Effects of germination inhibition on the dynamics of Quercus ilex stands

Abstract. Germination of Quercus ilex L. in coppice stands of this species in the western Mediterranean Basin was examined and a germination inhibitory process is proposed to explain some germination traits. Germination rate and seedling biomass of Q. ilex were greatly modified by watering acorns with various concentrations of aqueous soil extracts from a Q. ilex coppice stand but also when the acorns were sown in soil from Q. ilex coppice stands. In the aqueous extract experiment, Q. ilex germination and seedling weight both decreased as the aqueous extract concentration increased. In the soil type experiment, Q. ilex soil decreased the Q. ilex germination rate. Comparative studies with Q. pubescens germination (this species, replaced by Q. ilex around 5 000 B.P., is assumed to form the climax vegetation of the region) revealed that Q. pubescens was less sensitive to the aqueous extracts and soils of Q. ilex coppice stands. Inhibition of Q. ilex seed germination could be a major reason for the poor seed regeneration and suggested a possible comeback of Q. pubescens.     

Use of <Emphasis Type="Italic">Quercus ilex</Emphasis> subsp. <Emphasis Type="Italic">ballota</Emphasis> phenological and pollen-production data for interpreting <Emphasis Type="Italic">Quercus</Emphasis> pollen curves

Although aerobiological data are often used in phenological research as an indicator of flowering, airborne pollen concentrations are influenced by a number of factors that could affect pollen curves. This paper reports on a study of various aspects of reproductive biology in Q. ilex subsp. ballota, together with environmental factors influencing pollen release and transport, with a view of achieving reliable interpretation of Quercus pollen curves in Ourense (NW Spain). Aerobiological data were recorded from 2002 to 2004 at two sites in the province of Ourense. From 1st February to the end of the flowering period, phenological observations were carried out on 19 trees from the Q. ilex subsp. ballota population found in the Ourense area. Pollen production was calculated for the same trees. The chilling and heating requirements for triggering development were also calculated. The mean flowering period lasted 11-15 days. Reduced pollen output per catkin and, especially, a reduced number of catkins per tree in 2003 and 2004, prompted a marked decline in overall pollen production. Major differences observed in Q. ilex subsp. ballota pollen curves were attributed to the considerable influence both of weather conditions during pollination and pollen production. In years with high pollen production and weather conditions favouring pollen release, Q. ilex subsp. ballota contributed almost 10% to the total Quercus pollen curve. Around 20% of the pollen trapped was captured before or after flowering periods.     

Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks

The contribution of pre-dispersal seed predation to inter-specific differences in recruitment remains elusive. In species with no resistance mechanisms, differences in pre-dispersal predation may arise from differences in seed abundance (plant satiation) or in the ability of seeds to survive insect infestation (seed satiation). This study aimed to analyse the impact of pre-dispersal acorn predation by weevils in two co-occurring Mediterranean oaks (Quercus ilex and Quercus humilis) and to compare its relevance with other processes involved in recruitment. We monitored the patterns of acorn production and acorn infestation by weevils and we conducted experimental tests of acorn germination after weevil infestation, post-dispersal predation and seedling establishment in mixed forests. Monitoring and experimental data were integrated in a simulation model to test for the effects of pre-dispersal predation in recruitment. In both oaks pre-dispersal acorn infestation decreased with increasing acorn crop size (plant satiation). This benefited Q. ilex which exhibited stronger masting behaviour than Q. humilis, with almost a single and outstanding reproductive event in 6 years. Acorn infestation was more than twice as high in Q. humilis (47.0%) as in Q. ilex (20.0%) irrespective of the number of seeds produced by each species. Although germination of infested acorns (seed satiation) was higher in Q. humilis (60%) than in Q. ilex (21%), this could barely mitigate the higher infestation rate in the former species, to reduce seed loss. Conversely to pre-dispersal predation, no inter-specific differences were observed either in post-dispersal predation or seedling establishment. Our results indicate that pre-dispersal predation may contribute to differences in seed supply, and ultimately in recruitment, between co-existing oaks. Moreover, they suggest that seed satiation can barely offset differences in seed infestation rates. This serves as a warning against overemphasising seed satiation as a mechanism to overcome seed predation by insects. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of winter cold stress on photosynthesis and photochemical efficiency of PSII of the Mediterranean <Emphasis Type="Italic">Cistus albidus</Emphasis> L. and <Emphasis Type="Italic">Quercus ilex</Emphasis> L.

This study examined the photosynthetic and growth performances of potted plants of Cistus albidus L. and Quercus ilex L. submitted either to natural Mediterranean winter conditions or to mild greenhouse conditions. Plants grown outdoors exhibited lower light and CO₂-saturated CO₂ assimilation rates (A_sat) and apparent quantum yield (_i) than those indoors. Until mid-winter, C. albidus had higher A_sat than Q. ilex, but differences disappeared after a period of severe cold. Maximal photochemical efficiency of PSII (Fv/Fm) measured predawn was higher in C. albidus than in Q. ilex, and decreased throughout the season in outdoor plants. Fv/Fm also decreased at light saturation (A_sat) in both species. Fv/Fm was correlated with photosynthetic capacity and efficiency (quantum yield), but the resulting regression slopes were different between the two species. At the physiological level, C. albidus seemed to cope better with cold stress than Q. ilex. However, winter stress induced reduction of leaf absorptance, increased leaf mass per area, extensive leaf damage and high plant mortality in C. albidus. This suggests that the high performance of C. albidus leaves is not likely to be maintained for long periods of cold stress, and may therefore depend on continuous leaf replacement. Quercus ilex showed a conservative behaviour, with low net assimilation rates but greater leaf and plant survival than C. albidus.     

Increasing carbon discrimination rates and depth of water uptake favor the growth of Mediterranean evergreen trees in the ecotone with temperate deciduous forests

Tree populations at the low‐altitudinal or ‐latitudinal limits of species' distributional ranges are predicted to retreat toward higher altitudes and latitudes to track the ongoing changes in climate. Studies have focused on the climatic sensitivity of the retreating species, whereas little is known about the potential replacements. Competition between tree species in forest ecotones will likely be strongly influenced by the ecophysiological responses to heat and drought. We used tree‐ring widths and δ¹³C and δ¹⁸O chronologies to compare the growth rates and long‐term ecophysiological responses to climate in the temperate‐Mediterranean ecotone formed by the deciduous Fagus sylvatica and the evergreen Quercus ilex at the low altitudinal and southern latitudinal limit of F. sylvatica (NE Iberian Peninsula). F. sylvatica growth rates were similar to those of other southern populations and were surprisingly not higher than those of Q. ilex, which were an order of magnitude higher than those in nearby drier sites. Higher Q. ilex growth rates were associated with high temperatures, which have increased carbon discrimination rates in the last 25 years. In contrast, stomatal regulation in F. sylvatica was proportional to the increase in atmospheric CO₂. Tree‐ring δ¹⁸O for both species were mostly correlated with δ¹⁸O in the source water. In contrast to many previous studies, relative humidity was not negatively correlated with tree‐ring δ¹⁸O but had a positive effect on Q. ilex tree‐ring δ¹⁸O. Furthermore, tree‐ring δ¹⁸O decreased in Q. ilex over time. The sensitivity of Q. ilex to climate likely reflects the uptake of deep water that allowed it to benefit from the effect of CO₂ fertilization, in contrast to the water‐limited F. sylvatica. Consequently, Q. ilex is a strong competitor at sites currently dominated by F. sylvatica and could be favored by increasingly warmer conditions.     

Predicting the Recovery of <Emphasis Type="Italic">Pinus halepensis</Emphasis> and <Emphasis Type="Italic">Quercus ilex</Emphasis> Forests after a Large Wildfire in Northeastern Spain

Quercus ilex and Pinus halepensis are two of the most common tree species of the western Mediterranean basin. Both species regenerate reliably after fire: P. halepensis colonizes recently disturbed areas by effective seedling recruitment, while Q. ilex resprouts vigorously after disturbances. For this reason, the natural regeneration of these species after fire should ensure the re-establishment of a forest similar to that which existed before the fire. This study analyzes with a simple simulation model whether or not the relative abundance of monospecific and mixed forests of these species in the landscape is altered by fire. We also analyze the topographic factors and the forest structure before the fire that determine the changes in forest composition after fire. This study has been carried out in a large fire that occurred in NE Spain. Overall, 33% of plots changed to another community type, but this probability of change varied considerably among community types before the fire. Monospecific forests of P. halepensis or Q. ilex had a high probability of remaining in their original composition after the fire, whereas the resilience of mixed forests of these two species was quite low. Mixed forests changed for the most part to monospecific P. halepensis or Q. ilex forests. Analysis of several factors determining these changes indicated that only elevation as a significant topographical variable. The effect of fire was to increase the altitudinal differentiation between the two species. P. halepensis forests that changed to mixed or Q. ilex forests were those of highest elevation, while the mixed and Q. ilex plots that changed to P. halepensis forests were those located at the lowest elevations. Concerning structural variables before fire, density of Q. ilex trees before the fire showed a much greater effect than P. halepensis density in determining the post-fire community. Finally, burn severity also influenced the changes observed. For both P. halepensis and Q. ilex forests, plots that changed to another forest type were mainly those that burned more severely. In the case of mixed forests, even low fire severities involved high probabilities of change to monospecific forests.     

Release of Juniperus thurifera woodlands from herbivore‐mediated arrested succession in Spain

Question: Do abiotic constraints maintain monospecific woodlands of Juniperus thurifera? What is the role of biotic (livestock) versus abiotic (climate) drivers in the recruitment and growth of the different tree species? Location: Cabrejas range, Soria, north‐central Spain, 1200 m altitude. Methods: Stand history was reconstructed using dendro‐ecology and spatial pattern analysis, combined with historical data of livestock abundances and climatic records. Results: J. thurifera establishment occurred in two distinct pulses, with a tree component establishing in the late 1800s to early 1900s. Quercus ilex and Pinus sylvestris establishment was evident only from the late 1970s onward. Recruitment events were related to reductions in livestock browsing. J. thurifera spatial structure was clumped and Q. ilex showed a short‐scale aggregation to J. thurifera trees and saplings. Radial growth trends of J. thurifera saplings, Q. ilex and P. sylvestris were negatively related to livestock density. Summer drought limited the radial growth of all the study species, and P. sylvestris and Q. ilex grew faster than J. thurifera even after considering an age effect. Conclusions: The differences in radial growth patterns and recruitment pulses between species indicate that livestock browsing and not abiotic factors is the main factor controlling plant succession and structural development. In this process, J. thurifera acts as a nurse plant, facilitating the establishment of other tree species. Under the current low pressure from herbivores, formerly pure J. thurifera woodlands will change towards dense stands of mixed species composition.     

Water relations,gas exchange,and growth of resprouts and mature plant shoots of Arbutus unedo L. and Quercus ilex L.

Resprout and mature plant shoot growth, leaf water status and gas exchange behavior, tissue nutrient content, flowering, and production were studied for co-occurring shallow-rooted (Arbutus unedo L.) and deeprooted (Quercus ilex L.) Mediterranean tree species at the Collserola Natural Park in Northeast Spain Resprouts showed higher growth rates than mature plant shoots. During fall, no differences in eco-physiological performance of leaves were found, but mobilization of carbohydrates from burls strongly stimulated growth of fall resprouts compared to spring resprouts, despite low exposed leaf area of the fall shoots. During summer drought, resprouts exhibited improved water status and carbon fixation compared to mature plant shoots. Shoot growth of Q. ilex was apparently extended due to deep rooting so that initial slower growth during spring and early summer as compared to A. unedo was compensated. Tissue nutrient contents varied only slightly and are postulated to be of minor importance in controlling rate of shoot growth, perhaps due to the relatively fertile soil of the site. Fall flowering appeared to inhibit fall shoot growth in A. unedo, but did not occur in Q. ilex. The results demonstrate that comparative examinations utilizing vegetation elements with differing morphological and physiological adaptations can be used to analyze relatively complex phenomena related to resprouting behavior. The studies provide an important multi-dimensional background framework for further studies of resprouting in the European Mediterranean region.     

Effects of a severe drought on Quercus ilex radial growth and xylem anatomy

We assessed the response of Quercus ilex subsp. ballota to the severe summer drought recorded in 1994 in NE Spain through the study of changes in radial growth and wood anatomy. We selected a coppice stand in the Iberian Peninsula, which is characterized by a Mediterranean climate under continental influence. We measured internode length, tree-ring width, mean and maximum vessel diameter, and vessel density for 1981–1997. The annual predicted hydraulic conductance (K_h) was calculated following Hagen-Poisseuille's law. We compared the tree-ring width, vessel diameter and K_h of Q. ilex subsp. ballota and co-existing ring-porous oaks (Q. faginea, Q. pyrenaica) for a dry summer (1994) and a wet summer (1997). To evaluate the drought-resistance of xylem for Q. ilex subsp. ballota (dominant under continental conditions) and Q. ilex subsp. ilex (dominant in mild areas) we determined vulnerability curves. Dimensionless indices of internode length, tree-ring width, and vessel density were compared with climatic data (monthly total precipitation and mean temperature) using correlation analyses. Internode length, tree-ring width, K_h, and mean and maximum vessel diameter declined in 1994. According to vulnerability curves, Q. ilex subsp. ballota showed a greater drought resistance than Q. ilex subsp. ilex. During the year of growth, we found a positive influence of January and June–August precipitation on the internode length, tree-ring width, and vessel density. The response of Q. ilex subsp. ballota radial-growth to summer drought was comparable to that of Q. faginea latewood. Overall, growth and wood anatomy of Q. ilex subsp. ballota showed a plastic response to drought.     

Dampening effects of long‐term experimental drought on growth and mortality rates of a Holm oak forest

Forests respond to increasing intensities and frequencies of drought by reducing growth and with higher tree mortality rates. Little is known, however, about the long‐term consequences of generally drier conditions and more frequent extreme droughts. A Holm oak forest was exposed to experimental rainfall manipulation for 13 years to study the effect of increasing drought on growth and mortality of the dominant species Quercus ilex, Phillyrea latifolia, and Arbutus unedo. The drought treatment reduced stem growth of A. unedo (?66.5%) and Q. ilex (?17.5%), whereas P. latifolia remained unaffected. Higher stem mortality rates were noticeable in Q. ilex (+42.3%), but not in the other two species. Stem growth was a function of the drought index of early spring in the three species. Stem mortality rates depended on the drought index of winter and spring for Q. ilex and in spring and summer for P. latifolia, but showed no relation to climate in A. unedo. Following a long and intense drought (2005–2006), stem growth of Q. ilex and P. latifolia increased, whereas it decreased in A. unedo. Q. ilex also enhanced its survival after this period. Furthermore, the effect of drought treatment on stem growth in Q. ilex and A. unedo was attenuated as the study progressed. These results highlight the different vulnerabilities of Mediterranean species to more frequent and intense droughts, which may lead to partial species substitution and changes in forest structure and thus in carbon uptake. The response to drought, however, changed over time. Decreased intra‐ and interspecific competition after extreme events with high mortality, together with probable morphological and physiological acclimation to drought during the study period, may, at least in the short term, buffer forests against drier conditions. The long‐term effects of drought consequently deserve more attention, because the ecosystemic responses are unlikely to be stable over time.Nontechnical summaryIn this study, we evaluate the effect of long‐term (13 years) experimental drought on growth and mortality rates of three forest Mediterranean species, and their response to the different intensities and durations of natural drought. We provide evidence for species‐specific responses to drought, what may eventually lead to a partial community shift favoring the more drought‐resistant species. However, we also report a dampening of the treatment effect on the two drought‐sensitive species, which may indicate a potential adaptation to drier conditions at the ecosystem or population level. These results are thus relevant to account for the stabilizing processes that would alter the initial response of ecosystem to drought through changes in plant physiology, morphology, and demography compensation.     

Establishment of co‐existing Mediterranean tree species under a varying soil moisture regime

We investigated the responses of two co‐existing Mediterranean trees with different regeneration strategies (Phillyrea latifolia seedlings and Quercus ilex sprouts) to experimental drought below the forest canopy. We considered different recruitment stages and used leaf isotopic discrimination to estimate water use efficiency (WUE) and nitrogen availability and use. Drought decreased the emergence and survival of seedlings and sprouts. Survival and growth of older saplings were not influenced by drought. Seedling emergence of P. latifolia was higher than Q. ilex sprout production, but Q. ilex sprouts had higher survival and growth rates. These differences disappeared in the sapling stage. Carbon isotopic discrimination suggested that Q. ilex sprouts had higher WUE than P. latifolia seedlings. Drought increased WUE of recruits, particularly in Q. ilex. Water use regulation increased with ageing, particularly in P. latifolia. Q. ilex had higher δ¹⁵N values than P. latifolia; these were also higher under drier soil conditions. Current year seedlings had higher δ¹⁵N than saplings, particularly in P. latifolia, suggesting they exploit superficial soil layers. These results suggest that sprouts obtain benefit from resources stored in parent plants. At earlier stages, they perform better than seedlings. This response is not coupled to adult vulnerability to drought for these species, revealing the difficulty of predicting species dynamics during climate change.     

Biodiversity in different successional stages of Mediterranean enclaves distributed along Sinop Peninsula (Turkey)

The aim of this research was to evaluate plant diversity and the relationships between the distribution of Raunkiaer life forms and community structure, and species richness, at different successional stages in communities of Quercus ilex L., Erica arborea L. and Sarcopoterium spinosum (L.) Spach., distributed as enclaves in Sinop Province. Permanent sample plots were selected to determine plant diversity. The cover percentage of each plant species was recorded monthly during two vegetation periods. Raunkiaer life forms, and the Shannon–Wiener, Evenness, Simpson and Margalef indexes were determined. Twenty-three species in Quercus ilex, 96 species in Erica arborea, and 148 species in Sarcopoterium spinosum were identified. Hemicryptophyte dominancy was observed followed by phanerophytes in the Q. ilex community, and therophyte and hemicryptophyte dominancy in the E. arborea and S. spinosum communities, respectively. It was determined that the S. spinosum community was the most heterogeneous community while the Q. ilex community was more uniform than other communities. The variation in diversity indexes, homogeneity, and composition of life forms among communities adopting a similar climatic environment could result from a differentiation of environmental factors, which impact on community structuring, from biotic to abiotic at different successional stages of Mediterranean communities.     

The efficiency of nitrogen retranslocation from leaf biomass in Quercus ilex ecosystems

Nitrogen retranslocation from senescing leaves represents a crucial adaptation by tree species towards a more efficient use of this nutrient. As a result, this part of the nitrogen cycle has received increasing attention in recent years. However, there remain strong discrepancies with respect to the factors responsible for interspecific differences in the efficiency of this process.In the present work the seasonal pattern of leaf growth and the movement of nitrogen in leaves have been studied in a series of Quercus ilex plots with different levels of rainfall and soil quality in central-western Spain, as well as in 20 other woody species typical of this area. The percentage of nitrogen retranslocated was estimated from the difference between the maximum mass of nitrogen stored in the leaf biomass and the amount of this nutrient returned annually to the soil through leaf fall. Q. ilex appears as one of the least efficient species in the Mediterranean region in the recovery of nitrogen from senescing leaves (29.7% of the maximum pool). Furthermore, the older leaves of Q. ilex do not show the cycles of nitrogen withdrawal during new flushes of shoot growth, such as occurs in Pinus spp. This suggests that older leaves in Q. ilex do not play an important role as nitrogen storage organs.     

Elimination of oxalate contamination in RNA isolation from<Emphasis Type="Italic">Rumex obtusifolius</Emphasis>

Many plant RNA isolation techniques aim to prevent contamination by means of secondary phenolics, carbohydrates, RNase, and other chemicals. However, when applied in our laboratory to the isolation of RNA fromRumex obtusifolius, these protocols failed to produce good quality RNA. A major problem was contamination of the RNA samples with the secondary metabolite oxalate. The relative quantities of guanidine isothiocyanate extraction buffer to plant tissue used in the protocol had significant effects on oxalate contamination. An increase in extraction buffer, from 1.5 mL in the original method to 15 mL per 200–300 mg of tissue in our protocol, removed the oxalate from the RNA. This RNA was of a good quality and was suitable for molecular biology applications.     

Extracting DNA from ‘jaws’: high yield and quality from archived tiger shark (Galeocerdo cuvier) skeletal material

Archived specimens are highly valuable sources of DNA for retrospective genetic/genomic analysis. However, often limited effort has been made to evaluate and optimize extraction methods, which may be crucial for downstream applications. Here, we assessed and optimized the usefulness of abundant archived skeletal material from sharks as a source of DNA for temporal genomic studies. Six different methods for DNA extraction, encompassing two different commercial kits and three different protocols, were applied to material, so‐called bio‐swarf, from contemporary and archived jaws and vertebrae of tiger sharks (Galeocerdo cuvier). Protocols were compared for DNA yield and quality using a qPCR approach. For jaw swarf, all methods provided relatively high DNA yield and quality, while large differences in yield between protocols were observed for vertebrae. Similar results were obtained from samples of white shark (Carcharodon carcharias). Application of the optimized methods to 38 museum and private angler trophy specimens dating back to 1912 yielded sufficient DNA for downstream genomic analysis for 68% of the samples. No clear relationships between age of samples, DNA quality and quantity were observed, likely reflecting different preparation and storage methods for the trophies. Trial sequencing of DNA capture genomic libraries using 20 000 baits revealed that a significant proportion of captured sequences were derived from tiger sharks. This study demonstrates that archived shark jaws and vertebrae are potential high‐yield sources of DNA for genomic‐scale analysis. It also highlights that even for similar tissue types, a careful evaluation of extraction protocols can vastly improve DNA yield.     

Variation in tissue element concentrations in Quercus ilex L. over a range of different soils

In order to study the variability in nutrient concentrations in four tissues of Q. ilex in relation to soil properties, we selected fifteen stands in both Quercus ilex forests and Q. ilex-Pinus halepensis mixed forests. These stands had developed on soils derived from eight different parent materials. Three soil groups were differentiated according to their chemical properties: calcareous soils, siliceous soils, and volcanic soils. Across sites, nutrient concentrations were generally less variable in current-year tissues than in older tissues. Nitrogen and potassium showed the lowest variability among sites, their concentrations in current-year leaves ranging from 1.17% to 1.39% for N and from 0.53% to 0.68% for K. There were few statistically significant correlations between tissue element concentrations, the most frequent being the antagonistic relationship between calcium and magnesium. Nitrogen concentration in current-year leaves was negatively correlated with soil chemical fertility (nitrogen, phosphorus and potassium). This may reflect a nutritional imbalance between nitrogen and other nutrients, some of which may be more limiting than nitrogen to Q. ilex growth in Catalonia forests. Negative correlations were also found between plant magnesium and soil calcium, and positive correlations between plant calcium and soil calcium.     

Summer water stress and shade alter bud size and budburst date in three mediterranean Quercus species

Current environmental conditions are known to affect plant growth, morphology, phenology, and therefore, plant performance. However, effects of the previous-year environmental conditions can also affect plant structure by altering bud growth, and proportion and date of budburst. Here, we analysed the effects of previous-year water stress and shade on bud size, percentage, and date of budburst in seedlings of three co-occurring Iberian Quercus species in two independent experiments. Responses of apical, lateral, and basal buds were checked during an annual cycle. In the first experiment, seedlings of two evergreens (Q. coccifera L., Q. ilex subsp. ballota (Desf.) Samp.) and a deciduous-marcescent tree (Q. faginea Lam.) were grown under two levels of summer watering. In the second experiment, seedlings were grown under three light intensities. Soluble sugars and starch in shoots and roots were measured before budburst. Summer drought increased bud size of all species and advanced budburst of Q. ilex and Q. coccifera. Moderate and/or intense shade tended to reduce bud size and delay budburst in all species. These responses seem related to changes in the date of bud formation rather than to the amount of carbon reserves, which were reduced both by drought and shade. Treatments affected percentage of budburst in lateral buds, which was reduced by shade and water stress, probably leading to narrower crowns. These results show that previous-year environmental conditions are relevant for plant phenology and structure. The different responses in budburst date between the deciduous and the evergreens might alter their competition relationships at seedling stage.     

Cytosolic ascorbate peroxidase in some species of the Quercus genus

ABSTRACT

Six species of the Quercus genus (Quercus ilex L., Q. coccifera L., Q. suber L., Q. trojana Webb, Q. macrolepis Kotschy, Q. cerris L.) have been screened for cytosolic ascorbate peroxidase (APX) by means of native polyacrylamide gel electrophoresis (PAGE). A single isozyme was found in five species (Q. trojana, Q. suber, Q. cerris, Q. macrolepis and Q. coccifera), while Q. ilex shows two different APX proteins. The data showed marked similarities among Q. trojana, Q. suber, Q. cerris and Q. macrolepis with respect to the electrophoretic mobility. The validity of APX electrophoretic patterns in systematic studies is discussed.     

Species-specific,seasonal, inter-annual,and historically-accumulated changes in foliar terpene emission rates in <Emphasis Type="Italic">Phillyrea latifolia</Emphasis> and <Emphasis Type="Italic">Quercus ilex</Emphasis> submitted to rain exclusion in the Prades Mountains (Catalonia)

Mediterranean vegetation emits large amounts of terpenes. We aimed to study the effects of the decreases in soil water availability forecast for the next decades by global circulation models and ecophysiological models on the terpene emissions by two widely distributed Mediterranean woody species, Phillyrea latifolia L. and Quercus ilex L. We subjected holm oak forest plots to an experimental soil drought of ca. 20% decrease in soil moisture by partial rainfall exclusion and runoff exclusion. We measured the emission rates throughout the seasons for two years with contrasting precipitation and soil moisture (16.6% average in 2003 vs. 6.4% as average in 2005). Among the detected volatile terpenes, only α-pinene and limonene were present in detectable quantities in all of the studied periods. Total terpene emitted ranged from practically zero (spring 2003) to 3.6 and 58.3 μg/(g dry wt h) (winter 2005 and summer 2003 for P. latifolia and Q. ilex, respectively). A clear seasonality was found in the emission rates (they were the highest in summer in both species) and also in the qualitative composition of the emission mix. Maximum emissions of α-pinene occurred in spring and maximum emissions of limonene in winter. Neither the inter-annual differences in water availability nor the rain exclusion treatment significantly affected the emissions in P. latifolia, but Q. ilex showed by 17% lower emissions during the drier second year of study, 2005, but more than two- and threefold increases with the drought treatment in summer 2003 and in summer 2005, respectively, showing historical accumulated effects. These results, which show increased monoterpene emission under the moderate drought produced by the treatment and decreased emission under the severe second year drought, and a much higher sensitivity to drought in Q. ilex than in P. latifolia, are useful in understanding the behavior of plant volatiles under Mediterranean conditions and in modeling future emission under changing climate conditions. They show that the usage of current models could lead to under- and overestimations of the emission under summer dry conditions, because most current algorithms are based on light and temperature only.     

Drought stress does not protect Quercus ilex L. from ozone effects: results from a comparative study of two subspecies differing in ozone sensitivity

Long‐term effects of ozone (O₃) exposure and drought stress were assessed on two subspecies of Quercus ilex: ssp. ilex and ssp. ballota. Two‐year‐old seedlings were continuously exposed for 26 months in open‐top chambers to three O₃ treatments: charcoal filtered air, non‐filtered air and non‐filtered air supplemented with 40 nl·l^?1 O₃. Additionally, two irrigation regimes were adopted: half of the plants were well‐watered and the others received half of the water supplied to control plants. Growth, shoot water potential and gas exchange rates were assessed seasonally, and biomass accumulation was determined at the end of the experiment. Drought stress caused higher reductions of gas exchange, growth and biomass accumulation than O₃ exposure in both subspecies. The combination of O₃ and drought stress caused further decreases of accumulated aboveground biomass but no additive effects were observed on gas exchange rates or root biomass. Thus, drought stress did not protect Q. ilex from O₃ effects on biomass when the response of the whole plant was considered. Q. ilex ssp. ballota was more sensitive to O₃ and ssp. ilex was more affected by drought stress. The different O₃ sensitivity was not only related to pollutant uptake but also to the ability of plants for resource acquisition and allocation. Based on biomass dose–response functions, Q. ilex is more resistant to O₃ than other European evergreen tree species, however, O₃ represents an additional stress factor that might be impairing plant ability to withstand current and future climate change.