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N FERTILIZATION EFFECTS ON DENITRIFICATION AND N CYCLING IN AN AGGRADING FOREST
Author(s) -
Wallenstein Matthew D.,
Peterjohn William T.,
Schlesinger William H.
Publication year - 2006
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/1051-0761(2006)016[2168:nfeoda]2.0.co;2
Subject(s) - cycling , denitrification , environmental science , ecology , human fertilization , nitrogen cycle , nutrient cycle , ecosystem , nitrogen , geography , biology , forestry , agronomy , chemistry , organic chemistry
We investigated N cycling and denitrification rates following five years of N and dolomite amendments to whole‐tree harvested forest plots at the long‐term soil productivity experiment in the Fernow Experimental Forest in West Virginia, USA. We hypothesized that changes in soil chemistry and nutrient cycling induced by N fertilization would increase denitrification rates and the N 2 O:N 2 ratio. Soils from the fertilized plots had a lower pH (2.96) than control plots (3.22) and plots that received fertilizer and dolomite (3.41). There were no significant differences in soil %C or %N between treatments. Chloroform‐labile microbial biomass carbon was lower in fertilized plots compared to control plots, though this trend was not significant. Extractable soil NO 3 − was elevated in fertilized plots on each sample date. Soil‐extractable NH 4 + , NO 3 − , pH, microbial biomass carbon, and %C varied significantly by sample date suggesting important seasonal patterns in soil chemistry and N cycling. In particular, the steep decline in extractable NH 4 + during the growing season is consistent with the high N demands of a regenerating forest. Net N mineralization and nitrification also varied by date but were not affected by the fertilization and dolomite treatments. In a laboratory experiment, denitrification was stimulated by NO 3 − additions in soils collected from all field plots, but this effect was stronger in soils from the unfertilized control plots, suggesting that chronic N fertilization has partially alleviated a NO 3 − limitation on denitrification rates. Dextrose stimulated denitrification only in the whole‐tree‐harvest soils. Denitrification enzyme activity varied by sample date and was elevated in fertilized plots for soil collected in July 2000 and June 2001. There were no detectable treatment effects on N 2 O or N 2 flux from soils under anaerobic conditions, though there was strong temporal variation. These results suggest that whole‐tree harvesting has altered the N status of these soils so they are less prone to N saturation than more mature forests. It is likely that N losses associated with the initial harvest and high N demand by aggrading vegetation is minimizing, at least temporarily, the amount of inorganic N available for nitrification and denitrification, even in the fertilized plots in this experiment.