The Impact of Root-Derived Resources on Forest Soil Invertebrates Depends on Body Size and Trophic Position

Abstract

Forest soil food webs have been assumed to be fueled substantially by root-derived resources. However, until today the flux of root-derived resources into soil animals has been investigated virtually exclusively using isotope labeling experiments, whereas studies on the consequences of disrupting the flux of root-derived resources into the soil animal food web are scarce. We here investigated the importance of root-derived resources for a wide range of soil animals by interrupting the resource flux into the soil of different forest types in Central Europe using a trenching experiment. We recorded the abundance of soil animal taxa varying in body size (micro-, meso-, and macrofauna) 1 and 3 years after root trenching, and quantified changes in biomass, species composition, and trophic shift using stable isotopes and NLFA analysis. Among the microfauna groups studied (trophic groups of Nematoda) only the abundance of plant feeding nematodes showed a trend in being decreased by -58% due to root trenching. Major soil mesofauna groups, including Collembola and Oribatida, suffered to a similar extent from root trenching with their abundance and biomass being reduced by about 30–40%. The soil macrofauna groups studied (Diplopoda, Isopoda, Chilopoda, Araneae, Coleoptera) generally were only little affected by root trenching suggesting that they rely less on root-derived resources than micro- and in particular mesofauna. Notably, the community structure of micro-, meso-, and macrofauna was not affected by root trenching. Further, we observed trophic shifts only in 2 out of 10 investigated species with the shifts generally being only minor. The results indicate that soil animal communities are markedly resilient to deprivation of root-derived resources suggesting that links to root-derived resources are non-specific. However, this resilience appears to vary with body size, with mesofauna including both decomposers as well as predators being more sensitive to the deprivation of root-derived resources than microfauna (except for root feeders) and macrofauna. Overall, this suggests that body size constrains the channeling of energy through soil food webs, with root-derived resources in temperate forests being channeled predominantly via soil taxa of intermediate size, i.e., mesofauna.

High consistency of trophic niches in generalist arthropod species (Oribatida, Acari) across soil depth and forest type

“…In addition to living as predator/scavenger, species such as Oppiella nova , the most abundant soil mesofauna species at our study sites, may also feed on ectomycorrhizal fungi, known to be enriched in 15 N (Potapov & Tiunov, 2016 ; Remén et al, 2008 ). The actual resource used by O. nova and other species of the predator/scavenger guild of Oribatida needs further attention including experiments manipulating the input of root‐derived resources (Bluhm et al, 2021 ).…”

High consistency of trophic niches in soil microarthropod species (Oribatida, Acari) across soil depth and forest type

“…However, some Oribatida species such as Oppiella nova has been suggested to feed on ectomycorrhizal fungi, known to be enriched in 15 N (Remén et al, 2008;. Notably, Oppiella nova was the most abundant soil mesofauna species at our study sites, and the resources used by this species, therefore, need further attention including experiments manipulating the input of root-derived resources (Bluhm et al, 2021).…”

Accelerated temporal turnover of the soil nematode community under alpine grassland degradation

“…For example, plant productivity is controlled by plant‐parasitic nematodes (Guo et al, 2016), and microbial biomass and community composition could be regulated by microbe‐eating nematodes (Jiang et al, 2017). Moreover, soil nematode itself was also a key prey for other soil animals (Bluhm et al, 2021). Thus, nematode was believed to work as a hub of soil food web and serve as an indicator to characterize the functional state of an ecosystem (Bongers & Ferris, 1999).…”