Free-living nematodes in soil ecosystems are vital in the decomposition of organic matter and recycling of nutrients. The effects of various types of disturbances on nematode assemblages were examined in several experiments on a single soil: a short-term detrimental disturbance from solarisation, a short-term beneficial disturbance from amendment addition, and a long-term detrimental disturbance from bare ground without plant cover. Comparison of solarised and non-solarised field plots revealed lower numbers of fungivores in solarised plots. As a result, indices involving ratios of fungivores to bacterivores and fungivores to total free-living nematodes were decreased as well. Addition of an amendment increased numbers of bacterivores. This change was also reflected in calculated indices that expressed trophic groups as percentages of the total free-living nematodes. A severely disturbed site with bare ground that was without plant cover for more than 5 years was compared with an adjacent site maintained in grass. No plant-parasitic nematodes were recovered from the bare ground site, which contained lower numbers of nematodes in all trophic groups than the grass site. However, the structure of the free-living nematode assemblages in both sites was similar, as indicated by the proportions of various trophic groups and by ratios of fungivores and bacterivores. The free-living nematode assemblage in a site with a perceived severe long-term disturbance maintained a trophic structure similar to a site with perennial plant cover.
Eudorylaimus, Aporcelaimellus and Mesodorylaimus are dominant members of the omnivorous nematode fauna in Florida, USA. Ecological studies that included numerical data on these genera were reviewed to determine key aspects of their ecology and behaviour. These three genera were also the dominant omnivores in many parts of Europe and often occurred together. Multiple species within genera may be present in samples as well. Although results varied with habitat, these omnivores were present in nearly all stages of succession but often reached their greatest numbers in later stages of succession such as old-growth forests. They also showed remarkable adaptation to extreme environments, including Antarctic habitats, dune sands and temperate sites without vegetation. They were found in a variety of soil types but limited by soil pH < 4.0. Compared with other nematode taxa, they were among the genera most sensitive to moisture levels in sandy soils and to pollution by heavy metals. Some reports also indicated adverse impacts from inorganic fertilisers and other agrichemicals. Much remains unknown about the ecology of these common nematodes, which are widely distributed in soil ecosystems.
Abundances of nematode genera were examined in several forest and field habitats located in close proximity in Florida, USA. Effects of selected habitat features were also evaluated, such as tree type, management and presence of litter, grasses or invasive species. Of 37 common taxa evaluated, ten were more abundant in forest and ten in field habitats. Several genera including Acrobeloides, Aphelenchoides and Mesocriconema were common in all habitats. Light management, consisting of mowing of grasses, negatively affected 19 taxa. More genera appeared adapted to closed forest over open forest, and most of these were more common in plots with oak trees or oak litter than in plots with pine. Numbers of Paratylenchus, Plectus and Xiphinema were further increased by the presence of herbaceous plants on the forest floor. When invasive elephantgrass (Pennisetum purpureum) was included in plots with other grasses, numbers of eight genera that typically were common in grass plots were further increased. Alaimus, Cervidellus and Wilsonema were negatively affected by the invasive elephantgrass. Most of the nine genera in guild Ba2 were more abundant in either forest (Acrobeles, Cervidellus, Plectus, Wilsonema) or grass (Eucephalobus, Zeldia) habitats, while Acrobeloides was common and two genera were rare in all habitats. The effects of habitats and habitat features on many different nematode taxa add to our growing knowledge of the ecological habits of free-living nematodes.
Traditional cover cropping systems for nematode management seldom consider weed and soil nutrient management concurrently. Integrating cover crops suppressive to plant-parasitic nematodes with a cover crop mulching system could improve traditional approaches. Two field experiments were conducted in 2003 and 2004 to evaluate 'Tropic Sun' sunn hemp (Crotalaria juncea) and 'Iron Clay' cowpea (Vigna unguiculata) as summer cover crops and as organic mulches. Both experiments were in a 3 × 3 split-plot design in which the main plots were summer planting of sunn hemp, cowpea or fallow, and the subplots were organic mulch of sunn hemp, cowpea or no mulch. The summer cover crop was followed by turnip (Brassica rapa) and lima bean (Phaseolus lunatus) in the autumn. Using sunn hemp as organic mulch suppressed root-knot nematodes more effectively than using it as a cover crop, but only on a less susceptible host such as turnip, and not on a very susceptible host such as lima bean. While sunn hemp as a cover crop failed to enhance beneficial free-living nematodes, sunn hemp as an organic mulch enhanced bacterial-feeding nematode population densities. Sunn hemp mulch also suppressed broadleaf weeds but not grasses or nutsedges. Although sunn hemp and cowpea cover crops did not increase lima bean N and K content, their mulches increased N and K content. Similar results were observed for turnip and lima bean yields. Population density of root-knot nematodes was positively related to abundance of omnivorous nematode in 2003. The abundance of plant-parasitic nematodes was negatively related to the infestation levels of Pasteuria penetrans, and the abundance of predatory nematodes in 2004. Factors that might have affected the performance of sunn hemp on nematode communities are discussed.