Observations and model simulations link stomatal inhibition to impaired hydraulic conductance following ozone exposure in cotton

Abstract

Ozone (O 3 ) inhibits plant gas exchange and productivity. Vapour phase (g s ) and liquid or hydraulic phase (K) conductances to water flux are often correlated as both change with environmental parameters. Exposure of cotton plants to tropospheric O 3 reduces g s through reversible short-term mechanisms and by irreversible long-term disruption of biomass allocation to roots which reduces K. We hypothesize that chronic effects of O 3 on gas exchange can be mediated by effects on K without a direct effect of O 3 on g s or carbon assimilation (A) Key-words: air pollution; allocation; dry deposition; evapotranspiration; oxidant; ozone flux; regional ozone concentrations; root-shoot communication; water relations Dodd et al. 1996;Muller et al. 1996;Puliga et al. 1996). Alternatively, the interaction could be mediated by effects of K on soil water acquisition and resulting water status of the leaf mesophyll (y m ) or epidermal (y e ) tissue in which the stomata are embedded (Fuchs & Livingston 1996;Shackel & Brinckmann 1985; Bunce 1996). Differences between y e and y m have been documented (Shackel & Brinckmann 1985), although associated stomatal control mechanisms and sensitivity to O 3 exposure have not been assessed..Rapid reductions in shoot gas exchange following exposure to O 3 may be associated with altered phloem loading (e.g. McCool & Menge 1983;McLaughlin & McConathy 1983;Mortensen & Engvild 1995;Grantz & Farrar 1999) and end-product inhibition of carbon metabolism. Reduced root system capacity may also lead to long-term reductions in carboxylase activity and gas exchange performance. Feedback from root to shoot following chronic exposure to O 3 would necessarily be long-term and slowly reversed, and would be expressed as a limit on maximal stomatal response to other environmental parameters. The potential mediation of chronic phytotoxic effects of O 3 on gas exchange by such a mechanism has not been investigated. Rapid shoot response to O 3In contrast, rapid gas exchange responses to O 3 have been well documented. In bean plants (Phaseolus vulgaris L.), stomatal conductance (g s ) was reduced within 6-12 min by 0·3-0·5 ppm O 3 (Moldau et al. 1990). While g s declined by about 50% within 3 h, the mesophyll conductance to CO 2 was unaffected. Similar apparent direct effects of O 3 on g s have been identified by Hill & Littlefield (1969) and by Amundson et al. (1987).Light-saturated carbon assimilation declined by about 25% in winter wheat (Triticum aestivum L.; Farage et al. 1991) and 40% in pea and oak (Pisum sativum L. and Quercus robur L.; Farage & Long 1995), while g s declined by about 40% (wheat, pea) and about 80% (oak) following 4 h of exposure to 0·4 ppm O 3 . This was associated with minimal effect on photosynthetic light reactions assayed as variable chlorophyll fluorescence and as quantum yield. Carboxylation capacity was reduced by about 30% (wheat, oak) to 45% (pea), consistent with O 3 -induced reductions in Rubisco protein and activity (Eckard & Pell 1995;Lehnherr et al. 1987;Pell...

Elevated ozone concentration decreases whole‐plant hydraulic conductance and disturbs water use regulation in soybean plants

“…Lower hydraulic conductance decreases the efficiency of water and nutrient transport to the canopy, limits carbon accumulation and plant growth, affects plant water relations, and can negatively affect plant survival during drought (Sperry et al , Sack and Holbrook , Woodruff et al ). Consistent with our data, eO 3 has been shown to inhibit hydraulic conductance of cotton plants ( Gossypium hirsutum ) and results in a reduction of the leaf water potential, especially during periods of high transpirational demand such as at midday (Grantz et al , Grantz ). If O 3 ‐treated plants face water‐stressed conditions, a decline in hydraulic conductance implies not only a decrease in leaf water potential (Ψ leaf ) but also a reduced ability to return to pre‐drought physiological functioning (Brodribb and Cochard , Pangle et al ).…”

“…Stomatal conductance ( g s ) often has a strong positive correlation with hydraulic conductance of the soil‐leaf continuum and thus changes in g s as a result of O 3 exposure could be accompanied by modifications in liquid‐phase water transport (Brodribb et al , Sack and Frole ). For instance, some studies on cotton ( Gossypium barbadense L.) found that chronic O 3 exposure simultaneously caused reductions in g s as well as reduction in whole‐plant and root hydraulic conductance expressed on per leaf area basis (Grantz et al , Grantz and Yang ). Moreover, the apparent changes in plant size, biomass and allometric relationships induced by O 3 can potentially cause remarkable changes in hydraulic architecture at the whole‐plant level due to the strong influence of plant allometric scaling on plant water supply and demand relations (Meinzer , Mills et al ).…”

Water use strategy affects avoidance of ozone stress by stomatal closure in Mediterranean trees—A modelling analysis

“…On the other hand, the anisohydric oaks had lower g ref in elevated O 3 regardless of different water regimes, whereas an O 3 ‐induced increase of m was found only in WS condition. The lower g ref with no change of m might be explained by an O 3 ‐induced reduction of hydraulic conductivity due to impairment of root function (Grantz, Zhang, & Carlson, ). Our previous results obtained in the same experiment showed that Q. ilex changed the anatomical structure of thin transport roots in the combination of 1.4 × AA and WW (Mrak et al, ); mean root vessel diameter in WW plants of Q. ilex was decreased by O 3 , resulting in a reduction of hydraulic conductivity in roots.…”

Diel trends in stomatal response to ozone and water deficit: a unique relationship of midday values to growth and allometry in Pima cotton?

“…; Meinzer & Grantz ; Grantz & Yang ; Grantz et al . ; Meinzer ). Reduced allocation to roots in this cultivar has been linked with reduced translocation of carbohydrates from source leaves (Grantz & Farrar , ).…”