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

Jan Frouz,Josef Starý,Petr Baldrián,Tomáš Cajthaml,Karel Tajovský,Jan Materna,Peter C De Ruiter,Ladislav Háněl,Sina Adl,Václav Pižl,Alena Nováková,Elisa Thébault,Luís A Amaral

doi:10.1371/journal.pone.0079694

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.

Highlights

Mechanisms behind ecological succession have been a lasting topic in ecosystem studies [1,2]
The decomposer food web substantially affects the nutrient status of soil [6,7], and changes in the decomposer food web may have an effect on plant succession [8,9]
The decomposer food web processes a majority of organic matter produced in terrestrial ecosystems [10]

Summary

Introduction

Mechanisms behind ecological succession have been a lasting topic in ecosystem studies [1,2]. Since the nutritional value of micro-organisms is much higher than that of dead plant material, they become crucial food source for other organisms in decomposer food webs [10,11] In this context, the bacterial and fungal pathways of the decomposer food web require particular attention in soil food web studies [12]. The soil biota substantially modifies its environment by bioturbation, aggregate formation, aeration and soil mixing [7,10] Some soil invertebrates, such as earthworms, may have strong engineering effects on soil and may completely alter humus forms, causing dramatic shifts in soil properties [7,10]. The consequences of these engineering effects on soil food web structure are still largely unknown

Methods

Results

Conclusion