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The contribution of nitrogen deposition to the photosynthetic capacity of forests
Author(s) -
Fleischer K.,
Rebel K. T.,
Molen M. K.,
Erisman J. W.,
Wassen M. J.,
Loon E. E.,
Montagnani L.,
Gough C. M.,
Herbst M.,
Janssens I. A.,
Gianelle D.,
Dolman A. J.
Publication year - 2013
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/gbc.20026
Subject(s) - canopy , eddy covariance , photosynthetic capacity , evergreen , carbon sequestration , environmental science , deciduous , atmospheric sciences , carbon sink , leaf area index , terrestrial ecosystem , ecosystem , deposition (geology) , nitrogen , photosynthesis , fluxnet , carbon cycle , sink (geography) , temperate rainforest , temperate forest , ecology , botany , carbon dioxide , chemistry , biology , geography , geology , organic chemistry , sediment , paleontology , cartography
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 A max is combined with modeled N deposition, environmental variables and stand characteristics to study the relative effects on A max for a unique global data set of 80 forest FLUXNET sites. Canopy A max relates positively to N deposition for evergreen needleleaf forests below an observed critical load of ~ 8 kg N ha –1 yr –1 , with a slope of 2.0 ± 0.4 (S.E.) µmol CO 2 m –2 s –1 per 1 kg N ha –1 yr –1 . Above this threshold canopy A max 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.