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

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 (NH₄NO₃) addition (0, 25, and 50 kg N ha⁻¹) were applied. Under increased N addition, NP exhibited low net N₂O production despite increased NH₄⁺ and NO₃⁻ availability, likely due to anoxic conditions favoring complete denitrification. In contrast, SF showed characteristics of advanced N saturation, with excess N primarily accumulating as NO₃⁻ and being released as N₂O, and limited microbial response, despite partial retention in dissolved organic N. IM, likely at an early stage of N saturation, exhibited increased net N₂O production but limited NO₃⁻ accumulation, possibly due to more favorable pH and higher microbial biomass. However, net CO₂ 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.