Nematode Community Characteristics Research Articles

Effects of heterogeneous habitat on soil nematode community characteristics in the Songnen Plain

Effects of heterogeneous habitat on soil nematode community characteristics in the Songnen Plain

Nematode Community Characteristics Indicate Soil Restoration under Different Revegetation Approaches in the Semiarid Area of the Chinese Loess Plateau

Soil nematode communities can offer valuable indicators for monitoring the status of soil ecosystems. However, their potential for assessing soil restoration under revegetation has been neglected in temperate arid and semiarid areas. This study examined the characteristics of soil nematode communities and their relationships with soil physicochemical properties under five typical revegetation approaches in the semiarid Loess Plateau of China. The results showed that planting an artificial Caragana korshinskii forest led to the recovery of the soil food web, which significantly increased soil nematode abundance (138.10 ± 11.60 inds./100 g dry soil) and community diversity (Shannon-Wiener diversity: 2.48 ± 0.13; trophic diversity: 3.08 ± 0.02), associated with the high contents of SOC and NH4+-N. However, establishing an artificial Prunus sibirica forest improved neither soil properties nor nematode community characteristics, reflecting poor soil ecosystem restoration. After establishing an artificial Prunus davidiana forest (PD) and an artificial Medicago sativa grassland (MS), substantial increases in herbivorous and fungivorous nematodes were observed, respectively, likely due to the accumulation of particular genera that fed on roots (e.g., Pratylenchus) or their symbiotic fungi (e.g., Tylencholaimus), which might result in the deterioration (in MS) or restoration (in PD) of the soil food webs. Natural grassland restoration greatly improved soil properties (i.e., SOC, NH4+-N, microbial biomass carbon) but did not change the nematode community obviously, probably due to top-down predation in natural habitats. In conclusion, the characteristics of nematode communities can effectively indicate the restoration of soil food webs and identify their possible driving forces under revegetation, which have important implications for vegetation restoration in arid and semiarid regions.

Soil nematode community characteristics of alfalfa field with different growing ages in the semi-arid Loess Plateau of Central Gansu, Northwest China

To clarify the impacts of long-term alfalfa plantation on the soil nematode community, soil samples were collected from different alfalfa growing ages (2 a, 9 a, 18 a) in the semi-arid area of Loess Plateau in Central Gansu by Illumina Miseq sequencing technology. The main controlling factors affecting its community change were also explored. The results showed that soil nematode belongs to 2 classes, 7 orders, 16 families and 21 genera. Among them, Chromadorea was the dominant group (44.6%-81.4%), the relative abundance of which decreased with alfalfa growing ages. Paratylenchus, Helicotylenchus, Xiphinema, Pristionchus, Ditylenchus, Panagrolaimus, Longidorus, Aprutides, Isolaimium and Aglenchus were the special nematode species of alfalfa, among which Paratylenchus (54.1%), Helicotylenchus (23.9%) and Xiphinema (21.9%) were the dominant nematodes in 2 a, 9 a and 18 a alfalfa soil respectively. Plant-parasitic nematode was the dominant group in alfalfa soil (31.8%-67.1%), and its relative abundance decreased at first and then increased with alfalfa growing ages. Results of redundancy analysis showed that soil available phosphorus and total nitrogen were the dominant environmental factors affecting community structure of soil nematodes in the region.

Impact of a dam construction on the intertidal environment and free-living nematodes in the Ba Lai, Mekong Estuaries, Vietnam.

The impact of high siltation and accumulation of organic and waste material in the intertidal of the dammed Ba Lai River in Vietnam as part of the Mekong estuarine system was investigated by means of marine free-living nematodes. Nutrients content (nitrate, ammonium, total phosphorus, total nitrogen), total suspended solids, total organic carbon, coliform, bacteria E. coli, pH, dissolved oxygen, total dissolved solids, methane and hydrogen sulfide concentration, and the nematode communities were characterized in sediment at selected stations along the river above and below the dam. Our results found elevated methane concentrations at the upstream side of the dam while hydrogen sulfide concentrations found to be highest in the downstream side of the dam. Furthermore, methane and hydrogen sulfide concentrations were correlated to nematode community characteristics such as trophic composition densities and genera composition. There was a clear difference between the communities above and below the dam. The discontinuous nematode community distribution indicated that the Ba Lai River is impacted by dam construction. Potentially the high deposition and eutrophication could turn the area into a methane-rich area related to predicted impact on nematodes.

Variations in the community patterns of soil nematodes at different soil depths across successional stages of subalpine forests

Nematodes are among the most important faunal groups in soil food webs and serve as important bioindicators in evaluating subsurface ecological processes and ecosystem functioning. Although previous studies have reported the effects of vegetation types on soil nematode communities, the community patterns of soil nematodes at different soil depths during secondary forest succession remain unclear. Through a field survey, we investigated how soil nematode community characteristics changed at two soil depths (0–10 cm and 10–20 cm) across subalpine forest successional stages consisting of grasslands, shrublands and forests in Southwest China. We measured soil properties and microbial biomass to analyze significant environmental factors influencing variations in soil nematode communities. With forest succession, we observed increases in the total nematode abundance and maturity index and a decreased plant parasitic index, indicating more stable food webs and lower root herbivory hazards in forests than in grasslands and shrublands. Fungivore diversity was significantly increased and herbivore diversity was significantly decreased during forest succession, despite no significant difference existing in the total nematode diversity among the three successional stages. The abundances of the dominant nematode genera Helicotylenchus and Tylencholaimus were significantly correlated with forest succession. In addition, the variations in soil nematode communities differed between the two soil depths, presumably due to various soil variables. NO-3-N and pH were the dominant determinants of the variations in soil nematode communities at 0–10 cm soil depth, while SOC was the dominant determinant at 10–20 cm soil depth. Overall, our results suggested that forest succession exhibited layer-specific effects on soil nematode communities via different soil variables, and that specific nematode genera could serve as useful bioindicators during forest succession.

Large-Scale Patterns of Soil Nematodes across Grasslands on the Tibetan Plateau: Relationships with Climate, Soil and Plants

Soil nematodes are important contributors to soil biodiversity. Nonetheless, the distribution patterns and environmental drivers of soil nematode communities are poorly understood, especially at the large scale, where multiple environmental variables covary. We collected 520 soil samples from 104 sites representing alpine meadow and steppe ecosystems. First, we explored the soil nematode community characteristics and compared community patterns between the ecosystems. Then, we examined the contributions of aboveground and belowground factors on these patterns. The genus richness and abundance of nematodes on the Tibetan Plateau are lower than other alpine ecosystems, but are comparable to desert or polar ecosystems. Alpine meadows supported a higher nematode abundance and genus richness than alpine steppes; bacterial-based energy channels were pre-dominant in both the ecosystems. Soil factors explained the most variation in the soil nematode community composition in the alpine meadows, while plant factors were as essential as soil factors in the alpine steppes. Unexpectedly, the climate variables barely impacted the nematode communities. This is the first study to explore the spatial patterns of soil nematode compositions on the Tibetan Plateau, and we found that the contributions of climate, plants, and soil properties on soil nematodes community were essentially different from the previous knowledge for well-studied plant and animal communities.

Seasonal Stabilities of Soil Nematode Communities and Their Relationships with Environmental Factors in Different Temperate Forest Types on the Chinese Loess Plateau

The bottom-up effects of vegetation have been documented to be strong drivers of the soil food web structure and functioning in temperate forests. However, how the forest type affects the stability of the soil food web is not well known. In the Ziwuling forest region of the Loess Plateau, we selected three typical forests, Pinus tabuliformis Carrière (PT), Betula platyphylla Sukaczev (BP), and Quercus liaotungensis Koidz. (QL), to investigate the soil nematode community characteristics in the dry (April) and rainy (August) season, and analyzed their relationships with the soil properties. The results showed that the characteristics of the soil nematode communities and their seasonal variations differed markedly among the forest types. Compared to P. tabuliformis (PT), the B. platyphylla (BP) and Q. liaotungensis (QL) forests had higher plant diversity and more easily decomposed litters, which were more effective for improving the soil resource availability, thus, leading to more beneficial effects on the soil nematode community. In both the dry and rainy season, the soil nematode abundance was the highest in the BP forest. The Shannon–Wiener diversity index (H’), Pielou’s evenness index (J’), and nematode channel ratio index (NCR) were higher, while the Simpson dominance index (λ) and plant parasite index (PPI) were lower, in the BP and QL forests compared with in the PT forest. From the dry to rainy season, the total nematode abundance and the abundance of fungivores, bacterivores, and omnivore-predators, significantly increased in the QL and PT forests, and the values of the Wasilewska index (WI), maturity index (MI), H’, J’, λ, and NCR showed the most significant seasonal variability in the PT forest, which were mainly driven by changes in the soil labile C and N and the moisture content between the two seasons. Generally, the seasonal stability of the soil nematode communities was the highest in the BP forest and the poorest in the PT forest, probably due to variations in the plant diversity. Our results suggest the importance of tree species and diversity as bottom-up regulating factors of the soil food web structure, function, and seasonal stability, which has important implications for sustainable forest management in the Loess Plateau and other temperate regions.

植茶年限对土壤团聚体线虫群落结构的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 植茶年限对土壤团聚体线虫群落结构的影响 DOI: 10.5846/stxb201904010627 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41271307）；四川省科技厅支撑计划项目（2013NZ0044） Effects of tea plantation age on soil nematode community characteristics within soil aggregate Author: Affiliation: Fund Project: China Postdoctoral Science Foundation, 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在野外调查的基础上，采用干筛法和改良的Baermann漏斗法，研究植茶年限（19年、26年、34年和56年）对土壤团聚体线虫群落结构的影响。本研究共捕获线虫6602条，隶属于46属，以Acrobeloides为优势属，食细菌线虫为优势营养类群。线虫总数和大多数营养类群数量均随植茶年限的延长先升高后降低，在植茶26年时数量达到最高，且随粒径的减小而减少。线虫类群数则随着植茶年限的延长，虽随着粒径的减小而减少，但对 > 2 mm粒径团聚体中响应不敏感。线虫结构指数（Structure index，SI）多数小于50，富集指数（Enrichment index，EI）均大于50。随着植茶年限的延长，茶园生态系统土壤食物网逐渐退化；与大粒径团聚体相比， < 0.25 mm粒径团聚体中食物网受扰动相对较小。以上结果表明，植茶26年土壤更适合线虫繁殖且大粒径团聚体更有利于线虫生存；随着植茶年限的延长，土壤食物网退化， < 0.25 mm粒径团聚体受到的干扰较少，这一结果有助于揭示茶园土壤团聚体中线虫群落变化和土壤食物网对植茶年限的响应特征。 Abstract:This study began in July 2018 at Zhongfeng long-term agricultural research site of Sichuan Agricultural University in Ya'an, Sichuan, China. The prevailing climate surrounding the study site is a subtropical monsoon climate. Mean annual temperature is 15.4℃, with the lowest and highest mean daily temperatures of 4.3℃ and 35.2℃, respectively. Mean annual precipitation is 1500 mm with 72.6% of the precipitation occurring during July and September. The layer being exposed belongs to sedimentary rock predominantly formed since the Mesozoic age, with the soil being Luvisols with a texture of clay loam. "Sichuan tea" has been cultivated since 1950s, forming a large-scale tea plantation with different ages. As a useful approach, the space-for-time substitution method is often used to monitor soil changes occurring along a tea plantation chronosequence that has developed with similar soils and similar climatic conditions. Establishment of tea plantations at different times creates an opportunity for elucidating the tea planting process because the geomorphologic processes can determine soil conditions before tea planting. In order to explore the effects of tea plantation age on the soil nematode community characteristics within soil aggregate and provide theoretical basis for formulating scientific and reasonable soil management measures in tea plantations, soil samples were obtained from tea plantations with different ages (19, 26, 34 and 56 a). The four tea plantations were collected on similar geomorphologic units, slope direction and gradient, and fertilization practices Soil aggregates were separated into four fractions:large (> 2 mm), medium (2-1 mm), small macro-aggregates (1-0.25 mm), and micro-aggregates (< 0.25 mm). The nematodes were extracted from 50 g fresh soil by a modified Baermann funnel methodology. In this study, a total of 6602 nematodes were captured, which belonged to 46 genera and the mean density was 421 ind·100g-1 dry soil. Acrobeloides was the dominant genus and bacterial nematodes were the dominant trophic group. Soil aggregate-associated total nematode abundance decreased significantly with decreasing of aggregate size regardless of the tea plantation age. Additionally, the abundance of different trophic groups (including bacterivores, plant-parasites and fungivores) showed a trend similar to the abundance of total nematodes within different aggregates. In the macro-aggregates, the abundance of total nematodes as well as different trophic groups, with the exception of omnivores-predators, was significantly higher in the 26a tea plantation compared to that in other plantations. In the micro-aggregates, on the contrary, no significant differences were observed among the different aged tea plantations. Nematode structure index (SI) was less than 50, and enrichment index (EI) was more than 50. In this tea plantation ecosystem, the soil food web gradually degraded alongside plantations. Compared with the large macro-aggregates, the structure of soil food web was relatively less disturbed in the micro-aggregates. Notably, the degradation of soil food web alongside plantations underscores the need for sustainable soil management practices that would maintain soil health in the hilly area of western Sichuan in China. 参考文献 相似文献 引证文献

Nematode community characteristics are associated to loggerhead turtle hatching success

Abstract Nematodes represent an important group of animals in the decomposer food web, because of high diversities, abundances and functional roles supporting ecological processes, such as decomposition. They have been relatively well studied in numerous ecosystems, but have rather skipped attention in sea turtle nests at sandy shores, where a massive supply of nutrients is taking place after turtle egg hatching. Being excellent indicators of ecological functioning, we hypothesized that nematode community characteristics could be indicative of the ecological/functional state of sea turtle nests as affected by hatching characteristics (e.g. number of eggs, hatching success rate etc.). In our study, conducted in Zakynthos (Greece), we perform a pioneer in-depth analyses of nematode communities in Caretta caretta nests after egg hatching. We further explore whether turtle reproductive success, measured through a number of metrics reflecting stages and portion of alive/dead hatchlings, are linked to nematode community characteristics. We found 14 different nematode genera in total. Our analyses demonstrate that nematodes play a critical role in functionality and energy flow in sandy shore ecosystems and that sea turtle nests present an ephemeral micro-habitat hosting communities with specific characteristics. These include rather high nematode abundances and communities in early successional stages with a simple trophic structure, almost exclusively dominated by bacterivore nematodes (mostly opportunistic/c-p 1) and without top-down control. Variables either showing success or failure of hatching explained a large amount of variability of nematode community characteristics, supporting our hypothesis. The nematode Metabolic Footprint was strongly associated with the amount of dead hatchlings concentrated in the turtle nest. Nematode taxonomic diversity and richness were closely associated with an increased hatching success rate at nest level. Our findings can offer a base for developing a framework for comprehensive and standardized assessments of sea turtle nests that could ensure comparability of results over spatial or temporal scales in monitoring projects. Further research might show how increased diversity of nematode communities could be achieved so to improve reproduction output and success of loggerhead sea turtles.

Meiofauna and nematode community characteristics indicate ecological changes induced by geomorphic evolution: A case study on tidal creek systems

The meiofauna represent a highly informative faunal group for ecological evaluation in marine ecosystems, but few studies have investigated their spatial distribution patterns in tidal creeks. As an important component of the tidal flat, tidal creeks tend to have unique, contrasting habitats associated with erosion and accretion beds within a short distance of each other. The gradient represented by these habitats is expected to have consequences on the meiofauna and nematode communities. Based on sediment samples from two tidal creeks on a tidal flat covered with very fine-grained sediments, we show that there are distinct relationships between the benthic habitats, meiofauna/nematode communities and the erosion/accretion status of the tidal creek bed. Although there were no differences in sediment grain size between the eroding and accretion sides of the creek, higher sedimentary phaeopigment, total organic carbon and water contents were observed at the accreting side compared to the eroding side. The meiofauna exhibited a significant spatial variability between the two sides. The dominant taxon, nematodes, was more abundant on the accretion side, whilst copepods were more abundant on the erosion side of the creeks. The nematode/copepod ratio was in agreement with the observation that more pollutants and/or organic matter settled down on the accretion side. A total of 53 nematode genera were identified, belonging to 3 orders and 22 families. The prevalence of tolerant nematode genera such as Desmodora, Sabatieria and Viscosia, suggested that nematodes inhabiting highly dynamic environments are well adapted to the physical disturbance. Our results show that geomorphic evolution as implied by erosion/accretion patterns are reflected in the meiofauna and nematode communities and can be assessed using different community characteristics.

氮添加对贝加尔针茅草原土壤线虫群落特征的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 氮添加对贝加尔针茅草原土壤线虫群落特征的影响 DOI: 10.5846/stxb201704170689 作者: 作者单位: 沈阳农业大学园艺学院,农业部环境保护科研监测所,农业部环境保护科研监测所,内蒙古鄂温克旗草原工作站;内蒙古鄂温克旗草原工作站,德州学院,农业部环境保护科研监测所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31170435） Effects of nitrogen addition on soil nematode community characteristics in Stipa baicalensis steppe Author: Affiliation: shenyangnongyedaxueyuanyixueyuan,,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以内蒙古贝加尔针茅草原为研究对象，通过氮素添加（0、15、30、50、100、150、200、300 kg N hm-2 a-1）模拟氮沉降的控制实验，研究氮沉降对内蒙古贝加尔针茅草原土壤线虫的群落结构和多样性的影响。结果表明，在本实验所有样品中共鉴定出52个属，优势类群为螺旋属（Helicotylenchus）、丽突属（Acrobeles）和真滑刃属（Aphelenchus）。土壤线虫具有明显的表聚现象，相对密度变化不显著。从功能类群上看，随着氮素添加水平的增加，食细菌类群（Bacterivores）线虫和捕食类群/杂食类群（Predators/Omnivores）线虫氮素添加水平均成负相关。从生态指标来看，在SR）、多样性（H'）、均匀度（J'）等生态指标有促进作用；通路指数在试验的所有处理中都小于0.75，表明土壤中的有机质分解途径是以真菌为主；瓦斯乐思卡指数表明，少量施氮可以改善土壤的环境状况，减少植物寄生类群（Plant parasites）线虫对植物群落及生产力的影响。当施氮量>N100时，土壤pH值显著降低，硝态氮和铵态氮显著增加，土壤中生活史k对策者的线虫显著减少，r对策者显著增加，世代交替加快，土壤线虫群落结构显著变化。 Abstract:The community characteristics of soil nematodes in a Stipa baicalensis steppe in Inner Mongolia under different nitrogen treatments (0, 15, 30, 50, 100, 150, 200, 300 kg N hm-2 a-1) were studied by field investigation and sample analysis using the morphological classification method. In total, 52 genera were identified in all the samples. The dominant species were Helicotylenchus, Acrobeles, and Aphelenchus. Soil nematodes showed an obvious surface convergence phenomenon, and their relative density was not significant. Based on the functional groups, the addition of Bacterivores nematodes and Predators/Omnivores showed a negative correlation with the increase in nitrogen application level. The ecological indices such as abundance (SR), diversity (H'), and evenness (J') of soil nematodes increased with the increase in nitrogen application level, reaching their maximum values at N50. In all treatments, the pathway index was less than 0.75, indicating that fungi decomposed organic matter in the soil. The ecological indicators showed that nitrogen application at N100, the soil pH value decreased significantly, the nitrate nitrogen and ammonium nitrogen contents increased significantly, the soil life history k countermeasures were significantly reduced, and r countermeasures were significantly increased,significantly altering the soil nematode community structure. 参考文献 相似文献 引证文献

Forest fires alter the trophic structure of soil nematode communities

The impact of fires on nematode diversity, abundance and biomass was assessed in 20 burnt forests and 20 adjacent control plots across a 3000-km-long north-south transect in European Russia. The transect covered five main forest types (Mediterranean and broadleaved forests, southern, middle, and northern taiga). In spring 2015, we assessed major abiotic parameters of soil, soil microbial PLFA markers, and nematode community characteristics (genus richness, abundance, biomass and trophic structure) in the burnt and control plots.Generic richness was the highest in the southern taiga (22 genera) declining both northwards (down to 16) and southwards (down to 13 genera). The highest abundance of nematodes was recorded in the Mediterranean forests (139.4 ± 15.1 ind. g−1 soil dwt, control site) and the lowest in the northern taiga (10.8 ± 1.2 ind. g−1 soil dwt, burnt site). Biomass followed the same pattern with slight deviations. Abundance and biomass of soil nematodes was not significantly affected by fires in any ecoregion with the exception of Mediterranean forests.We detected consistent fire effects on the abundance of particular nematode feeding groups. Trophic groups abundance of soil nematode communities were considerably modified in burnt forests due to the increase in abundance of bacterial-feeding nematodes and reduced number of hyphal-feeding, plant-associated and plant-feeding nematodes. This increase in bacterial-feeding nematode biomass coincided with the growth of the ratio between bacterial and fungal biomass in pyrogenic soils. pH of soil solution and actual denitrification rate in the burnt forests correlated with the biomass of predatory nematodes. We conclude that, five years after fire, the structure of the microbial community, pH of soil solution and denitrification activity correlate with the ratio of feeding groups of belowground nematode communities in these forests. Taking into account considerable nematode biomass in soil, shifts in the ratio of trophic groups after fires induced by these factors may potentially lead to changes in the level of ecosystem functions which they deliver in burnt forests.

Soil Fertility, Salinity and Nematode Diversity Influenced by Tamarix ramosissima in Different Habitats in an Arid Desert Oasis

The aim of this paper was to assess the influence of tamarisk shrubs on soil fertility, salinity and nematode communities in various habitats located in an arid desert-oasis region in northwest China. Three habitats were studied: sand dune, riparian zone and saline meadow, where tamarisk shrubs have been established in recent decades in order to vegetation restoration used as desertification control and saline land rehabilitation projects and become the dominant plant community. The parameters measured include soil organic carbon (SOC), total nitrogen, available phosphorus (P) and potassium (K), pH, salt component, and nematode community characteristics. Enrichment ratios (a comparison of the soil measurements between soils under canopy and in the open interspaces) for soil nutrients and salinity were used to evaluate fertility and salinity islands underneath the tamarisk shrubs. The soil nematode community was used as a biological indicator of soil condition. SOC and available P and K were higher beneath the plant canopy than in the open interspaces outside that canopy. The enrichment ratios for SOC and nutrients were highest for the sand dune habitat and tamarisk shrubs clearly created islands of greater salinity under the canopies. Nematode abundance per 100 g dry soil varied considerably between the locations and habitats, with the highest abundance found in sand dune and the lowest in saline meadow. A significantly higher nematode abundance and a lower trophic diversity were found in soils under the canopy compared to the soils in the open interspaces. With the exception of saline meadow, the abundance of bacterivores increased and fungivores decreased under the canopy relative to the open interspaces, and bacterivores dominated under the canopies in the sand dune and riparian habitats. The enrichment ratios for salinity were higher than for fertility, suggesting that improved soil fertility can not limit the impact of salinization beneath tamarisk shrubs. The adverse effect of salt accumulation on the soil environment should be taken into account when using tamarisk as restoration plant species, especially in saline meadow and controlling of tamarisk density should be considered when undertaking re-vegetation projects in the arid desert oasis regions.

English

Effects of banana wilt disease caused by&nbsp;Fusarium oxysporum&nbsp;f. sp. cubense(FOC) on soil nematode community composition were investigated in Hainan province China. The results show that 31 nematode genera in the disease and control regions were identified. The disease area was mainly dominated byAcrobeles,&nbsp;Acrobeloides,&nbsp;Chiloplacus&nbsp;and&nbsp;Aphelenchus, while&nbsp;Pelodera,Protorhabditis,&nbsp;Ditylenchus&nbsp;and&nbsp;Basiria&nbsp;dominated in the control area.Paratylenchus&nbsp;was the dominant genus in both areas.&nbsp;The abundance of total nematodes, bacterivore&nbsp;(10 to 30 cm),&nbsp;plant&nbsp;parasites&nbsp;and omnivores-predators, the&nbsp;values of&nbsp;diversity (H&prime;), maturity index (MI),&nbsp;plant parasite index (PPI),&nbsp;structure index (SI), enrichment index (EI),&nbsp;soil pH, the contents of total organic&nbsp;carbon(TOC), total nitrogen (TN), total phosphorus (TP) and alkaline nitrogen (AN)&nbsp;in the disease area were significantly lower (P&nbsp;&lt; 0.01) than in the control. However,&nbsp;those of&nbsp;fungivores&nbsp;(10 to 20 cm) and&nbsp;dominance (&lambda;)&nbsp;exhibited quite a reverse result. In the disease area,&nbsp;the abundance of&nbsp;total nematodes and bacterivore&nbsp;decreased (P&lt; 0.01) and&nbsp;plant&nbsp;parasites&nbsp;increased&nbsp;(P&lt;0.01) with&nbsp;the increase of soil depth. Thevalues of&nbsp;SI increased (P&nbsp;&lt;0.01) with the increase of soil depth in the disease and control areas in 0 to 20 cm.&nbsp;The results indicate that FOC changed soil nematode community characteristics and decreased diversity of soil nematode community. &nbsp; Key words:&nbsp;Banana wilt disease,&nbsp;Fusarium oxysporum&nbsp;f. sp. cubense&nbsp;(FOC), soil nematode community, diversity. &nbsp

Influence of soil organic amendments on suppression of the burrowing nematode, Radopholus similis, on the growth of bananas

Radopholus similis is a major constraint to banana production in Australia and growers have relied on nematicides to manage production losses. The use of organic amendments is one method that may reduce the need for nematicides, but there is limited knowledge of the influence of organic amendments on endo-migratory nematodes, such as R. similis. Nine different amendments, namely, mill mud, mill ash, biosolids, municipal waste compost, banana residue, grass hay, legume hay, molasses and calcium silicate were applied to the three major soil types of the wet tropics region used for banana production. The nutrient content of the amendments was also determined. Banana plants were inoculated with R. similis and grown in the soil-amendment mix for 12-weeks in a glasshouse experiment. Assessments of plant growth, plant-parasitic nematodes and soil nematode community characteristics were made at the termination of the experiment. Significant suppression of plant-parasitic nematodes occurred in soils amended with legume hay, grass hay, banana residue and mill mud relative to untreated soil. These amendments were found to have the highest N and C content. The application of banana residue and mill mud significantly increased shoot dry weight at the termination of the experiment relative to untreated soil. Furthermore, the applications of banana residue, grass hay, mill mud and municipal waste compost increased the potential for suppression of plant-parasitic nematodes through antagonistic activity. The application of amendments that are high in C and N appeared to be able to induce suppression of plant-parasitic nematodes in bananas, by developing a more favourable environment for antagonistic organisms.

Soil nematode community characteristics around the Gangue hill of Fushun West Open-pit mine

Abstract Diversity and nematode abundance were investigated in soils collected around the Gangue hill of Fushun West open-pit mine to evaluate soil pollution, due to heavy metals contents, using nematodes as bioindicators. Nematodes were collected from soil samples using elutriate-sievingflotation and centrifugation methods. The species richness and ecological indices were analyzed. On the base of chemical and nematological analysis, the results indicated that the area around the Gangue hill of Fushun West Openpit mine was polluted by heavy metal, but the degree of pollution was not very serious. According to the results obtained from single-factor analysis, cadmium soil content was ten times higher than the background; 29 genera of nematodes were identified and Acrobeloides, Cervidellus and Mesorhabtidis were the dominant genera in almost all sampling sites. The dominant genera were different as the distances to the Gangue hill changed. In particular, in the investigated areas bacterivores and plant-parasites nematodes were more diffuse than fungivores and omnivorepredators. Copper soil content was significantly correlated with plant parasitic trophic group and with total number of nematodes, thus suggesting that nematode communities studies are important scientific basis for understanding the healthy development of soil ecosystem.

Spatial variation in biodiversity and trophic structure of soil nematode communities in a subtropical savanna parkland: Responses to woody plant encroachment

Woody plant encroachment into grasslands generally increases spatial heterogeneity of soil properties and processes and creates “islands of fertility” beneath woody canopies. However, little is known regarding the potential for these changes to influence spatial variation in soil fauna. We quantified population sizes, biodiversity, and trophic structure of soil nematode communities in a savanna parkland where woody plant clusters developed in grassland during the past century. Total nematode density was constant across transects from centers of woody clusters into grasslands. Family richness and Simpson's Dominance Index indicated nematode communities in grasslands and grassland/cluster edges were significantly more diverse than positions within the woody clusters. Relative densities of all nematode trophic groups changed significantly along the transect. Bacterivores nearly doubled in relative density from grassland (35%) to cluster centers (60%), apparently in response to higher concentrations of soil microbial biomass in wooded areas. Relative densities of plant parasitic nematodes decreased along transects from grasslands (35%) to centers of woody clusters (10%), implying decreased nematode herbivory in woody clusters despite much higher root biomass there. The structure index indicated nematode communities within woody clusters were more simplified than those in grassland and edge communities due to reductions in densities of omnivores and predators. Although nematode densities were lower at 10–20 than 0–10 cm, nematode community characteristics were generally similar between soil depths. Changes in nematode community and trophic structure described here could influence biogeochemical processes, species interactions, and successional processes in regions where woody plants are encroaching into grasslands.

Uptake of phytodetritus by meiobenthos using 13C labelled diatoms and Phaeocystis in two contrasting sediments from the North Sea

Meiobenthic uptake of 13C labelled diatom Skeletonema costatum and Prymnesiophyte Phaeocystis was investigated in permeable and fine grained depositional sediments from the Southern Bight of the North Sea at different sediment horizons. Both the diatom and Phaeocystis–derived organic matter (OM) cascaded into meiobenthic biomass in low but similar percentages and label uptake was highest at the upper cm in both stations. Phaeocystis–derived OM might be as important as diatoms as a food source for the meiobenthos. Meiobenthic biomass in the coarse sediment was lower than in the fine sediment; however label uptake per unit of organism carbon was higher. This was explained as an adaptation to an environment where only low amounts of labile OM are present. In this station, the so-called “stout nematodes” (length to width ratio < 15, [Vanaverbeke, J., Soetaert, K., Vincx, M. 2004a. Changes in morphometric characteristics of nematode communities during a spring phytoplankton bloom deposition. Mar. Ecol. Prog. Ser. 273, 139–146]) showed lower uptake compared to the slender nematodes. Therefore their previously reported opportunistic response to a pulsed food supply must rely then on their life-history characteristics. In finer sediments Sabatieria showed the highest uptake at the 1–3 cm layer, reflecting migration to the sediment-water interface to feed on freshly deposited labile OM. Richtersia 13C uptake was fairly low, indicating the exploitation of another carbon source than the one derived from Skeletonema costatum or Phaeocystis. Enoploides presented the highest uptake, indicating that these predacious nematodes have another food source besides meiobenthic preys. Generally total uptake was low and not nearly sufficient to meet nematode carbon requirements.

Short-term changes in nematode communities from an abandoned intense sand extraction site on the Kwintebank (Belgian Continental Shelf) two years post-cessation

We investigated short-term changes (two years) in nematode communities (density, diversity, biomass and community composition) in an area on the Kwintebank (Belgian Continental Shelf) that was closed for sand extraction activities and compared these patterns to nematode community characteristics from another area on the Kwintebank were sand extraction was still ongoing. Six stations were sampled in 2003 and 2004 and nematode community composition and univariate measures of diversity were compared with values obtained during the extraction period and with a “pre-impact situation” sampled in 1978. Although nematode density, diversity and biomass did not change two years after cessation of the exploitation, nematode community composition did and was more stable than in the extracted site. This is attributed to the absence of continuous disturbances associated with the extraction activities such as the creation and filling up of dredge furrows. As a consequence of the typical life history traits of nematodes, recovery seems to follow different pathways when compared to macrobenthic recovery from the same impact.

Changes in morphometric characteristics of nematode communities during a spring phytoplankton bloom deposition

Nematode body size was investigated in terms of body length, width and length/width (L/W) ratios, before, during and shortly after a spring phytoplankton bloom deposition in a station in the southern North Sea (20 m depth). Sediments consisted of medium sand (median grain size: 333 µm) and were devoid of mud. Redox values in the upper 6 cm of the sediment were positive (>100 mV) throughout the sampling period. During the peak of the spring phytoplankton bloom in May 1999, several small-sized species (adult length < 700 µm) emerged. Most prominent was the appearance of a 'stout' nematode assemblage characterised by low L/W ratios. Most of these small nematode spe- cies were virtually absent before the peak blooming, and they decreased in abundance shortly after deposition of phytoplankton to the seafloor. This indicates the opportunistic behaviour of these nema- todes, which is consistent with their small length, enabling them to reach adulthood rapidly. The net rate of increase of the stout nematodes during the bloom was estimated as 6.4% d -1 . This is much larger than the estimated net rate of 1.5% d -1 for the total nematode community. The species compo- sition of the stout nematode assemblage differed from similar stout assemblages described for conti- nental slope and deep-sea areas. In the southern North Sea, Epsilonematidae were dominant while members of the Desmoscolecidae were prominent in offshore deeper areas. Possibly these differ- ences reflect the relatively strong hydrodynamic forces at the North Sea site. In contrast with their short temporal appearance at our coastal North Sea site, stout nematodes seem to be a consistent member of deep-sea nematode communities. We hypothesise that this is caused by the quality of organic matter reaching the seafloor, together with differences in sedimentology and temperature, influencing the duration of the presence of suitable food items for these nematodes.