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Impact of fertilization on tree ring 15 N and 13 C in beech stands : a retrospective analysis
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Edité par CCSD ; Oxford University Press (OUP) -
We studied the effects of two fertilization treatments (N and NPKCa) on wood nitrogen (N) isotope composition (15N), water-use efficiency (WUE) estimated by carbon isotope composition (13C) analyses, and ring width of trees in 80-year-old beech (Fagus sylvatica L.) stands in the forest of Fougères, western France. Four replicates were fertilized in two successive years (1973 and 1974), 20 years before core sampling. Unfertilized control trees displayed a decreasing 15N trend with time. The N and NPKCa treatments both increased 15N compared with the control treatment. Wood extraction by organic solvents enhanced the 15N signal. Thus, N addition to the beech ecosystem, even in moderate amounts, could be traced back in tree-ring 15N, suggesting that wood N isotope analysis is a promising tool for studying the long-term effects of N deposition on forests. Although WUE decreased for about 6 years after N fertilization, WUE in NPKCa-treated trees did not differ significantly from that in control trees. Results were similar whether based on cellulose or total wood 13Canalysis, suggesting that extraction of cellulose is not necessary when studying fertilization impacts on WUE. The NPKCa treatment had a large impact on radial growth, causing a significant long-lasting increase of 29% compared with the control trea
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