PHOTOSYNTHETICA

Photosynthetica 2006, 44(3):387 | DOI: 10.1007/s11099-006-0040-7

Different ability of three Mediterranean oak species to tolerate progressive water stress

F. Manes^1,*, M. Vitale¹, E. Donato¹, M. Giannini¹, G. Puppi¹

¹ Department of Plant Biology, University of Rome "La Sapienza", Rome, Italy

Inter-comparisons in the gas exchange patterns and root characteristics under both well-watered and drought conditions were done in three-years-old seedlings of three oak species (Quercus cerris L., Q. frainetto Ten., and Q. ilex L.) growing in controlled environment. Well-watered Q. cerris had greater physiological performances than other oaks, but under drought it was not able to face the water stress showing also structural modifications such as reduction of root length and average diameter. On the other hand, Q. ilex maintained root growth both in drought or well-watered soils. Moreover, it was able to keep open stomata also under water stress, although stomatal conductance (g _s) was low. Q. frainetto had an intermediate position in regard to its physiological and root structural characteristics between Q. cerris and Q. ilex under drought stress. For all oaks the relationship between g _s and the ratio of sub-stomatal and ambient CO₂ concentration (C _i/C _a) highlighted the dynamic adaptation of g _s to the increase of hydraulic resistances of leaf, stem, and roots portions, more evident during the air humidity change and progressive soil dehydration. This suggests a well-triggered above-and under-ground mechanism to endure the drought stress.

Additional key words: gas exchange; Quercus; net photosynthetic rate; root morphology; seedlings; species differences; stomatal conductance to water vapour; transpiration; xylem

Received: July 25, 2005; Accepted: December 20, 2005; Published: September 1, 2006  Show citation