Directory UMM :Data Elmu:jurnal:S:Soil Biology And Chemistry:Vol32.Issue10.Sep2000:
Soil Biology & Biochemistry 32 (2000) 1383±1392
www.elsevier.com/locate/soilbio
Denitri®cation rates in organic and mineral soils from riparian
sites: a comparison of N2 ¯ux and acetylene inhibition methods
Susan H. Watts*, 1, Sybil P. Seitzinger
Rutgers, The State University of New Jersey, Institute for Marine and Coastal Sciences, P.O. Box 231, New Brunswick, NJ 08903-0231, USA
Received 22 June 1999; received in revised form 15 February 2000; accepted 23 February 2000
Abstract
Denitri®cation rates were measured in relatively dry mineral soils and water-saturated organic soils by both direct N2 ¯ux and
acetylene inhibition methods to compare the relative sensitivity of the two methods and their applicability to dierent soil types
and saturation conditions. The direct N2 ¯ux method, previously used only in submerged sediments, was modi®ed for use in
terrestrial soils. Our experiments demonstrated that the N2 ¯ux method is adaptable for both mineral and water-logged organic
soils, and that denitri®cation rates based on direct N2 ¯uxes can be measured after only 2 days of incubation in most cases. We
used a diusive ¯ux model to separate the portion of total N2 ¯ux attributable to denitri®cation from that due to passive
diusion of atmospheric N2 from soil porespaces. Denitri®cation rate measurements were taken during spring, summer, and fall
seasons using replicate cores from four dierent riparian sites (two with mineral soil, two with organic soil). Rates determined
by N2 ¯ux were 35±130 and 10±245 mmol N mÿ2 hÿ1 for mineral and organic soils, respectively. Those by acetylene inhibition,
for the same sites were one, and sometimes two, orders of magnitude less with rates of 0.1±10 mmol N mÿ2 hÿ1 for mineral soil
and 0.2±3 mmol N mÿ2 hÿ1 for organic soil. This study has demonstrated that denitri®cation measured by acetylene inhibition in
riparian sites may be underestimated by at least an order of magnitude in both mineral and organic soils. 7 2000 Elsevier
Science Ltd. All rights reserved.
Keywords: Denitri®cation; Riparian zone; Organic soil; Mineral soil; Acetylene inhibition; N2 ¯ux
1. Introduction
Denitri®cation is an important component of the
nitrogen cycle that returns to the atmosphere inorganic
nitrogen that resides in the plant and soil pools of terrestrial and aquatic ecosystems. Under low oxygen tension, nitrate (NOÿ
3 ) instead of O2, is used by
denitrifying bacteria as the terminal electron acceptor
for energy production, forming dinitrogen gas and
* Corresponding author. Tel.: +1-915-747-6851; fax: +1-915-7475808.
E-mail address: [email protected] (S.H. Watts).
1
Present address. Department of Biological Sciences, University of
Texas, 500 W. University Avenue, El Paso, TX 79968-0519, USA.
nitrous oxide (N2 and N2O) which are lost to the atmosphere.
Accurate measurements of denitri®cation are important for many studies (e.g. assessing N loss from
N-limited ecosystems or N removal from eutrophied
ecosystems), however, the determination of N2 ¯ux
is dicult to quantify against the large background of
atmospheric N2. Several methods have been developed
to cope with this diculty, but the majority involve an
indirect measurement of denitri®cation rather than the
measurement of actual N2 ¯ux. The acetylene (C2H2)
inhibition method is widely used and is based on the
principle that C2H2 blocks the enzymatic reduction of
N2O to N2, so that accumulated N2O can be measured
instead of N2 (Yoshinari et al., 1977). However, it
adds an inhibitor to the system, and the inhibitor may
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 5 6 - 0
1384
S.H. Watts, S.P. Seitzinger / Soil Biology & Biochemistry 32 (2000) 1383±1392
not always be eective. Furthermore, a number of
speci®c problems are associated with acetylene inhibition, including uneven penetration of acetylene into
soil microsites (Rudolph et al., 1991) and incomplete
inhibition at low soil nitrate concentration (
www.elsevier.com/locate/soilbio
Denitri®cation rates in organic and mineral soils from riparian
sites: a comparison of N2 ¯ux and acetylene inhibition methods
Susan H. Watts*, 1, Sybil P. Seitzinger
Rutgers, The State University of New Jersey, Institute for Marine and Coastal Sciences, P.O. Box 231, New Brunswick, NJ 08903-0231, USA
Received 22 June 1999; received in revised form 15 February 2000; accepted 23 February 2000
Abstract
Denitri®cation rates were measured in relatively dry mineral soils and water-saturated organic soils by both direct N2 ¯ux and
acetylene inhibition methods to compare the relative sensitivity of the two methods and their applicability to dierent soil types
and saturation conditions. The direct N2 ¯ux method, previously used only in submerged sediments, was modi®ed for use in
terrestrial soils. Our experiments demonstrated that the N2 ¯ux method is adaptable for both mineral and water-logged organic
soils, and that denitri®cation rates based on direct N2 ¯uxes can be measured after only 2 days of incubation in most cases. We
used a diusive ¯ux model to separate the portion of total N2 ¯ux attributable to denitri®cation from that due to passive
diusion of atmospheric N2 from soil porespaces. Denitri®cation rate measurements were taken during spring, summer, and fall
seasons using replicate cores from four dierent riparian sites (two with mineral soil, two with organic soil). Rates determined
by N2 ¯ux were 35±130 and 10±245 mmol N mÿ2 hÿ1 for mineral and organic soils, respectively. Those by acetylene inhibition,
for the same sites were one, and sometimes two, orders of magnitude less with rates of 0.1±10 mmol N mÿ2 hÿ1 for mineral soil
and 0.2±3 mmol N mÿ2 hÿ1 for organic soil. This study has demonstrated that denitri®cation measured by acetylene inhibition in
riparian sites may be underestimated by at least an order of magnitude in both mineral and organic soils. 7 2000 Elsevier
Science Ltd. All rights reserved.
Keywords: Denitri®cation; Riparian zone; Organic soil; Mineral soil; Acetylene inhibition; N2 ¯ux
1. Introduction
Denitri®cation is an important component of the
nitrogen cycle that returns to the atmosphere inorganic
nitrogen that resides in the plant and soil pools of terrestrial and aquatic ecosystems. Under low oxygen tension, nitrate (NOÿ
3 ) instead of O2, is used by
denitrifying bacteria as the terminal electron acceptor
for energy production, forming dinitrogen gas and
* Corresponding author. Tel.: +1-915-747-6851; fax: +1-915-7475808.
E-mail address: [email protected] (S.H. Watts).
1
Present address. Department of Biological Sciences, University of
Texas, 500 W. University Avenue, El Paso, TX 79968-0519, USA.
nitrous oxide (N2 and N2O) which are lost to the atmosphere.
Accurate measurements of denitri®cation are important for many studies (e.g. assessing N loss from
N-limited ecosystems or N removal from eutrophied
ecosystems), however, the determination of N2 ¯ux
is dicult to quantify against the large background of
atmospheric N2. Several methods have been developed
to cope with this diculty, but the majority involve an
indirect measurement of denitri®cation rather than the
measurement of actual N2 ¯ux. The acetylene (C2H2)
inhibition method is widely used and is based on the
principle that C2H2 blocks the enzymatic reduction of
N2O to N2, so that accumulated N2O can be measured
instead of N2 (Yoshinari et al., 1977). However, it
adds an inhibitor to the system, and the inhibitor may
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 5 6 - 0
1384
S.H. Watts, S.P. Seitzinger / Soil Biology & Biochemistry 32 (2000) 1383±1392
not always be eective. Furthermore, a number of
speci®c problems are associated with acetylene inhibition, including uneven penetration of acetylene into
soil microsites (Rudolph et al., 1991) and incomplete
inhibition at low soil nitrate concentration (