U. Meyer et al., Effects of different ozone exposure regimes on photosynthesis, assimilatesand thousand grain weight in spring wheat, AGR ECO ENV, 78(1), 2000, pp. 49-55
The aim of the study was to compare two ozone exposure patterns with differ
ent peak concentrations under equal dose conditions. Spring wheat (Triticum
aesthivum cv. 'Nandu') was 'pre-cultivated' under glasshouse conditions an
d exposed to two different ozone exposure scenarios (A: 1700-0900 h: 20 ppb
, 0900-1700 h: 65 ppb; B: 1600-1200 h: 20 ppb, 1200-1600 h: 110 ppb) in lar
ge fumigation chambers for two weeks during anthesis. Control plants receiv
ed charcoal filtered ambient air (<5 ppb ozone 24 h/day) (CF). Chlorophyll
content as well as chlorophyll fluorescence (Fv:Fm ratio) and carbohydrate
composition (hexoses, sucrose, starch) were monitored in flag leaves and in
the case of carbohydrate content also in the penultimate internode during
and after ozone exposure. Thousand grain weight (TGW) was determined for es
timating yield effects, photosynthesis decreased markedly in both treatment
s expressed as Fv :Fm ratio. in treatment B chlorophyll content (a + b) of
leaves was reduced by 40% after 7 and 14 days of exposure (p less than or e
qual to 0.001). Carbohydrate content decreased significantly as compared wi
th CF-plants to 20% (p less than or equal to 0.001) in the case of sucrase
and starch. Effects were especially pronounced in treatment B (110 ppb for
4 h) and could be observed even seven days after exposure under CF conditio
ns. After 14 days of exposure during anthesis, plants were incapable of rec
overy as shown by a significant reduction in thousand grain weight of ozone
treated plants compared with CF-plants (treatment B: 22% at p less than or
equal to 0.001). Effects on photosynthesis and carbon content even under m
oderate daily ozone peaks as in treatment A induced a significant yield los
s of 11% (p less than or equal to 0.001) as well, when applied during anthe
sis. It can be concluded that under equal dose conditions ozone treatments
with comparatively high peak concentration induce more pronounced effects t
han ozone patterns with moderate peaks. (C) 2000 Elsevier Science B.V. All
rights reserved.