Effect of moisture, texture and aggregate size of paddy soil on production and consumption of CH4

Effect of moisture,texture and aggregate size of paddy soil on production

and consumption of CH 4

Udo Ja

Èckel,Sylvia Schnell,Ralf Conrad *Max-Planck-Institut fu

Èr terrestrische Mikrobiologie,Karl-von-Frisch-Strasse,D-35043Marburg,Germany Received 8March 2000;accepted 4December 2000

Abstract

Laboratory experiments were conducted to ®nd out under which conditions the soil from Italian rice ®elds could change from a source into

a sink of atmospheric CH 4.Moist (30%H 2O 68%of the maximum water holding capacity (whc))rice ®eld soil oxidized CH 4with biphasic kinetics,exhibiting both a low (145ppmv CH 4)and a high (20,200ppmv CH 4)K m value and V max values of 16.8and 839nmol gdw 21h 21,respectively.The activity with the low K m allowed the oxidation of atmospheric CH 4.Uptake rates of high CH 4concentrations (16.5%v/v)and of O 2linearly decreased with aggregate size of soil between 2and 10mm.Atmospheric CH 4(1.8ppmv)was consumed in soil aggregates ,6mm,but soil aggregates .6mm released CH 4into the atmosphere.Similarly,net uptake of atmospheric CH 4turned into net release of CH 4when the soil moisture was decreased below a water content of about 20%whc.The uptake rate of atmospheric CH 4increased threefold when the soil was amended with sterile quartz sand.Flooded microcosms with non-amended and quartz-amended soil emitted CH 4into the atmosphere.The CH 4emission rate increased when the ¯ux was measured under an atmosphere of N 2instead of air,indicating that 30±99%of the produced CH 4was oxidized in the oxic soil surface layer.Removal of the ¯ood water resulted in increase of CH 4emission rates until a water content of about 75±82%whc was reached,and subsequently in a rapid decrease.However,the soil microcosms never showed net uptake of atmospheric CH 4.Our results show that the microorganisms consuming atmospheric CH 4were inactivated at an earlier stage of drainage than the microorganisms producing CH 4,irrespective of the soil porosity which was adjusted by addition of quartz sand.Hence,it is unlikely that the Italian rice ®elds can act as a net sink for atmospheric CH 4even when drained.q 2001Elsevier Science Ltd.All rights reserved.

Keywords :Methane consumption;Rice ®eld soil;Drainage;Atmospheric CH 4

1.Introduction

The ¯ux of CH 4from rice ®elds into the atmosphere is determined by the balance between CH 4production in the anoxic soil and CH 4oxidation in the oxic soil layers at the surface and around the rice roots.Whereas ¯ooded rice ®elds are an important source of atmospheric CH 4,an important greenhouse gas (Cicerone and Oremland,1988;Crutzen,1995;Watson et al.,1992),rain-fed rice ®elds have been shown to act as a sink except when the soil is saturated with water after rainfall (Singh et al.,1998a).

Many studies have addressed the balance between production and oxidation of CH 4in ¯ooded rice ®elds

(Holzapfel-Pschorn et al.,1985;Schu

Ètz et al.,1989;Denier van der Gon and Neue,1996;Sigren et al.,1997)and have studied the CH 4oxidation process in the oxic soil surface layer and the rhizosphere (Conrad and Rothfuss,1991;

Bosse and Frenzel,1997;Kumaraswamy et al.,1997;Wata-nabe et al.,1997;Gilbert and Frenzel,1998;Bodelier and Frenzel,1999).These studies found that 20±90%of the CH 4produced is oxidized before it reaches the atmosphere.The CH 4emission rate is drastically reduced when ¯ooded rice ®elds are drained due to the decreased production of CH 4(Sigren et al.,1997;Ratering and Conrad,1998).However,it is unclear whether these ®elds can act as a sink for atmo-spheric CH 4upon drainage (Thurlow et al.,1995).

The methanotrophic bacteria in ¯ooded rice soil are exposed to rather high CH 4concentrations in the millimolar range.These methanotrophs are characterized by a rela-tively low af®nity for CH 4,the K m values for CH 4typically being .1m M.On the other hand,methanotrophic bacteria exhibiting much lower K m values,typically 20±200nM (Conrad,1996),consume CH 4at low atmospheric concen-trations.These methanotrophs typically occur in upland soils that consume atmospheric CH 4(Bender and Conrad,1993),but can also be activated in paddy soil (Bender and Conrad,1992).However,the oxidation of atmospheric CH 4

Soil Biology &Biochemistry 33(2001)

965±971

0038-0717/01/$-see front matter q 2001Elsevier Science Ltd.All rights reserved.PII:S0038-0717(00)00248-0

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*Corresponding author.Tel.:149-6421-178801;fax:149-6421-78809.E-mail address:conrad@mailer.uni-marburg.de (R.Conrad).