Mechanisms for drought tolerance in two Mediterranean seasonal dimorphic shrubs

Abstract

Pressure-volume curves were constructed on a seasonal basis in two malacophyllous, drought semi-deciduous Mediterranean species (Phlomis fruticosa L. and Cistus creticus L.). Summer reduction of water potential at the turgor loss point in both species was less pronounced than corresponding changes in relative water content (RWC) at the turgor loss point, implying the existence of turgor maintenance mechanisms. However, actual summer leaf water potentials and RWCs in the field indicate that plants may experience zero or negative turgor pressure during the dry period. In both species, gradual decreases in osmotic potential and apoplastic relative water content, as well as increases in tissue elasticity, were observed during the summer. In particular, P. fruticosa exhibited a remarkable elasticity throughout the year. Indications for osmotic adjustment processes were also recorded. Critical (sublethal) RWCs measured during the winter and summer were lower not only from the corresponding RWCs at turgor loss point but also from the actual midday RWCs usually observed in the field. Both species seem to use a combination of elastic and osmotic adjustments in order to maintain their turgidity during the dry period. However, even though turgor may be lost during part of the summer, water deficits do not usually surpass critical levels under field conditions. This is probably achieved through the occurrence of two leaf populations (summer and winter leaves) with differential physiological drought tolerance.

Tissue-water relations of two co-occurring evergreen Mediterranean species in response to seasonal and experimental drought conditions

“…Thus, the discrepancy in ranking of π 100 and π 0 appeared to be related to differences in tissue elasticity (Ranney et al 1991). Nonetheless, in response to drought, the species studied relied on elastic rather than osmotic adjustment (Lo Gullo and Salleo 1988;Grammatikopoulos 1999). Elastic adjustment has been identified as an important mechanism for turgor maintenance and drought tolerance in tree species (Kwon and Pallardy 1989;White et al 2000).…”

Age-related physiological and structural traits of chestnut coppices at the Castelli Romani Park (Italy)

“…Gas exchange measurements were carried out during the morning (from 9.00 to 12.00 a.m.) in the following days: 20 in the same position considered for gas exchange. Ψ was measured using a portable pressure chamber (SKPM 1400, Skye Instruments, Llandrindod Wells, UK) with a sheet of wet filter paper inside the chamber to avoid water loss during measurements [37].…”

“…Ψ was measured using a portable pressure chamber (SKPM 1400, Skye Instruments, Llandrindod Wells, UK) with a sheet of wet filter paper inside the chamber to avoid water loss during measurements [37]. RWC was calculated by 100 × (fresh mass -dry mass) / (water saturated massdry mass) [20]; the sample leaves were enclosed in plastic sheaths immediately before cutting [63].…”

Differential osmoregulatory capabilities of common spiny mice (Acomys cahirinus) from adjacent microhabitats

“…During the dry season, the vegetation in the Mediterranean ecosystem is expected to have an increased particle (or osmotic) concentration owing to higher evaporation of water (Main, 1986;Haim & Izhaki, 1994;Grammatikipoulos, 1999). Therefore, animals such as A. cahirinus, which may depend upon vegetation as a water source, face an increasing osmotic load as the dry season progresses.…”