© 2005 Heron Publishing—Victoria, Canada
Seasonal and interannual variability of photosynthetic capacity in relation to leaf nitrogen in a deciduous forest plantation
in northern Italy
Giacomo Grassi (1, 2), Elisa Vicinelli (1), Francesca Ponti (1), Lucia Cantoni (1) and Federico Magnani (1)
1. Dipartimento di Colture Arboree, University of Bologna, via Fanin 46, 40127 Bologna, Italy / 2. Corresponding author (grassi@agrsci.unibo.it) / Received December 22, 2003; accepted August 7, 2004; published online January 4, 2005
Summary
Gas exchange was measured in a forest plantation dominated by Fraxinus angustifolia Vahl. and Quercus robur L. in northern Italy, over three growing seasons that differed in water availability (2001, 2002 and 2003). The objectives
were to: (1) determine variability in the photosynthetic parameters Vcmax (maximum carboxylation capacity) and Jmax (maximum rate of electron transport) in relation to species, leaf ontogeny and drought; and (2) assess the potential of the
photosynthesis–nitrogen relationship for estimating leaf photosynthetic capacity.
Marked seasonal and interannual variability in photosynthetic capacity was observed, primarily caused by changes in leaf ontogeny
and water stress. Relatively small differences were apparent between species. In the absence of water stress (year 2002),
the seasonal patterns of Vcmax and Jmax were characterized by a rapid increase during spring, a relatively steady state during summer and a rapid decline during
autumn. In years with a moderate (year 2001) or a severe (year 2003) water stress, photosynthetic capacity decreased during
the summer in proportion to drought intensity, without a parallel decline in leaf nitrogen content. The Vcmax–nitrogen relationship was significantly affected by both leaf ontogeny and drought. As a consequence, the use of a single
annual regression to predict Vcmax from leaf nitrogen yielded good estimates only during the summer and in the absence of water stress. Irrespective of the
mechanisms by which photosynthetic capacity is affected by water stress, its large seasonal and interannual variability is
of great relevance for modeling the forest carbon cycle.
Keywords:
ash, drought, leaf ontogeny, oak, photosynthesis–nitrogen relationship, photosynthetic capacity.
