Responses of nitrogen transformation and microbial community composition to nitrogen enrichment patch

Fertilization produces many nutrient patches that have been confirmed to affect root growth. However, it is not clear how nutrient transformation and microbial community composition are affected in an inorganic nutrient patch. In this experiment, a nitrogen enrichment patch was formed by the diffusion of a urea fertilizer layer in a specially-designed container. Responses of nitrogen transformation and microbial community composition to the nitrogen enrichment patch were investigated at different incubation times. Results showed that nitrogen status and microbial community composition were slightly affected in the control patch (CK patch). In the nitrogen enrichment patch, however, soil pH was significantly increased in most soil layers close to the urea fertilizer layer; NO(2)(-)-N was the predominant form of mineral N, and its transformation to NO(3)(-)-N was delayed. Microbial community composition shifted significantly, especially before day 28 of incubation. Principal components analysis (PCA) of phospholipid fatty acids (PLFAs) patterns showed that the microbial community presented different sensitivity to high nitrogen concentration. Fungi (18:2 omega 6,9) showed the least sensitivity to high concentrations of NO(2)(-)-N and NO(3)(-)-N. Gram-positive bacteria showed the most sensitivity to NO(2)(-)-N. Gram-negative bacteria (cy17:0, cy19:0, 18:1 omega 9, and 18:1 omega 7) and actinomycetes (10Me17:0 and 10Me18:0) presented similar responses to NO(2)(-)-N and NO(3)(-)-N. Results of this study indicate that changes in nitrogen transformation and microbial community composition are likely to occur in nitrogen enrichment patches, but the extent of those changes depend on the microbial species and the distance of soil layers from the urea layer. (C) 2010 Elsevier GmbH. All rights reserved.