Photosynthetic adaptation ofEuphorbia fractiflexa(Euphorbiaceae) and survival in arid regions of the Arabian Peninsula

Abstract

Arid regions of the Arabian Peninsula are characterized by a short wet season with erratic rainfall, high temperature, and high evaporation. In these arid regions, the leafless stem succulent Euphorbia fractiflexa S. Carter & J.R.I.Wood (Euphorbiaceae) is an abundant perennial. Work presented in this paper aimed at investigating crassulacean acid metabolism (CAM) as a physiological adaptation crucial for survival of E. fractiflexa in arid regions of the Arabian Peninsula. Work involved investigations of stomatal diffusive conductance, chlorophyll fluorescence, and cell sap titratable acidity. Results represent the first report of obligate CAM in E. fractiflexa. Low values of stomatal conductance and dampening of CAM acidificationÁ deacidification cycles during the long dry season also denoted tendency of this species to shift from obligate CAM to CAM-idling. Results also showed water stress-induced reduction in Photosystem II (PSII) activity occurring in concomitance with increased non-photochemical quenching of chlorophyll fluorescence denoting operation of non-photochemical energy dissipation mechanisms that are important for photoprotection of the photosynthetic machinery under stress conditions.

Continuous high and low temperature induced a decrease of photosynthetic activity and changes in the diurnal fluctuations of organic acids in Opuntia streptacantha

“…This decrease in Φ PSII was attributed to an over-energized of PSII during phase III of CAM photosynthesis [ 38 ]. Likewise, the same behavior was observed in other CAMs [ 19 ] and succulent plants [ 20 ]. In no-succulent plants such as wheat and peach, Fv/Fm and ΦPSII were dramatically decreased at temperatures between 30°C and 45°C, while the F 0 values were greatly increased as result of a severe stress in which complex antenna disconnection and severe disintegration of PSII was observed [ 32 , 33 ].…”

“…Therefore, differences in photosynthetic efficiency determined from the parameters and ratios mentioned above can be used to detect physiological changes resulting from environmental conditions such as extreme temperatures [ 18 ]. For instance, in the obligate CAM Euphorbia fractiflexa , temperatures of 40°C in field induced a decrease of Fv/Fm and Φ PSII , suggesting that this response is given by the physiological adaptation to tolerate drastic environmental conditions [ 19 ]. Moreover, Musil et al (2009) [ 20 ] found that in southern African succulents growing to high temperatures (40–54°C), a decrement of the photosynthetic performance was the principal cause of massive mortalities of endemic desert plants.…”

Comprehensive review of morphological adaptations and conservation strategies of cactiform succulents: A case study of Euphorbia species in arid ecosystems

“…Cactiform Euphorbia with ribbed stems, resemble "columnar cacti", and are often confused with the Cactaceae, but are identifiable by their twin spines carried on a spine shield and their ability to secrete a "milky sap" called latex in response to physical aggression (Chaudhary et al, 2023). Furthermore, these cactiforms adopt the CAM photosynthetic system (Edwards & Donoghue, 2006;Al-Turki et al, 2014;Niechayev et al, 2019). This photosynthetic regime specifically allows it to adapt to prolonged drought (Evans et al, 2014;Masrahi et al, 2015).…”