Foliar Nitrogen Uptake from Wet Deposition and the Relation with Leaf Wettability and Water Storage Capacity
This study assessed the foliar uptake of 15N-labelled nitrogen (N) originating from wet deposition along with leaf surface conditions, measured by wettability and water storage capacity. Foliar 15N uptake was measured on saplings of silver birch, European beech, pedunculate oak and Scots pine and the effect of nitrogen form (NH 4 + or NO 3 − ), NH 4 + to NO 3 − ratio and leaf phenology on this N uptake was assessed. Next to this, leaf wettability and water storage capacity were determined for each tree species and phenological stage, and the relationship with 15NH 4 + and 15NO 3 − uptake was examined. Uptake rates were on average five times higher (p < 0.05) for NH 4 + than for NO 3 − and four times higher for deciduous species than for Scots pine. Developing leaves showed lower uptake than fully developed and senescent leaves, but this effect was tree species dependent. The applied NH 4 + to NO 3 − ratio did only affect the amount of N uptake by senescent leaves. The negative correlation between measured leaf contact angles and foliar N uptake demonstrates that the observed effects of tree species and phenological stage are related to differences in leaf wettability and not to water storage capacity.
KeywordsFoliar uptake Nitrogen deposition Wettability Water storage capacity 15N labelling
We gratefully acknowledge L. Willems, G. De bruyn, K. Van Nieuland, J. Vermeulen, K. Ceunen and A. De Mey for field and laboratory assistance. The first and sixth authors are granted a Ph.D. fellowship by the Research Foundation—Flanders (FWO) and the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen), respectively. The second and fourth authors are funded as postdoctoral fellows of FWO and the third author as postdoctoral fellow of the Special Research Fund of Ghent University (BOF). The seventh author is funded by the Flemish institute for support of Scientific-Technologic Research in Industry.
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