c3.2.5 – The response of mature Pinus laricio trees to a three-year restriction of water supply: structural and functional acclimation to drought

Borghetti M (1)*, Cinnirella S (2), Magnani F (3), Saracino A (1)

(1) Dip.to Produzione Vegetale, Università della Basilicata, v. N. Sauro, 85 – 85100 Italy (2) IEIF – CNR, Rende CS (3) IMGPF-CNR, v. A. Vannucci 13 – 50134 Firenze
Collocazione: c3.2.5 – Tipo Comunicazione: Presentazione orale
3° Congresso SISEF *
Sessione 2: “Foreste e selvicoltura per gli equilibri climatici” *

Contatto: Marco Borghetti (borghetti@unibas.it)

Abstract: The response of mature forest stands to future reductions in water availability expected in Mediterranean areas as a result of Climate Change has received surprisingly little attention. To what extent the short-term reduction in gas exchange can be alleviated in the long-term by acclimation processes, in particular, is not well understood. We studied the impact of a severe reduction in water availability on the water relations and growth of 35-yr-old Pinus laricio trees by a replicated roof expriment. Sapwood and needle increments, soil and tree water status, stand transpiration, xylem embolism and plant hydraulic architecture were monitored over a period of three years in control and droughted plots. Needle lenght was reduced in droughted trees by 30, 19 and 29%, and sapwood increments by 66, 25 and 13% over the three years. Drought did not result in tree mortality, however, nor in extensive xylem embolism and foliage dieback. On the contrary, a strictly isohydric behaviour was observed, as minimum leaf water potentials did not differ among treatments or over the season. Plant hydraulic resistance was also not affected by the restriction in water availability. Stand transpiration was the same in the two treatments over the winter, despite significant differences in leaf area, 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, could control plant transpiration. The response of forest stands to drought is rather different from what would be expected from experiments on seedlings, or even from short-term experiments on mature trees. Several acclimation mechanisms, involving changes both in growth allocation and in tissue functional characteristics, enable mature trees to maintain a high degree of functional homeostasis in water relations, so reducing forest vulnerability even to extreme events.

Citazione: Borghetti M , Cinnirella S , Magnani F , Saracino A (2001). The response of mature Pinus laricio trees to a three-year restriction of water supply: structural and functional acclimation to drought . 3° Congresso Nazionale SISEF, Viterbo, 15 – 18 Ott 2001, Contributo no. #c3.2.5