Trophic shift of soil animal species with forest type as indicated by stable isotope analysis

Abstract

Anthropogenic land use shapes the dynamics and composition of central European forests and changes the quality and availability of resources of the decomposer system. Th ese changes likely alter the structure and functioning of soil animal food webs. Using stable isotope analysis ( 13 C, 15 N) we investigated the trophic position and resource use of soil animal species in each of four forest types (coniferous, young managed beech, old managed beech and unmanaged beech forests) across three regions in Germany. Twenty-eight species of soil invertebrates were analyzed covering three consumer levels and a representative spectrum of feeding types and morphologies. Data on stable isotope signatures of leaf litter, fi ne roots and soil were included to evaluate to which extent signatures of soil animals vary with those of local resources. Soil animal δ 15 N and δ 13 C signatures varied with the respective signatures of leaf litter and fi ne roots. After calibration to leaf litter signatures, soil animal stable isotope signatures of the diff erent beech forests did not diff er signifi cantly. However, thick leaf litter layers, such as those in coniferous forests, were associated with low animal stable isotope signatures presumably due to reduced access of decomposer animals to root-derived resources, suggesting that the decomposer food web is shifted towards leaf litter based energy pathways with the shift aff ecting all consumer levels. Variation in stable isotope signatures of soil animal species with litter quality parameters suggests that nutrition of third level but not fi rst and second level consumers is related to litter quality, potentially due to microorganisms locking up litter resources thereby hampering their propagation to higher trophic levels.

Shifts in trophic interactions with forest type in soil generalist predators as indicated by complementary analyses of fatty acids and stable isotopes

“…Trophic niche variation with forest type was more pronounced in L. mutabilis than in L. crassipes presumably due to variations in the effect of habitat structure with lithobiid body size. Thickness of the litter layer of beech forests is known to vary with forest age but is generally lower as compared to spruce forests where litter decomposes slowly (Swift et al , Scheu et al , Klarner et al ). This also affects decomposer animals feeding on litter (primary decomposers) or grazing on litter inhabiting microorganisms (secondary decomposers).…”

“…Also, microbial communities change with forest management as indicated by increasing fungal‐to‐bacterial phospholipid fatty acid (PLFA) ratios in older stands (Pennanen et al , Moore‐Kucera and Dick ). These changes are likely to propagate into higher trophic levels which is supported by decomposer animal communities responding sensitively to forest age and type (Scheu et al , Cesarz et al , Digel et al , Klarner et al ).…”

Regional Conditions and Land-Use Alter the Potential Contribution of Soil Arthropods to Ecosystem Services in Grasslands

“…Physiological traits of plants in different regions (Chevillat et al, 2005;Kuptz et al, 2011) and regional differences in nitrogen deposition, precipitation, mean temperature (Boeckx et al, 2005), or land-use history (Kleinebecker et al, 2014) may lead to systematic differences between study regions. Studies in forest ecosystems have shown that both leaf litter and fine roots are suitable basal resources to calibrate signatures of animal species (Klarner et al, 2014). In grassland ecosystems, plant litter is not very abundant, as the limited amount of grass or herb litter is rapidly incorporated into the soil by macrodecomposers (e.g., earthworms).…”

“…This, for example, has been demonstrated for the effects of fertilization (King and Hutchinson, 1980;Birkhofer et al, 2008), grazing (King and Hutchinson, 1976;Ponge et al, 2015), and cutting (Jensen et al, 1973;Lemanski and Scheu, 2015). As a consequence, critical shifts within soil food webs may occur (Haubert et al, 2009;Birkhofer et al, 2011;Crotty et al, 2014;Klarner et al, 2014). Unfortunately, the greening measures recently implemented by the European Commission to protect and maintain species-rich permanent grasslands do not take such human interventions into account (Common Agricultural Policy 2013: Regulation No 1307.…”

Decreasing Stoichiometric Resource Quality Drives Compensatory Feeding across Trophic Levels in Tropical Litter Invertebrate Communities

“…Moreover, research on terrestrial systems, and especially detritus-based systems, has traditionally been underrepresented (Sterner and Elser 2002), although their resource C∶N ratios tend to deviate strongly from those of their heterotrophic consumers (Elser et al 2000). In recent years, this gap has been reduced by studies on the structure of soil and litter food webs Klarner et al 2014) and the effects of basal resource stoichiometry on consumer biomass densities (Ott et al 2014a). Nevertheless, a broader perspective of resourcequality effects on various consumer community aspects across trophic levels is still lacking.…”