气候和土地利用变化影响下生态屏障带水土流失趋势研究

受气候和地形等诸多因素影响，我国"两屏三带"国家生态屏障带中的川滇-黄土高原区域和南方丘陵带水土流失十分严重，自然灾害频发。但是，针对川滇-黄土高原区域和南方丘陵带水土流失时空格局变化，特别是未来气候变化和土地利用变化影响下水土流失变化趋势的研究很少。因此，本研究以川滇-黄土高原区域和南方丘陵带为研究对象，利用修正土壤流失方程（RUSLE）定量分析了该区在2000-2015年水土流失的时空变化规律及其影响因素，并预测了在RCP2.6和RCP4.5的未来气候情景下及土地利用变化条件下水土流失的变化趋势。研究结果表明：（1）黄土高原地区在植被恢复的积极作用下，水土流失显著缓解；（2）川滇地区的西南部因植被盖度的增长和降雨的减少水土流失显著缓解，但四川省境内人口密集区农田面积增加以及降水增加造成水土流失大幅度加剧；（3）南方丘陵带受降水增加影响导致了部分区域的水土流失恶化；（4）在未来气候变化情景下，由于大部分地区降雨将减少使土壤侵蚀趋于缓解，但四川、黄土高原和南方丘陵带大部分地区仍然面临未来农田面积增加带来的水土侵蚀压力。考虑到未来气候变化情景下降雨减少的趋势，建议在黄土高原地区提高草地在土地利用类型中的占比，在减少耗水量的同时维持地表盖度，缓解水土侵蚀；此外，各区域仍需控制农田面积，而且需通过加强坡耕地上保水保土耕作措施降低农田区域的土壤侵蚀压力。     

Variations of soil structure and microbial population in a compost amended soil

Changes in soil structure and in microbial population were recorded in a long term field experiment over the growing season of maize (June–November). Determinations were made on samples from plots which had received, for two years, the following treatments: mineral fertilizers, farmyard manure and three rates of compost. Seasonal variations were observed for the stability of soil aggregates, total porosity, pore size distribution, mycorrhizal infection and aerobic cellulolytic microorganisms. The stability of the soil aggregates changed in a similar way to that found for both mycorrhizal infection and the number of aerobic cellulolytic microorganisms. Physical characteristics were not affected in any instance by the organic dressings and microbiological populations were generally influenced only by the higher doses of compost.     

Development of a low input system for growing wheat (Triticum vulgare) in a permanent understorey of white clover (Trifolium repens)

In three field experiments carried out during 1989-91, a permanent sward of pure white clover (Trifolium repens) was established to provide a source of N for winter or spring wheat crops (Triticum vulgare) directly drilled into the legume. Spring-sown wheat failed to compete with the clover, but wheat sown in the autumn established successfully. N fertiliser was applied to all three experiments at rates of 0, 50 and 100 kg N ha“¹ measurements of grain and whole-crop silage yields were made. Yields were low for all treatments, probably because of the dry conditions prevailing and the low soil N status of the site used. Yield responses to fertiliser were significant, despite the contribution to plant nutrition that the clover was intended to make. A key feature of the work was that the clover survived successive cereal crops and could be grazed and used as an understorey for later crops. Further, response to fertiliser N diminished with a successive crop implying a build-up of available soil N, which measurements confirmed had occurred. Use of the system obviated the need to use pesticides, although reasons for the lack of pest damage were not clear.     

Microbial production and uptake of nitric oxide in soil

Abstract Fluxes of NO from three different soils have been studied by a flow-through system in the laboratory as a function of gas flow rate, of NO mixing ratio, and of incubation conditions. The dependence of net NO fluxes on gas flow rates and on NO mixing ratios could be described by a simple model of simultaneous NO production and NO uptake. By using this model, rates of gross NO production, rate constants of NO uptake, and NO compensation mixing ratios could be determined as function of the soil type and the incubation condition. Gross NO production rates were one to two orders of magnitude larger under anaerobic than under aerobic conditions. NO uptake rate constants, on the other hand, were only 5–8 times larger so that the compensation mixing ratios of NO were in a range of about 1600–2200 ppbv under anaerobic and of about 50–600 ppbv under aerobic conditions. The different soils exhibited similar NO uptake rate constants, but the gross NO production rate and compensation mixing ratio was significantly higher in an acidic (pH 4.7) sandy clay loam than in other less acidic soils. Experiments with autoclaved soil samples showed that both NO production and NO uptake was mainly due to microbial metabolism.     

Survival of Escherichia coli in the environment: fundamental and public health aspects

In this review, our current understanding of the species Escherichia coli and its persistence in the open environment is examined. E. coli consists of six different subgroups, which are separable by genomic analyses. Strains within each subgroup occupy various ecological niches, and can be broadly characterized by either commensalistic or different pathogenic behaviour. In relevant cases, genomic islands can be pinpointed that underpin the behaviour. Thus, genomic islands of, on the one hand, broad environmental significance, and, on the other hand, virulence, are highlighted in the context of E. coli survival in its niches. A focus is further placed on experimental studies on the survival of the different types of E. coli in soil, manure and water. Overall, the data suggest that E. coli can persist, for varying periods of time, in such terrestrial and aquatic habitats. In particular, the considerable persistence of the pathogenic E. coli O157:H7 is of importance, as its acid tolerance may be expected to confer a fitness asset in the more acidic environments. In this context, the extent to which E. coli interacts with its human/animal host and the organism''s survivability in natural environments are compared. In addition, the effect of the diversity and community structure of the indigenous microbiota on the fate of invading E. coli populations in the open environment is discussed. Such a relationship is of importance to our knowledge of both public and environmental health.     

Landscape-level seagrass–sediment relations in a coastal lagoon

We investigated the relationships between sediment (subaqueous soil) properties and eelgrass (Zostera marina L.) distribution to develop landscape-level soil-based strategies for choosing eelgrass restoration locations. Subaqueous soils were sampled and eelgrass cover determined for 14 soil-landscape units within a 116 ha area of Ninigret Pond, a coastal lagoon in Rhode Island, USA. Of the 14 soil-landscape units sampled for eelgrass cover, 52% had virtually no eelgrass cover (<10%), while 18% had high eelgrass cover (>90%). The Lagoon Bottom, Shallow Lagoon Bottom, Flood-tidal Delta Slope, and Barrier Cove subaqueous soil-landscape units had the highest eelgrass cover (66–100%). A weak relationship between eelgrass cover and water depths (r² = 0.10) was observed suggesting that properties other than water depth may also control eelgrass distribution. Subaqueous soils on landscapes with >60% eelgrass cover had relatively high levels of acid-volatile sulfides (>90 μg/g), high soil salinity levels (34–44 ppt), fine textures (silt loam), and relatively high total nitrogen levels (>0.15%). Four principal components accounted for 81% of the variability in eelgrass cover. The first component reflected particle-size distribution (i.e. sand, silt, and clay contents) effects and accounted for 43% of the variability. The other components suggested that eelgrass cover is correlated to carbonaceous remains, non-calcareous rock fragments and soil salinity. These data suggest that the current distribution of eelgrass within the study area is strongly influenced by physical and chemical subaqueous soil characteristics. Soil survey techniques proved useful for the delineation of sediment characteristics (e.g. texture, salinity) that influence eelgrass distribution patterns at landscape-level scales.