Soil energy pathways of different ecosystems using nematode trophic group analysis: a meta analysis

We analysed 67 raw data sets of nematode genera from three types of ecosystems (grassland, cropland, and forest) to compare relative magnitude of energy pathways through the soil food web. Bacterial-, fungal- and herbivorous-based energy pathways were compared by percentages (in either abundances or biomass) of three soil nematode trophic groups (i.e., bacterivore, fungivore and herbivore). The patterns of soil energy pathways were similar whether expressed as relative abundance or relative biomass. However, the percentage values of bacterivorous biomass in each type of ecosystem exceeded the percentage values of their abundance. Specifically, relative abundance of bacterivorous nematodes was similar among ecosystems but mean values of biomass were greatest in grassland and similarly less in cropland and forest ecosystems. By contrast, both relative abundance and biomass of fungivorous nematodes decreased progressively from forest to cropland and grassland ecosystems. The opposite pattern across ecosystems was observed for both relative abundance and biomass of herbivorous nematodes. We conclude that energy pathways are bacterial-dominated in all of the ecosystems whether expressed as abundance or biomass. Fungal and herbivorous pathways are second in dominance in forest and grassland ecosystems, respectively. The relative size of the fungal-based energy pathway suggests a gradient of resource quality among ecosystems. We suggest that herbivorous-based energy pathways are more important in grassland ecosystems than reported previously.