Untitled

Abstract

C(). H• anti CH4 uptake by the soil of an arable field and a forest soil (360 m apart) was measured by a closed-chamber method in temperate Japan for about 1 year. CO production observed was exponentially dependent on top soil temperature. CO production was greater in the forest soil than in the soil of the arable field at the same soil temperature. (Gross) CO H•, and CH4 deposition velocities ranged from 0 to 7x 10-:, from 0 to 9x 10-24-2-1 ß and from 0.•)5 to 0.1X 10 cm s •n the arable field and from 1.5 to 4.5x 10-• , 5 to 8X 10-• , and from 0.3 to 0.6X 10-: cm s-• in the forest, respectively. Variations in the deposition vel()cities were smaller in the forest than in the arable field and corresponded to variations in soil moisture in the top soil. Seasonal trends caused by the variation in temperature were observed only for CH4 deposition, reflecting the clear dependence on soil temperature. Application of dead plant material to the arable field led to acceleration of CO and H: deposition onto the soil. The deposition velocities of GO and It: were positively correlated (n=36, R-'*=0.881, p<0.0001' R z* is the coefficient of determination adjusted by R =0.408, p<0.000l) in the forest, degrees of freedom) in the arable field and (n=37, suggesting diffusion c()ntrol on their deposition velocities. 1. Uptake of CO. HA. and CH4 is caused by the oxidation of the gases by' s()il bacteria or enz3mes. Several types of methanotrophs oxidize CHz [e.g., King, 1992' Conrad, 1996]. Various bacteria oxidize CO [B&tard and IO•owles, 1989; Bender and Courad, 1994a]. Among them, nitriflers are reported to be the most probable oxidizers of atmospheric CO [Jones and Moriia, 1983' Conrad. 1988' Moxley and Smith, 1998a]. H2 consumption by soil is thought to be due to extracellular enzymes in the soil [Cozzrad e! al., 1983]. Generally. atmospheric gases are absorbed or emitted from soil depending on the net balance between production and uptake by the soil. CO production obeys zero-order kinetics; Copyright 20()0 by the American Geophysical Union. Paper numbc• 199:)JD)01156. 0 ..... o/)/1999JD901156509.00 uptake obeys first-order kinetics with respect to gas concentration. If there is no transport in the soil, the compensation (equilibrium) concentration of the gas in the soil, C,,,4, is determined by the balance between the in situ uptake rate on •', .... • (s •). and the in situ production rate on the spatial base, P ........ as follows: Pii'I sltu Ccq = (1) /d 1,/m s•tu where ['7• is air-filled porosity (volumetric content of gas phase). If ('•,t > (',t,, (atmospheric concentration), the gas is emitted from the soil; if C•q < C,tm the gas is absorbed by the soil [Conrad a,d Seiler, 1985a]. Detailed formulations are shown by Yo,emura el aL [2000]. Production rates of ('}t•, and H, in aerated soils are low, and Qq is very low in comparison to F()r ('0. simultaneous processes of production and uptake (•ccur in s(•il. CO is thought to be produced abiologically from organic matter in a temperature sensitive reaction [Conrad and Soild...