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Juniperus drupacea Labill is a unique representative tree which, nowadays, has limited geographical range. In Greece, it exists only in the southeastern part of the Peloponnese, and it is labeled as endangered according to the IUCN in Europe. In the light of climatic changes, a conservation plan which will secure its adaptation and resilience is important. Knowledge of the genetic and the epigenetic diversity of J. drupacea in Greece can establish a pledge for sustainability. In this study, genetic diversity with amplified fragment length polymorphism (AFLP) markers and epigenetic diversity assessed with methylation-sensitive amplification polymorphism (MSAP) were used for eleven subpopulations of the species. Simultaneously, first assessment between midday water potential (Ψmd) and epigenetic diversity was calculated in order to determine drought response of the species. Results showed that genetic diversity was higher than epigenetic diversity and no subpopulation differentiation was observed. No significant correlations were found between geographic, epigenetic, and genetic diversity, indicating that the genetic diversity is uncoupled from epigenetic diversity. A significant negative correlation between epigenetic Shannon index and Ψmd was found. The holistic research of genetic and epigenetic diversity paves the way for an effective conservation plan for the species. [ABSTRACT FROM AUTHOR]

The increase in the duration and severity of summer droughts due to global climate change will adversely affect forests, and it is very important to examine the drought stress that trees are exposed to as a species due to increasing drought and to understand the response of the species. In this study, the effects of drought stress on physiological (midday water potential, relative water content, gas exchange parameters) and biochemical (total soluble sugar content) characteristics were investigated in Quercus trojana P.B. Webb. seedlings. Under greenhouse conditions, two treatments were applied to 1+0 old seedlings: control (2-3 times a week for watering) and drought stress (no watering for 30 days). Drought stress was repeated twice, consecutively. At the end of the two-month stress cycle, drought stress decreased the midday water potential, relative water content, net photosynthesis rate, stomatal conductance and transpiration rate, while increasing the water use efficiency and total soluble sugar content. In the study, strong relationships were found between midday water potential, net photosynthesis rate, stomatal conductance, transpiration rate and total soluble sugar content.

This paper investigated the effect of summer drought conditions on physiological and biochemical parameters in Pinus nigra subsp. pallasiana, Pinus brutia, Quercus infectoria and Crataegus monogyna under field conditions and determined seasonal changes in those parameters. The study focused on soil water content, soil temperature, midday water potential, proline, total soluble sugar and photosynthetic pigment (chlorophyll a, chlorophyll b, chlorophyll a+b and carotenoid) contents during the growing period. Seasonal changes in those parameters in Pinus nigra subsp. pallasiana, Pinus brutia, Quercus infectoria and Crataegus monogyna were determined under the same environmental conditions in the natural forest area of the western Mediterranean region. P. nigra, P. brutia, Q. infectoria and C. monogyna had similar seasonal changes in physiological responses, though they had different seasonal changes in biochemical responses in natural habitat. Crataegus monogyna had the lowest midday water potential at all sampling dates. In general, Q. infectoria had the highest photosynthetic pigment content, whereas P. nigra and P. brutia had the lowest. P. nigra and P. brutia (coniferous) had lower photosynthetic pigment content and higher midday water potential than those presented by Q. infectoria and C. monogyna (broad-leaved) during the short-term dry period. The results showed that P. nigra and P. brutia (coniferous) were more sensitive than Q. infectoria and C. monogyna (broad-leaved) during summer drought in the natural forest. [ABSTRACT FROM AUTHOR]

Table olive trees which grow under high evaporative demand with no rainfall in arid zones such as the Azapa Valley, Arica and Parinacota Region, Chile, depend exclusively on irrigation; a common practice recommended in areas with low water availability is regulated deficit irrigation (RDI). The aim of the study was to describe the response of olive to variable water supply after pit hardening to harvest (167–199 days) in a mature orchard of cv. Azapa in a biennial cycle. Full replenishment was scheduled until the end of pit hardening (11 weeks after full bloom), then four treatments were compared: T 0 , 100% of crop evapotranspiration (ET c ); T 1 , 80% ET c ; T 2 , 60% ET c and T 3 , 40% ET c . The water stress imposed was considered as moderate, according to stomatal conductance data. Water relations were affected more by the level of water supply than by crop load, with a significant reduction of midday water potential in the most restrictive treatment. Vegetative growth occurred mainly during the unstressed period, while shoot growth rate was affected by crop load level. Fruit size distribution in the “on” year (12100 kg ha −1 ) were 14 and 20% higher in control and T 1 (−2.0 MPa), while a reduction in fruit volume was found with −2.7 MPa (T 3 ). In the “off” year, yield in RDI treatments were 49 and 67% lower than control, without differences in fruit size distributions. This response could be related to the increase in the rigidity of the cell wall and osmotic adjustment in the most restrictive treatment, as an adaptive response of the trees to arid conditions. [ABSTRACT FROM AUTHOR]

The capacitative release of water from sapwood allows photosynthesis to continue for longer into dry periods, both diurnally and seasonally. However, costs of high capacitance include increased vulnerability to xylem cavitation. The degree of reliance on stored water is predicted to differ among environments as a result of this trade-off., Xylem water potential and sapwood capacitance were measured on 32 evergreen sclerophyll shrub and tree species in eastern Australia, sampled from four sites contrasting in soil nutrients and rainfall., Capacitance calculated over species' typical shoot water potential operating range was threefold higher for species from high compared to low-rainfall sites, and 1·5-fold higher for species from high compared to low-nutrient sites., To determine whether these site differences were related to extrinsic (e.g. water availability) or intrinsic (e.g. species anatomical construction) factors, we calculated capacitance at two common operating ranges; that is, the mean range in water potential observed for low-rainfall species (ΔΨlow rain) and the mean range for high-rainfall species (ΔΨhigh rain). While no difference was seen between low- and high-rainfall species in release of stored water across ΔΨhigh rain, across ΔΨlow rain, the high-rainfall species released 38% more stored water than low-rainfall species. Presumably these differences reflect underlying differences in anatomy, such as wood density, which was lower in high-rainfall species., These results accord with predictions that (i) species from wetter sites exhibit less negative stem water potentials and high sapwood capacitance, enabling them to maintain function under variable conditions characterized by many short, dry periods, while (ii) species from low-rainfall sites have wood anatomies conferring tolerance to very low water potentials, with low sapwood capacitance, enabling them to survive longer through unpredictable and extended periods of low rainfall. The finding that the degree to which species rely on stem-stored water varies with site rainfall suggests that changes in drought regimes (e.g. incidence, duration and severity) under future climates could differentially affect species according to the capacitance properties of their woody tissues. [ABSTRACT FROM AUTHOR]