Rubén Retuerto

Presence of Developing Ramets of Fragaria vesca L. Increases Photochemical Efficiency in Parent Ramets

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.

Effects of windspeed on the growth and biomass allocation of white mustard Sinapis alba L.

SummaryWe 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-environment 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.

Developmentally-programmed division of labour in the clonal invader Carpobrotus edulis.

Invasive species are one of the main causes for the loss of global biodiversity. However, the mechanisms that explain the success of invasive species remain unsolved. Clonal growth has been pointed out as an attribute that could contribute to the invasiveness of plants, however little research has been conducted to determine the importance of clonal traits in successful invaders. One of the most interesting attributes related to clonal growth is the capacity for division of labour. In this experiment we investigated the capacity for division of labour in the aggressive invader Carpobrotus edulis, and how clonal integration can contribute to the expansion of this species. Division of labour was determined by studying the degree of morphological and physiological specialization of individual ramets to a specific activity: acquisition of soil or aboveground resources and aboveground expansion. Our results showed that there is division of labour in the clonal fragments, with older ramets increasing the biomass allocated to roots (specialization in the uptake of belowground resources) and younger ramets increasing the chlorophyll content and aboveground biomass (specialization in the uptake of aboveground resources). Physiological integration allows division of labour, and as consequence the overall performance of the clonal fragment was enhanced, with connected clonal fragments showing a higher total biomass than severed clonal fragments. Division of labour increased the aboveground growth of apical ramets of C. edulis, and therefore could contribute to an effective colonization of the surrounding area by this aggressive invader. Our study is the first exploring the role of division of labour in the expansion of an invader, and supports the idea that clonal traits could increase the invasiveness of plant species.

D665/D665a INDEX VS. FREQUENCIES AS INDICATORS OF BRYOPHYTERESPONSE TO PHYSICOCHEMICAL GRADIENTS

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.

Clonal integration in Fragaria vesca growing in metal-polluted soils: parents face penalties for establishing their offspring in unsuitable environments

Clonal plants often establish descendent ramets in sites with contrasting presence of favourable and unfavourable factors. Connections between ramets allow translocation of essential resources from established ramets to developing ramets and, as consequence, integration confers net benefits to ramets growing under unfavourable conditions. Therefore, integrated ramets may survive in habitat patches that would be lethal to independent ramets or non-clonal plants. This experiment aimed to investigate the physiological and morphological responses of the clonal plant Fragaria vesca growing in heterogeneous substrate with patches of contrasting quality (i.e. uncontaminated or heavy-metal-contaminated). We observed that parents reduced their photosynthetic efficiencies and growth as consequence of maintaining their offspring. This cost did not affect survival of the parents. Physiological integration brings about benefits to offspring ramets growing both at uncontaminated and heavy-metal-contaminated soils. The benefits of integration were detected in both physiological and morphological traits, enhancing the survivorship of offspring ramets in the Cu-polluted soils. We conclude that integration improves the performance of developing ramets of F. vesca growing in heavy-metal-contaminated habitats, allowing clone systems to overcome the establishment risks and maintain their presence in these less favourable sites.

Defining phytoclimatic units in Galicia, Spain, by means of multivariate methods

. 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 describe 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 bio-geographic regions. The gradient can be characterized by means of the Vernet bioclimatic index. A value ≥ 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.

Quercus ilex shows significant among-population variability in functional and growth traits but maintains invariant scaling relations in biomass allocation

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 μmol 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.

Development, photosynthetic activity and habitat selection of the clonal plant Fragaria vesca growing in copper-polluted soil

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.

CHANGES IN PHOTOCHEMICAL EFFICIENCY IN RESPONSE TO HERBIVORY AND EXPERIMENTAL DEFOLIATION IN THE DIOECIOUS TREE ILEX AQUIFOLIUM

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 (Fo), 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.

Phytoecological importance, mutual redundancy and phytological threshold values of certain climatic factors

A combination of methods (intensity of indication, floristic and mesological redundancy analysis, beta-diversity analysis, principal components analysis and Wildis interactive ranking procedure) were used to evaluate redundancy and relative phytoecological importance among 80 climatic variables in Galicia (N.W. Spain). The information they contained was found to be adequately summarized by just 3 factors thought to play a major role in regulating the distribution of the species considered in the study area and similar areas: Baudieres QE index, mean minimum temperature in the coldest month and mean temperature range in the coldest month. For these three factors, phytoclimatic thresholds were determined by examining beta-diversity and were used to define phytoclimatic zone types. Se valora la redundancia e importancia fitoecológica relative de 80 variables climáticas en Galicia (N.O. de España) empleando una combinacion de diferentes metodos (intensidad indicadora, análisis de la redundancia florística y mesológica, análisis de beta-diversidad, análisis de componentes principales y el método de ordenación interactiva de Wildi). La información contenida en esta variables es adecuadamente resumida por 3 factores que juegan un papel predominante en regular la distribución de las especies consideradas en el area de estudio y areas similares: el índice QE de Baudiere, la temperatura media de las mínimas del mes más frío y la oscilación térmica del mes más frío. Para estos factores el análisis de la beta-diversidad permitió determinar los umbrales fitoclimáticos utilizados en la definición y cartografía de las zonas fitoclimáticas.