Natural abundance of 15N in forests across a nitrogen deposition gradient

Autor: Sleep, D., Tietema, A., Gundersen, P., Emmett, B. A., Kjonaas, O. J., Koopmans, C.
Předmět:
Zdroj: Forest Ecology & Management. Feb1998, Vol. 101 Issue 1-3, p9. 0p.
Abstrakt: Chronic atmospheric nitrogen deposition can alter the rate of internal nitrogen cycling and increase the magnitude of N leaching losses in forested ecosystems. As fractionation of nitrogen in favour of the lighter 14N occurs during various transformations associated with N-enrichment and nitrogen loss, it has been proposed that the15N signal of vegetation may provide a useful tool in evaluating the past and current N status of forested ecosystems. A series of coniferous forests across a European nitrogen deposition gradient within the NITREX project provided an opportunity to test the relationships between nitrogen supply from atmospheric deposition and the relative 15N-enrichment of vegetation to soil, across a large geographical area. Most delta15N values for above- andbelow-ground tree components, soil at four depths, bulk precipitation and/or throughfall water and soil solution or outflow water values were within those observed elsewhere except for a few notable exceptions. There was a significant positive relationship between the delta15N enrichment of the tree foliage relative to the soil horizons (or the enrichment factor), and nitrogen flux in the throughfall if Aber forest, N. Wales, was excluded from the regression analysis. An unusually high enrichment factor at the Aber site indicated thata the high rate of N cycling at the site was in excess of that predicted from current N deposition. This was attributed to the effect of ploughing and tree planting on the relatively N- and clay-rich mineral horizons at Aber compared to other sites. Highly significant relationships (P < 0.01) between enrichment factors and parameters describing internal rates of N cycling, such as litterfall N flux and nitrification rates in upper soil horizons, supported this conclusion. Thereappears to be a strong link between the rate of N cycling and the delta15N enrichment factor, rather than N deposition or nitrate [ABSTRACT FROM AUTHOR]
Databáze: GreenFILE
Externí odkaz: