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

Abstract

Plant responses to ozone (O3 ) and water deficit (WD) are commonly observed, although less is known about their interaction. Stomatal conductance (gs ) is both an impact of these stressors and a protective response to them. Stomatal closure reduces inward flux of O3 and outward flux of water. Stomatal measurements are generally obtained at midday when gas exchange is maximal, but these may not be adequate surrogates for stomatal responses observed at other times of day, nor for non-stomatal responses. Here, we find in Pima cotton that stomatal responses to O3 observed at midday do not reflect responses at other times. Stomata were more responsive to O3 and WD near midday, despite being at quasi-steady state, than during periods of active opening or closing in morning or evening. Stomatal responsivity to O3 was not coincident with maximum gas exchange or with periods of active regulation, but coincident with plant sensitivity to O3 previously determined in this cultivar. Responses of pigmentation and shoot productivity were more closely related to stomatal responses at midday than to responses at other times of day under well-watered (WW) conditions, reflecting higher stomatal responsivity, sensitivity to O3 , and magnitude of midday gs . Under WD conditions, shoot responses were more closely related to early morning gs. Root responses were more closely related to early morning gs under both WW and WD. Responses of stomata to O3 at midday were not good surrogates for stomatal responses early or late in the day, and may not adequately predicting O3 flux under WD or when maximum ambient concentrations do not occur near midday.

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

“…The eO 3 limited the growth of aboveground organs of soybean, but no changes in root growth and root/shoot ratio were found due to the similar decreases in shoot and root dry biomass, consistent with previous study on soybean (Morgan et al 2003, Hewitt et al 2016. Besides its influence on biomass accumulation, eO 3 caused an increase in height growth at the expense of diameter growth (Table 1), consistent with the findings that O 3 alters plant allometry towards slender stem shapes (Pretzsch et al 2010, Grantz et al 2016. Increased specific leaf area, whole-plant leaf-area to biomass ratio and whole-plant leaf-area to root biomass ratio would increase carbon acquisition at the cost of higher transpiring surface per unit of carbon fixation (Poorter 1999, Brunner et al 2015.…”

“…The enhanced whole‐plant height to biomass ratio (HMR) and total leaf area/root biomass imply that eO 3 also restricts the uptake capacity of root for higher transpiring leaf surface of soybean plants (Sultan , Oikawa and Ainsworth ). These altered growth patterns would have important consequences for plant hydraulic properties and plant water relations, which can potentially affect the growth and survival of O 3 ‐sensitive species under O 3 pollution and changing climate in the future (Grantz , Wilkinson and Davies , Grantz et al ).…”

Ozone effects on plants in natural ecosystems

“…In droughted Pima cotton ( Gossypium barbadense L.) exposed to elevated O 3 , the relative reduction in stomatal conductance was half that of well‐watered plants with elevated O 3 and 20% that of well‐watered plants grown in low O 3 in early to mid‐morning (Grantz et al . (). Production in Pima cotton was correlated with early morning, not midday assimilation.…”

Plants and the changing environment

“…; Grantz et al . ). The complexity of the physiological basis of ozone tolerance is considered in soybean genotypes differing in ozone tolerance (Chutteang et al .…”

“…It is suggested that the integration of responses to multiple stresses may not be synergistic, as is often assumed (see Visser et al 2016), and that responses to specific stresses, such as drought and salinity, may be linked through metabolomics, and distinguished from responses to other stresses, such as high temperature (Sun et al 2016). A number of studies investigate the interaction of ozone with specific aspects of changing climate, emphasising impacts on photosynthesis, plant water relations and antioxidant metabolism in tree and crop species (Fusaro et al 2016;Grantz et al 2016). The complexity of the physiological basis of ozone tolerance is considered in soybean genotypes differing in ozone tolerance (Chutteang et al 2016).…”