Organic carbon availability limiting microbial denitrification in the deep vadose zone

We experimentally studied the factors that affect denitrification in soils collected down to 10.5 meters deep along the soil profile. After an anoxic preincubation, denitrification rates moderately increased and the N 2 O/(N 2 O1N 2 ) ratios declined while the microbial abundance and diversity did not change significantly in most of the layers.

Denitrificationrate was significantly enhanced and the abundance of the denitrification genes was simultaneously elevated by the increased availability of organic carbon in all studied layers, to a greater extent in the subsurface layers than in the surface layers, suggesting the severe scarcity of carbon in the deep vadose zone. The genera Pseudomonas and Bacillus, which are made up of a number of species that have been previously identified as denitrifiers in soil, were the major taxa that respond to carbon addition.