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In animal‐pollinated hermaphroditic species, larger and xenogamous flowers increase male‐biased resource allocation, whereas smaller and selfing flowers invest disproportionally more resources to female function. In Cistaceae, an entomophilous and hermaphroditic Mediterranean family, this pattern generally follows a phylogenetic signal. However, resource allocation to carpels is independent of phylogeny, which suggests trait divergences among closely related species during the diversification into different environmental conditions.We tested this hypothesis across 37 species of Cistaceae along a temperature and precipitation gradient, including semiarid, dry, subhumid and humid sites. We quantified the proportions of dry mass and nutrient investment to carpels and tested the influence of the climatic gradient and site‐specific precipitation on the interspecific variation in carpel resource allocation.Lowest and highest percentages of resource allocation to carpels ranged from 1.5–4.2% to 24.2–36.6%, respectively. The proportion of resources comprised in carpels significantly decreased with increasing precipitation/decreasing temperature. Thus, carpels comprised proportionally more resources under drier and hotter conditions, especially in semiarid sites.Our results demonstrate how the extent of climatic constraints is more important than phylogenetic relationships in determining stress‐induced differences in carpel resource allocation across species of Cistaceae in a Mediterranean environment. We suggest that allocation of proportionally more resources to carpels in drier and hotter sites lies within a strategy to deal with the most stressful conditions by means of a high reproductive effort. Resource allocation to carpels in Cistaceae is a non‐conservative trait that increases in hotter and drier sites. [ABSTRACT FROM AUTHOR]

The phenology of anthocyanin accumulation in leaves has been widely studied in perennial plants; several hypotheses have been proposed to explain their adaptive significance. Here, we explored the photoprotection hypothesis in Silene germana, a Mediterranean annual plant with late‐spring/summer flowering.We analysed the temporal patterns of anthocyanin accumulation in photosynthetic calyces, leaves and stems and throughout the reproductive season, and their relationship with flower abortion, florivory and plant mortality due to drought. In addition, the flavonoid production and the photoinhibitory response were measured in a shading experiment.The whole plant becomes red at the end of the flowering and remains red until fruiting and senescence. Calyces were redder on the side with more sun exposition. Aborted flowers showed redder calyces than those of fruiting flowers. No effect of plant redness on florivory or plant mortality was found. The shading experiment showed a positive relationship between anthocyanin accumulation and intensity of solar radiation, but plants growing in absence of UV showed similar redness than full sunlight plants. Plants growing in natural shade lack anthocyanins but produced the same amount of non‐anthocyanin flavonoids. Anthocyanic and non‐anthocyanic plants showed similar photochemical efficiency (Fv/Fm) after sun exposition, but in early morning, the former showed lower Fv/Fm values. Plants growing in full sunlight produced more fruits than those of natural shade plants.Whole‐plant reddening during fruiting and senescence appears to be a property of S. germana. Our results suggest that anthocyanin accumulation depends on sunlight intensity, but non‐anthocyanin flavonoids are produced constitutively. [ABSTRACT FROM AUTHOR]

In animal-pollinated hermaphroditic plants, optimal floral allocation determines relative investment into sexes, which is ultimately dependent on flower size. Larger flowers disproportionally increase maleness whereas smaller and less rewarding flowers favour female function. Although floral traits are considered strongly conserved, phylogenetic relationships in the interspecific patterns of resource allocation to floral sex remain overlooked. We investigated these patterns in Cistaceae, a hermaphroditic family., We reconstructed phylogenetic relationships among Cistaceae species and quantified phylogenetic signal for flower size, dry mass and nutrient allocation to floral structures in 23 Mediterranean species using Blomberg's K-statistic. Lastly, phylogenetically-controlled correlational and regression analyses were applied to examine flower size-based allometry in resource allocation to floral structures., Sepals received the highest dry mass allocation, followed by petals, whereas sexual structures increased nutrient allocation. Flower size and resource allocation to floral structures, except for carpels, showed a strong phylogenetic signal. Larger-flowered species allometrically allocated more resources to maleness, by increasing allocation to corollas and stamens., Our results suggest a major role of phylogeny in determining interspecific changes in flower size and subsequent floral sex allocation. This implies that flower size balances the male-female function over the evolutionary history of Cistaceae. While allometric resource investment in maleness is inherited across species diversification, allocation to the female function seems a labile trait that varies among closely related species that have diversified into different ecological niches. [ABSTRACT FROM AUTHOR]

Although decline of Aleppo pine was observed long ago and several climatic and biotic factors have been previously associated with this complex process, site factors involved in this decline remain poorly understood. The objective of the work described here was to identify site factors associated with canopy condition. Canopy condition was estimated both by a visual estimation of defoliation, and by an indirect estimation of leaf area index ( LAI) and other stand- and light-related parameters through the analysis of hemispherical photographs. A high percentage of damaged trees (81%) along with high levels of defoliation in plots (up to 53%) and trees (up to 85%) were recorded. Regression models showed that the site factors associated with defoliation were basal area, age, crown depth and elevation, while those associated with LAI were diameter at breast height, tree density and canopy openness. Analysis of hemispherical photographs proved to be a useful method for LAI estimation, but not for estimation of defoliation due to heterogeneous defoliation patterns caused by fungal pathogens detected in the study area. Soils and climatic conditions were common to all plots, so their influence could not be tested, but poor soil conditions and climatic restraints are known in this area, including low soil productivity, frequent summer droughts and high numbers of frost days. The results obtained suggest that several factors were associated with the decline of Pinus halepensis, including age, basal area, canopy openness, diameter, height and tree density. These factors can influence canopy condition, and thus, they might be acting as predisposing factors for the decline. The modulation of these factors is possible if suitable forest management strategies are applied, which could lead to a decrease of the decline incidence. [ABSTRACT FROM AUTHOR]

Ecological limits to phenotypic plasticity ( PP), induced by simultaneous biotic and abiotic factors, can prevent organisms from exhibiting optimal plasticity, and in turn lead to decreased fitness. Herbivory is an important biotic stressor and may limit plant functional responses to challenging environmental conditions such as shading. In this study we investigated whether plant functional responses and PP to shade are constrained by herbivory, and whether such constraints are due to direct effects based on resource limitation by considering ontogeny. We used as a model system the relict tree Prunus lusitanica and implemented an indoor experiment to quantify the response of saplings of different ages to shade and herbivory. We measured five functional traits and quantitatively calculated PP. Results showed that herbivory did not constrain functional responses or PP to shade except for shoot:root ratio ( SR), which, despite showing a high PP in damaged saplings, decreased under shade instead of increasing. Damaged saplings of older age did not exhibit reduced constraints on functional responses to shade and generally presented a lower PP than damaged saplings of younger age. Our findings suggest that herbivory-mediated constraints on plant plasticity to shade may not be as widespread as previously thought. Nonetheless, the negative effect of herbivory on SR plastic expression to shade could be detrimental for plant fitness. Finally, our results suggest a secondary role of direct effects (resource-based) on P. lusitanica plasticity limitation. Further studies should quantify plant resources in order to gain a better understanding of this seldom-explored subject. [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

The Brazilian Atlantic Forest is a typically multi-layer tropical forest, while cerrado (savanna) is a patchy habitat with different physiognomy. Despite these differences, both habitats have high light heterogeneity. Functional traits of Dalbergia nigra and D. miscolobium from the Atlantic Forest and cerrado, respectively, were evaluated under shade (25% of full sunlight) and full sunlight in a nursery experiment. We hypothesised that both species should benefit from high phenotypic plasticity in relation to light. Plasticity was estimated using the relative distance phenotypic index (RDPI). D. miscolobium had lower shoot growth under both light conditions, suggesting it has low competitive capacity in the forest environment, which could explain its limited ability to expand over areas of Atlantic Forest. The studied species exhibited photoprotection strategies under high light and improved light capture under low light. Stomatal conductance, ETRmax (maximum electron transport rate), PPFDsat (saturating photosynthetically active photon flux density), chlorophyll and carotenoid content had higher RDPI than stem morphological traits. Although both species showed considerable phenotypic plasticity, D. miscolobium had higher RDPI for eight of 11 evaluated traits. This high plasticity could be one of the factors that explain the occurrence of this species in a wide range of environmental conditions, from open grassland to dense woodlands, and it could also reflect its adaptation to high light. D. nigra also had considerable plasticity and good growth performance in both shade and full sunlight, but its absence in areas of cerrado suggests that factors other than light limit its occurrence in these habitats. [ABSTRACT FROM AUTHOR]

Flowering phenology is an important and poorly understood plant trait that may possibly be related to the invasiveness potential of alien species. The present work evaluates whether flowering time of invasive alien species is a key trait to overcome the climatic filters operating in continental Mediterranean ecosystems of Spain (characterised by summer drought and low temperatures in winter). We conducted comparisons between the flowering phenology of the invasive species in their native range and in Spain, and between flowering phenology of 91 coexisting invasive–native species pairs. For the alien species, geographical change from the native to the invaded region did not result in shifts in the start and the length of the flowering period. Overall, climatic conditions in the native range of species selected for a flowering pattern is maintained after translocation of the species to another region. Flowering of tropical and temperate invasive alien species peaked in summer, which contrasts with the spring flowering of native and invasive alien species of Mediterranean climate origin. By exploiting this new temporal niche, these invasive alien species native to tropical and temperate regions benefit from reduced competition with natives for abiotic and biotic resources. We suggest that human-mediated actions have reduced the strength of the summer drought filter in particular microhabitats, permitting the invasion of many summer-flowering aliens. [ABSTRACT FROM AUTHOR]

Drought is the main selection agent in Mediterranean ecosystems and it has been suggested as an important evolutionary force responsible for population diversification in these types of environments. However, population divergence in quantitative traits can be driven by either natural selection, genetic drift or both. To investigate the roles of these forces on among-population divergence in ecophysiological traits related to drought tolerance (carbon isotope discrimination, specific leaf area, leaf size and leaf nitrogen content), we compared molecular and quantitative genetic differentiation in a common garden experiment including thirteen cork oak ( Quercus suber L.) populations across a gradient of rainfall and temperature. Population differentiation for height, specific leaf area, leaf size and nitrogen leaf content measured during a dry year far exceeded the molecular differentiation measured by six nuclear microsatellites. Populations from dry-cool sites showed the lowest nitrogen leaf content and the smallest and thickest leaves contrasting with those from humid-warm sites. These results suggest (i) these traits are subjected to divergence selection and (ii) the genetic differences among populations are partly due to climate adaptation. By contrast, the low among-population divergence found in basal diameter, annual growth and carbon isotopic discrimination (a surrogate for water use efficiency) suggests low or no divergence selection for these traits. Among-population differentiation for neutral markers was not a good predictor for differentiation regarding the quantitative traits studied here, except for leaf size. The correlation observed between the genetic differentiation for leaf size and that for molecular markers was exclusively due to the association between leaf size and the microsatellite QpZAG46, which suggests a possible linkage between QpZAG46 and genes encoding for leaf size. [ABSTRACT FROM AUTHOR]

Question: What is the influence of management on the functioning of vegetation over time in Mediterranean ecosystems under different climate conditions? Location: Mediterranean shrublands and forests in SE Iberia (Andalusia). Methods: We evaluated the Normalized Difference Vegetation Index (NDVI) for the 1997-2002 time series to determine phenological vegetation patterns under different historical management regimes. Three altitudinal ranges were considered within each area to explore climate × management interactions. Each phenological pattern was analysed using time series statistics, together with precipitation (monthly and cumulative) and temperature. Results: NDVI time series were significantly different under different management regimes, particularly in highly transformed areas, which showed the lowest NDVI, weakest annual seasonality and a more immediate phenological response to precipitation. The NDVI relationship with precipitation was strongest in the summer-autumn period, when precipitation is the main plant growth-limiting factor. Conclusions: NDVI time series analyses elucidated complex influences of land use and climate on ecosystem functioning in these Mediterranean ecosystems. We demonstrated that NDVI time series analyses are a useful tool for monitoring programmes because of their sensitivity to changes, ease of use and applicability to large-scale studies. [ABSTRACT FROM AUTHOR]

Effects of temperature and photoperiod and their interactions on budburst and on the use of carbon reserves were examined in two Mediterranean oaks differing in wood anatomy and leaf habit. Seedlings of Quercus ilex subsp. ballota (evergreen and diffuse-porous wood) and Q. faginea (semi-deciduous and ring-porous wood) were grown under two temperatures (12 and 19 °C) and two photoperiods (10 and 16 h) in a factorial experiment. In the 16 h photoperiod at 19 °C, photosynthesis was suppressed in half of the seedlings by covering leaves with aluminium foil. The concentration of soluble sugars, starch and lipids in leaves, stems and roots was assessed before and after budburst. Under the 12 °C treatment (mean current temperature in early spring in the Iberian Peninsula), budburst in Q. faginea occurred earlier than in Q. ilex. Higher temperature promoted earlier budburst in both species, mostly under the 16 h photoperiod. This response was less pronounced in Q. faginea because its budburst was also controlled by photoperiod, and because this species needs to construct a new ring of xylem before budburst to supply its growth demands. Therefore, dates of budburst of the two species became closer to each other in the warmer treatment, which might alter competitive relations between the species with changing climate. While Q. ilex relied on carbon reserves for budburst, Q. faginea relied on both carbon reserves and current photoassimilates. The different responses of the two Quercus species to temperature and photoperiod related more to xylem structure than to the source of carbon used for budburst. [ABSTRACT FROM AUTHOR]

Question: What is the main ecological process determining species assemblage in roadside herbaceous plant communities? Location: Roadside slopes (roadcuts and embankments) in the south (Málaga, mesic Mediterranean) and east (Valencia, dry and continental) of the Iberian Peninsula. Methods: We identified 417 plant species, from which we selected the 331 most abundant (within the 70th abundance percentile) at each site. We compiled information on 28 functional traits and on the biogeographic range of each of these 331 species. We quantified the phylogenetic signal of each trait for the species of each community and determined the number of functional convergences or divergences over the phylogenetic tree for each of the four situations (roadcuts and embankments in the two sites). Results: There was a significant phylogenetic signal in many traits, being positive in Valencia embankments and negative in Valencia roadcuts with almost no signal in any type of slope in Málaga. Each trait was significantly correlated with 20% - 35% of all other traits but correlation coefficients were low. No significant phylogenetic signal was found for the species' distribution range in any of the four communities studied, which might be the consequence of the complex mixture of biogeographic origins of the species found in these communities. Conclusion: The lack of a phylogenetic signal in most traits in Málaga, a climatically favourable locality, suggests that competitive exclusion was the main process involved in the assemblage of these communities. The significant and either positive or negative phylogenetic signal (in embankments and roadcuts respectively), the latter coupled with a significant number of functionally convergent nodes in the phylogenetic tree, suggests that environmental filtering is the most likely process involved in the harsh locality of Valencia. [ABSTRACT FROM AUTHOR]

We have studied here the cellular distribution of several regulatory peptides in hormone-producing cells of the human pituitary during the fetal period. Immunohistochemistry was used to show the expression of several regulatory peptides, namely Angiotensin-II, Neurotensin and Galanin, at successive gestational stages and their co-localization with hormones in the human fetal adenohypophysis. Somatotrophs, gonadotrophs and thyrotrophs were differentiated earliest. At gestational week 9, Angiotensin-II immunoreactivity was co-localized only with growth hormone immunoreactivity in somatotrophs, one of the first hormone-producing cells to differentiate. This co-localization remained until week 37. Neurotensin immunoreactivity was present in gonadotrophs and thyrotrophs in week 23, after FSH and TSH hormone differentiation. Galanin immunoreactivity was present in all hormone-producing cell types except corticotrophs. The different pro-opiomelanocortin-derived peptides were detected at different stages of gestation and adrenocorticotrophic hormone immunoreaction was the last to be detected. Our results show an interesting relationship between regulatory peptides and hormones during human fetal development, which could imply that these peptides play a regulatory role in the development of pituitary function. [ABSTRACT FROM AUTHOR]

Question: Do specific environmental conditions affect the performance and growth dynamics of one of the most invasive taxa (Carpobrotus aff. acinaciformis) on Mediterranean islands? Location: Four populations located on Mallorca, Spain. Methods: We monitored growth rates of main and lateral shoots of this stoloniferous plant for over two years (2002-2003) , comparing two habitats (rocky coast vs. coastal dune) and two different light conditions (sun vs. shade). In one population of each habitat type, we estimated electron transport rate and the level of plant stress (maximal photochemical efficiency Fv/Fm) by means of chlorophyll fluorescence. Results: Main shoots of Carpobrotus grew at similar rates at all sites, regardless habitat type. However, growth rate of lateral shoots was greater in shaded plants than in those exposed to sunlight. Its high phenotypic plasticity, expressed in different allocation patterns in sun and shade individuals, and its clonal growth which promotes the continuous search of available resources, contributed to a good growth and photochemical efficiency of Carpobrotus in the relatively moderate shade of the understories of Mediterranean shrublands and woodlands. Each main shoot of a Carpobrotus clone (which can have several dozens main shoots) grows ca. 40 cm per year, which explains its vigorous habitat colonization capacity. Conclusion: The highly plastic morphological response to different light regimes of this taxon contributes to a rapid colonization of heterogeneous coastal Mediterranean environments spreading well beyond the open sand dune systems where it has been often reported. [ABSTRACT FROM AUTHOR]

This article reviews the current status of research about the histogenesis and morphofunctional characteristics of chromaffin cells in the adrenal medulla. First, this study reports the selective migration, transcription and activation factors, and the morphological events of the chromaffin cell precursors during adrenal medulla development. Subsequently, the morphofunctional characteristics of adrenergic and non-adrenergic cells are considered, with particular reference to the characteristics of chromaffin granules and their biological steps, including their formation, traffic (storage, targeting and docking), exocytosis in the strict sense and recapture. Moreover, the relationship of chromaffin cells with other tissue components of the adrenal medulla is also revised, comprising the ganglion cells, sustentacular cells, nerves and connective-vascular tissue. [ABSTRACT FROM AUTHOR]

Spatial heterogeneity of abiotic factors influences the structure and function of forests and must be taken into account for their conservation and sustainable management. In this study, we evaluate the heterogeneity of abiotic environmental variables in managed cork oak ( Quercus suber L.) forests in southern Spain at patch, site and regional scales. The extent of spatial heterogeneity depended on the environmental variable examined and the scale considered. For example, soil Mn and P and light availability in the understorey were very heterogeneous at the regional scale, while soil N had low regional heterogeneity, but high spatial variability, at patch scale, attributed to open overstorey and grazing disturbance. There was a general trend of increasing heterogeneity with spatial scale. We also study the effects of a silvicultural practice—shrub clearing on the forest environment and its consequence for spatial heterogeneity. Shrub clearing increased understorey light and decreased its spatial heterogeneity with idiosyncratic effects on soil properties and their spatial heterogeneity at each site. Finally, we compare the heterogeneity (estimated by the coefficient of variation) obtained in these cork oak forests with a database compiled from published studies on other forest environments. The comparison revealed a remarkable extent of abiotic heterogeneity in the cork oak forests studied, suggesting that a sustainable management of these forests should combine intrinsic and human induced abiotic heterogeneity to preserve crucial ecological processes and to maintain high levels of biodiversity. [ABSTRACT FROM AUTHOR]

Question: What are the edge effect responses of epiphytic lichen communities in Mediterranean Quercus pyrenaica forest? Location: Central Spain. Methods: We established ten transects perpendicular to a road dissecting a well conserved remnant of Q. pyrenaica forest into two sections. Transects extended from the forest/road edge to 100 m into the forest. Data were collected from seven plots in each transect at different distances from the edge. Variables were grouped into stand scale variables (distance to edge, number of trees per plot, mean diameter per plot, irradiance) and tree scale variables (diameter and height of sampled trees, aspect of the sampled square and relative height of the square). We used General Mixed Linear Models and constrained ordination techniques to test the hypothesis that the spatio-temporal heterogeneity of light and water controls the occurrence of lichens and bryophytes along the edge-interior gradient in the Q. pyrenaica forest. Results: Microclimatic parameters vary in a non-linear way; edge and interior stands showed the most divergent and extreme values. Although the micro-environment within Mediterranean forests is heterogeneous, interior conditions are apparently suitable for the performance of some specific forest epiphytes. Consequently, species richness does not show significant differences along the gradient. Total epiphytic cover increases towards the forest interior, but distance to the edge together with other predictors at the tree scale (aspect and height of the square) are the most relevant predictors for the composition and structure of these communities. Conclusions: Composition and structure of epiphytic communities in a Mediterranean semi-deciduous forest are affected by the edge between the forest and the road constructed. Since some extremely rare lichens only occur at interior stands, the conservation of these threatened elements requires urgent conservation measures because well preserved and unmanaged forests in the Mediterranean region are very rare. [ABSTRACT FROM AUTHOR]

1. This paper explores the idea that functional heterogeneity (variability of a system property affecting ecological processes) is only a fraction of the available structural heterogeneity (variability of a property measured without reference to ecological effects) caused by non-random propagule dispersal. We report the effect of acorn dispersal by jays on the light environment experienced by Holm Oaks (Quercus ilexL.) during early recruitment in a Mediterranean montane forest.2. Four light variables were estimated by studying hemispherical photographs: direct site factor (DSF); indirect site factor (ISF); and potential direct radiation during April (PDRApril) and August (PDRAugust). Means and variances of these variables were compared before and after the dispersal of acorns by jays.3. The landscape occupied by Holm Oaks was very heterogeneous, which translated into differences in the available light among microhabitats of up to one order of magnitude.4. Because of the spatial pattern of acorn dispersal, the light environment of the oaks during their establishment was much more homogeneous than that in the whole landscape.5. This demonstrates that the heterogeneity relevant for plant recruitment is not necessarily that of the landscape as a whole.Functional Ecology(2004)18, 787–792 [ABSTRACT FROM AUTHOR]

ABSTRACT To understand the role of leaf-level plasticity and variability in species invasiveness, foliar characteristics were studied in relation to seasonal average integrated quantum flux density (Q int ) in the understorey evergreen species Rhododendron ponticum and Ilex aquifolium at two sites. A native relict population of R. ponticum was sampled in southern Spain (Mediterranean climate), while an invasive alien population was investigated in Belgium (temperate maritime climate). Ilex aquifolium was native at both sites. Both species exhibited a significant plastic response to Q int in leaf dry mass per unit area, thickness, photosynthetic potentials, and chlorophyll contents at the two sites. However, R. ponticum exhibited a higher photosynthetic nitrogen use efficiency and larger investment of nitrogen in chlorophyll than I. aquifolium . Since leaf nitrogen (N) contents per unit dry mass were lower in R. ponticum , this species formed a larger foliar area with equal photosynthetic potential and light-harvesting efficiency compared with I. aquifolium . The foliage of R. ponticum was mechanically more resistant with larger density in the Belgian site than in the Spanish site. Mean leaf-level phenotypic plasticity was larger in the Belgian population of R. ponticum than in the Spanish population of this species and the two populations of I. aquifolium. We suggest that large fractional investments of foliar N in photosynthetic function coupled with a relatively large mean, leaf-level phenotypic plasticity may provide the primary explanation for the invasive nature and superior performance of R. ponticum at the Belgian site. With alleviation of water limitations from Mediterranean to temperate maritime climates, the invasiveness of R. ponticum may also be enhanced by the increased foliage mechanical resistance observed in the alien populations. [ABSTRACT FROM AUTHOR]

Diurnal courses of leaf water potential (ψ[sub 1]), gas exchange and chlorophyll fluorescence were measured in natural sun and shade populations of Heteromeles arbutifolia throughout the seasons of an unusually dry El Niño year in Central California. The onset of drought resulted in decreased stomatal conductance and net photosynthesis in both sun and shade plants. However, the decline in ψ[sub 1] was much greater and carbon gain was much more strongly limited by the development of drought stress in the shade than in the sun. Photorespiratory energy dissipation was significantly higher in the sun than in the shade in spring and autumn, but not during the summer. Pre-dawn photochemical efficiency (F[sub v]/F[sub m]) was significantly higher in the shade than in the sun during the spring but the differences disappeared during the summer and autumn. The strong irradiance in the open field site studied led to a chronic but only mild reduction in F[sub v]/F[sub m], with values around 0.79. Summer sunflecks led to a sustained photo-inhibition in shade plants, which exhibited a significant reduction in pre-dawn F[sub v]/F[sub m] of 10% with the onset of drought. Photo-inhibition became relatively more important for carbon gain in the shade than in the sun due to the low photochemical efficiency under the low light that follows sunflecks. Sun plants of H. arbutifolia exhibited a rather efficient photoprotection against strong irradiance conferred by both the architecture of the crown and the physiology of the leaves. There is evidence that El Niño events and the associated droughts have become more frequent and severe. Counterintuitively, the effects on plant performance of such extreme droughts could be more critical in the shade than in the sun. [ABSTRACT FROM AUTHOR]

Examines population divergence in the phenotypic plasticity of the response of evergreen oak quercus coccifera to the light environment in the Mediterranean Basin. Description of quercus coccifera; Basis of light response analysis; Occurrence of quercus coccifera in the light environment.

Increasing tree species diversity in Mediterranean forests could reduce drought‐induced hydraulic impairments through improved microclimate and reduced competition for water. However, it remains unclear if and how species diversity modulates tree hydraulic functions and how impacts may shift during the growing season. Using unmanaged Mediterranean forest stands composed of one (i.e., monospecific) or four (i.e., multispecific) tree species, we examined the seasonal dynamics of in‐situ hydraulic traits (predawn and midday leaf water potential – Ψpd and Ψmd, xylem‐ and leaf‐specific hydraulic conductivity – KS and KL, percentage loss of conductivity – PLC, specific leaf area – SLA, and Huber value – HV) in four co‐existing Pinus and Quercus species over two years. We mainly observed adverse impacts of species diversity with lower Ψpd, Ψmd, KS, KL, and higher PLC in multispecific compared to monospecific stands, especially for the two pines. These impacts were observed all along the growing season but were stronger during the driest periods of the summer. Beneficial impacts of diversity were rare and only occured for oaks (Q. faginea) after prolonged and intense water stress. Our findings reveal that mixing oaks and pines could mainly enhance hydraulic impairments for all species during the dry season, suggesting a potential decline in mixed Mediterranean forests under future climate. [ABSTRACT FROM AUTHOR]

Gas exchange and chlorophyll fluorescence techniques were used to evaluate the acclimation capacity of the schlerophyll shrub Heteromeles arbutifolia M. Roem. to the multiple co-occurring summer stresses of the California chaparral. We examined the influence of water, heat and high light stresses on the carbon gain and survival of sun and shade seedlings via a factorial experiment involving a slow drying cycle applied to plants grown outdoors during the summer. The photochemical efficiency of PSII exhibited a diurnal, transient decrease (ΔF/Fm') and a chronic decrease or photoinhibition (Fv/Fm) in plants exposed to full sunlight. Water stress enhanced both transient decreases of ΔF/Fm' and photoinhibition. Effects of decreased ΔF/Fm' and Fv/Fm on carbon gain were observed only in well-watered plants since in water-stressed plants they were overidden by stomatal closure. Reductions in photochemical efficiency and stomatal conductance were observed in all plants exposed to full sunlight, even in those thatwere well-watered. This suggested that H. arbutifolia sacrificed carbon gain for water conservation and photoprotection (both structurally via shoot architecture and physiologically via down-regulation) andthat this response was triggered by a hot and dry atmosphere together with high PFD, before severe water, heat or high PFD stresses occur. We found fast adaptive adjustments of the thermal stability of PSII (diurnal changes) and a superimposed long-term acclimation (days to weeks) to high leaf temperatures. Water stress enhanced resistance of PSII to high temperatures both in the dark and over a wide range of PFD. Low PFD protected photochemical activity against inactivation byheat while high PFD exacerbated damage of PSII by heat. The greater interception of radiation by horizontally restrained leaves relative to the steep leaves of sun-acclimated plants caused photoi... [ABSTRACT FROM AUTHOR]