Response to drought stress differs among Pinus pinea provenances

Abstract

Severe drought causes decline in growth and stability of Mediterranean forests because autochthonous species and provenances may reach their drought tolerance limits. Stone pine (Pinus pinea L.), which is one of the pri-mary Mediterranean forest tree species due to its high economic value, has been extremely suffering from drought during the past years. We investigated turgor loss point traits of shoots derived from pressure-volume curves, vulnerability to cavitation of lateral shoots and the physiological response (water potential, photosyn-thetic activity) to an experimental drought of two-year-old seedlings of seven stone pine provenances native to Turkey with the aim of providing suggestions for selection of provenances for future afforestations. We moni-tored turgor loss point in the period from June-August and hydraulic vulnerability in July. Water potentials corresponding to 50% conductivity loss (P50) and 25% relative water loss were significantly higher (less nega-tive) in the northern provenances, indicating a higher hydraulic vulnerability to cavitation. Reaction to drought stress varied considerably among provenances. Provenances originating from higher latitudes (more northern regions) had higher relative water content at turgor loss point (RWCTLP) and modulus of elasticity (epsilon) in August, but also higher midday and pre-dawn water potentials as a result of the experimental drought. RWCTLP and epsilon in July were negatively related to ME (mean of the maximum temperatures of June, July and August) and positively to the pluviothermic quotient (Q). August RWCTLP was as well lower in provenances from regions with higher ME. Regarding the strategy towards drought, P. pinea provenances ranged from isohydry in the most northern provenance to anisohydry in the most southern provenances. Isohydry is usually related with avoidance of dehydration, while anisohydry is related with tolerance to dehydration and a lower P50. For future reforestation it is suggested to select provenances with a more anisohydric strategy towards drought stress.