Indicative Value of Soil Nematode Food Web Indices and Trophic Group Abundance in Differentiating Habitats with a Gradient of Anthropogenic Impact

摘要

Indicative value of nematode food web indices and trophic group abundance was assessed for differentiating habitats in two soil types. A total of 604 soil samples were collected from croplands, grassy borders, turfgrass lawns, shrublands and forests in Huron County, Ohio characterized by muck soils. Also, a total of 242 soil samples were collected from two habitats, turfgrass lawns and croplands, in Wayne County, Ohio characterized by mineral soils. All nematodes extracted from soil samples were identified to genus level, categorized to trophic groups and various nematode community indices were calculated. Multivariate analysis of variance using composite of nematode measures revealed that croplands were significantly different from forests, shrublands, turfgrass lawns and grassy borders in the muck soils. Turfgrass lawns in muck soils were not different from forests but were different from shrublands. No differences were observed between forests and shrublands. Turfgrass lawns in mineral soils differed significantly from croplands in the mineral soil. No differences were observed between the soil types when nematode data from croplands and turfgrass lawns from each county were lumped together. All habitats showed moderately enriched food webs [enrichment index (EI) 69-78%] in both soil types. Forests, shrublands and turfgrass lawns in muck soils had high maturity (MI) and structure index (SI) whereas grassy borders and turfgrass lawns in mineral soils had intermediate and croplands in both muck and mineral soils had the lowest MI and SI values. Principal component analysis (PCA) indicated that MI and EI contributed the most to differences between habitats in the PC1 while SI and channel index significantly influenced PC2 axis. Forests and shrublands had highly structured food webs as expected but their high enrichment may be unique to the muck soils. Ordination of habitats using nematode indices revealed that grassy borders and turfgrass lawns hold an intermediary position between undisturbed habitats (forests and shrublands) and highly disturbed habitats (croplands). Although overall contribution of plant-parasitic nematode index (PPI) was less compared to the other indices, PPI explained the variation among the habitats in the PC3 axis. Ordination using trophic group abundance showed lower resolution compared to the food web indices.