The ecological niche is a fundamental concept to understand species coexistence in natural communities. The recently developed framework of the multidimensional stoichiometric niche (MSN) characterizes species niches using chemical elements in living organisms. Despite the fact that living organisms are composed by multiple elements, stoichiometric studies have so far mostly focused on carbon (C), nitrogen (N), and phosphorus (P), and therefore a quantitative analysis of the dimensionality of the MSN in living organisms is still lacking, particularly for animals. Here we quantified ten elements composing the biomass of nine soil animal taxa (958 individuals) from three trophic groups. We found that all ten elements exhibited large variation among taxa, which was partially explained by their phylogeny. Overlaps of MSNs among the nine soil animal taxa were relatively smaller based on ten elements, compared with those based on only C, N, and P. Discriminant analysis using all ten elements successfully differentiated among the nine taxa (accuracy: 90%), whereas that using only C, N, and P resulted in a lower accuracy (60%). Our findings provide new evidence for MSN differentiation in soil fauna and demonstrate the high dimensionality of organismal stoichiometric niches beyond C, N, and P.

Before elemental analyses, each individual animal was freeze-dried for 72 h. Specimens larger than 20 mg were grounded individually into a homogenous powder using a bead mill homogenizer (Bead Ruptor 12, Omni International, USA). Approximately 2 mg of powder was used to quantify C and N contents (percentage of dry mass) using a vario EL cube CHNOS Elemental Analyzer (Elementar Analysensysteme GmbH, Germany). Another ~2 mg of powder was digested with nitric acid (2 ml and 70% by weight) and used to quantify the contents of Ca, Cu, K, Mg, Mn, Na, P, and Zn using an iCAP 6301 ICP-OES Spectrometer (Thermo Fisher, USA). During the grinding process, a fraction of powder cannot be retrieved and thus lost, making it difficult to quantify all elements for small individuals. Thus, for individuals smaller than 20 mg, we used the whole body or pooled a number of individuals from the same sampling plot (thus forming an “aggregated individual”) to measure either the C and N contents or contents of other eight elements.