Resource quality in a soil food web: Is nitrogen or labile carbon more important for soil nematodes?

Detritus is generally an abundant yet poor quality resource; detrital food webs may therefore be more sensitive to resource quality than resource quantity. Numerous factors affect detritus quality, including nitrogen content, lignin content, carbon lability, and concentrations of tannins or phenols. Although many studies have examined the responses of detrital food webs to resources of differing quality, few have independently varied different components of resource quality. I measured the response of soil nematodes to artificial substrates in which I manipulated two components of resource quality. I crossed two different nitrogen concentrations (carbon : nitrogen ratios of 21 and 41) with two different carbon labilities (sugar : cellulose : lignin ratios of  1.6 : 5.2 : 1 and 0.6 : 2.4 : 1). I measured the responses of nematodes from a grassland soil to the artificial substrates over two months. Bacterivorous nematodes were 1.2 to 3.4 times more abundant in high nitrogen treatments than low nitrogen treatments. Carbon lability had a smaller effect on bacterivores in one experiment and no effect in a second. Fungivorous nematodes were also more abundant in high nitrogen treatments in experiment one, although not experiment two. Fungivores did not respond to different carbon lability. Nitrogen appears more limiting for the bacterial channel of this soil food web than labile carbon, despite previous findings that soil bacteria are primarily carbon limited. The fungal channel appears less affected by resource quality, although the experiment may have been too short to observe fungivore responses.