Influence of clear-cutting and forest age on the nematode fauna in a Swedish pine forest soil

The abundance and composition of the soil nematode fauna in three seral stages of a pine forest chronosequence located in central Sweden was investigated. The aim of the study was to investigate faunal development during the forest cycle (120–160 years). Three sites, clear-cut 3–12 years before sampling but still without pine trees were compared to three sites with 10–130 year-old trees. Together, these provided sites that could be classified as clear-cut, young stand and mature forest. In most sites without trees and with a poor field layer vegetation, nematode abundance was much lower than in the forested plots. Similar major species/genera of nematodes were found in all age stages of the forest development. The development of the fauna could be related both to climatic shifts and to changes in production of food sources.The ratio of fungal to bacterial feeders and the proportions of two groups of bacterial feeders (Rhabditida BF and Adenophorea BF) varied in distinct ways related to soil layer and seral stage. Thus, in the clear-cut sites the proportion of fungal feeders was quite low. This was also the case with Rhabditida BF. These two groups also contributed a rather low proportion in the litter layer, whereas, their importance successively increased with increasing depth of the soil layers. Proportions of fungal feeding members of the Dorylaimida were highest in the 10–20 year-old stands. The effect of forest trees on nematodes was quite large and the faunal structure in sites with pine trees differed quite markedly from the sites without trees.Apparently, there are certain nematode species whose contribution to the fauna is greatest in the early tree-free stages, others are more abundant in the young forest and still others have their greatest abundance in the mature forest. There are also species whose abundance seems to be unaffected by forest age. Nematode abundance was correlated with the abundance of some other groups of soil organisms.     

Temporal dynamics of soil nematode communities in a grassland plant diversity experiment

We report here on an 8-year study examining links between plant and nematode communities in a grassland plant diversity experiment, located in the north of Sweden on previous agricultural soil. The examined plots contained 1, 4 and 12 common grassland plant species from three functional groups; grasses, legumes and forbs. The same plant species composition was maintained in the plots through weeding and resowing during the experimental period. The hypotheses were (i) that the nematode community would shift towards a more diverse and mature fauna over time and (ii) that the effects of both plant species identity and plant species richness would increase over time. As hypothesized, the Bongers’ Maturity Index (a measure of nematode responses to disturbance) increased over time, but not nematode diversity. Instead, the nematode community development in the present grassland experiment seemed to be more characterized by shifts in dominance patterns than by colonization of new taxa. Clear temporal trends were found for plant-feeders and Adenophorea bacterial-feeders which increased in abundance over time in almost all plant treatments. Rhabditidae bacterial-feeders decreased in abundance over time, in particular in plots with legumes. Fungal-feeders, omnivores/predators and the two nematode indices PPI (Bongers’ Plant Parasitic Index) and NCR (Nematode Channel Ratio) had significant interactions between plant composition and time giving some support to our second hypothesis. Our results highlight the need for long-term experiments to examine plant species effects on soil fauna, especially on taxa belonging to higher trophic levels. The results also stress the importance of plant composition for belowground soil faunal communities.     

Chaotic or deterministic development of nematode populations in pine forest humus incubated in the laboratory

Humus material from an old stand of Scots pine and from an open area clearcut 13–15 years ago was incubated in the laboratory. The incubations were started in different years and the differences in nematode faunal development between the years were compared with site characteristics. In all incubations there was an increase in total nematode abundance. The total number and diversity of nematodes were higher in humus from the forest than from the clearing. The results indicated that biotic control mechanisms were much weaker in the humus from the clearcut area, where a strong dominance of Acrobeloides nanus occurred in most incubations. The differences in faunal development between years were rather large. A certain pattern of unpredictability indicated that the nematode fauna was a rather labile component of the community of soil organisms in a pine forest soil.     

Nematode assemblages indicate soil restoration on colliery spoils afforested by planting different tree species and by natural succession

Soil nematodes were studied in 28 afforested sites on clay colliery spoil from opencast mining in the Czech Republic. The afforestations had four replicate sites and were represented by 20–33-year-old plantations of oak, alder, linden, spruce, larch, pine, and sites left to natural succession. The total abundance of nematodes in deciduous plantations plus natural successions was 1156 × 10³ ind/m² and in coniferous plantations 1236 × 10³ ind/m². The abundance of plant parasites and omnivores was significantly greater in deciduous than in coniferous plantations. The abundance of root–fungal feeders dominated by Filenchus was greater in spruce and pine plantations than in deciduous plantations. Bacterivorous Plectus predominated in larch plantations. Nematode assemblages in deciduous plantations had significantly greater numbers of species and genera, H’gen, MI, ΣMI, EI and SI values, and greater proportions of omnivores plus predators to other trophic groups than the assemblages in coniferous plantations. The nematode fauna indicated most advanced soil restoration on spoils under oak and alder plantations, intermediate under linden and spruce, and least under pine and larch. Nevertheless, some nematodes typical for developed forests were either found in low population densities (e.g. Teratocephalus) or were missing (e.g. Malenchus).     

Strong impacts of belowground tree inputs on soil nematode trophic composition

Trees have a key role in determining the composition of soil biota via both above and belowground resource-based mechanisms, and by altering abiotic conditions. We conducted an outdoor mesocosm experiment to investigate the relative impact of above and belowground tree inputs on soil nematode trophic composition, and examine whether tree-driven impacts differed between contrasting species (birch and pine). For both species, we created a factorial design of litter addition and root presence treatments. The litter addition treatment was equivalent to natural levels of litterfall; tree saplings were planted in mesocosms for the root presence treatment and an unplanted control treatment was established that had no litter or root inputs. Litter addition had a limited impact on soil nematode community composition: it primarily decreased omnivore and predatory nematode abundance in birch but had few other effects on the nematode community. By contrast, root presence markedly altered nematode community composition through changes in a range of trophic groups. For both birch and pine, there were significant increases in total, fungivore and predatory nematode abundance in root presence treatments, and furthermore, total and fungivore abundances were positively related to root biomass. Root presence of these contrasting tree species also had a distinctive impact on some specific nematode trophic groups; pine roots promoted bacterivore abundance while birch roots promoted root-hair feeding nematode abundance. These findings suggest strong bottom-up effects of belowground tree inputs, and indicate that particular components of the nematode community may be affected differently by resource quantity and quality. Consequently, we suggest that, in the short-term, belowground rather than aboveground tree inputs have a strong impact on soil food web structure and complexity.     

Dynamics and stratification of functional groups of nematodes in the organic layer of a Scots pine forest in relation to temperature and moisture

Nematode trophic groups were studied in litterbags in a Pinus silvestris forest using sampling periods of 8 weeks during 2.5 years. Temperature, moisture relationships and annual periodicity of nematodes were analyzed in the litter (L), fragmentation (F) and humus (H) horizons. Litterbags containing L, F and H material were placed in stacks and buried in the organic layer. Undisturbed core samples were used to compare the nematode abundance under normal field conditions with that in the litterbags. Time dependence of population growth and colonization was also studied in separate litterbags that were replaced every 8 weeks. During the first 4 to 6 months of the experiment, nematodes in the litterbag stacks grew rapidly to circa 5×10⁶m^–2. After that period, abundance gradually decreased to about 2.5×10⁶m^–2. These abundances were similar to those found in undisturbed cores. Nematode abundance during the first year was most pronounced in the top (L) litterbags; subsequently densities were more or less the same in the three organic horizons, reflecting the gradual change of L to F material. On average, during 2.5 years, bacterial feeding nematodes were the dominant group in the organic horizons (73%), with 17% hyphal feeders and 9% plant feeders. There were dissimilarities between layers and in the course of time. The number of hyphal feeding nematodes differed significantly between layers. In the first 2 to 4 months, hyphal feeding nematodes equalled the bacterial feeders in the L layer. Later bacterial feeders became dominant. The highest number of plant feeding nematodes was found in the F litterbags. Significant effects of temperature and moisture were mainly found on bacterial feeding nematodes. Regression coefficients for trophic group abundances and moisture were generally positive. Temperature was negatively correlated with the three functional groups in the L horizon only. Bacterial and hyphal feeding nematodes showed a significant decrease with time in the L layer, reflecting diminishing substrate quality (and food availability) during decomposition. A significant annual periodicity could be demonstrated for bacterial feeders in L litterbags and plant feeding nematodes in the H material. Received: 26 June 1997     

Structure of nematode communities in forest soils of southern British Columbia: relationships to nitrogen mineralization and effects of clearcut harvesting and fertilization

The effects of clearcut harvesting and fertilization of clearcuts on the structure of nematode communities were assessed at three sites in the southern interior of British Columbia. The Shannon-Weaver and Simpson indices of diversity were greater in clearcuts than in forests. The diversity of the bacterivorous and fungivorous trophic groups were not significantly different between clearcuts and forests, whereas the diversity of omnivorous and predacious nematodes was lower in clearcuts than in forests. The nematode maturity index (MI) was lower in clearcuts than in forests. Several ratios describing the prevalence of enrichment opportunists (the absolute abundance of Rhabditida, the relative abundance of Rhabditida, and the ratio of Aphelenchida/fungivorous nematodes) were greater in clearcuts than in forests. Nematode diversity tended to be lower in fertilizer treatments than in controls within clearcuts, but the effects were not consistent across sample dates. The MI was lower in fertilizer treatments than in controls. All ratios representing the relative abundance of enrichment opportunists were greater in fertilizer treatments than in controls. The MI was negatively correlated with N mineralization in data sets representing forests and fertilized and non-fertilized plots within clearcuts. None of the diversity indices were correlated with N mineralization. The absolute abundance of Rhabditida and the relative abundance of Rhabditida were both consistently positively correlated with N mineralization in the data set representing fertilized and non-fertilized plots within clearcuts, and the absolute abundance of Rhabditida was positively correlated with N mineralization in forests.     

Responses of soil nematode community structure to soil carbon changes due to different tillage and cover crop management practices over a nine-year period in Kanto,Japan

The response of the soil food web structure to soil quality changes during long-term anthropogenic disturbance due to farming practices has not been well studied. We evaluated the effects of three tillage systems: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tillage (NT), three winter cover-crop types (fallow, FL; rye, RY; and hairy vetch, HV), and two nitrogen fertilization rates (0 and 100 kg N ha⁻¹ for upland rice, and 0 and 20 kg N ha⁻¹ for soybean production) on changes in nematode community structure. Sixty-nine taxa were counted, total nematode abundance (ALL), bacterial feeders (BAC), predators (PRD), omnivores (OMN), and obligatory root feeders (ORF) were more abundant in NT than in MP and RC, but fungal feeders and facultative root feeders (FFR) were more abundant in RC than in NT and MP. Cover crop also influenced nematode community structure; rye and hairy vetch were always higher in ALL, BAC, FFR, ORF, and OMN than fallow. Seasonal changes in nematode community structure were also significant; in particular, as soil carbon increased, nematode abundance also increased. The relationship between nematode indices and soil carbon was significant only in NT, but not in MP and RC. In NT, with increasing soil carbon, enrichment index and structure index (SI) were positive and significant and channel index was negative. Bulk density was significantly negatively correlated with FFR and ORF. Seasonal difference in nematode community between summer and autumn was larger in an upland rice rotation than in a soybean rotation. Over the nine-year experiment, SI increased not only in NT but also in MP and RC, suggesting that repeated similar tillage inversions in agroecosystems may develop nematode community structures adapted to specific soil environmental conditions. Because NT showed the highest values of both SI and soil carbon, the increase of soil carbon in NT is expected to have a great impact on developing a more diverse nematode community structure.     

Nematofauna associated with exotic and native leguminous plant species in West Africa: effect of<Emphasis Type="Italic"> Glomus intraradices</Emphasis> arbuscular mycorrhizal symbiosis

Ten leguminous trees, four exotic species (Australian Acacia) and six indigenous species (three Sahelian Acacia spp. and three Sesbania spp.), were grown for 4 months in a natural Sahelian soil inoculated with or without the endomycorrhizal fungus, Glomus intraradices. In control trials, the determinant factor structuring the soil nematode fauna was the plant species, related plants having a similar influence on the nematode community in the soil. Soil nematode abundance increased from exotic acacias (3.3 g^-1 dry soil) to native acacias (11.5 g^-1 dry soil) and Sesbania species (17.6 g^-1 dry soil). Plant feeding nematodes (mainly Scutellonema and Tylenchorhynchus) were significantly less abundant under exotic acacias (1.4 g^-1 dry soil) than under native acacias (7.2 g^-1 dry soil) or Sesbania species (7.3 g^-1 dry soil). Bacterial feeding nematode density increased from exotic acacias (1.2 g^-1 dry soil) to native acacias (3.0 g^-1 dry soil) and Sesbania species (7.7 g^-1 dry soil) as total densities. However, the differences in the structure of the nematode communities between plant groups were suppressed in the presence of the mycorrhizal fungus. In fact, no difference in nematode densities remained between plant groups when G. intraradices developed in several dominant taxa belonging to different trophic groups, particularly: Tylenchorhynchus, Apelenchina, Cephalobus and Dorylaimoidea. This study clearly indicated that inoculation with the arbuscular mycorrhizal fungus G. intraradices diminished the plant-specific effect on the structure of the soil nematode community.     

Effect of irrigation on nematode population dynamics and activity in desert soils

Summary The nematode community in litter and soil was examined for a year in the Chihuahuan desert, before and after supplemental rainfall application. Proportions of nematode-active or anhydrobiotic forms and population densities were determined for 3 treatments: control (natural rainfall), a single, large (25-mm) monthly irrigation pulse, and 4 smaller (6-mm) irrigations spaced at weekly intervals. In litter the greatest nematode abundance was in the 6 mm week^–1 treatment (48 nematodes 20 g^–1 litter). Bacteriovores and fungivores accounted for approximately 95% of the numbers and biomass in all treatments. In soil, water amendments had no significant effect (P < 0.05) on annual mean densities of total nematodes, fungivores, bacterivores, or omnivore predators. Phytophage densities were greater on both irrigation treatments, with highest densities (9268 m^–2) in the 6 mm week^–1 soils, which was 5.9% of the total soil nematode density. Total densities of individual trophic groups were not significantly different before or after rainfall. Soil nematode densities fluctuated independently with trophic group, month, and season. Bacterial feeders and omnivore predators were the largest contributor to total soil nematode density and biomass. Prior to irrigation, there were no differences in the percentage of anhydrobiotes on the three treatments. Anhydrobiotes decreased after irrigation in all treatments, and were significantly lower in soils of the larger, monthly irrigation. Nematodes were inactive (anhydrobiotic) and decoupled from decomposition processes when soil water matric potentials reached –0.4 MPa.Dedicated to the late Prof. Dr. M.S. Ghilarov     

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.     

Effects of tillage and fertilizer on nematode communities in a Japanese soybean field

No-tillage (NT) cropping systems develop distinct soil ecosystems characterized by a diverse soil fauna and slow fungal decomposition. However, nematode community analyses sometimes fail to detect these characteristics because the treatment before study or the sampling period is too short or the studies are not comprehensive. Different nematode taxa may occur depending on the geographic region and soil type, thereby affecting the usefulness of nematode analyses for soil biological assessment. However, studies in Asia are scarce. Thus, in this 2-year study, we compared nematode populations, community structures, and soil physicochemical properties between long-term NT and conventional tillage (CT) treatments combined with chemical (CF), organic (OF), or no (NF) fertilizer treatments in a Japanese soybean field. We then examined whether nematode diversity and community indices could detect differences among the treatments in the Japanese andosols. Although the effects of tillage on nematode densities were significant, the overall trend in NT–CT differences was not clear, except for omnivores and Meloidogyne. The effects of tillage on nematode diversity and community indices were apparent: diversity indices, maturity index (MI) and related indices, structure index, and channel index were higher, whereas enrichment index (EI) was lower in NT because of higher densities of K-strategy taxa, fungal and facultative root feeders, and lower densities of r-strategy bacterial feeders. Fertilizer treatments also affected nematode densities: most feeding groups were less abundant in NF and predatory nematodes were more abundant in OF than in other treatments. OF increased nematode diversity via an increase in microbivorous and predaceous nematodes. However, the effects of fertilizer on most community indices were not apparent. Interactions between tillage and fertilizer effects were significant for Pratylenchus and total nematode densities, MI, and EI. Among the soil properties differing among treatments, Ca and Mg content, cation exchange capacity, and percent total nitrogen affected nematode community structure. In conclusion, nematode community analyses using index calculations are useful for assessing soil biological properties under different tillage treatments in Japanese andosols, as well as in soil types in other countries. However, index calculations were less sensitive at detecting fertilizer treatment effects, probably because of simultaneous increases in r- and K-strategy nematodes and OF compost that was too decomposed. Other community analyses such as indicator species analysis or diversity evaluations should be used to detect fertilizer effects.     

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.     

Defoliation effects on Plantago lanceolata resource allocation and soil decomposers in relation to AM symbiosis and fertilization

Plants can mediate interactions between aboveground herbivores and belowground decomposers as both groups depend on plant-provided organic carbon. Most vascular plants also form symbiosis with arbuscular mycorrhizal fungi (AMF), which compete for plant carbon too. Our aim was to reveal how defoliation (trimming of plant leaves twice to 6 cm above the soil surface) and mycorrhizal infection (inoculation of the fungus Glomus claroideum BEG31), in nutrient poor and fertilized conditions, affect plant growth and resource allocation. We also tested how these effects can influence the abundance of microbial-feeding animals and nitrogen availability in the soil. We established a 12-wk microcosm study of Plantago lanceolata plants growing in autoclaved soil, into which we constructed a simplified microfood-web including saprotrophic bacteria and fungi and their nematode feeders. We found that fertilization, defoliation and inoculation of the mycorrhizal fungus all decreased P. lanceolata root growth and that fertilization increased leaf production. Plant inflorescence growth was decreased by defoliation and increased by fertilization and AMF inoculation. These results suggest a negative influence of the treatments on P. lanceolata belowground biomass allocation. Of the soil organisms, AMF root colonization decreased with fertilization and increased with defoliation. Fertilization decreased numbers of bacterial-feeding nematodes, probably because fertilized plants produced less root mass. On the other hand, bacterial feeders were more abundant when associated with defoliated than non-defoliated plants despite defoliated plants having less root mass. The AMF inoculation per se increased the abundance of fungal feeders, but the reduced and increased root AM colonization rates of fertilized and defoliated plants, respectively, were not reflected in the numbers of fungal feeders. We found no evidence of plant-mediated effects of the AM fungus on bacterial feeders, and against our prediction, soil inorganic nitrogen concentrations were not positively associated with the concomitant abundances of microbial-feeding animals. Altogether, our results suggest that (1) while defoliation, fertilization and AMF inoculation all affect plant resource allocation, (2) they do not greatly interact with each other. Moreover, it appears that (3) while changes in plant resource allocation due to fertilization and defoliation can influence numbers of bacterial feeders in the soil, (4) these effects may not significantly alter mineral N concentrations in the soil.     

Effects of organic,low input,conventional management practices on soil nematode community under greenhouse conditions

A comparative study of organic, low input, conventional vegetable greenhouse systems was conducted to assess the effect of management practices on the soil nematode community. Bacterivores were the most dominant trophic group in all three systems with a mean proportion of over 80%, followed by omnivore-carnivores. In general, organic management practices increased the abundance of total nematodes, bacterivores, fungivores, and omnivore-carnivores in comparison with low input and conventional management practices. Though inhibitory effects of plant feeders were found in organic and low input systems, these effects were more evident in organic systems. However, small differences were observed in the composition of trophic groups and fauna analysis. All three systems displayed enriched soil conditions and structured food webs. We inferred that the bottom-up effect resulting from organic input in the soil food web may play a more important role than the disruption effects under our high input greenhouse conditions. The Shannon index (H′) and genus dominance (λ) suggested that in greenhouse conditions, excessive manure input would cause a decrease in nematode diversity but increase the dominance, particularly for enrichment opportunists. We concluded that management practices under greenhouse conditions were more influential on nematode biomass (including trophic groups) than community structure.     

Fluctuations of carabid populations inhabiting an ancient woodland (Coleoptera, Carabidae)

The changes in population size of carabid beetles inhabiting an ancient woodland were analysed in a long-term investigation covering a period of nine years (1994–2002). The amplitude of fluctuations of the relative density of these species was estimated and compared with those of carabid beetles inhabiting recent woodlands and more unstable habitats in open landscapes. To analyse this, 8 pitfall traps were set in an ancient beech and oak woodland in the nature reserve “Lüneburger Heide” in northern Germany and were emptied every fortnight the whole year round.Catching rates for some species (e.g. Carabus problematicus and Abax parallelepipedus) fluctuated only slightly, whereas those of other species (e.g. C. violaceus and C. auronitens) varied as much as ten-fold. Comparison of these results with those of other long-term investigations of recent woodlands and also of more open habitats showed that in each of the three habitat types some species varied very little in abundance and others, very widely. So it seems that the amplitude of fluctuations in abundance is a feature of each single species rather than a special attribute of their habitats.     

Dynamics and stratification of functional groups of micro- and mesoarthropods in the organic layer of a Scots pine forest

This paper addresses the abundance, biomass and microstratification of functional groups of micro- and mesoarthropods inhabiting the organic layers of a Scots pine forest (Pinus sylvestris L.). An experiment using stratified litterbags, containing organic material of four degradation stages, i.e., freshly fallen litter, litter, fragmented litter and humus, was performed over a period of 2.5 years. Statistical data analysis revealed that each organic layer had a different, characteristic species composition that changed with time following successive degradation stages. Species of Acari, Araneae and Collembola were assigned to different functional groups based on taxonomy, microstratification, food type or feeding mode. The abundance and biomass carbon of functional groups were dependent on the organic layer and most functional groups showed a particular preference for one of the upper organic layers. Temporal and spatial differences in density and biomass carbon of functional groups could partly be related to fluctuations in the soil climate, although effects of trophic interactions could not be ruled out. A general decline in abundance and biomass, especially in populations of fungal feeders, during the last year of the study could not be explained by a reduction in litterbag volume, changed litter chemistry or soil climate, but was attributed to an indirect effect of a remarkable increase in soil coverage by wavy hair grass, Deschampsia flexuosa (L.). The analysis demonstrated that species diversity, microhabitat specification, soil fauna succession, and degradation stages of organic material are interrelated. The results obtained indicate that both the chemistry of organic matter and decomposition rates have an important effect on trophic relationships and community structure. Received: 26 June 1997     

Effect of the earthworm Lumbricus rubellus on the nematode community in a peat meadow soil

The effect of different densities of Lumbricus rubellus on the nematode community was studied in a field experiment. The stand, a cultivated meadow on peat-muck soil developed from moderately decomposed alder peat, was located on drained fens in the central basin of the Biebrza valley in the north-eastern part of Poland. Samples were taken from soil isolators into which 0, 2, 4 or 6 earthworms were previously introduced. The abundance and trophic structure of the nematode fauna in the different treatments were compared 30, 60, 90 and 120 d after the introduction of L. rubellus. The effect of L. rubellus on soil nematodes was most pronounced at the beginning of the experiment. Thirty days after introduction of L. rubellus, the total number of nematodes in all trials with earthworms was significantly lower than in the control, and nematode numbers decreased with increasing L. rubellus density. On later sampling dates, the results were less clear and 120 d after introduction of L. rubellus no significant effect on the total number of nematodes was observed in the treatments. The abundance of the bacterial-, fungal- and plant-feeding nematodes in the treatments with earthworms was lower than in the control 30 d after introduction of L. rubellus, but significant differences were found only in the case of bacterial feeders.     

Nematode assemblages in the rhizosphere of spring barley (Hordeum vulgare L.) depended on fertilisation and plant growth phase

Nematodes from rhizosphere soil of barley grown at three fertiliser treatments (control (0), NK and NPK) were studied in a field experiment. Sampling was done twice, during vegetative growth and flowering, respectively, to determine how fertiliser effects on nematode assemblages depended on plant growth phase. At the growth stage the proportion of fungal feeding nematodes (dominated by Aphelenchoides spp. and Aphelenchus sp.) was highest in NK. During flowering, the abundance and proportion of fungal feeders in the 0 and NPK plots had increased and reached a level similar to the NK plot. Overall densities of bacterial feeders (mainly Cephalobidae and Rhabditidae) were similar, but opportunistic bacterial feeders constituted a higher proportion in the fertilised plots compared to the unfertilised. Ectoparasitic plant feeders (Tylenchorhynchus sp.) were more numerous in NK and NPK than in the control at both sampling dates. Endoparasite (Pratylenchus spp.) numbers were lower in the NPK plot at the growth stage. Numbers of Tylenchidae increased between samplings. The classification of Tylenchidae as epidermal cell and root hair feeders as opposed to hyphal feeders is discussed. Results thus indicate that: (i) bacterial and especially fungal feeding nematodes are stimulated by unbalanced fertilisation; (ii) ectoparasitic plant feeders are stimulated by N-fertilisation, while migratory endoparasites are inhibited at high and balanced fertilisation; (iii) nutrient effects diminish after plants reach the flowering stage.     

Rapid Changes in Soil Nematodes in the First Years after Technosol Construction for the Remediation of an Industrial Wasteland

Technosol construction is an emergent technology that uses an assemblage of technogenic materials for the ecological reclamation of derelict land and waste recycling. Knowledge about the colonisation of Technosols by soil biota is limited, despite the latter’s central role in ecosystem functioning. In this four-year field (2008 to 2011) study, we characterized the development over time of the diversity and the abundance of soil nematodes in two types of Technosols in North-Eastern France. We also studied the nematode community structure, abundance of taxa and functional groups in both Technosol profiles in the third year of the study. Samples were collected from the top soil layer (0–20 cm) each year in the spring (April), on a one ha. field experiment that had spatially divided in 24 sampling areas. For soil profiles, three samples were collected in three horizons within six pits (three pits per Technosol). Nematodes were extracted from soil and identified at the family or genus level and then classified into functional feeding guilds. In the first year, the community was dominated by opportunistic bacterial feeders. The taxonomic and functional nematode diversity increased with time, with a dominance of non-opportunistic bacterial feeders after four years, but also the significant presence of fungal feeders, omnivorous and carnivorous, as well as plant parasites and insect parasites. No significant difference was observed between the two Technosols. Each layer showed distinct communities, with nematode diversity and abundance decreasing with depth. Abundance and diversity, coupled with the analysis of several indexes, commonly used for nematodes, including Maturity index (MI), Enrichment index (EI), Structure index (SI) and Nematode channel ratio (NCR), lead to the conclusion that the high organic matter content, particularly in the upper horizon of both Technosols, guaranteed nematode colonization and progressive diversification, and is likely to be the key for successful biodiversity reclamation.