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| Titel |
Long-term nitrogen additions and the intrinsic water-use efficiency of boreal Scots pine. |
| VerfasserIn |
John Marshall, Göran Wallin, Sune Linder, Tomas Lundmark, Torgny Näsholm |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109274
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| Publikation (Nr.) |
 EGU/EGU2015-9167.pdf |
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| Zusammenfassung |
| Nitrogen fertilization nearly always increases productivity in boreal forests, at least in terms
of wood production, but it is unclear how. In a mature (80 yrs. old) Scots pine forest in
northern Sweden, we tested the extent to which nitrogen fertilization increased intrinsic
photosynthetic water-use efficiency. We measured δ13C both discretely, in biweekly phloem
sampling, and continuously, by monitoring of bole respiration. The original experiment was
designed as a test of eddy covariance methods and is not therefore strictly replicated.
Nonetheless, we compared phloem contents among fifteen trees from each plot and stem
respiration from four per plot. The treatments included addition of 100 kg N/ha for eight
years and a control. Phloem contents have the advantage of integrating over the
whole canopy and undergoing complete and rapid turnover. Their disadvantage is
that some have observed isotopic drift with transport down the length of the stem,
presumably as a result of preferential export and/or reloading. We also measured the
isotopic composition of stem respiration from four trees on each plot using a Picarro
G1101-I CRDS attached to the vent flow from a continuous gas-exchange system. We
detected consistent differences in δ13C between the treatments in phloem contents.
Within each treatment, the phloem δ13C was negatively correlated with antecedent
temperature (R2= 0.65) and no other measured climate variable. The isotopic composition
of stem CO2 efflux will be compared to that of phloem contents. However, when
converted to intrinsic water-use efficiency, the increase amounted to only about
4%. This is a small relative to the near doubling in wood production. Although
we were able to detect a clear and consistent increase in water-use efficiency with
N-fertilization, it constitutes but a minor cause of the observed increase in wood production. |
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