© 2002 Heron Publishing—Victoria, Canada
Response of a mature Pinus laricio plantation to a three-year restriction of water supply: structural and functional acclimation to drought
Sergio Cinnirella (1), Federico Magnani (2), Antonio Saracino (3) and Marco Borghetti (3, 4)
1. Istituto di Ecologia e Idrologia Forestale, CNR, Cosenza, Italy / 2. CNR-IMGPF, Firenze, Italy / 3. Dipartimento di Produzione Vegetale, Universitá della Basilicata, Potenza, Italy / 4. Author to whom correspondence should be addressed (borghetti@unibas.it) / Received February 22, 2001; accepted June 8, 2001; published online December 1, 2001
Summary
The response of mature forest stands to a reduction in water availability has received little attention. In particular, the
extent to which a short-term reduction in gas exchange can be alleviated in the long-term by acclimation processes is not
well understood. We studied the impact of a severe reduction in water availability on the water relations and growth of 35-year-old
Pinus laricio Poiret. trees in a replicated experiment. Sapwood and needle increments, soil and tree water status, stand transpiration,
xylem embolism and plant hydraulic architecture were monitored over a 3-year period in control and drought-treated plots.
Needle length was reduced in drought-treated trees by 30, 19 and 29%, and sapwood increments by 50, 27 and 24% over the 3
years. Drought did not result in tree mortality or in extensive xylem embolism or foliage dieback. On the contrary, a conservative
water-use strategy was observed, because minimum leaf water potentials did not differ between treatments or over the season.
Plant hydraulic resistance was also unaffected by restricted water availability. Stand transpiration was strongly reduced
by drought treatment over the summer, but not during the winter, despite significant differences in leaf area between control
and drought-treated trees, implying higher transpiration rates per unit leaf area in the droughted plants. This suggests that
water transport capacity, rather than the amount of leaf area, controlled stand transpiration, which is at variance with expectations
based on experiments with seedlings and short-term experiments with mature trees.
Keywords:
growth, homeostasis, hydraulic resistance, long-term effects, transpiration.
