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- Title
Effect of chronic nitrogen additions on soil nitrogen fractions in red spruce stands
- Authors
David, M. D.; Vogt, K.; Cupples, A. M.; Wargo, P. M.; Lawrence, G. B.; Shi, G.
- Abstract
The responses of temperate and boreal forest ecosystems to increasednitrogen (N) inputs have been varied, and the responses of soil N pools have been difficult to measure. In this study, fractions and poolsizes of N were determined in the forest floor of red spruce stands at four sites in the northeastern U.S. to evaluate the effect of increased N inputs on forest floor N. Two of the stands received 100 kg Nha-1yr-1 for three years, one stand received 34 kg N ha-1yr-1 for six years, and the remaining stand received only ambient N inputs. No differences in total N content or N fractions were measured in samples of the Oie and Oa horizons between treated and control plots in the three sites that receivedN amendments. The predominant N fraction in these samples was amino acid N (31-45 % of total N), followed by hydrolyzable unidentified N (16-31 % of total N), acid-soluble N (18-22 % of total N), and NH4+-N(9-13 % of total N). Rates of atmospheric deposition varied greatly among the four stands. Ammonium N and amino acid N concentrations in the Oie horizon were positively related to wet N deposition, with respective r(2) values of 0.92 and 0.94 (n = 4, p < 0.05). These relationships were somewhat stronger than that observed between atmospheric wet N deposition and total N content of the forest floor, suggesting that these pools retain atmospherically deposited N. The NH4+-N pool may represent atmospherically deposited N that is incorporated into organic matter, whereas the amino acid N pool could result from microbial immobilization of atmospheric N inputs. The response of forest floor N pools to applications of N may be masked, possibly by the largesoil N pool, which has been increased by the long-term input of N from atmospheric deposition, thereby overwhelming the short-term treatments.
- Subjects
FORESTS &; forestry; NITROGEN; ATMOSPHERIC deposition; BIOGEOCHEMISTRY
- Publication
Water, Air & Soil Pollution, 1998, Vol 105, Issue 1-2, p183
- ISSN
0049-6979
- Publication type
Article
- DOI
10.1023/A:1005012400047