G. Lorenzini et al., A GAS-EXCHANGE STUDY OF THE DIFFERENTIAL RESPONSE OF QUERCUS SPECIES TO LONG-TERM FUMIGATIONS WITH A GRADIENT OF SULFUR-DIOXIDE, Water, air and soil pollution, 85(3), 1995, pp. 1257-1262
Young oak plants (Qeuercus pubescens Willd. and 9. cerris L.) were exp
osed for 23 weeks to a gradient of sulphur dioxide concentrations (28,
61, 93 ppb in vol., compared with charcoal filtered-air ventilated co
ntrols) in fumigation chambers. Foliar gas exchange was analyzed by an
IRGA methodology after 11 weeks and chlorophyll was assessed in a non
-destructive way. At the end, foliar biomass produced during the exper
imental period was determined and its total sulphur and carbohydrate c
ontent analyzed. Visible foliar injury, as well as reduction in chloro
phyll content was not observed. Carbon dioxide assimilation was linear
ly ;I depressed by sulphur dioxide in both the species, with a maximum
depression of 25% in e. pubescens and 44% trend. The two species show
ed a similar behaviour in water use efficiency, this parameter being r
educed in a in Q. cern's. Stomatal conductance and transpiration were
negatively affected only in e. pubescens, with a linear linear fashion
. The intracellular/ambient carbon dioxide concentration ratio was aff
ected in a differential way: while in e. pubescens no alteration was e
vident, a linear increase was shown by e. cerris. Total foliar sulphur
content was dramatically increased in both the species. Average leaf
area was unaffected in both the species. Reduction in foliar dry weigh
t was only observed in e. cerris (-30% at the highest sulphur dioxide
concentration). We speculate that in Q. pubescens photosynthetic limit
ations are mainly of stomatal nature, and in Q. cerris the major const
raints are probably associated with mesophyll disturbances. Foliar sta
rch content was linearly increased by the pollutant.