Nematode food webs associated with native perennial plant species and soil nutrient pools in California riparian oak woodlands

• Nematode metabolic footprints varied with riparian plant community.
• Leaf functional traits affected nematode communities and metabolic footprints.
• The distribution of individual nematode groups varied with soil particle size.

The Coast Range mountains in California (CA), USA, may harbor remnant communities of soil biota that no longer occur in the intensively-managed agricultural valleys nearby. Relationships between nematode communities, riparian vegetation, soil carbon (C) and nitrogen (N) pools, and other soil properties were studied at a reserve managed for biodiversity conservation. Differences between riparian habitats were assessed using nematode community identification and metabolic footprint analysis (a method that evaluates ecosystem functioning based on nematode biomass). Nematode communities and metabolic footprints were compared across 12 riparian sites. Those from the sites with evergreen shrubs had high levels of predators but few prey while communities from under deciduous trees were more metabolically balanced, with high levels of both predators and prey. To examine how leaf functional traits affected nematode community structure, metabolic footprints, and soil C and N pools, a second study focused on two riparian woodland sites. Bacterivore and predator metabolic footprints increased with proximity to the creek-bank, where deciduous trees were prevalent. Leaf litter C:N ratio, soil C:N ratio, and the ratio of predators:prey also varied with plant functional traits. Both the complexity of the nematode communities and soil C storage were higher than in previous studies conducted along riparian corridors within intensive agriculture. In these relatively undisturbed areas, stream hydrology has created a patchy distribution of soil texture classes and woody plant species, which in turn, has resulted in diverse nematode assemblages and soil food webs associated with high levels of soil organic matter.