Influence of different litter quality on the abundance of genes involved in nitrification and denitrification after freezing and thawing of an arable soil

Due to disruption of soil aggregates and cell lysis and the subsequent release of organic C and N, increased microbial N transformation processes can be observed after freeze-thaw cycles. In a microcosm study, we investigated the influence of plant residues with different C/N ratios (lucerne-clover-grass-mix and wheat straw) on N transformations and the abundance pattern of the corresponding functional genes in an arable soil after freezing and thawing. Unfrozen soil samples, continuously incubated at 10°C, served as control. Concentration of soil NH₄⁺, NO₃^-, and water-extractable organic C (WEOC) as well as genes involved in nitrification and denitrification, quantified by real-time PCR, were determined before freezing and 1,3, and 7 days after thawing. The amounts of inorganic N and WEOC as well as the investigated gene abundance pattern did hardly differ between control samples and samples subjected to freezing and thawing that have been amended with straw. In contrast, clear alterations of the measured parameters and abundances were observed after freezing and thawing in samples being amended with the lucerne-clover-grass-mix compared to the control samples.