N-process-level regulation of nitrogen trace gas flux in Hawaiian montane rainforest

Nutrient amendments and inhibition experiments were used to evaluate factors controlling the production of N trace gases in soils. Sampling was conducted at five sites which form a 200−4.5 × 106 y chronosequence in Hawaiian montane rainforest. The pattern of nitric oxide (NO) and nitrous oxide (N2O) flux from soils in the laboratory was similar to that observed in the field, with emissions of NO + N2O increasing with soil age. Autoclaving of soils indicated that there was little or no abiological production of N2O. The response of N2O and NO flux to sieving and acetylene addition is consistent with N trace gas production being primarily denitrification-based in all but the oldest site, where nitrification-based production is significant. All the soils had increased emissions of N2O in response to additions of N. Soils from the 185,000-y-old Kohala site, however, had the lowest proportional N2O response, did not have elevated NO emissions in response to addition of N, and had a small, but significant NO response to addition of carbon. This intermediate-age site represents a transition stage in soil development in which N trace gas production is the least limited by N-availability.