Abstract: The gender of dimorphic plant species is often affected by ecophysiological variables. Differences have been interpreted as a response of the sexes to meet specific resource demands associated with reproduction. This study investigated whether sex-specific variations in ecophysiological traits in response to water availability determine the performance of each sex in different habitats, and therefore promote extreme spatial segregation of the sexes in the subdioecious plant, Honckenya peploides. Twenty-seven plants of each sex were individually potted in dune sand and assigned randomly to one of three water treatments. Well-watered plants were watered daily to field capacity, whereas plants in the moderate and high-water stress treatments received 40% and 20%, respectively, of the water given to well-watered plants. Photochemical efficiency, leaf spectral properties and components of relative growth rate (leaf area ratio and net assimilation rate) were measured. Photochemical efficiencies integrated over time were higher in male than in female plants. Water deficit decreased maximum quantum yield in female plants more rapidly than in male plants, but female plants (unlike male plants) had recovered to initial values by the end of the experiment. Maximum quantum yield in male plants was more affected by water stress than in female plants, indicating that male plants were more susceptible to photoinhibition. The two sexes did not differ in growth rate, but male plants invested a higher proportion of their biomass in leaves, had a higher leaf area per unit biomass and lower net assimilation rate relative to female plants. Female plants had a higher water content and succulence than male plants. Differences in stomatal density between the sexes depended on water availability. The results suggest that the two sexes of H. peploides have different strategies for coping with water stress. The study also provides evidence of sex differences in allocation traits. We conclude that between-sex differences in ecophysiological and allocation traits may contribute to explain habitat-related between-sex differences in performance and, therefore, the spatial segregation of the sexes.

Abstract: Analysis of the intraspecific patterns of variation in ecologically relevant traits is important for knowing the genetic potential of a species to adjust to the expected increase in the severity of drought in the Mediterranean region. In this study, we aim to know to what extent phenotypic variation in functional and structural attributes of three provenances of Quercus ilex L. subsp. ballota (Desf.) Samp. saplings is genetically based. In an experiment conducted in growth chambers, we assessed the effects of two levels of water ( well watered and water stressed) and light ( 20 and 130 mu mol m(-2) s(-1)) on gas exchange, chlorophyll fluorescence, and leaf reflectance at different times throughout the experiment. At the end of the experiment, we measured leaf area, stem length and diameter, stomatal density, dry mass, and biomass allocation. Saplings from one of the populations ( Sayago) performed better than those from the other two, showing higher photochemical efficiency and chlorophyll content and greater leaf, stem, and root dry mass. Saplings from Sayago also showed higher transpiration rates, stomatal density, and conductance and were less susceptible to photoinhibition than other two. The significant population- associated variations in functional and structural attributes provided indirect evidence indicating that the holm oak exhibits an important degree of heterogeneity in the genetic constitution of its populations. However, the slopes of the biomass allometric relationships and allocation ratios showed that, irrespective of population, plants followed the same patterns of development in terms of biomass allocation, suggesting that evolutionary pressures may be acting to maintain allometric ratios at specific values.

Abstract: Vegetative multiplication allows clonal systems to spread horizontally and to establish (descendents) ramets in sites of contrasting resource status. Stolon or rhizome connections between ramets permit the transport of resources within the clone. As a result of such physiological integration, clones can act as cooperative systems, enabling buffering of any differences in resource supply among ramets due to local heterogeneity. This study tests the hypothesis that parent ramets of Fragaria vesca L. enhance their photosynthetic activity when connected to shaded or drought-stressed offspring ramets as result of the assimilate demand from those ramets. The study also investigated the extent to which small-scale topographic heterogeneity (i.e. offspring ramets at higher or lower level than parents) may influence the physiological integration, in terms of photosynthetic efficiencies, biomass and production of new ramets. Results showed that the photosynthetic efficiencies of parent ramets were increased in response to the assimilate demand made by drought-stressed offspring ramets, especially under shade conditions. We attribute this response to a mechanism of feed-back regulation in line with the source-sink hypothesis. We also found that offspring ramets at a raised topographic position with respect to parents showed a significant decline in the production of new ramets and a reduction in total biomass relative to offspring at a lower level or the same level. We conclude that microtopographic aspects of environmental heterogeneity may involve additional costs for ramet establishment of ramets. (C) 2007 Elsevier B.V. All rights reserved.

Abstract: Changes in photosynthetic performance following partial defoliation may play a role in alleviating the negative effects of herbivores. We investigated effects of simulated and larval herbivory and the different spatial pattern of leaf tissue removal on the photosynthetic efficiency in the dioecious holly tree. We also addressed whether effects of herbivory on photosynthesis were sex specific. Experiments were conducted with third-year plants growing under natural light and temperature. Photosynthesis was evaluated by chlorophyll fluorescence parameters. Larval herbivory significantly increased the maximum quantum yield of photosystem II and decreased minimum fluorescence (F-o), while experimental defoliation had exactly the opposite effect. The effect of experimental defoliation on the effective quantum yield of photosystem II was significantly influenced by previous herbivory and time. The effect of larval herbivory on Fo changed significantly with time and plant gender. Our results indicate that compensatory photosynthesis can be affected by which kind of damage occurs, the light-adaptation state of plants, the timing of data collection, and plant gender. In the literature, these effects have created misunderstandings because they have not been properly accounted for. Our study illustrates the need to rethink approaches to estimating compensatory photosynthesis and its potential ecological consequences.

Abstract: The ability of clonal systems to spread by ramet production may expose the clone to spatial heterogeneity. This study explored the physiological and morphological responses in the clonal plant Fragaria vesca L. growing in homogeneous (Cu-contaminated or uncontaminated) or in heterogeneous environments with patches of contrasting quality (Cu-contaminated or uncontaminated). We also investigated the potential of this species to selectively establish ramets within a heterogeneous environment. In heterogeneous environments, plants expanded ramets randomly, but selectively established ramets in the favourable patches. We discuss whether the selective establishment of ramets is a consequence of direct suppression of plant growth due to copper toxicity. The assimilate demand from offspring ramets in unfavourable environments increased the chlorophyll content and photosynthetic efficiency of parents by a feedback regulation process. Integration ameliorated the effects of copper on the photochemical efficiency of the offspring ramets. We did not observe integration costs, in terms of total biomass, for parents supporting ramets in Cu-contaminated environments, although we did detect costs in terms of ramet production. Parents with offspring ramets in Cu-contaminated environments produced 25 times more reproductive biomass than parents with offspring ramets in uncontaminated environments. We interpret this as a strategy for escaping from stressful environments. In this study, we extend the concept of physiological integration in clonal plants to include photochemical responses.

Abstract: Background and Aims In clonal plants, internode connections allow translocation of photosynthates, water, nutrients and other substances among ramets. Clonal plants form large systems that are likely to experience small-scale spatial heterogeneity. Physiological and morphological responses of Fragaria vesca to small-scale heterogeneity in soil quality were investigated, together with how such heterogeneity influences the placement of ramets. As a result of their own activities plants may modify the suitability of their habitats over time. However, most experiments on habitat selection by clonal plants have not generally considered time as an important variable. In the present study, how the foraging behaviour of clonal plants may change over time was also investigated. Methods In a complex of environments with different heterogeneity, plant performance was determined in terms of biomass, ramet production and photosynthetic activity. To identify habitat selection, the number of ramets produced and patch where they rooted were monitored. Key Results Parent ramets in heterogeneous environments showed significantly higher maximum and effective quantum yields of photosystem II than parents in homogeneous environments. Parents in heterogeneous environments also showed significantly higher investment in photosynthetic biomass and stolon/total biomass, produced longer stolons, and had higher mean leaf size than parents in homogeneous environments. Total biomass and number of offspring ramets were similar in both environments. However, plants in homogeneous environments showed random allocation of offspring ramets to surrounding patches, whereas plants in heterogeneous environments showed preferential allocation of offspring to higher-quality patches. Conclusions The results suggest that F. vesca employs physiological and morphological strategies to enable efficient resource foraging in heterogeneous environments and demonstrate the benefits of physiological integration in terms of photosynthetic efficiency. The findings indicate that short-term responses cannot be directly extrapolated to the longer term principally because preferential colonization of high-quality patches means that these patches eventually show reduced quality. This highlights the importance of considering the time factor in experiments examining responses of clonal plants to heterogeneity.

Abstract: Small-scale heterogeneity in soil characteristics and the facility of clonal systems to spread may lead to situations where parent ramets in favourable microhabitats are connected to offspring in stressful conditions. Clonal plants are physiologically integrated if connections among ramets allow transport of resources. Thus, ramets in favourable habitats may provide support to developing or stressed ramets. We examined effects of integration in Fragaria vesca growing in patches of contrasting quality (potting compost vs serpentine soil). Serpentine soil was used to create unfavourable growing conditions. We assessed whether survival, biomass and photosynthetic efficiency (estimated by fluorescence and reflectance) of parents and offspring were affected by integration and soil quality. Integration increased photochemical efficiencies of parents but more consistently in parents with offspring growing in serpentine soils. We suggest that the assimilate demand from offspring enhanced the photosynthetic efficiency of parents by a mechanism of feedback regulation. This result extends the concept of physiological integration in clonal plants to include photochemical responses. Connected parents also showed significantly higher biomass than disconnected parents. In our system, integration did not entail costs for the whole clone in terms of biomass. Integration also improves the survival, growth and photochemical efficiency of developing ramets, suggesting that integration represents a mechanism for increasing survival in stressful habitats, as the serpentine soils.

Abstract: Clonal plants may translocate photosynthates, water, and nutrients from established ( source) ramets to developing ( sink) ramets. The sink/source hypothesis states that photosynthesis may be regulated, at least in part, by the balance between source and sink tissues. We investigated the influence of physiological integration on photosynthetic efficiencies to test predictions based on the sink/source hypothesis that photosynthetic efficiencies in parent ramets may be increased by the assimilate demand made by connected offspring ramets. We grew parent ramets of Fragaria vesca connected to four, one, or no offspring ramets. They were grown in well-watered or drought-stress conditions. All parent ramets survived at the end of the experiment, regardless of the number of offspring ramets they supported or the moisture conditions in which these were growing. However, the survivorship of offspring ramets was higher for well-watered and connected ramets than for drought-stressed and disconnected ramets. In parent ramets, spectral and fluorescence parameters related to photochemical efficiency increased with the number of interramet connections. We conclude that developing ramets of F. vesca, by acting as sinks for assimilates, induce an enhancement of the photosynthetic activity of the parental ramets by a feedback regulation process.

Abstract: We characterised the climatic behaviour of 53 woody species in terms of the climatic factors that play the main role in controlling species distribution in the study area. Floristic and climatic data were obtained from 150 stands in sites under climatic control (i.e. eu-climatopes). The sampling strategy used allowed a reliable match between floristic and climatic observations. Different methods of frequency analysis and goodness-of-fit tests were used to identify associations between species occurrence and climatic characteristics. The species' responses were summarised by statistics describing ecological preferences and amplitudes, and species were grouped accordingly. A Gaussian response model was fitted to the abundance data along the main climatic gradients for selected species and response surfaces were derived by spatial analysis for a set of indicator species. Frequency analysis methods detected 42 indicator taxa for the Baudiere's Qe drought index, and lower numbers, 34 and 22, respectively, for the mean minimum coldest-month temperature and the daily temperature range in the coldest month. Goodness-of-fit tests revealed a lower number of ecological profiles with statistically significant deviations from equidistribution. We discuss the relative performance of the different methods and suggest that the combined use of statistical tests and frequency analyses may improve estimation of the environmental requirements of species. We also recommend using the species' responses to key environmental factors as reliable criteria in the definition of plant functional types.

Abstract: 1. Changes in plant physiological features after herbivory may alleviate the adverse effects of herbivores. We examined the ability of Ilex aquifolium L. (European Holly) plants to compensate for scale insect herbivory through increased photosynthesis. Based on assumptions of the source-sink hypothesis, we predicted that scale insects, by inducing supplementary sinks for photosynthates, would increase photosynthesis. 2. Photosynthetic performance was evaluated by measuring chlorophyll fluorescence parameters in plants growing under natural light and temperature at the field station of the University of Santiago (north-west Spain). We measured photosynthesis on infested leaves of infested trees; scale-free leaves of infested trees; and scale-free leaves of scale-free trees. 3. Insect infestation significantly increased photosynthetic efficiency. Effects of scale insects on photosynthesis were particularly enhanced by high temperature and light. Scale insects also altered the photosynthesis of leaves not directly affected by the insects. 4. Our study showed that changes in the balance between source and sink tissues, induced by scale insects, may partly explain host plant photosynthesis. We suggest that increased feeding rates of scale insects promoted by high temperature and light conditions would increase the carbon demand of infested plants, resulting in greater compensatory photosynthesis.

Abstract: Three hypotheses were examined in order to explain the existence of sexual size dimorphism in the dioecious tree Ilex aquifolium (Aquifoliaceae): cost of reproduction, sexual selection (pollen competition) and physiological differentiation between sexes. Here we present both published and new experimental and observational results. At flowering, males allocated more in reproduction than females; however at fruiting females allocated about ten times more in terms of carbon and about five times more in terms of nitrogen than males. Both sexes did not differ in leaf dynamics. Branch RGR usually showed greater values in male branches, but the results depended on the ecological context. Tree growth rate, estimated from mean width of annual rings over 10-30 yr, was significantly higher for males. Experimental debbuding in reproductive branches of females accounted for an increase in RGR compared to branches that matured fruits. When competition among males was examined, there were significant differences among male trees in pollen production per flower. The experimental crossing of five males and five females demonstrated strong maternal effects on fecundity, while non significant differences among males were found in their probability of sire progeny. There were some physiological differences between sexes. The efficiency of photosynthesis of leaves (measured as Fv' / Fm') on nonfruiting branches of females was higher than for leaves on branches of male trees under low-light conditions. On the other side, the water-use efficiency, measured by carbon isotope discrimination, was greater in males under xeric conditions. These results are used to discuss the importance of the above mentioned hypothesis.

Abstract: Plant responses to short-term stress are usually extrapolated to long-term effects, neglecting examination of the capacity of plants to compensate for stress. We examined the capacity of Sinapis alba plants to compensate for wind and density stress through responses in growth and fecundity traits. Plants were grown under three wind speeds and two densities for three periods (11, 17, or 24 d). During these periods, there were significant losses in growth, thus confirming that plants were stressed. The plants were then allowed to recover in the absence of wind and at reduced density. Following this recovery, measurements of growth, allocation, and reproductive parts were taken. Biomass had been regained in wind-stressed plants relative to control plants, and reproductive attributes were no different, except that flowering time was delayed until 4 d with increased wind. Plants compensated less effectively for density stress with respect to growth and reproduction, but root : shoot allocation was greater in the control plants. Plants were unable to fully compensate for the longest exposure times. We conclude that the effects of short-term stress cannot be extrapolated to long-term effects and that under favorable environmental conditions, the compensatory capacity of Sinapis depends on the severity and duration of the stress.

Abstract: 1. Detailed understanding of the specific physiology of sexes in dioecious species is required to explain patterns in gender dimorphism. Under controlled-environment conditions we tested the hypothesis that sexes of the dioecious tree holly Ilex aquifolium L. (Aquifoliaceae) differed in growth and long-term potential water-use efficiency, as measured by carbon isotope discrimination (Delta C-13), and that these differences were dependent on the environmental context. 2. Patterns of response in Delta C-13 to the various combinations of light and water were gender-specific. Under more xeric conditions, females maintained significantly higher Delta C-13 than males. 3. Female plants exhibited significantly greater relative diameter growth rates than male plants. 4. As expected, Delta C-13 significantly increased with decreasing irradiance, and decreased with increasing limitation in water supply. Light and water effects were not independent, with a more pronounced drought effect in decreasing leaf Delta C-13 under unshaded than under shaded conditions. 5. Our results suggest that between-sex differences in physiology are context-dependent. Future studies attempting to assess gender dimorphism should take more account of gender-specific interactions with the environment. Gender-specific efficiency in water use could play a decisive role in explaining gender differences in growth and ecological interactions.

Abstract: Sex ratio and sexual dimorphism in physiology and growth were studied in the dioecious tree Ilex aquifolium at two localities in northern Spain. Genet sex ratio was significantly male biased in one locality but not in the other. However, ramet and flowering ramet sex ratios were male biased at both study sites. Males had significantly thicker main trunks than females in one locality and produced more ramets in the other. Growth rate, estimated from mean width of annual rings, did not differ between localities, but males produced wider rings than females at both sites. Mean annual growth rates over the last 10, 20, and 30 yr were significantly higher for males. Measurements of chlorophyll fluorescence indicated that the efficiency of photosynthesis of leaves on nonfruiting branches of females was higher than for leaves on branches of male plants under low-light conditions, though not under saturating-light conditions. Efficiency of photosynthesis was significantly lower on fruiting branches of female plants than on nonfruiting branches. We discuss whether the observed between-sex differences are attributable to the higher cost of reproduction in females and/or to pollen competition.

Abstract: The chlorophyll-to-phaeophytin (D665/D665a) ratio is an index of physiological stress in aquatic bryophytes. In the present study, the usefulness of this index for evaluating water contamination was investigated. Samples of bryophytes and water were collected from 188 stretches of river in northwest Spain. Water quality was characterized by standard procedures. Ecological profile methods were used to investigate (for each species and each water quality variable) whether stress index or frequency of occurrence varied significantly along environmental gradients. Most stress profiles showed significant departures from uniformity, whereas many frequency profiles did not, indicating that the stress index approach is more sensitive to differences in water quality than are approaches based simply on presence/absence data. To further investigate relationships between water quality variables and D665/D665a ratio, canonical correspondence analysis (CCA) was used. The first axis extracted by CCA was clearly closely related to degree of organic pollution. The second axis was most strongly correlated with pH. Taken together, these results suggest that D665/D665a ratio in aquatic bryophytes may be of value as an indicator of river water pollution.

Abstract: Plants in nature live in populations of variable density, a characteristic which may influence individual plant responses to the environment. We investigated how the responses of Sinapis alba plants to different wind speeds and CO2 concentrations could be modified by plant density. In our wind-density experiment the expectation that mechanical and physiological effects of wind will be ameliorated by growing in high density, as a result of positive plant interactions, was realised. Although individual plants were smaller at higher densities, the effect of increasing windspeed was much less than at lower plant densities. A similar reduced sensitivity of individual plant growth under high densities was also observed under CO2 enrichment. When measured as a population or stand response, there was no effect of density on the CO2 responses, with all stands showing very similar increases in total biomass with CO2 enrichment. In the wind speed experiment, total biomass per stand increased significantly with density, although there was no effect of density on the wind speed response. Specific leaf area decreased with increasing wind speed and this response was significantly affected by the density at which the plants grew.

Abstract: We examined how independent and interactive effects of CO2 concentrations, water supply and wind speed affect growth rates, biomass partitioning, water use efficiency, diffusive conductance and stomatal density of plants. To test the prediction that wind stress will be ameliorated by increased CO2 and/or by unrestricted water supply we grew Sinapis alba L. plants in controlled chambers under combinations of two levels of CO2 (350 ppmv, 700 ppmv), two water regimes and two wind speeds (0.3 ms-1, 3.7 ms-1). We harvested at ten different dates over a period of 60 days. A growth analysis was carried out to evaluate treatment effects on plant responses. Plants grown both in increased CO2 and in low wind conditions had significantly greater stem length, leaf area and dry weights of plant parts. Water supply significantly affected stem diameter, root weight and leaf area. CO2 enrichment significantly increased the rate of biomass accumulation and the relative ratio of biomass increase to leaf area expansion. High wind speed significantly reduced plant growth rates and the rate of leaf area expansion was reduced more than the rate of biomass accumulation. Regression analysis showed significant CO2 effects on the proportion of leaf and stem dry weight to total dry weight. A marked plant-age effect was dependent on water supply, wind speed and CO2 concentration. A reduced water supply significantly decreased the stomatal conductance, and water use efficiency significantly increased with a limited water supply, low wind and increased CO2. We found significant CO2 x wind effects for water diffusion resistance, adaxial number of stomata and water use efficiencies and significant wind x water effect for water use efficiency. In conclusion, wind stress was ameliorated by growing in unrestricted water but not by growing in increased CO2.

Abstract: This paper reports a bioclimatic analysis of plant species in Galicia, NW Spain. A set of floristic data obtained from 150 plots located at euclimatopes (sites with monitored climate) was analysed using direct gradient analysis and clustering with respect to the 8 climatic variables thought to play a major role in regulating the distribution of the species considered in the study area. Principal component analysis (PCA) and hierarchical clustering were based on a matrix of species by climatic variables. Indicator taxa for the variables were identified on the basis of their Indicator values (Brisse & Grandjouan 1978) and grouped by cluster analysis. The groups produced were compatible with the results of principal component analysis and the frequential analysis of the species, which identified their phytoclimatic nature. The groups were then characterized by determining their climatic positions and indicator values with respect to the chief climatic variables. The first three PCA axes, which were associated with Oceanity, Mean minimum temperatures and the temperature range in the coldest month, together accounted for 97.2 % of the variance of the data.

Abstract: We examined how different wind speeds and interactions between plant age and wind affect growth and biomass allocation of Sinapis alba L. (white mustard). Physiological and growth measurements were made on individuals of white mustard grown in controlled-enviroment wind tunnels at windspeeds of 0.3, 2.2 and 6.0 ms-1 for 42 days. Plants were harvested at four different dates. Increasing wind speed slightly increased transpiration and stomatal conductance. We did not observe a significant decline in the photosynthetic rate per unit of leaf area. Number of leaves. stem length, leaf area and dry weights of total biomass and plant parts were significantly lower in plants exposed at high wind speed conditions. There were no significant differences in the unit leaf rate nor relative growth rates, although these were always lower in plants grown at high wind speed. Allocation and architectural parameters were also examined. After 42 days of exposure to wind, plants showed higher leaf area ratio, root and leaf weight ratios and root/shoot ratio than those grown at control treatment. Only specific leaf area declined significantly with wind speed, but stem and reproductive parts also decreased. The responses of plants to each wind speed treatment depended on the age of the plant for most of the variables. It is suggested that wind operates in logarithmic manner, with relatively small or no effect at lower wind speeds and a much greater effect at higher speeds. Since there is no evidence of a significant reduction in photosynthetic rate of Sinapis with increasing wind speed it is suggested that the effect of wind on plant growth was due to mechanical effects leading to changes in allocation and developmental patterns.

Abstract: Floristic and climate data from 150 plots in 25 sites in Galicia, Spain, were analysed to test the hypothesis that climate is the major factor governing the distribution of woody plant species. TWINSPAN classification, Detrended Correspondence Analysis and Canonical Correspondence Analysis were applied in successive stages of the data analysis to described vegetational variation in relation to climatic gradients. Six groups of species were defined, two clearly oceanic (Maritime and Cool Maritime), one mediterranean maritime, and three mediterranean (Cold Mediterranean, Cool Mediterranean and Temperate Mediterranean). An aridity gradient was revealed as the primary factor regulating the distribution of the species considered. This main gradient reflects the transition between the Eurosiberian and Mediterranean biogeographic regions. The gradient can be characterized by means of the Vernet bioclimatic index. A value greater-than-or-equal-to 4 for this index can be taken to define the mediterranean zone in our study area. The mean minimum temperature in the coldest month was the second most influential climatic variable. Partial ordination analysis revealed that the residual variation was insignificant and that the observed variation in vegetation can be fully accounted for by climatic variables.

Abstract: