Abstract It has been well documented by short-term artificial experiments that the CH
4 uptake is inhibited by N input, especially NH
4 p+-N input. To investigate the effect of the natural N input by throughfall and other factors on the CH
4 uptake in forest soils, we measured the CH
4 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 NH
4 p+-N and NH
3 p--N inputs ranged from 1.3 to 6.9 kg N ha
p-1 year
p-1 and from 0.8 to 2.9 kg N ha
p-1 year
p-1, respectively. The NH
4 p+-N input was generally higher than the NH
3 p--N input. Total N input by throughfall amounted to 2.3-9.4 kg N ha
p-1 year
p-1. The highest CH
4 uptake rate occurred within the period from July to September (41-215 μg CH
4 m
p-2 h
p-1) each year at most sites. CH
4 uptake rate was relatively low (~50 μg CH
4 M-2 h
p-1) at northern sites, while a high CH
4 uptake rate was observed throughout the year 100 (? CH
4 m
p-2 h
p-1) at southern sites. The mean CH
4 uptake rates were significantly different among the sites. Cumulative CH
4 uptake ranged from 1.4 to 6.6 kg CH
4 ha
p-1 [184 d]
p-1 with a mean values of 3.22 ± 1.36 kg CH
4 ha
p-1 [184 d]
p-1. Cumulative CH
4 uptake increased with increasing temperature and decreased with an increase in precipitation (Rain), NH
4 p+-N input (TF
NH4) WFPS, soil total C (TC), and total N (TN). There was a quadratic relationship between the CH
4 uptake and NH
3 p--N input (TF
NO3), soil pH, and C / N ratio in soil. A regression equation was obtained as follows to predict the CH
4 uptake in forest soils: Cumulative CH
4 uptake = 0.47 / Rain + 0.38 / TF
NH4 + 0.34 / TC - 0.30 / TF
N03 (
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 CH
4 uptake with precipitation, total carbon content in soil in Hokkaido, Japan.
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