Growth characteristics ofNelumbo nucifera Gaertn. in response to water depth and flooding

Three experiments on the effects of water depth and flooding onNelumbo nucifera Gaertn. were made in the artificial environment of concrete ponds. First, plants were harvested in autumn after growing under seven different water levels ranging from 0.2–3 m The number of floating leaves, the total number of leaves and the leaf area index of emergent leaves were greatest in the tanks at 0.5 m depth. The petiole dry weight per unit length of emergent leaves and the ratio of aboveground to belowground biomass rose with increasing water depth up to 2 m. In contrast, that of floating leaves was constant at about 10 mg dry weight cm⁻¹. The proportion of biomass in tubers fell from 20% at 0.2 m to 6% at 2 m. Second, petiole elongation responses to the amplitude of flooding were investigated in early summer. The maximum rate of petiole elongation was 25 cm per day at 2.4 m water depth. This was the maximum depth at whichN. nucifera could grow. No petioles could elongate from 3 m to 5 m depth. Finally, the effects of timing of flooding on growth were investigated. At the end of growing season, the belowground biomass of plants in the flooding treatment in late summer was smallest among the flooding treatment plants (P<0.05), and was most severe when flooding occurred in this season. Based on the results of these experiments, the growth characteristics ofN. nucifera in relation to petiole elongation, biomass allocation, and flooding tolerance were discussed.     

Reproductive allocation,seed dispersal and germination of <Emphasis Type="Italic">Myricaria laxiflora</Emphasis>, an endangered species in the Three Gorges Reservoir area

Myricaria laxiflora is an endangered plant that grows in the flood zone along the Yangtze River in the Three Gorges area from 70 m to 155 m above sea level. To understand the spatial distribution patterns of the species and to provide information for developing conservation strategies, we used field surveys to study its seed reproduction and dispersion, and used growth chambers to study seed germination. Results showed that M. laxiflora produced many flowering branches, inflorescences and seeds. Seeds were very small and output was high although biomass allocation to reproduction was low (∼4%). Reproductive allocation was strongly correlated with the biomass of stems and leaves. Seeds were dispersed either by the wind or the river current. Wind-dispersed seeds usually settled within 25 m from parent plants leading to a clumped distribution of individuals in populations. Water-dispersed seeds often landed and established on strands of firth where the fine sediment and gentle sloping were available. Seedlings that emerged from water-dispersed seeds were distributed along the water flood line. The life-span of M. laxiflora seeds was about 7 days. Seeds could germinate within 24 h when they absorbed adequate amounts of water. Soil water content was a key factor limiting the establishment ability of M. laxiflora. Experiments showed that the minimum soil water content for germination to occur was 10% on sand or 17% on sandy soil substrates, and the optimal conditions were on saturated soils. The water content of sandy soils on the riverbank was lower than 10% in autumn, the dry season, and seeds were able to germinate only on sandy beaches that were intermittently inundated by the fluctuating river current. These characteristics of seed dispersal and germination limit the ability for M. laxiflora to expand its distribution. These results provide information essential for the conservation and reintroduction of this endangered species.     

Incidence and control of black spot syndrome of tiger nut

Tiger nut (Cyperus esculentum) is a very profitable crop in Valencia, Spain, but in the last years, part of the harvested tubers presents black spots in the skin making them unmarketable. Surveys performed in two consecutive years showed that about 10% of the tubers were severely affected by the black spot syndrome whose aetiology is unknown. Disease control procedures based on selection of tubers used as seed (seed tubers) or treatment with hot‐water and/or chemicals were assayed in greenhouse. These assays showed that that this syndrome had a negative impact on the germination rate, tuber size and yield. Selection of asymptomatic seed tubers reduced drastically the incidence of the black spot syndrome with respect to using seed tubers with severe symptoms (selection of healthy seed tubers was not possible because the causal agent is undetermined). Thermal treatment of seed tubers with severe symptoms reduced the number of unmarketable harvested tubers by half but was detrimental for the germination. Chemical treatments of seed tubers with severe symptoms decreased the incidence of the black spot syndrome about 40% for sodium hypochlorite and about 10% for hydrochloric acid, trisodium phosphate and the fungicide trioxystrobin.     

Germination of Teliospores of Tilletia bardayana, the Causal Agent of Kernel Smut of Rice, in Relation to Some Physical Factors

Teliospores of Tilletia harclayana germinated equally well on the surface of 2 % water agar, soil extract agar and in cavities made in water agar. Maximum germination occurred at 29 °C under 12 h photoperiod with artificial daylight (cool fluorescent light). There was marked increase in germination when the teliospores in bunted grains were pre-treated for 30 min at 60 °C. Seventeen-week-old tehospores did not germinate while 73 week-old-tehospores showed retention of good germinability. Teliospores buried at 2 mm depth showed no germination whereas those at the moist surface germinated to produce sporidia. Implications of these results in the disease development are discussed.     

Effects of water potential on the infection of potato tubers by Streptomyces scabies in soil

When soil was maintained at a mean water potential (Slatyer & Taylor, 1960) of the order of -80 J kg^-1 at 25 cm depth throughout the growing period, much infection of potato tubers by Streptomyces scabies occurred, but when soil was irrigated to maintain it at potentials greater than - 13 J kg^-1 at 10 cm depth infection was negligible. Until about 5 weeks after initiation, tubers were very susceptible to infection; irrigation during this period reduced scab considerably, but subsequent irrigation reduced it only slightly. At the low water potential, actinomycete populations on lenticels were high and bacterial populations low; these effects were reversed at the high water potential. Since also actinomycetes were more frequently isolated in the absence than in the presence of bacteria it was deduced that there was an interaction between these two groups. It is suggested that irrigation may decrease the population of S. scabies in tuber lenticels by increasing populations of bacteria antagonistic to it.     

The impact of the River Ntahangwa, the most polluted Burundian affluent of Lake Tanganyika, on the water quality of the lake

Sources of pollution at the north end of Lake Tanganyika are concentrated around Bujumbura, Burundi. The impact of River Ntahangwa on the water quality of this part of Lake Tanganyika was compared with that of an unpolluted river, the Mugere. A shallow bay, not influenced by a river, was used as a reference station. Chemical analyses were carried out at four week intervals during nearly a year. Samples were taken at different distances from the shore and at different depths. River impact was detected up to 100 m from both river mouths. Even at 50 m from the mouth of the polluted River Ntahangwa, no important decrease of dissolved oxygen was detected. Chlorophyll-a maxima were found 100 m from the Ntahangwa mouth, but this was also the case 100 m from shore in the unpolluted bay. Lake water at 60 m depth was saturated with oxygen during the dry season, as it used to be in 1956. The rivers studied descent initially within the lake due to greater sediment load and lower water temperature. Nevertheless, it appears that these rivers mix completely in the lake within 100–300 m from the river mouths. The direct effects from organic pollution of the Ntahangwa on the lake seem to be rather negligible. Appropriate anti-erosion measures should reduce massive sediment discharge into the lake.     

沙埋与水分对科尔沁沙地主要固沙植物出苗的影响

蒿属半灌木乌丹蒿(Artemisia wudanica)、白沙蒿(A. sphaerocephala)、差不嘎蒿(A. halodendron)是科尔沁沙地的主要固沙植物。其中乌丹蒿和差不嘎蒿是科尔沁沙地的本土植物,白沙蒿为来自于库布齐沙漠、毛乌素沙地的飞播植物。设置了 5个沙埋深度(0.5、1.0、1.5、2.0和3.0 cm)和 4个水分梯度(86、171、257和 342 mL,分别模拟每月25、50、75和100 mm的降雨量),以探讨3种植物幼苗出土对沙埋和水分的响应。结果表明,沙埋与水分均显著影响着3种蒿属植物的幼苗出土(P < 0.001)。3种植物最适沙埋深度在0.5-1.5 cm范围内,萌发出土时适宜水量要高于当地种子萌发期的平均降水量(50 mm/月)。两种固沙先锋植物乌丹蒿和白沙蒿的种子出苗率均显著高于差不嘎蒿,乌丹蒿较白沙蒿也明显为高,尤其在水分缺乏时,表现出两种先锋植物种子出苗对干旱有更好的适应性。协方差分析表明,乌丹蒿幼苗死亡率显著高于白沙蒿和差不嘎蒿(P < 0.05),在达到75 mm/月降水量时,3种植物的出苗较好,但不能满足乌丹蒿幼苗生长对水分的需求,而实际种子萌发期的降水量平均只有50 mm/月。因而降水的缺乏导致乌丹蒿种群更新出现问题,加之飞播植物的竞争,使得近几年科尔沁沙地较多乌丹蒿种群出现衰退。     

Developmental processes of achlorophyllous orchid, <Emphasis Type="Italic">Epipogium roseum</Emphasis>: from seed germination to flowering under symbiotic cultivation with mycorrhizal fungus

We have achieved the symbiotic cultivation of an apparently achlorophyllous orchid, Epipogium roseum Lindl., with a mycorrhizal fungus isolated from an underground organ of this orchid. Although the seed germination rate was extremely low, subsequent growth from protocorm to flowering was induced in a medium containing volcanic soils and sawdust. Stolons elongated from each protocorm, and rhizomes were formed at certain intervals on the stolons. Some of the rhizomes developed into a coralloid form, and tubers were formed from the coralloid rhizomes. The coralloid rhizomes degenerated concurrently with maturation of the tubers. Six months after seed sowing, around 80 tubers were produced from a single protocorm. An inflorescence appeared from each of the large tubers, and the process to flowering was observed in one of these. Consequently, the developmental processes from seed to flowering in E. roseum was clearly revealed in this study.     

Effect of environmental factors on seed germination and emergence of Lepidium vesicarium

Lepidium vesicarium is a weed species with a wide distribution in the rangelands and dry‐land farming in East Azarbaijan, Iran. The experiments were undertaken to assay the effects of light, temperature, pH, osmotic potential, NaCl concentration and burial depth on seed germination and emergence of L. vesicarium. Germination was maintained at high levels (> 80%) over a wide day/night temperature range (10/5 to 30/20°C), but a severe reduction in the germination rate of L. vesicarium was found below 20/10°C. Germination of L. vesicarium was influenced by different light/dark regimes, as the germination rate was highest at 16 h light for the all treatments (0, 8, 12, 16 and 24 h light). Germination was 92–95% over a wide range of pH (2‐10). Germination was >50% at a water potential of ?0.7 MPa and salinity of 21 dS/m, indicating that drought and salt conditions have a minimal impact on seed germination. With increasing burial depth from 0 to 2 cm, the number of days required for 50% emergence increased and no germination was observed at burial depths deeper than 3 cm. This suggests that L. vesicarium would become troublesome in the rangelands and for growers in reduced‐tillage cropping systems. The ability to emerge from shallow depths, coupled with tolerance of a wide pH range, drought and salinity at germination, should be taken into account when managing this weed species.     

Control of Fusarium solani rot of potato tubers with fungicides

Tecnazene (up to 33 ppm) and dichloran (up to 500 ppm) had little effect on germination of spores or growth of Fusarium solani isolated from and causing a rot of potato tubers; they also did not decrease rotting when applied to wounds later inoculated with the pathogen. Benomyl and thiabendazole (up to 500 ppm) also had little effect on spore germination but did greatly decrease growth at 5 ppm. A pronounced pink coloration developed in cultures growing slowly in the presence of benomyl; a similar though less striking effect appeared in agar cultures containing thiabendazole. Benomyl suspended in water or diluted with Fuller's earth gave good control of rotting when applied to wounds inoculated later with F. solani. Still better control was obtained with thiabendazole; dusts containing 1% a.i. substantially decreased rots and those containing 10 % a.i. gave almost complete control when applied to wounds shortly before inoculation. Thiabendazole was also very effective when used 24 h after inoculation and a fair measure of control was obtained when it was applied 24 h later. Benomyl and thiabendazole placed on apparently intact surfaces of tubers caused tissue 5 mm deep to become toxic to F. solani 10 days later, and, unexpectedly, this tissue prevented spore germination. Fuller's earth alone substantially decreased rotting. The results obtained suggest that dusts containing thiabendazole have some promise for the control of Fusarium rots of potato tubers, especially of early crops.     

蒸发条件下潜水埋深对土壤-柽柳水盐分布的影响

盐水矿化度下模拟设置4个潜水埋深(0.9、1.2、1.5、1.8 m),分析不同土层的土壤相对含水量(RWC)、含盐量(S_C)和土壤溶液绝对浓度(C_S)等水盐参数,及柽柳叶片和新生枝条的含水量及Na~+含量,探讨盐水矿化度下土壤-柽柳水盐参数对潜水埋深的响应规律。结果表明:各土层RWC与潜水埋深呈负相关,0.9 m潜水埋深下各土层的RWC均最高,且各土层RWC随土层深度的增加呈先降低后增加的趋势,其它潜水埋深下各土层RWC均逐渐增加,1.2 m是地下水所能上升且保持柽柳柱体土壤表层湿润的最高高度。各土层S_C和C_S与潜水埋深呈抛物线型,均表现为先增加后降低,潜水埋深1.2 m时,各土层S_C均最高。随土层深度的增加,各潜水埋深下S_C先降低后增加,而C_S呈现减少趋势;潜水埋深越高,土层间C_S变化幅度越激烈。潜水埋深对柽柳叶片和新生枝条的含水量无显著影响(P0.05),而随潜水埋深的增加,柽柳叶片Na~+含量逐渐增加,新生枝条Na~+含量则先增加后降低。从整个柽柳土柱看,随潜水埋深的增加,整个土壤剖面的RWC均值逐渐降低,而S_C和C_S均值先增加后降低,潜水埋深1.2 m是盐分变化的分界点,建议栽植柽柳的潜水埋深大于1.2 m。     

Effects of fungicides on the growth and conidial germination of Colletotrichum coccodes and on the development of black dot disease of potatoes

The effects of 10 fungicides on the growth of Colletotrichum coccodes in agar culture and on the germination of conidia was investigated. In field experiments in 1990 and 1991 the extent to which treating black dot-affected potato seed tubers with fungicides affected the development of the disease on stem bases, roots and tubers was assessed. Black dot was also assessed on plants from field trials in 1990 which were designed to investigate the efficacy of the soil sterilant 1,3-dichloropropene (Telone) and two nematicides, aldicarb (Temik) and ethoprophos (Mocap). Prochloraz and fenpiclonil were the most effective fungicides in decreasing the size of C. coccodes colonies on agar. Imazalil, propiconazole and dichlorophen were also effective, but at higher concentrations, whereas tolclofos-methyl, thiabendazole and benomyl were only moderately effective. Resistant sectors developed from inhibited colonies on agar containing fenpiclonil and tolclofos-methyl. Conidial germination was prevented at 1 mg/litre fenpiclonil and 5 mg/ litre dichlorophen; imazalil, benomyl and thiabendazole were also moderately effective. Fenpiclonil and propiconazole seed tuber treatments consistently decreased black dot infection on roots, stem bases and daughter tubers early in the season, but only fenpiclonil decreased disease on tubers at harvest in October. Propiconazole also delayed emergence and decreased stem numbers. Soil treatment with 1,3-dichloropropene, aldicarb or ethoprophos had no effect on black dot but Rhizoctonia solani tuber infection and black scurf were increased.     

不同水淹深度对鄱阳湖洲滩湿地植物生长及营养繁殖的影响

水淹深度是影响湿地植物生长和繁殖的关键因子,不同湿地植物对淹水深度存在着不同响应。然而,在水情不断变化的背景下,鄱阳湖洲滩湿地植物种群和群落如何变化还不清楚。为了探究淹水深度对湿地植物生长的影响,并预测鄱阳湖洲滩湿地植被分布的趋势,采用控制实验模拟了不同水淹深度(0、0.5、1 m和2 m)下鄱阳湖湿地3种优势植物(灰化薹草(Carex cinerascens)、南荻(Miscanthus lutarioriparius)和虉草(Phalaris arundinacea))的生长和繁殖情况。实验结果表明:1)水淹对灰化薹草总生物量的影响最显著。遭受水淹时,灰化薹草把大部分的生物量集中在地下部分;随着水淹深度逐渐增加,南荻的生物量逐渐减少;不同深度水淹对虉草生物量没有产生显著影响(P0.05)。就生物量而言,虉草对水淹的适应性强于其他两种植物。2)不同水淹深度下,灰化薹草的株高都显著降低;而南荻只在2 m水淹梯度下株高才显著降低。在枯水年时,下降的水位有利于南荻向较低高程迁移。3)不同深度水淹对灰化薹草的分株没有产生显著影响(P0.05);而虉草在经过2 m水淹后分株数显著高于其他水淹深度。在丰水年时,相比于灰化薹草和南荻,升高的水位对虉草的繁殖影响较小。在一个水位周期性变化的湿地生态系统中,不同深度的水淹对植物的生长及退水后的繁殖产生了严重影响,研究结果为预测水文变化对湿地植被的生存和分布提供了重要的依据。     

Interrelationships of petiolar air canal architecture,water depth,and convective air flow in Nymphaea odorata (Nymphaeaceae)

• Premise of the study: Nymphaea odorata grows in water up to 2 m deep, producing fewer larger leaves in deeper water. This species has a convective flow system that moves gases from younger leaves through submerged parts to older leaves, aerating submerged parts. Petiolar air canals are the convective flow pathways. This study describes the structure of these canals, how this structure varies with water depth, and models how convective flow varies with depth. • Methods: Nymphaea odorata plants were grown at water depths from 30 to 90 cm. Lamina area, petiolar cross-sectional area, and number and area of air canals were measured. Field-collected leaves and leaves from juvenile plants were analyzed similarly. Using these data and data from the literature, we modeled how convective flow changes with water depth. • Key results: Petioles of N. odorata produce two central pairs of air canals; additional pairs are added peripherally, and succeeding pairs are smaller. The first three pairs account for 96% of air canal area. Air canals form 24% of petiolar cross-sectional area. Petiolar and air canal cross-sectional areas increase with water depth. Petiolar area scales with lamina area, but the slope of this relationship is lower in 90 cm water than at shallower depths. In our model, the rate of convective flow varied with depth and with the balance of influx to efflux leaves. • Conclusions: Air canals in N. odorata petioles increase in size and number in deeper water but at a decreasing amount in relation to lamina area. Convective flow also depends on the number of influx to efflux laminae.     

The role of water level and salinity in the regulation of Juncus gerardi populations in former ricefields in southern France

Abstract. In the Rhône delta (southern France) Juncus gerardi is a dominant, strongly aggregating species in artificially flooded former rice fields. In order to explain this pattern, the effects of water depth, salinity and their interaction were measured on (1) seed germination and seedling development and (2) vegetative growth of J. gerardi in a controlled-environment experiment. The germination pattern of J. gerardi was affected by salinity. Low salinity (2 g/l NaCl) delayed germination while moderate salinity (12 g/l NaCl) reduced germination rate. In contrast, the germination of J. gerardi was not affected in the range of water depths tested (i.e. 0–10cm). Salinity negatively affected the development of below-ground parts, shoots and inflorescences. This negative effect of salinity on the vegetative growth of J. gerardi was amplified when combined with flooding. Flooding with fresh water (0–20 cm depth) did not limit biomass production during the experiment. However, a decrease in the ratio of below-ground/above-ground dry weight at deeper water depths suggests a limitation of the vegetative propagation of J. gerardi under prolonged flooding conditions. This hypothesis is supported by the negative correlation between the cover of J. gerardi and water depth found in an abandoned rice field. The limitation on seedling recruitment imposed by salinity and the depression of vegetative growth of J. gerardi due to a combination of salinity and water depth could explain the aggregate distribution of J. gerardi in former rice fields.     

Hoary cress (Cardaria draba (L.) Desv.) seed germination ecology,longevity and seedling emergence

The effects of gibberellic acid (GA₃), potassium nitrate (KNO₃), prechilling, temperature, salt stress and osmotic potential on seed germination and sowing depth on seedling emergence and burial depth on seed viability of hoary cress (Cardaria draba (L.) Desv.), were studied in a series of laboratory, glasshouse and outdoor experiments. The optimal temperature for hoary cress seed germination was 20°C, both in light/dark and darkness regimes. Seed germination of hoary cress at 400 ppm concentration of GA₃ in a light/dark regime was maximal. Potassium nitrate concentrations increased the percentage of germination in comparison with the control treatment. Increasing the duration of dry prechilling to 30 and 45 days promoted the seed germination of hoary cress. Germination of hoary cress markedly decreased as salt and drought stress increased. Seed germination of hoary cress occurred at a range of pH from 3 to 11. Seedling emergence significantly decreased as planting depth increased. Total seed viability decreased with increasing burial depth. The maximum increase in mortality occurred in seeds that were buried at 5‐cm depth.     

Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system

We measured the patch use behaviour of Bewick's swans (Cygnus columbianus bewickii) feeding on below ground tubers of fennel pondweed (Potamogeton pectinatus). We compared the swans’ attack rates, foraging costs and giving‐up densities (GUDs) in natural and experimental food patches that differed in water depth. Unlike most studies that attribute habitat‐specific differences in GUDs to predation risk, food quality or foraging substrate, we quantified the relative importance of energetic costs and accessibility. Accessibility is defined as the extent to which the animal's morphology restricts its harvest of all food items within a food patch. Patch use behaviours were measured at shallow (ca 0.4 m) and deep (ca 0.6 m) water depths on sandy sediments. In a laboratory foraging experiment, when harvesting food patches, the swan's attack rate (m³ s^?1) did not differ between depths. In deep water the energetic costs of surfacing, feeding and trampling were 1.13 to 1.21 times higher than in shallow water with a tendency to spend relatively more time trampling, the most expensive activity. Taking time allocation as measured in the field into account, foraging in deep water was 1.26 times as expensive as in shallow water. In the lake the GUD in shallow water was on average 12.9 g m^?2. If differences in energetic costs were the only factor determining differences in GUDs, then the deep water GUD should be 14.2 g m^?2. Instead, the mean GUD in deep water was 20.2 g m^?2, and therefore energetic costs explain just 18% of the difference in GUDs. At deep sites, 24% of tuber biomass was estimated to be out of reach, and we calculated a maximum accessible foraging depth of 0.86 m. This is close to the published 0.84 m based on body measurements. A laboratory experiment with food offered at a depth of 0.89 m confirmed that it was just out of reach. The agreement between calculated and observed maximum accessible foraging depths suggests that accessibility largely explains the remaining difference in GUDs with depth, and it confirms the existence of partial prey refuges in this system.     

Direct observations on the sublittoral marine algae of Argyll,Scotland

Summary The distribution with depth of sublittoral marine algae has been investigated at 11 sites on the west coast of Scotland. More than half of the species found were confined to the sublittoral zone. The greatest variety of species was found in shallow water at sites sheltered from excessive turbulence. With increasing depth the number of species found steadily decreased. There was no evidence of a specifically distinct algal flora confined to deeper water. No algae were found deeper than 36 m below ELWS at any site, but the lower limit of algal growth was reduced to 9 m in a turbid water loch and to 3 m at a site where the herbivorous echinoderm Ophiocomina nigra was abundant. Fairly distinct algal communities were found on different substrates. The major communities recognised underwater were algae attached to stable substrata, algae attached to unstable substrata and epiphytic on other algae, especially on the stipes of Laminaria hyperborea. On stable rock in areas subject to water movement L. hyperborea forest was the dominant vegetation whereas on unstable substrata and in sheltered localities L. saccharina was dominant.     

Potato water content impact on soil moisture measurement by neutron meter

A field study was conducted to examine the effect of the water content of potato tubers on the neutron count ratios of a neutron probe in an irrigated potato field. At the 20 cm depth, where tubers are concentrated, the neutron count ratios within the potato row (CW) were significantly higher than the neutron count ratios between the rows (CB). In contrast, the measured soil water contents within the rows (SW) at this depth, tended to be less than those measured between the rows (SB). At 45 cm depth, results were similar in a dry but not a wet year. The SW values, in contrast, were less than SB. Neither (CW-CB) or (SW-SB) were significant at 75 cm depth and values of (CW-CB) and (SW-SB) were similar. This study provides qualitative information regarding the influence of a potato tuber water content on neutron measurements, resulting in an overestimations of soil moisture in a potato field. Further studies should be conducted to develop relationships for corrections.Contribution no 3879215Contribution no 3879215     

Nematode Community Structure along the Continental Slope off the Kenyan Coast,Western Indian Ocean

Metazoan meiofauna and in particular nematode densities, diversity, community structure were studied in relation to water depth (20 m, 50 m, 500 m, 1000 m and 2000 m) along four bathymetric transects in the Western Indian Ocean off the Kenyan coast. Nematode densities ranged between 276–944 ind./10 cm², which is comparable to values from other oligotrophic areas in the world. Densities was correlated with oxygen concentrations in the overlying water, since they were lowest at mid‐depth (500–1000 m) coinciding with the minimum oxygen level. Nematode community structure (at genus level) resembles communities found in temperate slope regions, which are also characterized by a low productivity. The community structure showed correlations with sediment composition, water depth and oxygen levels in the overlying water. Sediment composition was mainly important at the shelf where nematodes separated into a silty sediment‐dwelling community with high abundances of Daptonema, Dorylaimopsis, Terschellingia and Halalaimus, and a sandy sediment‐dwelling community characterised by high abundances of Microlaimus and Halalaimus. The genera Monhystera, Acantholaimus, Sabatieria, Molgolaimus and Halalaimus dominated the slope communities. The characteristic deep‐sea taxa, the monhysterids and Acantholaimus increased in relative abundance with increasing depth, to become dominant at the lower slope (2000 m). The upper (500 m) and mid‐slope (1000 m), which coincided with the lowest oxygen concentrations, were colonised by Sabatieria, a genus that is known to inhabit suboxic sediments. Diversity at the level of the genera showed an unimodal trend along the sampled gradient, with highest values at mid‐depth (500 m). Although the oxygen minimum at mid depths is much less pronounced than in adjacent areas, the results of this study suggest an impact on the present communities.