© 1997 Heron Publishing—Victoria, Canada
Geographical variation in water relations, hydraulic architecture and terpene composition of Aleppo pine seedlings from Italian
provinces
Roberto Tognetti, Marco Michelozzi and Alessio Giovannelli
Istituto Miglioramento Genetico delle Piante Forestali, Consiglio Nazionale delle Ricerche, via Atto Vannucci 13, I 50134,
Firenze, Italy / Received February 8, 1996
Summary
Ecotypic variations in leaf conductance, soil-to-leaf hydraulic conductance, components of tissue water potential, hydraulic
architecture parameters and xylem embolism were examined in greenhouse-grown two-year-old Aleppo pine (Pinus halepensis Mill.) seedlings from six origins representing the geographic range of the species in Italy. Cortical resin composition of
the seedlings was also determined. Measurements were made on well-watered seedlings and on seedlings subjected to recurring
severe drought. Drought-stressed seedlings had lower mean leaf conductances, transpiration rates and soil-to-leaf hydraulic
conductances than well-watered seedlings. They also exhibited more negative osmotic potentials, higher relative water deficit
at incipient plasmolysis, but a similar maximum modulus of elasticity. Drought-stressed seedlings showed a higher degree of
xylem embolism, a lower Huber value, lower leaf specific conductivity and lower specific conductivity than well-watered seedlings.
Drought-stressed seedlings of provenances from more xeric habitats (Tremiti, Porto Pino and Mottola) had greater leaf conductances,
transpiration rates and soil-to-leaf hydraulic conductances than drought-stressed seedlings of provenances from more mesic
habitats (Imperia, Otricoli and Vico del Gargano). They also showed higher osmotic adjustment and a lower degree of xylem
embolism. Among provenances, there were no significant differences in hydraulic architecture parameters in response to the
drought treatment; however, Tremiti and Porto Pino seedlings displayed smaller drought-induced reductions in specific conductivity
and leaf specific conductivity, respectively, than seedlings from other provenances. These differences suggest that seedlings
from xeric provenances, especially Tremiti, have greater resistance to desiccation than seedlings from mesic provenances.
No clear association was found between terpene variability and the other traits investigated, although terpene composition
was related to the geographical distribution of the provenances. We conclude that the drought-tolerance responses of Tremiti
make it a more suitable provenance than the others for establishment on sites prone to severe soil water deficits.
Keywords:
drought, ecotypic variation, embolism, monoterpene.
