施氮肥对落叶松和水曲柳人工林土壤动物群落的影响

土壤动物对环境变化反应敏感, 全球变化导致土壤氮(N)有效性增加将影响土壤动物群落结构和功能。本文以落叶松(Larix gmelinii)和水曲柳(Fraxinus mandshurica)人工林为研究对象, 通过施肥处理, 在不同季节和土层取样, 研究土壤N有效性增加对土壤动物的数量、类群数和不同功能团的影响。结果表明: (1) 施肥影响两林分土壤动物密度, 导致当年密度增加, 翌年则下降, 这种先增加后降低的趋势在不同土层中均表现出来; (2) 施肥增加了两林分土壤动物类群数, 其中落叶松林分从34类增加到43类, 水曲柳林分从43类增加到48类; (3) 施肥改变了两林分不同食性土壤动物的密度, 腐食性土壤动物数量降低、植食性数量增加、捕食性数量变化不明显。这些结果说明: 土壤N有效性增加显著影响两林分土壤动物群落结构, 可能改变地下碳分配格局和养分循环过程。     

Dating fire events in Pinus heldreichii forests by analysis of tree ring cores

Bosnian pine (Pinus heldreichii Christ, also known as Pinus leucodermis Antoine) is a relict species found in isolated locations in the mountains of the Balkan Peninsula and Southern Italy. The forests are of high conservational value because they are extremely rich in rare and endemic species of plants and fungi. Yet, the natural history and disturbance regime of P. heldreichii ecosystems is not well understood. Fire traces show that fires played a major role, but there is very limited historical data. Therefore proxy methods to reconstruct past events have to be used. The analysis of tree rings provides such an opportunity. To our knowledge, there have been no attempts to use tree ring cores from P. heldreichii trees to date fire events. Our aim was therefore to test if tree ring cores collected with an increment borer could successfully be used to date fires and verify other tree ring indicators caused by the fire events. We tested an approach that was based on extracting multiple cores from fire-scarred trees and nearby standing trees without injuries. A total of 136 cores from 99 trees were collected from which we dated all 34 cores with fire scars. We found the exact fire years for 29 of the samples, and the remaining 5 samples were approximately dated. Up to 83% of all sampled trees had additional growth reactions, mostly suppressions lasting 5–10 years after the fire years.     

Net and gross sedimentation in relation to the phosphorus budget of Eau Galle Reservoir,Wisconsin

We compared P retention with direct measures of Psedimentation, estimated fromsediment cores (annual P sedimentation) and sedimenttraps (daily P sedimentation),to quantify P sedimentation in Eau Galle Reservoir,Wisconsin. Mean annual Pretention was similar to mean annual P sedimentation,as estimated from sediment corerates integrated over the entire lake basin,indicating that annual P mass balanceapproximated annual net P sedimentation in thisreservoir. However, sediment trap Prates, measured over the summer stratified period,overestimated P retention ratesdetermined over the same period, suggestingsubstantial deposition of internally-derived P.Inclusion of measured internal P loadings from avariety of sources in EauGalle Reservoir in a P mass balance only accounted foran additional 24% of thesummer sediment trap P rate, indicating substantialuncertainty in the overall P budget.Imbalances in the P budget may also suggest depositionof sediment from other as yetunquantified internal sources. Potential internalsources of P include sedimentresuspension and chemical release and direct uptake ofP from the sediment byphytoplankton.     

Rhizobium inoculation trials designed to support a tropical forage legume selection programme

Summary Three phases of Rhizobium inoculation trials were carried out as part of a programme to select forage legume germplasm adapted to acid, infertile Oxisols of tropical America. Firstly, a range of tropical forage legumes were evaluated for their response to N fertilization or inoculation with strains previously shown to be effective in Leonard jars, using cores of undisturbed soil or in the field at Carimagua, Meta, Colombia. In pure legume stands onlyCentrosema macrocarpum andC. pubescens showed increases in N yield due to both inoculation and N fertilization;C. brasilianum responded only to N fertilization;Zornia latifolia, Z. brasiliensis andStylosanthes capitata responded to neither treatment. Trials in cores and in grass-legume mixtures showed responses ofDesmodium ovalifolium, Pueraria phaseoloides andS. capitata to N fertilization but not to inoculation. In the second phase of experiments strains were screened in soil cores with 16 ecotypes ofDesmodium, Centrosema, Stylosanthes andPueraria spp. Significant increases in N yield due to inoculation occurred with at least one strain in all the legumes exceptS. guianensis tardio, and in some trials withS. capitata. In the third phase of trials the most effective strains were tested in the field. Significant response ofP. phaseoloides andC. macrocarpum to inoculation at two sites and in the second year after establishment were shown. Further screening trials and field trials at different sites are needed in order to provide better recommendations for inoculation of grazing trials being set up in the region under study.     

A biological consequence of reducing Arctic ice cover: arrival of the Pacific diatom Neodenticula seminae in the North Atlantic for the first time in 800 000 years

The Continuous Plankton Recorder survey has monitored plankton in the Northwest Atlantic at monthly intervals since 1962, with an interegnum between 1978 and 1990. In May 1999, large numbers of the Pacific diatom Neodenticula seminae were found in Continuous Plankton Recorder (CPR) samples in the Labrador Sea as the first record in the North Atlantic for more than 800 000 years. The event coincided with modifications in Arctic hydrography and circulation, increased flows of Pacific water into the Northwest Atlantic and in the previous year the exceptional occurrence of extensive ice‐free water to the North of Canada. These observations indicate that N. seminae was carried in a pulse of Pacific water in 1998/early 1999 via the Canadian Arctic Archipelago and/or Fram Strait. The species occurred previously in the North Atlantic during the Pleistocene from∼1.2 to∼0.8 Ma as recorded in deep sea sediment cores. The reappearance of N. seminae in the North Atlantic is an indicator of the scale and speed of changes that are taking place in the Arctic and North Atlantic oceans as a consequence of regional climate warming. Because of the unusual nature of the event it appears that a threshold has been passed, marking a change in the circulation between the North Pacific and North Atlantic Oceans via the Arctic. Trans‐Arctic migrations from the Pacific into the Atlantic are likely to occur increasingly over the next 100 years as Arctic ice continues to melt affecting Atlantic biodiversity and the biological pump with consequent feedbacks to the carbon cycle.     

Ice sheets and nitrogen

Snow and ice play their most important role in the nitrogen cycle as a barrier to land–atmosphere and ocean–atmosphere exchanges that would otherwise occur. The inventory of nitrogen compounds in the polar ice sheets is approximately 260 Tg N, dominated by nitrate in the much larger Antarctic ice sheet. Ice cores help to inform us about the natural variability of the nitrogen cycle at global and regional scale, and about the extent of disturbance in recent decades. Nitrous oxide concentrations have risen about 20 per cent in the last 200 years and are now almost certainly higher than at any time in the last 800 000 years. Nitrate concentrations recorded in Greenland ice rose by a factor of 2–3, particularly between the 1950s and 1980s, reflecting a major change in NO_x emissions reaching the background atmosphere. Increases in ice cores drilled at lower latitudes can be used to validate or constrain regional emission inventories. Background ammonium concentrations in Greenland ice show no significant recent trend, although the record is very noisy, being dominated by spikes of input from biomass burning events. Neither nitrate nor ammonium shows significant recent trends in Antarctica, although their natural variations are of biogeochemical and atmospheric chemical interest. Finally, it has been found that photolysis of nitrate in the snowpack leads to significant re-emissions of NO_x that can strongly impact the regional atmosphere in snow-covered areas.     

Diatoms in sediment cores in Utah Lake,Utah, U.S.A.

Diatoms from sediment cores taken from Provo Bay, Geneva and midlake sites in Utah Lake, Utah County, Utah were studied. Algal communities from strata at four centimeterintervals of the cores were analyzed. This study has demonstrated that the diatom flora in Utah Lake has changed through time and that the diatom communities of Provo Bay are floristically unique from those of the main body of the lake.     

High heritability for heartwood in north Swedish Scots pine

 In 44-year-old full-sibs of north Swedish Scots pine (Pinus sylvestris L.), the estimated heritability of heartwood diameter was 0.5 despite the influence of environmental changes (caused by an earlier thinning) which apparently had reduced the heritabilities of height and diameter to around zero. The heritability of bole straightness was estimated to be 0.6. The coefficient of additive genetic variation of heartwood diameter was estimated at 0.2. If a reliable ‘heartwood-meter’ becomes available that allows nondestructive measurements to be rapidly made in the field it should be possible to breed for or against heartwood formation with less effort compared with that required in breeding aimed at improving regular production traits. Received: 10 June 1998 / Accepted: 8 September 1998     

大肠杆菌sigma70启动子预测

统计了大肠杆菌sigma70启动子在不同基因间的分布。计算了683条大肠杆菌sigma70启动子的每个位点六联体的保守性M6(l)值及涨落限,以大于涨落限7.2的21个保守位点的六联体频数作为参数,利用离散增量理论对大肠杆菌全序列进行启动子搜索。结果显示683条启动子序列被全部正确预测且得到126条预测序列,利用启动子在不同基因间的分布和TSS到TIS的距离分布进行二次筛选,推测其中的84条序列是实验未测定的启动子序列。     

Sediment distribution and accumulation in lagoons of the Southern Mediterranean Region (the MELMARINA Project) with special reference to environmental change and aquatic ecosystems

Surface sediments and sediment cores were collected from coastal lagoons and lakes located in the Southern Mediterranean Region (SMR) as part of the MELMARINA Project which involved integrated eco-hydrological monitoring and modelling. This study uses surface sediments and sediment cores to infer spatial characteristics and temporal changes at the MELMARINA primary sites, Merja Zerga in Morocco, Ghar El Melh in Tunisia and Lake Manzala in Egypt. In addition, surface sediment sampling was undertaken at Egyptian Lake Bardawil and sediment cores were collected from the Lagune de Nador (Morocco). Sediment distribution patterns are investigated using GIS with georeferenced sample locations to facilitate display and resurvey. Major variations in sedimentary organic matter and, particularly, carbonate content, occur within and between sites. Local landscapes combined with hydrological and biogeochemical processes influence the distributions of sediment bulk components (carbonates, organic material and clastic matter) and molluscan shells and shell debris are an important source of sedimentary carbonate at all three primary sites. Sediment cores were dated using natural (²¹⁰Pb) and artificial (¹³⁷Cs) radionuclides, and sediment accumulation rate changes indicate that sources of sediment supply varied markedly through the twentieth century but have generally diminished after the mid-1960s. Sedimentary siliceous microfossils (diatoms) were generally poorly preserved, but mollusc shell remains were well represented. Sediment chronologies and sediment bulk composition allow discussion of some recent changes in bulk, minerogenic and biogenic sediment accumulation patterns in the SMR lagoons. Sediment accumulation rates also varied between sites and multiple cores from Lake Manzala indicated that rates showed considerable spatial variability. Low-level sediment contamination by fossil fuel combustion particulates and trace metals was demonstrated for Ghar El Melh and Lagune de Nador where Pb and Zn accumulation rates were highest in twentieth century sediment. It is emphasized that sediment quality and quantity have strong influences on lagoon ecosystem function and sedimentation is relevant to hydromorphology and to concepts of ecological quality. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons