Ecophysiological characterization of Citrus sinensis (L.) Osbeck and relationships with type and amount of biogenic emissions

In this paper are shown the results obtained on Citrus sinensis (L.) Osbeck during the sampling campaigns performed in Burriana (Spain) in the frame of B.E.M.A. project. The daily trends of photosynthesis (A) showed higher values at morning and a decrement during the hottest hours of the day; for leaf transpiration (E) we observed a slight increment during the day. During different months (May '96, June '97 and July '95) we noted a progressive reduction in gas exchange of the leaves in relation to build-up of summer stress condition (-49% and -60% for June and July respect to May). In particular, net photosynthesis and leaf transpiration measured on Citrus leaves were, in general, characterised by low average values (2.7 +/- 0.06 (s.e.) mu mol CO2 m(-2)s(-1) and 0.665 +/- 0.021 (s.e.) mmol H2O m(-2)s(-1) for current leaves, respectively). The relationship between biogenic volatile organic compound (BVOC) emission rates normalised by assimilation (A) and gas exchange parameters as E/A ratio is reported. This latter is considered as an useful functional index to determine different vegetation types on a functional basis. We also found a good correlation between BVOC normalised emissions with air temperature. This behaviour has been reported for other species having monoterpene compounds in storage structures as Pinus species. Moreover, it is evident an uncoupling between BVOC emissions and photosynthesis. (C) 1999 Elsevier Science Ltd. All rights reserved.