Variation in trophic niches of oribatid mites in temperate forest ecosystems as indicated by neutral lipid fatty acid patterns

Abstract

Shifting of trophic niches of soil microarthropods may allow them to adapt to changing resource conditions as induced by global change processes. However, the capability of microarthropods to shift their trophic niches is little studied. Whereas some studies based on stable isotopes ( 15 N/ 13 C) point to distinct and narrow trophic niches, others indicate that trophic niches are plastic. Here, we investigated shifts in trophic niches of oribatid mites (Oribatida, Acari), a major soil detritivore microarthropod group, due to forest management, i.e., plantation of beech and spruce forests in Central Europe, using neutral lipid fatty acid (NLFA) markers. Due to differential microbial communities, we expected a fungibased diet of oribatid mites in beech forest, but more bacterial contributions to the diet in spruce forest. Supporting these hypotheses, NLFA markers indicated that the trophic niches of each of the studied oribatid mite species differed between beech and spruce forests and shifted from feeding predominantly on litter and fungi in beech forest to more intensively feeding on bacteria in spruce forest. Oribatid mite species with the most pronounced differences in trophic niches included Achipteria coleoptrata, Eupelops hirtus, Eupelops plicatus and Liacarus xylariae, which had been classified as primary or secondary decomposers in previous studies. Overall, the results indicate that the ability of oribatid mite species to colonize different habitats and ecosystems is due to their ability to adjust their diet, i.e., to trophic plasticity. Changes in trophic niches in each of the studied oribatid mite species suggest that detritivores in soil may better cope with future changes in environmental conditions and associated changes in resource composition than species above the ground.

Stable isotopes of amino acids indicate that soil decomposer microarthropods predominantly feed on saprotrophic fungi

“…In most species, the contribution of bacterial eAAs was higher in spruce than in beech forests, although differences in the use of basal resources between forest types were not significant. A similar study investigating differences in trophic niches of Oribatida between beech and spruce forests using the neutral lipid fatty acid composition also found a shift of many Oribatida species toward the bacterial energy channel in spruce forests (Maraun et al 2020). They concluded that Oribatida may shift trophic niches according to resource availability and that this trophic plasticity may facilitate coping with changing environmental conditions.…”

“…In feeding studies, both Collembola and Oribatida can survive, grow, and reproduce on a variety of food sources (Ruess et al 2005, Endlweber et al 2009, Heethoff and Scheu 2016), and Oribatida therefore have been termed “choosy generalists” (Schneider and Maraun 2005). In natural habitats, trophic niches of Collembola and Oribatida are assumed to be rather conserved among species (Schneider et al 2004, Chahartaghi et al 2005, Ferlian et al 2015, Potapov et al 2016 a ), but may also shift, for example, in different cropping systems (Li et al 2020) and forest types (Krause et al 2019, Maraun et al 2020). In part, contrasting findings may be attributed to the use of different methods; while bulk stable isotope analyses mainly identify trophic positions of species, they only provide limited insight into the basal resource utilized, and fatty acid analyses only allow characterizing relative differences in basal resources (Ruess et al 2005, Ruess and Chamberlain 2010, Kühn et al 2019).…”

“…Higher management intensity, disturbance, and nutrient inputs as well as acidic conditions have been assumed to favor the bacterial energy channel, whereas the fungal energy channel has been proposed to be favored by lower levels of disturbance, higher pH, and higher C‐to‐N ratios of resources (Moore 1994, Wardle 2002). Conform to these assumptions, in leaf litter of beech forests the fungal energy channel predominates, whereas in leaf litter of spruce forests the bacterial energy channel gains in importance (Pollierer et al 2015, Maraun et al 2020). Further, the fungal energy channel has been assumed to be favored by litter materials, whereas the bacterial channel has been suggested to benefit from root‐derived resources and therefore to predominate in the rhizosphere (Scharroba et al 2012, Moll et al 2015).…”

Cheliceral chelal design in free-living astigmatid mites

“…What is stable, for at least oribatids, even in the face of trophic plasticity (i.e., adjustment of their exact diet in different habitats and ecosystems Maraun et al. 2020 ) is their role (usually detritivore in this instance). So, does one fit species to a pre-existing trophic classification (i.e., a set of roles), or does one let the design of mites with known lifestyles define the appropriate trophic dimensions for any functional groups?…”

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

“…However, forest types vary in litter quality and microbial communities (Albers et al, 2004;Lu and Scheu, 2021), and different resource availability across forest types may induce changes in the use of basal resources and trophic positions of Oribatida species (Krause et al, 2019;Maraun et al, 2020). To date, only a few Oribatida species have been shown to respond flexibly by adjusting their trophic positions across land-use systems, but no agreement has been reached why some Oribatida species change their trophic niches with forest type while others do not (Gan et al, 2014;Krause et al, 2019;Maraun et al, 2020). The contrasting response calls for more detailed analyses including a wide range of Oribatida species with different traits across ecosystems.…”