© 1997 Heron Publishing—Victoria, Canada
Influence of environmental and plant factors on canopy photosynthesis and transpiration of apple trees
Rita Giuliani (1), F. Nerozzi (2), E. Magnanini (1) and L. Corelli-Grappadelli (1)
1. Dipartimento di Colture Arboree, University of Bologna, via Filippo Re 6, 40126 Bologna, Italy / 2. Istituto di Ecofisiologia delle Piante Arboree da Frutto, National Research Council, Bologna, Italy / Received July 5, 1996
Summary
We estimated carbon and water flows, canopy conductance and the assimilation/transpiration ratio of fruiting and non-fruiting
apple trees grown in the field, from daily gas exchange measurements taken during the summer with a whole-canopy enclosure
device. The relationships between photosynthetic and transpirational responses and environmental conditions were also investigated,
as well as the role of canopy conductance in controlling carbon dioxide and water vapor exchange.
Light-saturated net photosynthetic rates, which were higher for the fruiting canopy than for the non-fruiting canopy, showed
a general decrease in the afternoon, particularly for the non-fruiting canopy, compared with rates in the morning. When light
was not limiting, the afternoon decrease in net photosynthesis appeared to be regulated more by non-stomatal factors than
by changes in canopy conductance. Canopy conductance, which was higher for the fruiting canopy than for the non-fruiting canopy,
may actively regulate photosynthetic activity and may also be modulated by feedback control in response to assimilation capacity.
We conclude that adjustments in canopy conductance, which were partially dependent on the vegetative–reproductive status of
the tree, control the equilibrium between photosynthesis and transpiration. We also demonstrated that whole-canopy chambers
can be used to estimate photosynthetic and transpirational responses thereby overcoming the difficulty of scaling these physiological
responses from the leaf to the whole-canopy level.
Keywords:
assimilation/transpiration ratio, canopy conductance, whole-canopy enclosure system.
