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Abstract:
In this study, drivers for ammonia-oxidation and the related microbial communities (ammonia-oxidizing
bacteria and archaea) were investigated in grassland soils on the local as well as on the regional scale
focusing on the role of land-use intensity (LUI). To this end, 150 sites from three distinct regions across
Germany were selected, covering the whole range of LUI levels (from natural grasslands up to intensive
managed meadows). Furthermore, the role of contrasting soil types was analyzed in one of the regions
(high vs low organic matter content) for ammonia-oxidation. We revealed a significant increase in potential
nitrification rates and abundance of ammonia-oxidizing microbes at two sites on the local level
from extensively to intensively managed sites, which indicates that the response pattern of ammoniaoxidizing
microbes in grassland soils is likely triggered to a large extent by LUI. However at a third site,
where two different soil types were investigated, no correlation between LUI and potential nitrification
rates was observed, and only a site-specific effect was apparent. At this site, on the one hand the specific
soil type (Histosol) and the related continuous nutrient mobilization from the former peat matrix, as well
as the high groundwater level, which could induce a high abundance of methane- oxidizing microbes in
the top soil, may be of greater importance as a driver for potential nitrification rates and abundance of
ammonia- oxidizing microbes than LUI. On the other hand, the mineral soils of this site were characterized
by extreme water shortage, which may also explain the lack of potential nitrification and the
abundance of ammonia-oxidizing bacteria and archaea. Thus any extrapolation of local data to regional
predictions must be made with care, as factors other than LUI may be of importance if the nitrification
potential of a soil is to be described.
