Title
The contribution of nitrogen deposition to the photosynthetic capacity of forests The contribution of nitrogen deposition to the photosynthetic capacity of forests
Author
Faculty/Department
Faculty of Sciences. Biology
Publication type
article
Publication
Washington, D.C. ,
Subject
Physics
Chemistry
Biology
Source (journal)
Global biogeochemical cycles. - Washington, D.C.
Volume/pages
27(2013) :1 , p. 187-199
ISSN
0886-6236
ISI
000318275300018
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
Global terrestrial carbon (C) sequestration has increased over the last few decades. The drivers of carbon sequestration, the geographical spread and magnitude of this sink are however hotly debated. Photosynthesis determines the total C uptake of terrestrial ecosystems and is a major flux of the global C balance. We contribute to the discussion on enhanced C sequestration by analyzing the influence of nitrogen (N) deposition on photosynthetic capacity (A(max)) of forest canopies. Eddy covariance measurements of net exchange of carbon provide estimates of gross primary production, from which A(max) is derived with a novel approach. Canopy Amax is combined with modeled N deposition, environmental variables and stand characteristics to study the relative effects on Amax for a unique global data set of 80 forest FLUXNET sites. Canopy Amax relates positively to N deposition for evergreen needleleaf forests below an observed critical load of similar to 8 kgN ha(-1) yr(-1), with a slope of 2.0 +/- 0.4 (S.E.) mmol CO2 m(-2) s(-1) per 1 kgN ha(-1) yr(-1). Above this threshold canopy Amax levels off, exhibiting a saturating response in line with the N saturation hypothesis. Climate effects on canopy A(max) cannot be separated from the effect of N deposition due to considerable covariation. For deciduous broadleaf forests and forests in the temperate (-continental) climate zones, the analysis shows the N deposition effect to be either small or absent. Leaf area index and foliar N concentration are positively but weakly related to A(max). We conclude that flux tower measurements of C fluxes provide valuable data to study physiological processes at the canopy scale. Future efforts need to be directed toward standardizing measures N cycling and pools within C monitoring networks to gain a better understanding of C and N interactions, and to disentangle the role of climate and N deposition in forest ecosystems. Citation: Fleischer, K., K. T. Rebel, M. K. van der Molen, J. W. Erisman, M. J. Wassen, E. E. van Loon, L. Montagnani, C. M. Gough, M. Herbst, I. A. Janssens, D. Gianelle, and A. J. Dolman (2013), The contribution of nitrogen deposition to the photosynthetic capacity of forests, Global Biogeochem. Cycles, 27, doi: 10.1002/gbc. 20026.
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