Impact of heavy metal remediation by soil washing with EDTA on carbon turnover - closing the functional link between microorganisms and microarthropods by 13C fatty acids analysis

Heavy metal contamination of soils has a great impact on soil biota and carbon turnover. Assisted soil washing using a chelating agent such as ethylenediaminetetraacetic acid (EDTA) is a potential remediation technique to remove heavy metals (HM). The recovery of the soil biota following EDTA washing and associated impact on the soil carbon cycle were investigated in a pot trial using the HM contaminated soil and two washed variants, one amended with vermicompost and biochar. Carbon stable isotope labelled plant residue was applied as a carbon source. Stable isotopes were measured in the microbial phospholipid fatty acids (PLFA) and total fatty acids (FA) of single microarthropodal groups (Collembola, Gamasina, Oribatida, Astigmata). Plant residue mineralisation and total microbial biomass decreased after soil washing, while fungi profited and carbon uptake into microorganisms was significantly increased. In contrast, the abundance of microarthropods as well as carbon uptake strongly increased coinciding with lower FA content per individuum after remediation. This indicates increased biomass build up and reproduction after soil washing possibly also driven by carbon and nutrient starvation. Response of single microarthropodal groups was strongly governed by life and reproduction strategies, with constant carbon uptake in K-strategist (Oribatida) and higher incorporation of mainly r-strategist (Gamasina, Astigmata and Collembola) after soil washing. Revitalization of the washed soil using vermicompost and biochar amendments fostered microbial biomass which supports its application. • Soil washing increased plant residue 13 C incorporation in microbial PLFA and microarthropodal FA. • 13 C uptake into microarthropodal FA was governed by life and reproduction strategy. • FA pattern of microarthropods was not affected by soil remediation. • 13 C FA pattern was better suited to discover recent food sources.