Photosynthetic stimulation under long-term CO2 enrichment and fertilization is sustained across a closed Populus canopy profile (EUROFACE).
The long-term response of leaf photosynthesis to rising CO2 concentrations [CO2] depends on biochemical and morphological feedbacks. Additionally, responses to elevated [CO2] might depend on the nutrient availability and the light environment, affecting the net carbon uptake of a forest stand. After 6 yr of exposure to free-air CO2 enrichment (EUROFACE) during two rotation cycles (with fertilization during the second cycle), profiles of light, leaf characteristics and photosynthetic parameters were measured in the closed canopy of a poplar (Populus) short-rotation coppice. Net photosynthetic rate (A(growth)) was 49% higher in poplars grown in elevated [CO2], independently of the canopy position. Jmax significantly increased (15%), whereas leaf carboxylation capacity (Vcmax), leaf nitrogen (N(a)) and chlorophyll (Chl(a)) were unaffected in elevated [CO2]. Leaf mass per unit area (LMA) increased in the upper canopy. Fertilization created more leaves in the top of the crown. These results suggest that the photosynthetic stimulation by elevated [CO2] in a closed-canopy poplar coppice might be sustained in the long term. The absence of any down-regulation, given a sufficient sink capacity and nutrient availability, provides more carbon for growth and storage in this bioenergy plantation.
Liberloo
Marion
M
University of Antwerp, Research Group of Plant and Vegetation Ecology, Department of Biology, Campus Drie Eiken, Universiteitsplein 1, 2610 Wilrijk, Belgium.
Tulva
Ingmar
I
Institute of Botany and Ecology, University of Tartu, Lai 40, 51005 Tartu, Estonia.
Raïm
Olaf
O
Institute of Botany and Ecology, University of Tartu, Lai 40, 51005 Tartu, Estonia.
Kull
Olevi
O
Institute of Botany and Ecology, University of Tartu, Lai 40, 51005 Tartu, Estonia.
Ceulemans
Reinhart
R
University of Antwerp, Research Group of Plant and Vegetation Ecology, Department of Biology, Campus Drie Eiken, Universiteitsplein 1, 2610 Wilrijk, Belgium.
D000704:Analysis of Variance; D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D005308:Fertilizers; D008027:Light; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology* / Q000528:radiation effects; D032107:Populus / Q000033:anatomy & histology / Q000502:physiology* / Q000528:radiation effects
D005308:Fertilizers; D002734:Chlorophyll; D002245:Carbon Dioxide; D009584:Nitrogen