Soil nematode assemblages as bioindicators of primary succession along a 120-year-old chronosequence on the Hailuogou Glacier forefield,SW China

Successional dynamics in terrestrial ecosystems is important for interactions between aboveground and belowground subsystems. In this study, nematode communities in a Hailuogou Glacier Chronosequence from seven stages were investigated to determine whether changes in soil phosphorus (P) and nematode assemblages parallel those observed in aboveground communities, and whether the primary succession in this chronosequence has entered a retrogressive phase after 120 years of succession. The initial 40-year succession, including stages 2, 3 and 4, can be viewed as a build-up phase. Especially at stage 3, vegetation succession from grassland to forest accelerated the accumulation of plant litter and bioavailable P, paralleled with a sharp increase in nematode abundance. The mature phases covering stages 5, 6 and 7 displayed most balanced nematode communities, in which abundance, taxon richness, maturity index and structure index were at highest. However, the last stage 7 appeared to show some retrogressive characteristics, as suggested by the reduced bioavailability of P and a significant decrease in nematode densities, along with the disappearance of some rare genera of nematodes from higher trophic guilds, resulting in decreases in the nematode channel ratio, plant parasite index and enrichment index. Thus, the Hailuogou Glacier Chronosequence may enter its retrogressive phase during the next decade or century. A bacterial-based nematode energy channel dominated the chronosequence during the development; by contrast, a fungivore-based channel was activated at the early and late stages, because fungivores are better adapted to nutrient-poor environments. Our results demonstrated that different nematode guilds have contrasting responses to chronosequence stages, possibly due to their different responses to bottom-up and top-down controls. Furthermore, soil nematode communities could be used as sensitive bioindicators of soil health in glacial-retreat areas.     

Diversity and distribution of nematode communities in grasslands from Romania in relation to vegetation and soil characteristics

The nematode communities of 36 grassland ecosystems in Romania, belonging to different plant associations and soil types, were studied. The abundance of nematodes, the species and trophic types present, as well as their distribution in relation to plant community and soil characteristics are analyzed and discussed.The abundance of nematodes from the 36 grasslands studied ranged between 0.41 × 10⁶ and 8.57 × 10⁶ individuals/m², and a total of 121 genera and 145 species of nematodes were found. The highest diversity was found in grasslands developed on brown earth soil (65–67 genera and 74–76 species), with least diversity in those evolving on podzol and lithosol (33–36 genera with 25–28 identified species). Most of the dominant taxa were found in specific soil layers; some obligate plant parasitic genera (e.g., Paratylenchus, Rotylenchus, Criconema) showed preference for deeper soil layers. The nematode diversity index (H′), with values ranging between 2.38 and 3.47, did not differ significantly between the different types of grasslands. Plant feeding, bacterial feeding, hyphal feeding and omnivorous nematodes were the main groups in mountainous grasslands developed on different soil types. Plant feeding and bacterial feeding nematodes dominated the trophic structure and more plant feeders (62–69%) were found in communities of subalpine and alpine grasslands developed on podzol and alpine meadow soil, than in those developed on rendzina and lithosol (27–33%). The ratio of hyphal feeding to bacterial feeding nematodes (Hf/Bf) is constantly in favour of the bacterial feeding group, the values being an indicator of good soil fertility for most studied grasslands. The nematode communities of grasslands are grouped into six main clusters according to their genera affinity and distinguished by different grassland and soil types. Communities from subalpine grasslands developed on rendzina, acid brown and lithosol have the greatest similarities. An ordination of nematode communities in relation to important environmental variables is presented. Environmental variables relevant in explaining the patterns of nematode composition in grasslands, using canonical correspondence analysis (CCA), are: humus, pH, total nitrogen, exchangeable bases and soil type. No single factor could be selected.     

Successional trajectories of soil nematode and plant communities in a chronosequence of ex-arable lands

Conversion of arable land into semi-natural grassland or heath land is a common practice for restoring and conserving plant diversity. However, little is known about the effectiveness of land conversion for restoring and conserving taxonomic and functional diversity in the soil. We studied soil nematode community development in a chronosequence of abandoned fields and related this to plant community development. The taxonomic and functional composition of the soil nematode community was analyzed to detect changes in soil food web structure, using semi-natural sites and theoretical plant and soil communities as references.While plant communities clearly developed towards the semi-natural references, there was less direction in succession of nematode taxa. The number of fungal feeding nematodes increased after land abandonment. Numbers of omni-carnivorous nematodes expanded only during the first years, after which there were no substantial changes for the next three decades. Plant communities on the ex-arable fields developed towards the theoretical reference plant associations Galio hercynici-Festucetum ovinae and Genisto anglicae-Callunetum. Nematode communities developed away from a theoretical community indicative of arable land, but there was no clear development towards a theoretical (semi-)natural reference. Our results show that restoration and conservation of plant communities is of limited indicative value for developments belowground: successful restoration of plant diversity does not necessarily imply successful restoration of belowground diversity. Assessing the impact of conservation measures on restoring soil biodiversity requires information on belowground community composition of (semi-)natural areas in order to establish proper references for restoration sites.     

施用无机肥对农田生态系统线虫群落的扰动

Nematode communities were monitored in a field study at depths of 0-10cm and 10-20cm throughout a corn (Zea mays L.) growing season in the balck soil region of Northeast China.Plots were cropped corn with (IF) and without (NF) nitrogen fertilization.Fifteen families and 16 genera were observed in the nematode suspensions.Cephalobidae,Rhabditidae,Aphelenchus,Filenchus,and Helicotylenchus were found to be dominant genera/families in both plots at both depths.Significant differences were found between treatments and corn growing stages in the total numbers of nematodes during the study period.The total numbers of nematodes at the 0-10cm depth were higher in the inorganic fertilizer plot than in the control plot (no fertilizer applications) across jointing,filling,and mature stages.Bacterivores were the most abundant trophic groups under two treatments and at both depths,and the relative abundance averaged 42.8%.Omnivores-predators at both depths were lower in the inorganic fertilizer plot than in the control plot during the study period,excluding corn jointing stage.Maturity index (MI) and plant parasite index (PPI) were used to detect the differences between the two treatments,MI and PPI were effective in distinguishing differences in nematode communities during corn growing season.The role of nematode communities as bioindicators of ecosystem disturbance due to fertilization in noted.     

Exotic plant influences soil nematode communities through litter input

The impact of exotic plant invasions on soil communities and nutrient cycling processes has received an increasing attention in recent years. To test whether the exotic plant invasions affect nematode communities through altering litter quality, we compared mass loss and nematode colonization during the stem litter decomposition of invasive Spartina alterniflora and native Phragmites australis in salt marshes of the Yangtze River estuary, China. Plastic drinking straws were synchronously used as controls. The addition of plant residues was found stimulating the growth of nematodes, particularly bacterial feeders on day 16 after burial. A top-down control of bacterivous nematodes by carnivores existed in nematode succession during the litter decomposition. With higher nitrogen content and lower C:N ratio, stem litter of the invasive S. alterniflora decayed faster and supported more abundant nematodes than the native P. australis. The greater nematode abundance in S. alterniflora was mainly due to two dominant genera of bacterial nematodes, namely Diplolaimelloides and Diplolaimella. Lower values of maturity index and structure index in S. alterniflora than in P. australis litter indicate that a more degraded food web condition resulted from the faster litter decay. A considerable difference in nematode community structures between two litter types only occurred in a certain period of the decomposition (from 8 to 32 days after burial), suggesting that the changes in faunal community structure are time dependent. In summary, this study confirmed the hypothesis that the invasion of S. alterniflora stimulates the growth of bacterial nematodes by producing higher quality of litter than the native P. australis. The results obtained here suggest that the invasion of exotic plant is likely to alter ecosystem functions indirectly through exerting its effect on soil decomposer communities such as nematodes.     

Secondary succession of nematodes in power plant ash dumps reclaimed by covering with turf

An analysis of successive changes in nematode assemblages in reclaimed waste area offers information about the sensitivity of species or groups of nematodes to specific conditions and ability to colonise new habitats. The study was carried in ash dumps being a by-product of the combustion of hard coal and reclaimed by covering with mineral turf (light loam warp soil) or organic turf (alder peat). In the first 3 years of reclamation diversity of nematodes was low, especially in the dump covered with mineral turf—Shannon diversity index below 3. Later on the value of Shannon index increased and did not differ from those recorded for meadows in Poland. In the ash dump reclaimed for a longer time period (8–11 years) the contribution of K strategist species was higher than in the dumps reclaimed for a shorter time period (2–5 years). At the earlier stages of succession bacterivores Acrobeloides, and two fungivores Aphelenchoides and Aphelenchus, predominated. In the ash dump reclaimed longer the dominance of these three genera decreased and some plant feeders achieved high contribution (> 30%). The composition of nematode communities depended significantly on the period of reclamation, but did not depend either on the soil moisture and pH or on season.     

藏北高寒草甸土壤线虫群落对围封及自由放牧的响应

为了解放牧干扰对藏北高寒草甸的影响,以及连续围封措施对草地的恢复作用,2013—2015年连续3年对那曲县围封、自由放牧天然高寒草甸土壤线虫群落进行取样调查及数据分析。结果表明:围封、放牧样地的线虫个体数量在年际间的变化均较明显,植食性线虫是整个线虫群落个体数量变化的主要贡献者;围封样地的线虫个体密度、多样性指数H′、丰富度指数SR,以及优势度指数λ的年际变化幅度均大于放牧样地;食细菌性线虫个体数量及线虫通路比值(NCR)表明放牧样地的有机质转化效率高于围封样地;成熟度指数(MI)、植物寄生线虫指数(PPI)分析表明,所研究区域经5年围封,高寒草甸生态系统稳定性没有明显的提高,相反,现有放牧强度维持或者增加了线虫群落的物种多样性,利于物种共存和草地生态系统稳定性的维持。     

地中海农业生态系统中土壤自生线虫种群多样性及动态研究

To determine the effect of agricultural management on the dynamics and functional diversity of soil nematode communities in a carrot field at Kibbutz Ramat Hakovesh, Israel, soil samples from 0--10 cm and 10--20 cm depths were collected during the growing season of carrot. Indices were used to compare and assess the response of soil free-living nematode communities to agricultural management. Eighteen nematode families and 20 genera were observed during the growing period, with Cephalobus, Rhabditidae, Aphelenchus, Tylenchus, and Dorylaimus being the dominant genera/families. During the planting, mid-season and post-harvest periods the total number of nematodes at both depths was significantly lower (P < 0.01) in the carrot treatment than in the control plots, while during the harvest period at both depths total nematodes and bacterivores were significantly higher in the treatment plots (P < 0.01). The values of the maturity index (MI) at both depths were found to be significantly lower in the treatment plots than in the control plots during the pre-planting period (P < 0.05). Overall, WI, MI and PPI were found to be more sensitive indicators than other ecological indices for assessing the response of nematode communities to agricultural management in a Mediterranean agroecosystem.     

Effects of crumb rubber waste as a soil conditioner on the nematode assemblage in a turfgrass soil

The impacts of waste crumb rubber soil amendment on nematode abundance, community structure and soil characteristics were studied in pot grown Lolium perenne L. Three treatments, no crumb rubber (CK), 10% and 15% crumb rubber (CR), were arranged in a randomized complete design. After 3 months’ turfgrass growth, soil nematodes were extracted and identified to genus level, and populations of total, bacterivorous, fungivorous, omnivorous, predatory and plant parasite nematodes were counted. Genus diversity, richness, evenness, plant parasite index (PPI) and maturity index (MI) were calculated to compare nematode community structure. Thirteen genera of soil nematodes in all treatments were identified, of which Helicotylenchus was dominant. Crumb rubber incorporation significantly decreased plant parasite and omnivorous nematode populations, but increased the abundance of predatory nematodes. However, fungivorous and bacterivorous nematode populations were not significantly affected by crumb rubber amendment. Pots treated with 15% CR had the lowest number of plant parasite, omnivorous nematodes and the highest number of fungivorous, predatory nematodes. Shannon's diversity index (H′), evenness (J′), PPI and PPI/MI reduced in pots receiving crumb rubber, whereas dominace (λ) and maturity index (MI) increased in crumb rubber treatments. In addition, CR application decreased soil bulk density and pH value, but increased soil moisture.     

不同农业管理措施对土壤线虫的影响

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.     

放牧管理对青藏高原东缘高寒草甸土壤线虫的影响及作用机制

不同强度、季节的放牧是草地生态系统中主要的放牧管理措施,在生物多样性维持以及生态过程发挥中起着重要的作用,然而,关于青藏高原东缘高寒草甸地区放牧对土壤线虫群落的研究甚少。本文调查了放牧（轻度、中度和重度）对植物群落、土壤理化性质和线虫群落的影响。结果表明：植物群落、土壤理化性质和线虫群落受到放牧、时间以及放牧和时间共同作用的影响;食细菌线虫、植物凋落物生物量、根生物量、土壤含水量、土壤有机碳含量在轻度放牧草地内最高（p＜0.05）;杂类草生物量在中度放牧草地内最高;杂食线虫数量在重度放牧地内最低（p＜0.05）。植物群落和土壤特性与土壤线虫群落有明显的相关关系（p＜0.05）。结构方程模型显示食草动物主要通过植物群落影响植食和食细菌线虫,进一步的研究应针对植物群落多样性以及个体特征对线虫群落的影响。     

设施菜地种植年限对土壤理化性质和生物学特征的影响

【目的】 研究分析北京郊区不同种植年限设施菜地的土壤生态环境、土壤理化性状、土壤微生物数量、土壤线虫群落结构的差异,为不同种植年限设施菜地土壤管理提供科学依据。 【方法】 以露地土壤为对照 (CK),采集种植 3年、5年、8年和 12年的0—30 cm设施蔬菜土壤样品,采用常规土壤理化性质检测方法测定了土壤的理化性状,采用荧光定量法和线虫形态学鉴定方法,分析土壤细菌、真菌数量以及土壤线虫群落组成。 【结果】 随种植年限增加,设施菜地土壤容重和pH值均明显下降,总孔隙度、EC值、SO₄2–、Ca2+、有机碳、NH₄+-N、NO₃–-N含量均持续升高。与CK相比,种植年限 3年、5年、8年、12年的样地土壤细菌和真菌的数量均显著增加 (P < 0.05)。随种植年限增加,根结线虫属 ( Meloidogyne)、螺旋属 (Helicotylenchus)、异皮属 (Heterodera) 丰度逐渐增加;土壤线虫密度、植物寄生性线虫丰度显著增加 (P < 0.05),而食细菌、食真菌、杂食/捕食线虫丰度逐渐降低。线虫群落的多样性 H′、SR指数和均匀性J′ 指数均呈现出先增加后降低趋势,与CK相比,种植年限 12年样地的指标值显著降低 (P < 0.05)。所有种植样地NCR > 0.5,表明样地土壤食物网以食细菌通道为主,土壤有机质以细菌分解途径为主。WI、MI指数逐渐降低,而PPI指数表现出相反的趋势,其中种植年限12年样地WI < 1,这表明土壤矿化途径转变为以植物到植食性线虫为主要参与者,土壤生态系统受干扰程度逐渐增强,土壤健康状况变差。土壤环境因子与土壤生物数量间的冗余分析表明,土壤pH 、总孔隙度、容重、EC值、有机碳、SO ₄2–、NH₄+-N、NO₃–-N是影响细菌、真菌和线虫数量的关键因子,不同种植年限设施菜地由于改变这些因素而影响土壤生物群落组成。 【结论】 连续种植导致京郊设施菜地盐分含量显著升高、养分失衡、土壤酸化。理化性状的变化改变了细菌和真菌数量,进而导致土壤线虫总数、植物寄生性线虫比率逐渐增加,尤其根结线虫属比率增加显著,食细菌、真菌和杂食/捕食线虫比率逐渐降低。以种植12年后的土壤受干扰程度最大,土壤微生态失衡最严重。      

茅苍术间作对连作花生土壤线虫群落的影响

以连作10年花生的红壤为基质,分别设置花生单作和花生/茅苍术间作处理,于花生成熟期采集单作花生根际土壤、间作处理花生和茅苍术根际土壤,分析土壤线虫的数量、多样性和群落结构,以揭示茅苍术间作对土壤线虫群落的影响及对花生连作障碍的缓解机制。结果表明,与花生单作相比,间作处理花生的株高、主根长、秸秆干重和荚果干重显著增加(p0.05)。茅苍术间作减少了连作花生土壤线虫的总数,显著提高了花生根际土壤食细菌线虫、食真菌线虫和捕食/杂食线虫的相对丰度,降低了植物寄生线虫的相对丰度(p0.05)。与花生单作相比,间作提高了花生根际土壤线虫的Shannon-Wiener多样性指数(H′)和均匀度指数(J),而土壤线虫群落的优势度指数(λ)显著降低。间作处理花生根际土壤线虫的瓦斯乐斯卡指数(WI)和自由生活线虫成熟度指数(MI)显著升高,植物寄生线虫成熟度指数(PPI)显著降低,而线虫通道比(NCR)无显著变化。综合分析得出,茅苍术间作可以提高花生连作土壤线虫多样性、优化土壤线虫群落结构,进而增强有益线虫的生态功能、改善花生连作障碍。     

Microcosm experiments on the development of different plant parasitic nematode fauna in two soils from the Soudanese-Sahelian zone of West Africa

To test the hypothesis that the structure of plant parasitic nematode communities is affected by soil characteristics, experiments were conducted in a greenhouse with two soils with different physical and chemical characteristics and land management histories (fallow and a cultivated field) from adjacent plots. The cultivated soil was more sandy and had lower organic matter and nutrient contents than the fallow soil. Four nematode assemblages of Scutellonema cavenessi, Helicotylenchus dihystera and Tylenchorhynchus gladiolatus were inoculated in the soils. The pot experiment was conducted on millet during 2 months. Multiplication rates of H. dihystera were not significantly different in the two soils. T. gladiolatus had a lower multiplication rate in the fine-textured soil. S. cavenessi seemed to reproduce better in the coarse-textured soil when inoculated in low density with H. dihystera. The presence of plant parasitic nematodes in the cultivated soil caused a significant decrease of millet biomass, whereas plants in the fallow soil were less sensitive to nematode damage and were only affected when the soil was inoculated with T. gladiolatus alone. This experiment did not explain the distribution of plant parasitic species observed in the field. However, parameters other than the presence of a favourable host plant and micro-climatic conditions were found to induce differences in the reproductive rates of several species of plant parasitic nematodes. Received: 14 January 1996     

土壤线虫群落对过量施用农用化学品的响应

为研究施用过量的农用化学品对土壤线虫群落组成及多样性的影响,采用定点试验的方法,在哈尔滨市呼兰区选择典型农田生态系统进行试验,对比研究土壤线虫群落对施用过量的氮肥、磷肥、钾肥、除草剂及杀虫剂的响应。在试验田中共鉴定出土壤线虫27科45属,其中Cephalobus和Aphelenchus为优势属。施用不同浓度的各类农用化学品对土壤线虫群落组成、多样性均产生一定影响。线虫总数及食细菌线虫、食真菌线虫、植物寄生线虫数量在不同处理间均存在显著差异(P<0.05);其中,植物寄生线虫的相对丰度随化肥施用量的升高呈增加趋势。从土壤线虫的生态指数来看,除PPI(植物寄生线虫成熟指数)外,其他生态指数[MI(成熟度指数)、F/B(食真菌线虫与食细菌线虫数量比值)、Evenness(均匀度指数)、SR(丰富度指数)、H’(多样性指数)]在施用不同农用化学品处理之间也存在显著差异,并且,MI随着施用钾肥、氮肥浓度的增加而降低。土壤线虫可以作为揭示施用农用化学品过程中土壤质量变化的生物学指标,其群落及多样性的变化表明土壤线虫群落对农用化学品的过量施用产生了响应,过量施用农用化学品会增加土壤生态系统的干扰,对土壤环境造成威胁。     

Birch invasion of heather moorland increases nematode diversity and trophic complexity

To determine whether successional changes in plant communities may influence belowground community structure, we quantified nematode abundance, trophic structure and diversity along two separate chronosequences from heather moorland to birch woodland in the Scottish uplands. Tree invasion markedly altered plant community composition, and hence litter inputs, both directly, and indirectly through changes in understorey species. In turn, these changes in detrital inputs were reflected in consistent changes in nematode community structure. Nematode abundance increased from moorland to birch woodland, with moorland soils being dominated by a few taxa, notably root-hair and fungal feeders, compared to the more diverse composition of the birch woodland soils. Trophic structure was altered through an increase in the abundance of bacterial feeding relative to fungal-feeding nematodes, and an increase in the abundance of predatory nematodes. The increase in predators during the succession from moorland to woodland was associated with an increase in soil pH, highlighting that not only changes in the plant community, but also changes in soil properties associated with tree invasion may influence soil nematodes. Nematode diversity increased from moorland to birch woodland, with nematode richness being positively related to both plant species richness and soil pH. These results suggest that trees may control soil community structure through the manipulation of resources and the soil physico-chemical environment, promoting greater nematode diversity and trophic complexity.     

Functional diversity of nematodes

Nematodes are the most abundant metazoa. Their food specificity, the high number of species and high abundance in every habitat where decomposition takes place indicates that the structure of the nematode community has a high information content. Since nematodes respond rapidly to new resources, and the nematode fauna can be efficiently analyzed, the structure of the nematode community offers an instrument to assess (changes in) the conditions of soils. A functional grouping of nematodes is generally synonymous with allocation into feeding groups. However, soil quality assessment indices based on the presence of all feeding groups still provide insufficient information regarding the functioning of soil ecosystems and their threats. An alternative concept of functional groups is based on the life history of nematodes. In this paper we present the most recent colonizer–persister allocation and the application of this scaling in the Maturity Index, cp-triangles, MI(2–5) and PPI/MI-ratio. We propose to integrate the life strategy approach and trophic group classification to obtain a better understanding of nematode biodiversity and soil functioning. Attention is given to competitive exclusion and coexistence and we summarize present concepts regarding succession and degradation.     

Responses of soil nematode community structure to different long-term fertilizer strategies in the soybean phase of a soybean–wheat–corn rotation

The impact of long-term application of fertilizers in soybean fields on soil nematode community structure was studied. The long-term application model of fertilizers lasted 13 years in a soybean–wheat–corn rotation, and included three treatments: no fertilizer (NF), chemical fertilizer (urea and ammonium phosphate, CF), and pig manure combined with chemical fertilizer (MCF). The soil nematode community structures and ecological indices were determined from soil samples taken at five soybean growth stages from May to October in the soybean phase of the rotation. Fertilizer application had significant effects on abundance of plant parasites, bacterivores and fungivores (P < 0.05), but had no significant effects on total nematodes and omnivores-predators. Abundance of plant parasites was higher in NF than in MCF and CF, and abundance of bacterivores was highest in MCF. Fertilizer application significantly affected Plant-parasitic Nematode Maturity Index (PPI) and Nematode Channel Ratio (NCR) ecological indices (P < 0.05). Shannon–Weaver Index (H′) and Species Richness (SR) indices were higher in MCF than in either NF or CF. The abundances of total nematode and plant parasites showed increasing trend with soybean growth in all three treatments. This is probably due to soil environment being more suitable for soil nematode survival with more food available for plant parasites as the soybean grows. Soybean growth stage significantly affected the H′, Free Living Nematode Maturity Index (MI) and PPI. Bacterivores significantly correlated with soil nutrient status suggesting that they could be used as a potential indicator of soil fertility.     

Plant parasitic nematodes and spatio-temporal variation in natural vegetation

In this paper, the possible role of plant parasitic nematodes as a driving force of change in natural vegetation is analysed using the succession at coastal foredunes as a model. In pot trials, when grown in natural substrates from mature stands, seedlings of dominant foredune plants showed poor growth when compared to sterilised substrates. In natural substrates from preceding stages, growth reduction was far less, or even non-significant. Chemical soil treatment with nematicides resulted in enhanced growth of the seedlings. Inoculation of ectoparasitic nematodes reduced plant growth, but only at densities much higher than those occurring in control pots with unsterilised field soil. Identification at species level showed that endoparasitic nematodes are specifically associated with particular plant species. Therefore, it is hypothesised that the distribution of endoparasitic nematodes may be an important factor leading to the specific nature of soil pathogen complexes in coastal foredunes. We discuss the role of endoparasitic nematodes as possible key species in soil communities and compare the possible effects of specific vs. generalistic plant parasitic nematodes in soil communities on vegetation processes.     

Nematodes as soil indicators: functional and biodiversity aspects

Since it has become appreciated that soil nematode assemblages are abundant, diverse and contribute to soil nutrient turnover, they have been increasingly used as indicators of soil condition. Use of nematodes as functional indicators relies on the allocation of nematodes to feeding groups and reproductive strategies; in both cases groupings are uncertain. Species within feeding groups vary in their food resources and response to environmental variables, as shown by the difficulties in managing plant-pathogenic nematodes. Therefore species-level discrimination is necessary to permit further advances in understanding the role of nematodes in soil processes and thus in ecosystem resilience. Analysis of published nematode lists shows that among the bacterial-feeding nematodes Cephalobidae are often the most abundant group in soils; Rhabditidae may increase following a resource pulse; in stressed, natural environments Plectidae may be important. To be comparable with other biota, nematode biodiversity assessment requires species-level identification. In many jurisdictions such identification will be difficult due to inadequate systematic knowledge of the nematode fauna.