The effect of ozone and drought on the photosynthetic performance of canola

Abstract

Canola plants were fumigated in open-top chambers with ozone (O 3) (120 ppb) under well-watered (WW) and water-stressed (WS) conditions for 4 weeks. Non-fumigated plants were also studied to facilitate comparison between treatments for the same week and over time. Therefore, the treatments were: WW, WW-O 3 , WS and WS-O 3. The fast chlorophyll a fluorescence transients OJIP for the four treatments emitted upon illumination of dark-adapted leaves were measured after week 1, 2, 3, 4 and analysed by the JIP-test to evaluate the resulting changes in photosynthetic performance. Ozone fumigation led to a decline of total performance index (PI total) in well-watered plants. The effect of O 3 was minor under drought conditions, as revealed by a decrease of PI total by 3%. The PI total decreased as the treatment was prolonged, due to leaf ageing for all cases and the decline was more pronounced under WW-O 3. Taking the average of all weeks, WW had the highest PI total and the lowest WW-O 3 (decrease by 27%), while in WS and WS-O 3 , it was lower than WW (14 and 17%, respectively). We found that the absorption (ABS)/reaction centre (RC) increases, while the maximum quantum yield of primary photochemistry (φ Po) undergoes slight changes, and trapping (TR 0)/RC closely followed the increase in ABS/RC. This indicates that O 3 and drought caused an increase in the functional antenna size. The maximum quantum yield of primary photochemistry showed slight differences for all treatments and over time, suggesting that this parameter is less sensitive to drought and O 3 stress. Therefore, the more sensitive components of the photosynthetic electron transport chain appeared to be the probability that an electron from the intersystem electron carriers is transferred to reduce end electron acceptors at the PSI acceptor side (δ Ro) and the RC density on a chlorophyll basis (RC/ABS).

Photosynthetic Responses of Canola and Wheat to Elevated Levels of CO2, O3 and Water Deficit in Open-Top Chambers

“…Under drought conditions, the decrease was significant only in wheat plants. This indicates that the effect of O 3 was minor under drought conditions in canola plants [53]. The reduction of the PI total was caused by the efficiency with which an electron from the intersystem electron carriers was transferred to reduce end electron acceptors at the PSI acceptor side, as well as the decline of the density of reaction centers, which, taking into account that φ Po remained nearly unchanged, represented an increase of the functional PSII antenna size [26].…”

The interactive effects of drought and heat stress on photosynthetic efficiency and biochemical defense mechanisms ofAmaranthusspecies

“…The effect of drought and heat stress on photosynthetic parameters has been extensively studied and different plants were considered in this respect (Bahrami et al, 2019 ; Goltsev et al, 2016 ; Kalaji et al, 2017 ; Lazár, 2015 ; Lichtenthaler et al, 2005 ; Maliba et al, 2018 ; Osipova et al, 2019 ; Oukarroum et al, 2012 ; Singh et al, 2019 ; Xue et al, 2017 ). However, the comparative analysis of the interactive effect at different intensities of drought and heat stress on photosynthetic parameters' response and other biochemical parameters across temperature regimes remained untouched in the cited studies.…”