A study of geographic variation of maritime pine (Pinuspinaster Ait.) 9 years old, regarding height growth, transpiration and sap pressure daily kinetics has been performed in two sites, one in coastal sand dune and the other one in a more interior well-drained sandy moor. Successive height increments were measured from the 4th to the 9th year of growth and the year × provenance interaction was investigated. Transpiration and sap pressure were measured on 2-year-old needle fascicles. Results show discriminant variations between provenances and suggest some hypotheses about the possible ways of natural selection concerning drought resistance. The provenances North Landes (France) and Leiria (Portugal) grow best and strongly react to any variation of environmental factors as reflected by the high value of the slope of their regression lines (regression of their annual mean on the overall annual mean). Such a genotypie instability coincides with an intense physiologic activity (large flux of water correlated with a strong loss of weight by transpiration, reaching after 3 min 2% of the total dry weight of the separated needles and associated with the lowest sap pressure when the sun is around zenith). On the contrary, the Morocan provenance Tamjoute shows a large stability; its daily curves of transpiration and sap pressure reach early their maximum and minimum and therefore express a stress avoidance. Between these two extreme behaviours, the provenances Cazorla (south Spain) and Porto-Vecchio (Corsica) have intermediate values of transpiration and sap pressure, and their height growth shows a relative stability of response to environmental change.
Vegetation zonation on a Natal coastal sand-dune system in relation to salt spray and soil salinity
