Water relations, photosynthesis, xylem embolism and accumulation of carbohydrates and cyclitols in twoEucalyptusspecies (E. camaldulensisandE. torquata) subjected to dehydration-rehydration cycle

摘要

Key message Resilience to xylem embolism and the accumulation of cyclitols are promising criteria for the selection of drought-resilientEucalyptusspecies. 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 usedEucalyptusspecies (E. camaldulensisandE. 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 thatE. camaldulensiswas more resilient to drought thanE. torquata. During the dehydration phase, plant water status, cell turgor, net photosynthetic rate (P-n) and photosynthetic machinery integrity were less affected inE. camaldulensisthanE. torquata. After rehydration, these variables were at levels similar to those of control plants in the case ofE. camaldulensis, but not in the case ofE. torquata. The restoration rate was 96% and 88% for predawn leaf water potential (psi(pd)), and it was 98% and 77% forP(n)inE. camaldulensisandE. torquata, respectively. The resilience ofE. camaldulensisagainst drought may be due to the efficiency of two determinant survival mechanisms: osmotic adjustment and resistance to xylem embolism. Indeed,E. camaldulensiswas less vulnerable to drought-induced xylem embolism and more able to repair embolized xylem vessels thanE. torquata. Xylem refilling reduced embolism rate (percent loss of conductivity) to 15% inE. camaldulensis, compared to 22% inE. torquata. Furthermore,E. camaldulensiswas found capable of efficient osmotic adjustment thanE. torquataby accumulating soluble carbohydrates, especially cyclitols. Indeed, under severe drought (psi(pd)of - 7 MPa),E. camaldulensisaccumulated 9.27 mg g(- 1)DW of quercitol and 3.81 mg g(- 1)DW of pinitol; it also had three times moremyo-inositol in its leaves thanE. torquata. We suggest the use of resilience to xylem embolism and the accumulation of cyclitols to screenEucalyptusgermplasm for drought resistance.