a European beech forest and a black pine plantation: the case of Mount Faito,(Campania,Southern Italy)OA

Both climate and land-use changes, including the introduction and spread of allochthonous species, are forecast to affect forest ecosystems. Accordingly, forests will be affected in terms of species composition as well as their soil chemical and biological characteristics. The possible changes in both tree cover and soil system might impact the amount of carbon that is stored in living plants and dead biomass and within the soil itself. Additionally, such alterations can have a strong impact on ...     

Durum wheat varieties in N‐deficient environments and organic farming: a comparison of yield,quality and stability performances

Stability and reliability of yield and quality for 15 durum wheat genotypes (old and modern) were evaluated in a 5‐year experiment (southern Italy) in organic farming. Genotypes were grown at two N levels (0 and 80 kg/ha), with the aim of evaluating ‘genotype × environment’ (GE) interactions and their role on genotype selection in N‐limited environments. Several approaches to stability were used, within the frame of mixed models and additive main effects and multiplicative interaction analysis, and their validity in stressful conditions and organic farming was discussed. Especially for protein and gluten content, results indicate high environmental variability and the presence of crossover ‘N × environment’ interactions, which supports the need for specific breeding programmes in N‐deficient environments. The average response was strongly affected by N availability (on average, yield was 2.95 and 3.42 t/ha, protein content was 11.6% and 12.85%, gluten content was 8.55% and 9.92%, respectively, at 0 and 80 kg N/ha), and few genotypes gave high yield and quality at both fertilization levels. Only ‘Gargano’ and ‘Fortore’ showed a good inter‐year stability at both N levels. The old cultivars gave minimal responsiveness to increased N input, but gave good results in limiting conditions, indicating that they may play a role in organic farming.