Soil Food Web Changes during Spontaneous Succession at Post Mining Sites: A Possible Ecosystem Engineering Effect on Food Web Organization?

Abstract

Parameters characterizing the structure of the decomposer food web, biomass of the soil microflora (bacteria and fungi) and soil micro-, meso- and macrofauna were studied at 14 non-reclaimed 1– 41-year-old post-mining sites near the town of Sokolov (Czech Republic). These observations on the decomposer food webs were compared with knowledge of vegetation and soil microstructure development from previous studies. The amount of carbon entering the food web increased with succession age in a similar way as the total amount of C in food web biomass and the number of functional groups in the food web. Connectance did not show any significant changes with succession age, however. In early stages of the succession, the bacterial channel dominated the food web. Later on, in shrub-dominated stands, the fungal channel took over. Even later, in the forest stage, the bacterial channel prevailed again. The best predictor of fungal bacterial ratio is thickness of fermentation layer. We argue that these changes correspond with changes in topsoil microstructure driven by a combination of plant organic matter input and engineering effects of earthworms. In early stages, soil is alkaline, and a discontinuous litter layer on the soil surface promotes bacterial biomass growth, so the bacterial food web channel can dominate. Litter accumulation on the soil surface supports the development of the fungal channel. In older stages, earthworms arrive, mix litter into the mineral soil and form an organo-mineral topsoil, which is beneficial for bacteria and enhances the bacterial food web channel.

Earthworms affect growth and competition between ectomycorrhizal and arbuscular mycorrhizal plants

“…The effect of the earthworms on EcM fungi was previously demonstrated based on the ergosterol content (as a unique biomarker of EcM fungal biomass) of the soil (Frouz et al. ). Frouz et al.…”

“…Frouz et al. () reported a decrease in soil ergosterol content with the appearance of earthworms and a simultaneous shift in the fungal–bacterial ratio toward the prevalence of bacteria.…”

“…The effect of the earthworms on EcM fungi was previously demonstrated based on the ergosterol content (as a unique biomarker of EcM fungal biomass) of the soil (Frouz et al 2013). Frouz et al (2013) reported a decrease in soil ergosterol content with the appearance of earthworms and a simultaneous shift in the fungalbacterial ratio toward the prevalence of bacteria.…”

“…Although both pathways have received considerable attention, their combination remains underexplored. Here, we investigate interactions between mycorrhizal fungi, which are dominant root symbionts contributing to plant-soil feedback (Frouz et al 2015), and earthworms, which help mediate the effect of plant litter on soil quality (Frouz et al 2013).…”

Spontaneous establishment of late successional tree species English oak (Quercus robur) and European beech (Fagus sylvatica) at reclaimed alder plantation and unreclaimed post mining sites

“…(Ponge, 2003). Earthworms also contribute to shifting the decomposer food web from a fungal-driven one to a bacteriadriven one (Frouz et al, 2013b). All these changes may promote grasses and hence increase competition between grasses and seedlings.…”