Biopore history determines the microbial community composition in subsoil hotspots
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Biopores are hotspots of nutrient mobilisation and shortcuts for carbon (C) into subsoils. C processing relies on microbial community composition, which remains unexplored in subsoil biopores. Phospholipid fatty acids (PLFAs; markers for living microbial groups) and amino sugars (microbial necromass markers) were extracted from two subsoil depths (45–75 cm ; 75–105 cm) and three biopore types: (I) drilosphere of Lumbricus terrestris L., (II) 2-year-old root biopores and (III) 1.5-year-old root biopores plus six 6 months of L. terrestris activities. Biopore C contents were at least 2.5 times higher than in bulk soil, causing 26–35 times higher Σ PLFAs g-1 soil. The highest Σ PLFAs were found in both earthworm biopore types; thus, the highest soil organic matter and nutrient turnover were assumed. Σ PLFAs was 33% lower in root pores than in earthworm pores. The treatment affected the microbial community composition more strongly than soil depth, hinting to similar C quality in biopores: Gram-positives including actinobacteria were more abundant in root pores than in earthworm pores, probably due to lower C bioavailability in the former. Both earthworm pore types featured fresh litter input, promoting growth of Gram-negatives and fungi. Earthworms in root pores shifted the composition of the microbial community heavily and turned root pores into earthworm pores within 6 months. Only recent communities were affected and they reflect a strong heterogeneity of microbial activity and functions in subsoil hotspots, whereas biopore-specific necromass accumulation from different microbial groups was absent.
KeywordsAmino sugars Biomarkers Carbon sequestration Carbon turnover Detritusphere Drilosphere Phospholipid fatty acids
This study was supported by the German Research Foundation, grants DFG KU 1184/29-1 and INST 186/1006-1. We would like to thank PD Dr. Timo Kautz and the colleagues from the Institute of Organic Agriculture of the University of Bonn for establishing and managing the field trial Klein-Altendorf, as well as the Centre for Stable Isotope Research and Analysis, Goettingen, for δ13C determination.
Compliance with ethical standards
Role of the funding source
DFG KU 1184/29-1.
Conflict of interest
The authors declare that they have no conflicts of interest.
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