Soil community changes during secondary succession to naturalized grasslands

Succession to a naturalized grassland from former agricultural land and pastures is accompanied by changes in plant biodiversity and in the soil community. These changes are the result of a reduction or elimination of management, fertilizer applications and of grazing by large herbivores. We review soil biology studies on agricultural land that are in various successional stages towards naturalized grasslands, where interactions between plant species composition changes and the soil ecology affect each other. In many chronosequence studies, the soil microbial community tends to shift towards a less bacterial, and more fungal dominated food web energy channel following a reduction in fertilizer inputs and grazing intensity. Whereas changes in microarthropod communities are obscured, nematode trophic functional group (ecological guild) changes respond to both plant and soil community changes. There are opportunities to further study the feedback interactions between roots and soil organisms in grasslands. A better understanding of the molecular feedback mechanisms would be beneficial in long-term grassland management.     

电感耦合等离子体质谱法(ICP-MS)同时测定土壤中多种元素

为优化ICP-MS法同时测定土壤中多种元素的测定条件,采用在线加人内标的方法,探讨同时测定元素Li、Be、Sc、Ge、Mo、Sb、W、Tl、Bi、Th、U的参数条件,并对优化后的条件进行质量水平评价.试验结果表明:元素检出限为0.003～0.450 μg/L;△lgc＜0.04;RSD%＜10(n=12);加标回收率在98%-108%之间.     

Rapid virulence typing of Pasteurella multocida by multiplex PCR

The gram-negative bacterium Pasteurella multocida constitutes a heterogeneous species associated with wide range of disease in many animals. Isolates are classified into five groups based on capsular antigen (capA, B, D, E and F). Recently, a new valuable PCR-based method was introduced to determine the epidemiological correlation between P. multocida infection and existence of virulence genes including tbpA, pfhA, toxA and hgbB. However, this method is tedious and laborious. Thus, in the current study, we designed a reliable multiplex PCR method for rapid detection of virulence genes in P. multocida. Eighty seven strains of P. multocida isolated from various clinically healthy and infected hosts were examined by uniplex PCR method for each virulence associated genes. Based on our improved and simplified multiplex PCR method, rapid detection of four virulence genes was accomplished. It is proposed that its implementation may benefit the epidemiological investigations.     

The effects of topical oxygen therapy on equine distal limb dermal wound healing

Topical oxygen therapy (TOT) has been used in human medicine to promote healing in chronic wounds. To test the efficacy and safety of TOT in horses, an experimental wound model was created by making 1 standardized dermal wound on each limb of 4 healthy horses (n = 16). Each wound was fitted with an oxygen delivery cannula and covered with a bandage. One limb of each front and hind pair was randomly assigned to the treatment group (fitted with an oxygen concentrator device), with the contralateral limb assigned to the control group (no device). Wound area, epithelial area, and contraction were measured every 3 to 4 d. Biopsy samples and culture swabs were taken on days 16 and 32 to evaluate angiogenesis, fibroplasia, epithelial hyperplasia, inflammation and bacterial growth. Mean healing time in treated wounds (45 d, range: 38 to 52 d) was not significantly different from that in the paired control wounds (50 d, range: 38 to 62 d). Topical oxygen therapy had little effect on dermal wound healing in this experimental wound model in healthy horses.     

Stable isotopes reveal the importance of terrestrially derived resources for the diet of the freshwater pearl mussel (Margaritifera margaritifera)

1. The freshwater pearl mussel (FPM) is among the most endangered freshwater species worldwide. The few remaining populations suffer from low recruitment rates and are subject to habitat fragmentation, pollution, siltation, decline or loss of host fish populations, and climate change.
2. Successful conservation strategies for FPM require a holistic understanding of its ecological requirements, life history, population dynamics, and habitat prerequisites. Although habitat requirements are well described, food requirements at different life stages have received less attention.
3. Stable isotope analyses of FPM and potential food resources in three German streams were combined with mixing model analysis to quantify organic matter resources assimilated by juvenile (first year after encystment from host fish) and semi-adult (10 years old, immature) individuals.
4. There were only slight differences in dietary contributions between the two life stages, and terrestrial particulate organic matter and benthic organic matter contributed substantially to the diet. Tissue type was more important in explaining variation in dietary contributions than individual variation for semi-adult FPM. The strong reliance on terrestrial resources sheds new light on the functional role of unionid mussels and the connection of streams to their riparian area.
5. The dependence of FPM on terrestrial resources also emphasizes the need for a stronger focus on the restoration and protection of intact riparian areas, including wetlands with their specific vegetation, when planning conservation and management strategies for threatened FPM populations.

     

2000-2011年中国-东盟农产品贸易变化分析

通过分析中国和东盟农产品比较优势和贸易互补性的变化,探讨了中国-东盟农产品贸易变化趋势及特征。研究发现,随着中国-东盟自贸区的建设,中国-东盟农产品贸易快速增长,朝着体现双边比较优势的方向发展,贸易额从2001年的30．27亿美元上升到2011年的275．46亿美元,年均增长率为24．71％。但中国对东盟农产品贸易逆差不断扩大,中国出口农产品结构和东盟进口农产品结构互补性呈现下降趋势,中国一东盟农产品贸易互补指数值由1996年的1．3下降到2011年的0．32,未来中国对东盟农产品出口的增长前景不太乐观。     

Strategic tillage in Australian conservation agricultural systems to address soil constraints: How does it impact weed management?

In the conservation agricultural systems practised in Australia, cultivation is not commonly utilised for the purpose of weed control. However, occasional use of tillage (strategic tillage) is implemented every few years for soil amelioration, to address constraints such as acidity, water repellence or soil compaction. Depending on the tillage method, the soil amelioration process buries or disturbs the topsoil. The act of amelioration also changes the soil physical and chemical properties and affects crop growth. While these strategic tillage practices are not usually applied for weed control, they are likely to have an impact on weed seedbank burial, which will in turn affect seed dormancy and seedbank depletion. Strategic tillage impacts on seed burial and soil characteristics will also affect weed emergence, plant survival, competitive ability of weeds against the crop and efficiency of soil applied pre-emergent herbicides. If growers understand the impacts of soil amelioration on weed demography, they can more effectively plan management strategies to apply following the strategic tillage practice. Weed seed burial resulting from a full soil inversion is understood, but for many soil tillage implements, more data is needed on the extent of soil mixing, burial of topsoil and the weed seedbank, physical control of existing weeds and stimulation of emergence following the tillage event. Within the agronomic system, there is no research on optimal timing for a tillage event within the year. There are multiple studies to indicate that strategic tillage can reduce weed density, but in most studies, the weed density increases in subsequent years. This indicates that more research is required on the interaction of amelioration and weed ecology, and optimal weed management strategies following a strategic tillage event to maintain weeds at low densities. However, this review also highlights that, where the impacts of soil amelioration are understood, existing data on weed ecology can be applied to potentially determine impacts of amelioration on weed growth.     

Ecological plasticity and commercial impact of invasive marbled crayfish populations in Madagascar

Background

As plants, algae and some sessile invertebrates may grow in nearly monospecific assemblies, their collective biomass increases and if they compete hard enough some die, freeing up space. The concurrent increase in biomass and decrease in density is called self-thinning, and its trajectory over time or maximum values represent a boundary condition. For a single stand developing over time the boundary defines the carrying capacity of the environment but the most extreme trajectories emulate the efficiency of species in packing biomass into space.

Results

Here we present a meta-analysis of compiled data on biomass and density from 56 studies of 42 species of seaweeds from 8 orders within 3 phyla scattered through the world’s oceans. Our analysis shows that, with respect to biomass, seaweeds are the most efficient space occupiers on Earth because they transgress previously fixed limits derived from land plants. This is probably because seaweeds are not limited by water and do not need structures for its transport or for transpiration; they photosynthesise and uptake nutrients over their entire surface; they are attached to the substrate by holdfasts that are small proportional to their volume or weight compared to roots; water provides them better support, reducing the need for tissues for rigidity. We also identified a biomass concentration common to plants and seaweeds which represents the threshold that no life on the planet can pass. Using each stand’s distance to the biomass–density boundary, we determined that within the seaweeds the efficiency of space occupation differed amongst taxonomic and functional groups as well as with clonality and latitude.

Conclusions

Algae occupy space more efficiently than plants, most likely because the watery environment facilitates the physical processes and integration of space occupation. The distance-to-the-boundary proves a good metric to discriminate among groups and may be useful for comparison of the most efficient biomass producing systems, or for the identification of systems impacted by pollution.

     

Effects of seed priming on growth and antioxidant components of hairy vetch (Vicia villosa) seedlings under chilling stress

Hairy vetch (Vicia villosa) is an important cover crop and green manure in dryland cropping system of Mediterranean regions. A delay in the onset of rainfall during autumn can inhibit hairy vetch seed germination, which exposes its early growth stages to low-temperature stress. The present study was carried out in a completely randomized design with four replications to evaluate the effects of seed priming on germination of hairy vetch under chilling stress. The treatments were seed-priming type (unprimed, hydro-priming, halo-priming, and osmopriming) and temperature (3, 6, 9, 12, and 15?°C). The results indicated that a decrease in temperature produced a linear decline in the germination rate of seeds treated with halo-priming and osmopriming (p?<?.01). The seedling length, seedling dry weight, and vigor index decreased in plants experiencing chilling stress (quadratic; p?<?.01) for hydro-priming, halo-priming, and osmopriming. The maximum germination rate was achieved using hydro-priming. Osmopriming prevented a decrease in the rate of germination at 3?°C. A decrease in temperature increased the proline and the soluble protein contents in all the seed priming treatments, but, decreased catalase and guaiacol peroxidase activity (p?<?.01). In brief, halo-priming, and hydro-priming enhanced establishment and growth of hairy vetch under chilling stress primarily through improvements in the physiological parameters and germination rate. This finding can increase the potential for cultivation of the hairy vetch in late planting date.