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Water relations, photosynthesis, xylem embolism and accumulation of carbohydrates and cyclitols in two Eucalyptus species (E. camaldulensis and E. torquata) subjected to dehydration-rehydration cycle

Abstract : Key message Resilience to xylem embolism and the accumulation of cyclitols are promising criteria for the selection of drought-resilient Eucalyptus species. Abstract Due to the aridity of the climate in the southern Mediterranean region, the choice of suitable species for afforestation projects is crucial. The present study aims to compare resilience mechanisms against drought in two frequently used Euca-lyptus species (E. camaldulensis and E. torquata). Two-year-old self-rooted cuttings of the two species were grown in sand-filled pots and subjected to a dehydration period followed by rehydration. At regular intervals, water relations, gas exchange, chlorophyll fluorescence and xylem embolism were measured on these plants. In addition, carbohydrates and cyclitols were quantified in their leaves. The results revealed that E. camaldulensis was more resilient to drought than E. torquata. During the dehydration phase, plant water status, cell turgor, net photosynthetic rate (P n) and photosynthetic machinery integrity were less affected in E. camaldulensis than E. torquata. After rehydration, these variables were at levels similar to those of control plants in the case of E. camaldulensis, but not in the case of E. torquata. The restoration rate was 96% and 88% for predawn leaf water potential (Ψ pd), and it was 98% and 77% for P n in E. camaldulensis and E. torquata, respectively. The resilience of E. camaldulensis against drought may be due to the efficiency of two determinant survival mechanisms: osmotic adjustment and resistance to xylem embolism. Indeed, E. camaldulensis was less vulnerable to drought-induced xylem embolism and more able to repair embolized xylem vessels than E. torquata. Xylem refilling reduced embolism rate (percent loss of conductivity) to 15% in E. camaldulensis, compared to 22% in E. torquata. Furthermore, E. camaldulensis was found capable of efficient osmotic adjustment than E. torquata by accumulating soluble carbohydrates, especially cyclitols. Indeed, under severe drought (Ψ pd of − 7 MPa), E. camaldulensis accumulated 9.27 mg g − 1 DW of quercitol and 3.81 mg g − 1 DW of pinitol; it also had three times more myo-inositol in its leaves than E. torquata. We suggest the use of resilience to xylem embolism and the accumulation of cyclitols to screen Eucalyptus germplasm for drought resistance.
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Samira Souden, Mustapha Ennajeh, Sarra Ouledali, Nooman Massoudi, Hervé Cochard, et al.. Water relations, photosynthesis, xylem embolism and accumulation of carbohydrates and cyclitols in two Eucalyptus species (E. camaldulensis and E. torquata) subjected to dehydration-rehydration cycle. Trees - Structure and Function, Springer Verlag, In press, 1, 14 p. ⟨10.1007/s00468-020-02016-4⟩. ⟨hal-02928663⟩

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