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THE FUNCTIONAL SIGNIFICANCE OF DENITRIFIER COMMUNITY COMPOSITION IN A TERRESTRIAL ECOSYSTEM
Author(s) -
Cavigelli Michel A.,
Robertson G. Philip
Publication year - 2000
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(2000)081[1402:tfsodc]2.0.co;2
Subject(s) - denitrification , nitrous oxide reductase , denitrifying bacteria , nitrite reductase , microbial population biology , soil water , ecosystem , nitrate , environmental science , nitrogen cycle , environmental chemistry , nitrate reductase , nitrous oxide , ecology , chemistry , nitrogen , biology , soil science , genetics , organic chemistry , bacteria
We tested the hypothesis that soil microbial diversity affects ecosystem function by evaluating the effect of denitrifier community composition on nitrous oxide (N 2 O) production. Denitrification is a major source of atmospheric N 2 O, an important greenhouse gas and a natural catalyst of stratospheric ozone decay. The major environmental controls on denitrification rate and the mole ratio of N 2 O produced during denitrification have been incorporated into mechanistic models, but these models are, in general, poor predictors of in situ N 2 O flux rates. We sampled two geomorphically similar soils from fields in southwest Michigan that differed in plant community composition and disturbance regime: a conventionally tilled agricultural field and a never‐tilled successional field. We tested whether denitrifier community composition influences denitrification rate and the relative rate of N 2 O production [△N 2 O/△(N 2 O + N 2 )], or rN 2 O, using a soil enzyme assay designed to evaluate the effect of oxygen concentration and pH on the activity of denitrification enzymes responsible for the production and consumption of N 2 O. By controlling, or providing in nonlimiting amounts, all known environmental regulators of denitrifier N 2 O production and consumption, we created conditions in which the only variable contributing to differences in denitrification rate and rN 2 O in the two soils was denitrifier community composition. We found that both denitrification rate and rN 2 O differed for the two soils under controlled incubation conditions. Oxygen inhibited the activity of enzymes involved in N 2 O production (nitrate reductase, Nar; nitrite reductase, Nir; and nitric oxide reductase, Nor) to a greater extent in the denitrifying community from the agricultural field than in the community from the successional field. The Nar, Nir, and Nor enzymes of the denitrifying community from the successional field, on the other hand, were more sensitive to pH than were those in the denitrifying community from the agricultural field. Moreover, the denitrifying community in the soil from the successional field had relatively more active nitrous oxide reductase (Nos) enzymes, which reduce N 2 O to N 2 , than the denitrifying community in the agricultural field. Also, the shape of the rN 2 O curve with increasing oxygen was different for each denitrifying community. Each of these differences suggests that the denitrifying communities in these two soils are different and that they do not respond to environmental regulators in the same manner. We thus conclude that native microbial community composition regulates an important ecosystem function in these soils.