Effects of ambient O₃ on wheat during reproductive development: Gas exchange, photosynthetic pigments, chlorophyll fluorescence, and carbohydrates

Abstract

The current concentrations of O 3 have been shown to cause significant negative effects on crop yield. The present levels of ozone may not induce visible symptoms in most of plants, but can result in substantial losses in reproductive output. This paper considers the impact of ambient O 3 on gas exchange, photosynthetic pigments, chlorophyll (Chl) fluorescence and carbohydrate levels in the flag leaf of wheat plants during various stages of reproductive development using open-top chambers. Mean O 3 concentration was 45.7 ppb during wheat growth and 50.2 ppb after flag leaf development. Reproductive stage showed higher exceedence of O 3 above 40 ppb compared to the vegetative stage. Diurnal variations in net photosynthetic rate (P N ) and stomatal conductance (g s ), intercellular CO 2 concentration (C i ), F v /F m ratio, photosynthetic pigments, soluble sugars, and starch were measured at 10, 30, and 50 days after flag leaf expansion (DAFE). The results showed reductions in P N , g s , F v /F m ratio, photosynthetic pigments and starch, and increases in C i , F 0 , and soluble sugars in nonfiltered chambers (NFCs) compared to filtered chambers (FCs). Maximum changes in measured parameters were observed at 50 DAFE (i.e. grain filling and setting phase). Diurnal variation in P N showed double peaked curve in both FCs and NFCs, but delayed peak and early depression in NFCs. Stomatal conductance was significantly lower in NFCs. The study suggests that higher prevalence of ambient O 3 during reproductive development led to significant alteration in physiological vitality of wheat having potential negative influence on yield.

The impact of elevated ozone on the ornamental features of two flowering plants (Tagetes erecta Linn. and Petunia hybrida Vilm.)

“…This response may have been due to the significant reductions in photosynthetic pigment contents in leaves exposed to elevated O 3 (Figures 4, 5). A positive relationship between Chl and photosynthesis was detected in previous studies (Black et al, 2007;Rai et al, 2011;Yendrek et al, 2013), further corroborating the important role of Chl in CO 2 reduction. Elevated O 3 exposure not only affects total biomass accumulation, but it also alters biomass partitioning into the shoot and root (Hoshika et al, 2013).…”

Effect of drought and heat stresses on photosynthesis, pigments, and xanthophyll cycle in alfalfa (Medicago sativa L.)

“…Illumination of cucumber seedlings under heat stress conditions resulted in inhibition of Chl biosynthesis by 60% (Tewari and Tripathy 1998). Chl content and the ratio of Chl a/b were significantly reduced under drought stress (Alonso et al 2001, Lu et al 2002, Guo et al 2005, Liu et al 2011, Rai et al 2011. Heat stress significantly reduced the Chl content of heat-sensitive alfalfa cultivars (Wassie et al 2019).…”

OlderThinopyrum intermedium(Poaceae) plants exhibit superior photosynthetic tolerance to cold stress and greater increases in two photosynthetic enzymes under freezing stress compared with young plants

“…To avoid issues of changing source versus sink balance, only leaves on vegetative tillers were chosen, even at the summer dates. As weather permitted, we took the measurements during either the morning (08:30–12:30h) or the afternoon (14:00–16:00h), matching peak times for wheat photosynthesis ( Rai et al , 2011 ), setting photosynthetically active irradiance equal to 1200 µmol m −2 s −1 , equivalent to mid-morning full sunlight in May. Chamber relative humidity was 55–75% and leaf temperatures were ~2 ºC above ambient: leaves were allowed to equilibrate until fluctuations in A were within 5%.…”