Linking thestructure and function of denitrifying communities in soil: Whatgroup of denitrifying bacteria is responsible for the rapidreduction of nitrate to nitrogen?

Antonopoulos, D.A., K. Huizinga, and T.M. Schmidt.

Presented at the All Scientist Poster Reception (2006-05-09 )

Culture independent clone libraries of the gene encoding nitrite reductase (nirK) were previously used to characterize the community structure of denitrifiers in different soil treatments at the Kellogg Biological Station Long-Term Ecological Research Site (KBS-LTER Site). The community structure of denitrifiers, represented by recovered nirK sequences, appeared more diverse (both richer and more even) in conventional agricultural soil (represented by Treatment 1) versus nirK community structures in mid-successional soils (Treatments 7 and 8). To investigate the influence of soil composition (specifically soil aggregate size distribution in different soil treatments) on denitrifier populations, blocks of soil from Treatments 1, 7, and 8 were collected and processed. Based on similar soil aggregate size distributions in Treatments 7 and 8, nirK libraries were constructed from three different soil aggregate size classes from Treatment 8. Sequences recovered from these libraries were aligned with nirK sequences recovered from unfractionated bulk soil. A large portion of recovered sequences from each of the three aggregate libraries grouped within one large phylogenetic cluster that contained almost no sequences from conventional agricultural soil (T1). We hypothesize that the organisms represented by this cluster are responsible for the rapid and complete reduction of nitrate (NO₃^-) to dinitrogen (N₂) in mid-successional soils at the KBS-LTER Site.