Peaks of in situ N2O emissions are influenced by N2O‐producing and reducing microbial communities across arable soils
Luiz A. Domeignoz‐HortaLaurent PhilippotCéline PeyrardDavid BruMarie‐Christine BreuilFlorian BizouardÉric JustesBruno MaryJoël LéonardAymé Spor
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Abstract Agriculture is the main source of terrestrial N 2 O emissions, a potent greenhouse gas and the main cause of ozone depletion. The reduction of N 2 O into N 2 by microorganisms carrying the nitrous oxide reductase gene ( nosZ ) is the only known biological process eliminating this greenhouse gas. Recent studies showed that a previously unknown clade of N 2 O‐reducers ( nos Z II ) was related to the potential capacity of the soil to act as a N 2 O sink. However, little is known about how this group responds to different agricultural practices. Here, we investigated how N 2 O‐producers and N 2 O‐reducers were affected by agricultural practices across a range of cropping systems in order to evaluate the consequences for N 2 O emissions. The abundance of both ammonia‐oxidizers and denitrifiers was quantified by real‐time qPCR , and the diversity of nosZ clades was determined by 454 pyrosequencing. Denitrification and nitrification potential activities as well as in situ N 2 O emissions were also assessed. Overall, greatest differences in microbial activity, diversity, and abundance were observed between sites rather than between agricultural practices at each site. To better understand the contribution of abiotic and biotic factors to the in situ N 2 O emissions, we subdivided more than 59,000 field measurements into fractions from low to high rates. We found that the low N 2 O emission rates were mainly explained by variation in soil properties (up to 59%), while the high rates were explained by variation in abundance and diversity of microbial communities (up to 68%). Notably, the diversity of the nos Z II clade but not of the nos Z I clade was important to explain the variation of in situ N 2 O emissions. Altogether, these results lay the foundation for a better understanding of the response of N 2 O‐reducing bacteria to agricultural practices and how it may ultimately affect N 2 O emissions.Keywords:
Nitrous oxide
Arable land
Nitrous-oxide reductase
Nitrogen Cycle
Nitrogen Cycle
Cycling
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In grassland ecosystems when ample organic N is present, both, mineralization and nitrification can play an important role in determining fertilizer use efficiency as well as N losses to the environment. Laboratory incubation studies were undertaken in a controlled environment at 20 °C to establish relative potential rates of nitrification and mineral N variation in soil collected from grassland fields. Soil samples of 0—2.5, 2.5—5.0, and 5.0—7.5 cm were collected to examine the depth distribution of mineral N. Mineralization potential was determined from soil without added N while nitrification activity was measured following the addition of NH4+-N during 42 days period. Net mineralization of N ranged from 13 to 64 mg (kg soil)—1. Of the total inorganic N found, more than 50 % was released from the surface 0—2.5-cm and the concentration decreased with depth. In a separate experiment when 15N was used, net mineralization was dominant over immobilization and of the gross mineralization, more than 70 % was released as inorganic N. Nitrification showed an initial lag phase, a maximum rate phase and a reduced rate phase. The maximum rate of nitrification ranged from 3.3 to 7.5 mg (kg soil)—1 day—1 being greatest in the 0—2.5 cm depth. The nitrification rate decreased and the delay phase increased with soil depth. During the study, 50 to 60 % of added NH4+-N was converted into NO3—-N indicating the presence of active nitrifiers and a large potential for nitrification in the soil. A significant variation in nitrification and mineralization rates within 0—7.5 cm was observed which is extremely important in transformations and dynamics of N in grassland ecosystems.
Nitrogen Cycle
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