Bacterial community structure of nirK-bearing denitrifiers and the development of properties of soils in created mitigation wetlands

We investigated the abundance and genetic heterogeneity of bacterial nitrite reductase genes (nir) and soil structural properties in created and natural freshwater wetlands in the Virginia piedmont. Soil attributes included soil organic matter (SOM), total organic carbon (TOC), total nitrogen (TN), pH, gravimetric soil moisture (GSM), and bulk density (D-b). A subset of soil attributes were analyzed across the sites, using euclidean cluster analysis, resulting in three soil condition (SC) groups of increasing wetland soil development (i.e., SC1 < SC2 < SC3; less to more developed or matured) as measured by accumulation of TOC, TN, the increase of GSM, and the decrease of D-b. There were no difference found in the bacterial community diversity between the groups (p = 0.4). NirK gene copies detected ranged between 3.6 x 10(4) and 3.4 x 10(7) copies g(-1) soil and were significantly higher in the most developed soil group, SC3, than in the least developed soil group, SC1. However, the gene copies were lowest in SC2 that had a significantly higher soil pH (similar to 6.6) than the other two SC groups (similar to 5.3). The same pattern was found in denitrifying enzyme activity (DEA) on a companion study where DEA was found negatively correlated with soil pH. Gene fragments were amplified and products were screened by terminal restriction fragment length polymorphism (T-RFLP) analysis. Among 146 different T-RFs identified, fourteen were dominant and together made up more than 65% of all detected fragments. While SC groups did not relate to whole nirK communities, most soil properties that identified SC groups did significantly correlate to dominant members of the community. (c) 2013 Elsevier B.V. All rights reserved.