|Robertson, G. - MSU|
Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 18, 1999
Publication Date: N/A
Interpretive Summary: Soil denitrifiers are an important group of bacteria that convert soil nitrogen in the form of nitrate to gaseous forms including dinitrogen and nitrous oxide. Nitrous oxide, the atmospheric concentration of which is increasing, is both a greenhouse gas and a catalyst of stratospheric ozone degradation. Because of its importance in global change scenarios, scientists have built models to predict nitrous oxide production from soils. These models include a number of environmental variables known to affect nitrous oxide production from soils. Unfortunately, these models do not work very well for nitrous oxide production. One reason these models do not work very well may be that nitrous oxide production may be regulated by the types of denitrifier communities in a soil, and not just by the environmental factors influencing denitrifiers. We tested this hypothesis by measuring nitrous oxide production by denitrifying bacteria in tightly controlled soil incubations. We measured nitrous oxide production by denitrifiers which controlling all known environmental regulators of denitrifier activity (soil carbon, soil nitrate, soil oxygen, soil pH, soil temperature). We did this for two different soils and found that the two soils produced different amounts of nitrous oxide under identical conditions, leading us to conclude that the denitrifier communities are functionally different in these two soils. Therefore, scientist that model soil nitrous oxide production might need to consider the denitrifier communities in their models.
Technical Abstract: We tested the hypothesis that soil microbial diversity affects ecosystem function by evaluating the effect of denitrifier community composition on nitrous oxide (N2O) production. We sampled two geomorphically similar soils from fields that differed in plant community composition and disturbance regime. We tested whether denitrifier community composition influences denitrification rate and the relative rate of N2O production [delta N2O/delta N2O + N2], 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 N2O. By controlling, or providing in non-limiting amounts, all known environmental regulator of denitrifier N2O production and consumption, we created conditions in which the only variable contributing to differences in denitrification rate and rN2O in the two soils was denitrifier community ycomposition. We found that both denitrification rate and rN2O differed from the two soils under controlled incubation conditions. Oxygen and pH affected the enzymes of the two denitrifying communities differently. These differences suggest 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.