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Summary The nematode community in litter and soil was examined for a year in the Chihuahuan desert, before and after supplemental rainfall application. Proportions of nematode-active or anhydrobiotic forms and population densities were determined for 3 treatments: control (natural rainfall), a single, large (25-mm) monthly irrigation pulse, and 4 smaller (6-mm) irrigations spaced at weekly intervals. In litter the greatest nematode abundance was in the 6 mm week–1 treatment (48 nematodes 20 g–1 litter). Bacteriovores and fungivores accounted for approximately 95% of the numbers and biomass in all treatments. In soil, water amendments had no significant effect (P < 0.05) on annual mean densities of total nematodes, fungivores, bacterivores, or omnivore predators. Phytophage densities were greater on both irrigation treatments, with highest densities (9268 m–2) in the 6 mm week–1 soils, which was 5.9% of the total soil nematode density. Total densities of individual trophic groups were not significantly different before or after rainfall. Soil nematode densities fluctuated independently with trophic group, month, and season. Bacterial feeders and omnivore predators were the largest contributor to total soil nematode density and biomass. Prior to irrigation, there were no differences in the percentage of anhydrobiotes on the three treatments. Anhydrobiotes decreased after irrigation in all treatments, and were significantly lower in soils of the larger, monthly irrigation. Nematodes were inactive (anhydrobiotic) and decoupled from decomposition processes when soil water matric potentials reached –0.4 MPa.Dedicated to the late Prof. Dr. M.S. Ghilarov 相似文献
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N.R. Maslen 《Soil biology & biochemistry》2006,38(10):3141-3151
Nematode worms are one of the most important soil faunal groups in Antarctica. However, relatively little is known about their wider distribution, biogeography and history in the region, and taxonomic information remains confused or incomplete. Here, we hypothesise that the Alexander Island (southern maritime Antarctic) fauna includes elements that have survived (at least) the period of Pleistocene glaciation in situ, forming a regional centre of endemism and biodiversity hotspot. We describe nematological surveys carried out across a latitudinal gradient between 68 and 77°S along the southern Antarctic Peninsula, comparing the data obtained with the maritime Antarctic fauna described in the few previous studies between northern Marguerite Bay and the South Orkney Islands (60-68°S). In general, our survey supports previous findings of a lack of overlap at species level between the maritime and continental Antarctic biogeographical zones, with the large majority of specimens obtained from all survey sites being attributable to known maritime or new and currently endemic taxa. However, collections from Alexander Island, Alamode Island and the most westerly site sampled, Charcot Island, include specimens morphologically very close to two known continental Antarctic species, which may indicate a link between the two regions. The fauna obtained at the northern study sites (ca. 68°S, Adelaide Island, Marguerite Bay) closely matches that described previously. However, in contrast with widely described patterns of decreasing diversity in other Antarctic biota, species richness increased markedly at locations on Alexander Island (ca. 72°S), including a substantial element of undescribed species (50% of taxa across all locations, 40% of taxa found on Alexander Island). Finally, the most southerly samples obtained, from inland nunataks in Ellsworth Land (75-77°S), indicate a fauna that does not include nematodes, which is exceptional not only in an Antarctic context but also for soils worldwide. 相似文献
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We tested a hypothesis that the effects of defoliation on plants and soil organisms vary with the number of successive defoliations. We established a 23-week greenhouse experiment using replicated grassland microcosms that were composed of three plant species, Trifolium repens, Plantago lanceolata and Phleum pratense, growing together in grassland soil with a diverse soil community. The experiment consisted of two treatment factors-defoliation and harvest time-in a fully factorial design. The defoliation treatment had two levels, i.e. no trimming and trimming of plants every 2 weeks, and the harvest time five levels, i.e. harvests after 1-3, 5 and 7 trimmings. Shoot production (trimmed plus harvested shoot mass), harvested shoot and root mass and root N and C concentrations increased with time but were reduced by defoliation. Colonization rates of arbuscular mycorrhizal (AM) fungi decreased with time in T. repens roots but were enhanced by defoliation, whereas AM colonization rates in P. pratense roots were not affected by harvest time or defoliation. The abundance of bacterivorous and fungivorous nematodes decreased and that of herbivorous and predatory nematodes increased with time, while the abundance of omnivorous nematodes and detritivorous enchytraeids varied in time without a linear trend. Defoliation had no effect on fungivores and predators but increased the abundance of bacterivores. Defoliation also increased the abundance of herbivores, omnivores and detritivores after 2 trimmings and that of omnivores and detritivores after 5 trimmings, but had a negative effect on omnivores after 3 trimmings and on herbivores after 7 trimmings. Among nematode genera, some deviation from the trophic group responses existed: for instance, defoliation reduced the abundance of bacterivorous Acrobeloides spp. and did not affect the abundance of herbivorous Filenchus spp. and Paratylenchus spp. Our results show that the effects of defoliation on plants, AM fungi and some soil animal trophic groups may remain constant all the way through several defoliations, whereas other animal trophic groups may have different and even opposite responses to defoliation depending on the length of the defoliation period before monitoring. This shows how separate studies with defoliation periods of different length can produce contradictory results of the effects of defoliation on the abundance of soil animals. 相似文献
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取闽南地区牛、羊消化道常见的8种线虫幼虫,对它们进行了形态学观察及比较,以期提供用于生前诊断的参考资料, 相似文献
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As part of a search for pathogens that might be useful agents for biological control of possums, the three largest offshore islands of New Zealand that still have possums were surveyed to determine the pathogens present in these isolated populations. Brushtail possums from Kawau Island (n = 158), Chatham Island (n = 214) and Stewart Island (n = 194) were examined for internal parasites. Possums from Kawau Island were infected with Eimeria spp. (16.7%), Bertiella trichosuri (5.2%) and Parastrongyloides trichosuri (15.5%). No Paraustrostrongylus trichosuri or Trichostrongylus spp. were found. Possums from Chatham Island were infected with Eimeria spp. (10.9%). Bertiella trichosuri (3.6%), T. colubriformis (6.6%), T. retortaeformis (1%) and T. vitrinus (0.5%). No Parastrongyloides or Paraustrostrongylus spp. were found. Possums from Stewart Island were infected only with Eimeria spp. (4.6%). Because of their paucity of some parasites, the opportunity exists to use these offshore islands to study the introduction and spread of a parasite into a possum population, and what technology would be required to bring it to hyperendemicity. 相似文献
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不同农业管理措施对土壤线虫的影响 总被引:2,自引:0,他引:2
研究了不同农业管理措施对土壤线虫的影响,结果表明:日光温室中土壤线虫的优势种群为食细菌的小杆线虫(Rhabditis),常规农田中优势种群为食细菌的小杆线虫和植食性的螺旋线虫(Helicotylenchus),休闲地中优势种群为植食性线虫,包括螺旋线虫、盘旋线虫(Rotylenchus)和丝尾垫刃线虫(Filenchus);线虫的多样性、丰富度、ΣMI、EI、SI指数表明日光温室所受到土壤线虫的扰动最强,常规农田次之,休闲地所受干扰最小;PPI/MI、WI、BI、CI指数表明日光温室土壤营养丰富,常规农田和休闲地营养贫瘠. 相似文献