Acclimation to future atmospheric CO₂ levels increases photochemical efficiency and mitigates photochemistry inhibition by warm temperatures in wheat under field chambers

Abstract

A study was conducted over 2 years to determine whether growth under elevated CO(2) (700 μmol mol(-1) ) and temperature (ambient + 4 °C) conditions modifies photochemical efficiency or only the use of electron transport products in spring wheat grown in field chambers. Elevated atmospheric CO(2) concentrations increased crop dry matter at maturity by 12-17%, while above-ambient temperatures did not significantly affect dry matter yield. In measurements with ambient CO(2) at ear emergence and after anthesis, growth at elevated CO(2) concentrations decreased flag leaf light-saturated carbon assimilation. The quantum yield of electron transport (Φ(PSII) ) measured at ambient CO(2) and higher irradiances increased at ear emergence and decreased after anthesis in plants grown at elevated CO(2) . At higher light intensities, but not in low light, photochemical quenching (qP) decreased after growth in elevated CO(2) conditions. Growth under CO(2) enrichment increased dark- (Fv:Fm) and light-adapted (Fv':Fm') photochemical efficiencies, and decreased the chlorophyll a:b ratio, suggesting an increase in light-harvesting complexes relative to PSII reaction centres. A relatively higher decrease in carbon assimilation than the decrease in Φ(PSII) pointed to a sink other than CO(2) assimilation for electron transport products at defined growth stages. With higher light intensities, warmer temperatures increased Φ(PSII) and Fv':Fm' at ear emergence and decreased Φ(PSII) after anthesis; in ambient-but not elevated-CO(2) , warmer temperatures also decreased qP after anthesis. CO(2) fixation increased or did not change with temperature, depending on the growth stage and year. We conclude that elevated CO(2) decreases the carbon assimilation capacity, but increases photochemistry and resource allocation to light harvesting, and that elevated levels of CO(2) can mitigate photochemistry inhibition as a result of warm temperatures.

The effect of elevated CO2 on photochemistry and antioxidative defence capacity in wheat depends on environmental growing conditions – A FACE study

“…Long-term exposure to e[CO 2 ], however, can reduce stimulation of carboxylation (manifested in a decrease in V cmax , a surrogate for in vivo activity of Rubisco) through a process called photosynthetic acclimation (Ghannoum et al, 2007;Seneweera et al, 2002). In wheat, for example, a decline of A was reported when acclimation effects of photosynthesis were assessed (Gutierrez et al, 2009;MartinezCarrasco et al, 2005;Sicher and Bunce, 1997).…”

Evaluation of chlorophyll fluorescence in different densities of spring barley

“…Another factor which may have influenced a decline in Fo values at BBCH 31 could be a high number of sunshine hours per day (Table 1), resulting in increased leaf temperature, which also affected the fluorescence. There is some evidence suggesting that higher temperature decreased photochemical quenching in spring wheat (Gutierrez et al 2009). Whereas, from barley sowing to BBCH 31 a very little rainfall occurred (25% of long-term mean), the soil surface was very dry and the reserves of productive moisture reached a critical threshold; however, with increase in moisture shortage, leaf temperature increases.…”

Response of common barley (Hordeum vulgare L.) physiological parameters to agricultural practices and meteorological conditions

“…The decline of A was found also for rice (Takai et al, 2010), maize (Efthimiadou et al, 2010), sugar beet (Tsialtas, Maslaris, 2008), cotton (Ko, Piccinni, 2009) during the growing season. Gutierrez et al (2009) found that A declined between heading and 10-13 days after anthesis. Other authors indicated that the A of wheat flag leaves initially increased after anthesis, reaching a maximum on the 21 st day after anthesis, then gradually decreased (Cai et al, 2008 (Table 4).…”