Nitrogen turnover in fresh Douglas fir litter directly after additions of moisture and inorganic nitrogen

Abstract

The effects of wetting and drying and inorganic nitrogen (N) addition on carbon (C) and N turnover in fresh Douglas fir litter (Speuld forest, the Netherlands) were investigated. Litter was incubated for 9 days in the laboratory, receiving different moisture and N addition treatments. Following the additions, a series of reactions were observed of which most notable were a rapid retention of added ammonium and nitrate (NO3-) and a sudden increase in CO2 respiration. For the rewetted-and-moist incubations, respiration levels remained elevated, N was net immobilized and nitrous oxide (N2O) production increased throughout the experiment. About 80% of the NO3- produced was lost again as N2O. In the rewetted-and-dried incubations, respiration decreased during the drying phase; no clear patterns in N mineralization were detected; and N2O production remained at constant levels, but still resulted in gaseous loss for half of the NO3- net produced. The experiments thus revealed two important NO3- sinks in LF1 litter, namely rapid retention of added NO3- and gaseous loss as N2O. The maximum NO3- loss via these sinks was estimated at 2 kg-N ha-1 yr-1, which is small compared to annual NO3- leaching at 90 cm soil depth (31 kg-N ha-1 yr-1).