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Abstract:
Although microbial-derived carbon (C) inputs to soil are increasingly acknowledged as an important
source of soil organic matter (SOM), the contribution of different microbial compounds to soil C
transformation and their role in aggregation remain poorly understood. This study assessed the
contribution of soil fungi and bacteria to the decomposition of maize residues by means of extracted
phospholipid fatty acids (PLFAs) and 13C in specific PLFAs and investigated the importance of soil fungi in
the formation of macroaggregates. Sieved soil (<250 mm) was incubated for 28 days with and without
addition of maize residues and fungicide. Our results show a significant relation between the amount of
fungal PLFA 18:2v6 and the amount of macroaggregates. Further, the amount of macroaggregates was
higher in the treatment with the higher amount of maize-derived C in fungal PLFA, suggesting that fungal
activity is important for macroaggregate formation. Based on an increased incorporation of maizederived
C into actinomycetes in fungicide treatments, we suggest that actinomycetes may take over the
role of soil fungi in the decomposition of SOM. Our study underpins the important role of soil fungi in the
decomposition of organic matter and structure formation in the soil, and shows that during inhibition of
soil fungi other soil microorganisms are promoted and adopt their function in the soil food web.
