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The response of spring wheat ( Triticum aestivum L.) to ozone at higher elevations. III. Responses of leaf and canopy gas exchange, and chlorophyll fluorescence to ozone flux
Author(s) -
GRIMM A. GRANDJEAN,
FUHRER J.
Publication year - 1992
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1992.tb04237.x
Subject(s) - stomatal conductance , chlorophyll fluorescence , canopy , ozone , photosynthesis , chemistry , flux (metallurgy) , horticulture , water use efficiency , chlorophyll , transpiration , botany , biology , organic chemistry
SUMMARY Spring wheat ( Triticum aestivum L., cv. Albis) was grown in open‐top chambers and exposed to four different levels of ozone (O 3 ) from the three‐leaf stage until maturity. The aim was to examine changes in leaf and canopy gas exchange, and in chlorophyll fluorescence, in response to O 3 flux. Measurements were carried out periodically between full expansion and complete senescence of flag leaves. Fluxes to the canopy of CO 2 (CER c .) (corrected for soilborne CO 2 ), water vapour (E c ) and O 3 were determined by using open‐top chambers as differential systems. Water use efficiency (WUE c .) was calculated from CER c , and E c . Leaf CO 2 (CER n ) and H 2 O (E n ) exchange rates, stomatal conductance (g,(H 2 O)), and WUE n , were analyzed with a portable gas exchange analyzer. Effects of O 3 flux on structural components of photosynthesis were examined by determining variable fluorescence (defined by the F v /F o ratio) in leaves after 60 minutes of dark‐adaptation or during the night. The decline in CER c and CER n associated with senescence was accelerated by O 3 . Average CER n between flag leaf unfolding and late milk stage declined linearly with increasing O 3 flux. The corresponding decline in average CER c was less pronounced. The quantitative effect of O 3 flux on CER c corresponded well with the effect on grain yield. In young leaves, g s (H 2 O) was reduced in response to O 3 but WUE n was unaffected. With progressing leaf age, WUE n declined. Thus, in the young leaves, O 3 affected the stomata directly and, consequently, limitation of photosynthesis was primarily due to reduced CO 2 diffusion. In contrast, in senescent leaves, the effect of O 3 was mainly due to reduced carboxylation. Compared with WUE n WUE c responded differently to increasing O 3 flux. During O 2 fluxes at above‐ambient levels, WUE C tended to increase rather than to decrease. It is suggested that under O 3 stress, factors controlling WUE at the canopy level differ from those operating at the level of single flag leaves. The decline in F v /F o measured after anthesis was stimulated by O 2 , but no effect of O 3 was detected when F v /F o was measured during the night. This leads to the conclusion that the effect of O 3 on photosynthetic structures is reversible and the reduction in photosynthesis in response to O 3 flux is due to metabolic changes rather than to direct damage to structural components.