Impact of Nitrogen Deposition on Carbon and Nitrogen Cycling in Peatlands Under Land‐Use Change

ABSTRACT Increasing nitrogen (N) deposition significantly alters carbon and N dynamics in peatlands by affecting microbial processes, enhancing greenhouse gas emissions and nutrient leaching into adjacent waters. However, how peatland conversion for agriculture and forestry influences the fate of added N under elevated atmospheric deposition remains unclear. We conducted a 30‐day laboratory incubation experiment using 0–10 cm peat samples, extracted from a near‐pristine bog (NP), a spruce forest (SF), and an intensively managed meadow (IM), all sharing a common origin. To simulate different N loads, three levels of ammonium nitrate (NH 4 NO 3 ) addition (0, 25, and 50 kg N ha −1 ) were applied. Under increased N addition, NP exhibited low net N 2 O production despite increased NH 4 + and NO 3 − availability, likely due to anoxic conditions favoring complete denitrification. In contrast, SF showed characteristics of advanced N saturation, with excess N primarily accumulating as NO 3 − and being released as N 2 O, and limited microbial response, despite partial retention in dissolved organic N. IM, likely at an early stage of N saturation, exhibited increased net N 2 O production but limited NO 3 − accumulation, possibly due to more favorable pH and higher microbial biomass. However, net CO 2 production remained unaffected, suggesting C quality limitation indicated by low C/N ratio and high HI value. These contrasting responses underscore that over 60 years of land use and management strongly influenced peat chemical and microbial properties, thereby altering N retention and loss pathways under N enrichment. These findings highlight the need for sustainable, land‐use‐specific management strategies in degraded peatlands to mitigate the resulting N loss risks under increasing atmospheric N deposition.