Effect of nitrogen deposition on CH4 uptake in forest soils in Hokkaido, Japan

Abstract

It has been well documented by short-term artificial experiments that the CH4 uptake is inhibited by N input, especially NH4 p+-N input. To investigate the effect of the natural N input by throughfall and other factors on the CH4 uptake in forest soils, we measured the CH4 uptake rates for 6 months during the snow-free period of the year and N input by throughfall throughout the year at 10 sites in Hokkaido, Japan, from 1997 to 2002. Water filled pore space (WFPS) and pH values in the soils varied widely among the sites (38-93% and 3.9-6.2, respectively). The rates of NH4 p+-N and NH3 p--N inputs ranged from 1.3 to 6.9 kg N hap-1 yearp-1 and from 0.8 to 2.9 kg N hap-1 yearp-1, respectively. The NH4 p+-N input was generally higher than the NH3 p--N input. Total N input by throughfall amounted to 2.3-9.4 kg N hap-1 yearp-1. The highest CH4 uptake rate occurred within the period from July to September (41-215 μg CH4 mp-2 hp-1) each year at most sites. CH4 uptake rate was relatively low (~50 μg CH4 M-2 hp-1) at northern sites, while a high CH4 uptake rate was observed throughout the year 100 (≽ CH4 mp-2 hp-1) at southern sites. The mean CH4 uptake rates were significantly different among the sites. Cumulative CH4 uptake ranged from 1.4 to 6.6 kg CH4 hap-1 [184 d]p-1 with a mean values of 3.22 ± 1.36 kg CH4 hap-1 [184 d]p-1. Cumulative CH4 uptake increased with increasing temperature and decreased with an increase in precipitation (Rain), NH4 p+-N input (TFNH4) WFPS, soil total C (TC), and total N (TN). There was a quadratic relationship between the CH4 uptake and NH3 p--N input (TFNO3), soil pH, and C / N ratio in soil. A regression equation was obtained as follows to predict the CH4 uptake in forest soils: Cumulative CH4 uptake = 0.47 / Rain + 0.38 / TFNH4 + 0.34 / TC - 0.30 / TFN03 (R p2 = 0.74, p = 0.0001). This equation indicates that atmospheric N input into forest soils is one of the main factors that control cumulative CH4 uptake with precipitation, total carbon content in soil in Hokkaido, Japan.