Nitrogen fixation and denitrification in a floodplain forest near Manaus, Brazil

✍ Scribed by Heidi Kreibich; Jürgen Kern

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 444 KB
• Volume: 17
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/hyp.1294

✦ Synopsis

Abstract

The Amazon floodplain (várzea) is seasonally affected by water level fluctuations of the Solimões/Amazon River. The drastic environmental changes that occur also include microbiological processes, such as nitrogen (N~2~) fixation and denitrification. Both processes were measured in the soil by the acetylene reduction assay and the acetylene block method in a várzea forest on Ilha de Marchantaria, Central Amazonia, Brazil. In the surface soil horizon (0–5 cm), N~2~ fixation was highest during the exposed period (0·04–0·26 nmolN h^−1^ g^−1^ dry weight (dw)). In contrast, denitrification varied from 0 to 1·40 nmolN h^−1^ g^−1^ dw, with high rates during the submerged and the transition periods. No significant difference between locations with legume trees, with non‐legume trees and without trees could be observed. N~2~ fixation rates of incubations (litter down to 450 cm depth) for samples collected during the exposed period ranged from 0 to 0·11 nmolN h^−1^ g^−1^ dw, with highest rates in the surface soil horizon (0–5 cm). Denitrification ranged from 0 to 0·05 nmolN h^−1^ g^−1^ dw, with the highest rate at 250–300 cm depth, which was just below the water table. The maximum N~2~ fixation rate (0·89 nmolN h^−1^ g^−1^dw) and denitrification rate (0·09 nmolN h^−1^ g^−1^ dw) occurred in the litter layer. On average, at least three times as much N is lost from the surface soil horizon via denitrification than is gained by N~2~ fixation annually, but the rates are strongly influenced by the flood pulse. Copyright © 2003 John Wiley & Sons, Ltd.