Rapid recovery of photosynthesis and water relations following soil drying and re-watering is related to the adaptation of desert shrub Ephedra alata subsp. alenda (Ephedraceae) to arid environments

Abstract

Rapid recovery of photosynthesis and water relations following soil drying and re-watering is related to the adaptation of desert shrub Ephedra alata subsp. alenda (Ephedraceae) to arid environments a b s t r a c t Ephedra alata subsp. alenda is the most important pioneer plant of the moving and semi-stable sand dunes in the deserts and steppes of south Tunisia and occurs naturally in the Grand Erg Oriental, one of the most extreme habitats for plant growth on the planet. A new analysis of physiological performance of this medically important and internationally threatened xerophytic shrub was conducted to assess possible mechanisms of drought tolerance and how these relate to its ecological success. Five-month old plants, grown under controlled climatic conditions, were subjected to a well-watered control treatment or progressive drought by withholding water for 14 d with subsequent recovery for 7 d. Soil water depletion significantly reduced stem relative water content (RWC) water potential (« w ) and osmotic potential (« ). Ephedra displayed more negative « w and « values of ca. −3.5 and −4.1 MPa, respectively, at the end of the drought treatment, and were associated with turgor loss. Low stem « w reduced stomatal conductance (g s ), photosynthetic CO 2 assimilation rates (A CO 2 ), transpiration (E) and internal CO 2 concentration (C i ). However, instantaneous (WUE; A CO 2 E −1 ) and intrinsic (WUE i ; A CO 2 g −1 s ) water use efficiency (WUE) increased gradually as water deficit was intensified. Stomatal closure therefore only exerted limited control against dehydration and could not compensate for decreases in soil water status, typical of anisohydric behavior. Drought-stressed stems accumulated high levels of proline up to 480% of control values, highlighting a pivotal role in osmotic adjustment during intense water deficit. In contrast, the osmotic adaptation to soluble sugars was limited. Drought-stressed plants increased A CO 2 , E, g s and C i and decreased WUE and WUE i during the first 48 h after re-watering, such that they reached similar values to those of control plants by the end of the experiment. Stem proline levels of drought-stressed plants returned to near control values with re-watering. Overall, rapid recovery of photosynthesis following drought-breaking moisture appears to be a critical mechanism allowing E. alata to withstand and survive dry environments.

Coordinated changes in photosynthetic machinery performance and water relations of the xerophytic shrub Ziziphus lotus (L.) Lam. (Rhamnaceae) following soil drying

“…The relationship between RWC and ψw has often been used to quantify the dehydration tolerance: tissues, which maintain a high RWC as ψw decreases are more tolerant to dehydration. In the present study, leaves of Z. lotus decreased their RWC values from 84 to 79% and did not drop below 60%, which is a typical characteristic of drought-tolerant species (Kawaguchi et al 2004, Gorantla et al 2007, Perera et al 2008, Gorai et al 2015.…”

“…(Maraghni et al 2014). It was found (Gorai et al 2015) that proline accumulation was significantly correlated to low ψw suggesting the involvement of this solute in osmotic adjustment. Similar trends of increase in proline and carbohydrates in leaves of some Ziziphus species during drought stress were also reported (Choudhary et al 1996, Clifford et al 1998, Arndt et al 2001, Maraghni et al 2011.…”

Relationship between leaf gas-exchange characteristics and the performance of Ziziphus spina-christi (L.) Willd. seedlings subjected to salt stress

“…The PN presented here clearly shows a correlation with shoot growth of Z. spina-christi treated with increased osmolarity of solutions. The relationship between PN and gs reveals a trade-off between water loss and carbon gain experienced by plants in contrasting environments (Gorai et al 2011(Gorai et al , 2015Maraghni et al 2019). The present study depicts that PN and gs under salt stress were positively associated (r = 0.93, P<0.01; Fig.…”

Responses of antioxidant enzymes, photosynthetic pigments and carbohydrates in micropropagated Pitcairnia encholirioides L.B. Sm. (Bromeliaceae) under ex vitro water deficit and after rehydration

“…alenda (Stapf) Trab. (Gorai et al, 2015) subjected to different periods of water stress followed by rehydration, with a reduction in proline content in leaves that had accumulated high amounts of this amino acid. Proline catabolism is an important regulator of cellular ROS balance and can influence in numerous additional regulatory pathways (Szabados and Savouré, 2010).…”