Community Structure Of Free-living Nematodes Research Articles

Free-living nematode community structure and distribution within vineyard soil aggregates under conventional and organic management practices

Soil biota play a crucial role in soil ecosystem stability, promoting decomposition of organic matter and nutrient cycling. The influence of organic farming versus conventional farming is known to improve soil properties such as aggregation. Despite the importance of soil microbial communities in soil biogeochemical processes, our knowledge of their community dynamics is rudimentary especially under different agricultural managements. Here we studied the effect of two types of vineyard managements (conventional, and organic), and three soil aggregate sizes (macro – LMA, 8,000-9,800 μm; meso – SMA, 500-2000 μm and micro – MA, <500 μm) on free-living soil nematodes. The abundance, diversity, and indices of free-living soil nematodes were determined. We found that the abundance of free-living soil nematodes increased with organic treatment, and that the nematode community guild structure altered toward changes in the Wasilewska index, where plant parasites were found to increase macro-aggregates in the agricultural practices that may be attributed to weed management (no-tillage and no herbicides) in the organic treatment. The network connectivity increased in complexity with increasing aggregate sizes, highlighting the importance of the interplay between nematodes and soil inter-aggregate pore size and connectivity.

Influences of nitrogen inputs on nematode populations under highbush blueberry.

This study examined the effects of nitrogen fertilization on populations of Rotylenchus robustus, Pratylenchus crenatus, and Paratrichodorus renifer, and indices of free-living nematode community structure, in relation to highbush blueberry production in British Columbia, Canada. The field experiment was established in fall of 2008 with six replicate plots of each of four experimental N fertilization treatments: 0, 100, 150, and 200% of the annual application rate recommended for conventional blueberry production in the region. Nematode populations were quantified annually from 2009 through 2015, and then nematode populations and root biomass were quantified at seven sample dates from 2016 through 2019. Population densities of R. robustus were consistently greater in the 100% treatment than in the 0, 150, and 200% treatments which did not differ from each other. Population densities of P. crenatus were consistently greater in the 150% treatment than in the 0, 100%, and 200% treatments. The nematode structure index and two indices of diversity declined monotonically with N fertilizer rate, indicating broader changes in the soil food web that could have had indirect, feedback effects on population dynamics of the plant-parasitic nematodes.

The Seasonal Variability in The Genus-Family Structure of Free-Living Nematode Communities in Organic Shrimp Farming Ponds, Ca Mau Province

The Seasonal Variability in The Genus-Family Structure of Free-Living Nematode Communities in Organic Shrimp Farming Ponds, Ca Mau Province

Trophic structure of free-living nematodes in the Saigon River, Vietnam

Sub-tidal free-living nematodes in 12 stations along the Saigon River were investigated in both dry and rainy seasons during 2014 and 2015. In total, 157 nematode genera were found to belong to 59 families, and 11 orders of two classes of Enoplea and Chromadorea were identified. The trophic structure of free-living nematode communities was analysed spanning the overall seasons to see that deposit-feeders developed dominantly in the Saigon River indicating their association with food types including particles, bacteria, diatom, etc.. The dominance of deposit-feeders was contributed to a high abundance of genera in each station, including Theristus, Teschellingia, Monhystera, Thalassomonhystera, Paraplectonema, Daptonema, Aphanonchus, Sphaerotheristus, and Geomonhystera. Epistrate-feeder types were found as the second most abundant group. The remaining feeding types, such as chewers and suction-feeders, were in rather low proportion at most stations.

Effect of long-term fertilization on free-living nematode community structure in Mollisols

The influence of long-term application of pig manure combined with chemical fertilizer (MCF) or chemical fertilizer (CF) on free-living nematodes was evaluated in this study. The application model of fertilizers lasted 14 years in Mollisols, and treatments included MCF, CF and no fertilizer (NF). A total of 26 free-living nematode genera belonging to seven functional guilds were found in maize fields, and the community structure of free-living nematodes was different in MCF, CF and NF. Pig manure increased the abundance of bacterivores, especially those belonging to c-p1 (Ba1) and c-p2 (Ba2) guilds. Channel index (CI) was higher in NF than in MCF and CF, but enrichment index (EI) was higher in MCF and CF compared to NF. The structure index (SI) was highest in NF among three treatments. Total bacterivores, Ba1 and Ba2 guilds were positively correlated to organic C, total N, available N, total P and available P, but fungivores only had correlation with organic C and soil moisture. The SI index was negatively related to organic C, total N, available N, total P and available P. Collectively, these results indicate that the pig manure or chemical fertilizer normally applied to increase soil nutrition also induce negative influence on soil food web structure as reflected from biological aspect, and that soil nematodes can enhance agroecological assessments of changes induced by long-term fertilizer application in maize field in Mollisols.

Effects of different soil management practices on soil free-living nematode community structure, Eastern China

An investigation was conducted in a Shouguang agroecosystem, Shandong Province, Eastern China, in order to determine the long-term (10–15 yr) disturbances of three different agricultural management practices. In this study, the main focus was on free-living soil nematodes, as a tool which will help differentiate between treatments according to their sensitivity to physical, chemical, and biota composition. In this study, three treatments were implemented in each of a total of four investigated sites: greenhouses, conventional farmlands, and fallows. Diversity, maturity (MI) and weight indices were used to assess the nematode community. The results indicated that greenhouses have a lower richness (SR), diversity, modified maturity index (ΣMI), modified maturity index for all nematodes with c-p = 2–5 [ΣMI (2–5)], plant parasite index (PPI), PPI/MI values, and fungi-feeding/bacteria-feeding (F/B) ratio, as well as lower basal index (BI) and channel index (CI) and higher dominance. These results elucidated the difference between the three treatments, where the greenhouses were an enriched disturbed system compared with the other treatments and were dominated by bacterivorous nematodes, the fallows were a relatively infertile and stable system dominated by plant parasites, and the conventional farmlands can be positioned between the above two treatments. Key words: Agricultural management, nematode, disturbance, indices

Comparison of nematode communities in Baltic and North Sea sublittoral, permeable sands – Diversity and environmental control

The structure of free-living nematode communities was investigated seasonally at two sandy locations representing typical shallow sublittoral, permeable environments of the North Sea and the Baltic Sea. At the Baltic study site the chlorophyll and organic carbon concentrations in the sediment were, on average, four times lower than at the North Sea. Highest nematode densities (1674–4100 ind. 10 cm −2) and a higher number of free-living nematode genera (66) were recorded in the North Sea (Baltic: 206–1227 ind. 10 cm −2, 30 genera). Despite lower salinity and lower food availability the less dense and less diverse Baltic nematode community was similar in generic composition to the North Sea community. At the North Sea site, all trophic groups according to Wieser's classification were present with omnivores/predators, dominated by Viscosia, prevailing and followed by epistrate-feeders. In the food-limited Baltic community, non-selective deposit feeders (mainly Ascolaimus, Axonolaimus and Daptonema) and omnivores/predators dominated by Enoplolaimus were the most abundant trophic groups while selective deposit feeders were absent or their contribution was negligible. An analysis of the vertical generic distribution revealed highest diversity of the Baltic community in deeper sediment layers, below the sediment surface affected by ripple migration and near the interface of oxic and anoxic conditions. The diversity pattern in the North Sea sediment was more variable but generally showed high diversity in the upper centimetre of the sediment. These observations suggest that food supply and sediment oxygenation are the most important factors influencing the vertical pattern of nematode generic diversity in sublittoral, permeable sands.

Intertidal meiofauna of a high-latitude glacial Arctic fjord (Kongsfjorden, Svalbard) with emphasis on the structure of free-living nematode communities

Meiofauna communities of four intertidal sites, two sheltered and two more exposed, in Kongsfjorden (Svalbard) were investigated in summer 2001 at two different tidal levels (i.e. the low-water line and close below the driftline, referred to as mid-water (MW) level). A total of seven meiofaunal higher taxa were recorded with nematodes, oligochaetes and turbellarians being numerically dominant. Mean total meiofaunal densities ranged between 50 ind. 10 cm−2 and 903 ind. 10 cm−2. Our data showed a clear decrease in total meiofaunal densities with increasing coarseness of the sediment. Total meiofaunal biomass varied from 0.2 g dwt m−2 to 2 g dwt m−2 and, in general, was high even at low meiofaunal densities, i.e. larger interstitial spaces in coarser sediments supported larger meiofauna, especially turbellarians. The results on the vertical distribution of meiofauna contrasted sharply with typical meiobenthic depth profiles on other beaches, probably in response to ice-scouring and concomitant salinity fluctuations. Oligochaetes were the most abundant taxon, with a peak density of 641 ind. 10 cm−2 at Breoyane Island. They were mainly comprised of juvenile Enchytraeidae, which prohibited identification to species/genus level. Nematode densities ranged between 4 ind. 10 cm−2 and 327 ind. 10 cm−2. Nematodes were identified up to genus level and assigned to trophic guilds. In total, 28 nematode genera were identified. Oncholaimus and Theristus were the most abundant genera. The composition of the nematode community and a dominance of predators and deposit feeders were in agreement with results from other arctic and temperate beaches. Nematode genus diversity was higher at the more sheltered beaches than at the more exposed ones. Low-water level stations also tended to harbour a more diverse nematode communities than stations at the MW level. Differences in nematode community structure between low- and MW stations of single beaches were more pronounced than community differences between different beaches and were mainly related to resources quality and availability.

Seasonal variation of biodiversity and assemblage structure in freshwater nematodes

In a three-year field study we determined the seasonal and annual variation of abundance, biomass, species richness, and community structure of freshwater nematodes at a single station in the eutrophic Lake Obersee. The seasonal patterns observed were consistent and varied little between sampling years. Nematode abundance and biomass were highest in summer. Species richness and diversity peaked in winter. With 152 identified species, Obersee is the most species-rich lake ever described. Species number was not constant over years but the main assemblage structure hardly changed. The community was dominated by the same 4 species throughout the study. Colonization was very strong in winter while extinction rates were high in summer. This study shows that the community structure of free-living nematodes depends strongly on the season investigated.

Changes in free-living nematode community structure in relation to progressive land reclamation at an intertidal marsh

Nematode communities were investigated at two locations along two transects on Chongming Island in the Changjiang Estuary, China, which had received different intensities of intertidal marsh reclamation. Our results demonstrate that marsh reclamation altered nematode community structure, and the frequency of reclamation also substantially affected nematode communities. Nematode generic richness and diversity were significantly lower at reclaimed stations than at tideland stations, whereas nematode abundance and evenness did not change significantly after reclamation. MDS ordination indicated that different nematode communities could be distinguished for un-reclaimed, newly reclaimed and old reclaimed stations. Stations on the same land type at two locations were grouped together, suggesting that land use management exerted greater influence on nematode communities than location.

Relationships between seagrass biodiversity and infaunal communities: implications for studies of biodiversity effects

Controlled experiments to elucidate links between ecosystem functioning and biodiver- sity have produced differing results. We investigate links between the species diversity in multi- species tropical seagrass beds in Thailand and the abundance, diversity and community structure of free-living nematodes within the beds. No relationship was found between seagrass diversity and nematode species richness or abundance, but a posteriori power analyses demonstrate that our sam- pling design had little prospect of detecting such relationships against a background of naturally occurring variability. We conclude that in a variable world biodiversity effects may be difficult to detect, even if they are large. Multivariate analyses show that there are relationships between seagrass diversity and the community structure of free-living nematodes, with different nematode assemblages occurring in patches of seagrasses with different numbers of seagrass species. We therefore conclude that biodiversity effects do exist in the real world. Different mixtures of sea- grass species alter environmental conditions and food availability within the sediment through a range of processes (ranging from sediment trapping to interspecific differences in photosynthate production) which in turn affect differences in nematode community structure directly or through indirect pathways.

Impact of predation and sediment disturbance by Carcinus maenas (L.) on free-living nematode community structure

A microcosm experiment was conducted to investigate the effects of continuous and episodic biological disturbance by Carcinus maenas on estuarine nematode assemblages from sand and mud for a period of 57 days. Univariate methods of data evaluation failed to reveal major changes in community structure. Distributional techniques (dominance curves) were more sensitive in detecting changes in diversity patterns in the sand assemblage. Results of multivariate analyses indicated that nematode assemblages had changed characteristically due to biological disturbance. The observed changes in nematode community structure were the result of confounded effects of predation and modification of the sediment due to crab activity. Nematode assemblages from the organic-poor sand were mainly affected by crab predation, those from the organic-rich mud were mainly affected by changes to the sediment due to crab feeding activity. Effects of biological disturbance on both nematode assemblages were dependent on the frequency of disturbance events.