Linking aboveground and belowground food webs through carbon and nitrogen stable isotope analyses

Abstract

Carbon and nitrogen stable isotope ratios (d 13 C and d 15 N) have been used for more than two decades in analyses of food web structure. The utility of isotope ratio measurements is based on the observation that consumer d 13 C values are similar (<1& difference) to those of their diet, while consumer d 15 N values are about 3& higher than those of their diet. The technique has been applied most often to aquatic and aboveground terrestrial food webs. However, few isotope studies have examined terrestrial food web structure that includes both above-and belowground (detrital) components. Here, we review factors that may influence isotopic signatures of terrestrial consumers in above-and belowground systems. In particular, we emphasize variations in d 13 C and d 15 N in belowground systems, e.g., enrichment of 13 C and 15 N in soil organic matter (likely related to soil microbial metabolism). These enrichments should be associated with the high 13 C ($3&) enrichment in belowground consumers relative to litter and soil organic matter and with the large variation in d 15 N ($6&) of the consumers. Because such enrichment and variation are much greater than the trophic enrichment generally used to estimate consumer trophic positions, and because many general predators are considered dependent on energy and material flows from belowground, the isotopic variation in belowground systems should be taken into account in d 13 C and d 15 N analyses of terrestrial food webs. Meanwhile, by measuring the d 13 C of key predators, the linkage between above-and belowground systems could be estimated based on observed differences in d 13 C of primary producers, detritivores and predators. Furthermore, radiocarbon ( 14 C) measurements will allow the direct estimation of the dependence of predators on the belowground systems.

Isotopic niche (δ13С and δ15N values) of soil macrofauna in temperate forests

“…A similar distribution of δ 13 C values of predators and saprophages (Fig. (B)) confirms that a detrital energy pathway predominates at the upper levels of soil food webs . Phytophages also participate in the energy budget of predatory invertebrates, which are therefore slightly depleted in 13 C compared with saprophages.…”

“…4(B)) confirms that a detrital energy pathway predominates at the upper levels of soil food webs. [52] Phytophages also participate in the energy budget of predatory invertebrates, which are therefore slightly depleted in 13 C compared with saprophages. Nevertheless, a unimodal distribution of δ 13 C values in predators suggests that detritus-based and plant-based energy pathways are tightly linked at higher levels of soil food webs.…”

Feeding habits of Hymenoptera and Isoptera in a tropical rain forest as revealed by nitrogen and carbon isotope ratios

“…and C. bengalense. This result suggests that the prey flies may depend on dead body or faeces of consumers at higher trophic level or on soil organic matters, both of which could exhibit high values of d 15 N (Hyodo et al, 2010a).…”

Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition

“…5). Direct feeding on plant tissue results in an enrichment in 13 C of herbivores by 0.5-1‰, whereas microbivores feeding on detritus typically are enriched by 3-4‰ as compared to leaf litter (Hobbie et al, 2007;Hyodo, Kohzu & Tayasu, 2010a;Potapov et al, 2013;Samoylova & Tiunov, 2017;Spence & Rosenheim, 2005; see Section VI). This 'detrital shift' allows distinguishing decomposers and herbivores ([2] and [3] in Fig.…”