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THE FATE AND RETENTION OF ORGANIC AND INORGANIC 15N-NITROGEN IN AN OLD-GROWTH FOREST SOIL IN WESTERN OREGON
Citation:
Holub*, S M. AND Lajtha. THE FATE AND RETENTION OF ORGANIC AND INORGANIC 15N-NITROGEN IN AN OLD-GROWTH FOREST SOIL IN WESTERN OREGON. ECOSYSTEMS 7(4):368-380, (2004).
Impact/Purpose:
Published Journal Article
Description:
Forests in the Pacific northwestern region of North America receive very little nitrogen through atmospheric deposition and thus can provide insights into how the nitrogen cycle functioned before heavy atmospheric deposition of inorganic nitrogen began in other regions. Our objectives were 1) to determine if the fate of organic nitrogen differed from the fate of inorganic nitrogen, 2) to determine the effect that polyphenols have on the fate of organic nitrogen, and 3) to determine the effect of season of addition on the fate of nitrogen inputs. We traced N added as ammonium, organic nitrogen, tannin-complexed organic nitrogen, and the N2-fixing lichen to in situ soil cores. Total 15N recovery was between 74 and 109% for all nitrogen additions. Total 15N recovery did not vary significantly from the first sampling date to the last date. The litter/organic horizon, as a bulk pool, was the largest nitrogen retention pool for all forms of nitrogen addition. Within the litter/organic horizon, the chloroform-extractable microbial biomass initially accounted for nearly all of the added nitrogen from the ammonium additions. Although on a different time scale, microbial biomass also played a significant role in the retention of nitrogen from organic nitrogen, tannin-complexed, organic nitrogen, and Lobaria. Complexing organic matter with tannin appeared to slow nitrogen cycling, but did not significantly change the ultimate distribution of added organic nitrogen. Season of nitrogen addition had little effect on the retention of added nitrogen although where differences occurred spring additions had lower recoveries than fall additions.
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THE FATE AND RETENTION OF ORGANIC AND INORGANIC 15N-NITROGEN IN AN OLD-GROWTH FOREST SOIL IN WESTERN OREGON