Nitrification is the microbial oxidation of ammonia to nitrate and is a key process in soil nitrogen cycling, affecting nitrogen availability for plants and, indirectly, nitrogen fertilizer losses. In this master's thesis, qPCR was used to study how inter-row management (permanent natural vegetation, PV, vs. cultivated, vegetation-free inter-row space, BC) and vineyard age (7, 12, and 25 years) affect soil physicochemical properties and the abundance of functional nitrifier groups. A one-month incubation experiment further examined how urea fertilization affects the abundance of the total bacterial 16S rRNA gene and the amoA genes of bacteria, archaea, and comammox clades A and B. Organic carbon and nitrogen parameters (Corg, DOC, Ntot, TDN, NH4+) were higher in PV than in BC soil, which also influenced nitrifier gene abundance. Ammonia-oxidizing archaea (AOA) and comammox clade B (ComB) responded more strongly than ammonia-oxidizing bacteria (AOB) and comammox clade A (ComA) to inter-row management and vineyard age, being more abundant mainly in PV and older vineyards. This was reflected in stronger positive correlations with organic carbon (r(AOA) = 0.66, r(ComB) = 0.85) and total nitrogen (r(AOA) = 0.78, r(ComB) = 0.85). AOB and ComA abundance rose sharply after urea addition (+ 2660,8 %, + 350,3 %), consistent with their response to greater mineral nitrogen availability, and confirmed by weaker correlations with organic carbon (r(AOB) = 0.51, p(ComA) ≥ 0.05) and total nitrogen (r(AOB) = 0.43, p(ComA) ≥ 0.05). These results show that inter-row management and vineyard age shape nitrifier gene abundance and composition long-term through soil organic matter accumulation, while short-term urea input selectively favors groups adapted to higher ammonium levels. Sustainable inter-row management can thus support more efficient nitrogen cycling and reduce nitrogen losses to the environment.
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