Resource quality in a soil food web

Abstract

Numerous factors affect the resource quality of detritus, including N content, lignin content, C 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 two components of resource quality were manipulated. Two different N concentrations (2% and 1%, corresponding to C/N ratios of 21 and 41) were crossed with two different C labilities (sugar/cellulose/lignin ratios of 1.6:5.2:1 and 0.6:2.4:1). The responses of nematodes from a coastal prairie soil to the artificial substrates were measured over 2 months in two separate experiments. Effects of resource quality were more pronounced in the first experiment, in which a larger quantity of substrate was added to microcosms. Bacterivorous nematodes were 3.4 and 1.2 times more abundant in high N treatments than low N treatments in the first and second experiments, respectively. Carbon lability had a smaller effect on bacterivores in the first experiment and no effect in the second. Fungivorous nematodes were more abundant in high labile C treatments in the first experiment, but not the second. Fungivores did not respond to different N levels. Despite previous findings that soil bacteria are primarily C limited, N appears more limiting than labile C for the bacterial channel of this soil food web, but other aspects of resource quality that correlate with N content may have driven treatment differences.