Carlos Granado-Yela

Genetic diversity and differentiation processes in the ploidy series of Olea europaea L.: a multiscale approach from subspecies to insular populations

Geographical isolation and polyploidization are central concepts in plant evolution. The hierarchical organization of archipelagos in this study provides a framework for testing the evolutionary consequences for polyploid taxa and populations occurring in isolation. Using amplified fragment length polymorphism and simple sequence repeat markers, we determined the genetic diversity and differentiation patterns at three levels of geographical isolation in Olea europaea: mainland‐archipelagos, islands within an archipelago, and populations within an island. At the subspecies scale, the hexaploid ssp. maroccana (southwest Morocco) exhibited higher genetic diversity than the insular counterparts. In contrast, the tetraploid ssp. cerasiformis (Madeira) displayed values similar to those obtained for the diploid ssp. guanchica (Canary Islands). Geographical isolation was associated with a high genetic differentiation at this scale. In the Canarian archipelago, the stepping‐stone model of differentiation suggested in a previous study was partially supported. Within the western lineage, an east‐to‐west differentiation pattern was confirmed. Conversely, the easternmost populations were more related to the mainland ssp. europaea than to the western guanchica lineage. Genetic diversity across the Canarian archipelago was significantly correlated with the date of the last volcanic activity in the area/island where each population occurs. At the island scale, this pattern was not confirmed in older islands (Tenerife and Madeira), where populations were genetically homogeneous. In contrast, founder effects resulted in low genetic diversity and marked genetic differentiation among populations of the youngest island, La Palma.

Phenotypic plasticity and integration across the canopy of Olea europaea subsp. guanchica (Oleaceae) in populations with different wind exposures.

Woody plants, as sessile and long-lived organisms, are expected to have effective mechanisms for dealing with recurrent environmental stresses. In the present study, we hypothesized that phenotypic plasticity (the ability to express alternative phenotypes) and integration (covariation among functionally related traits) are elicited in plants under stressful wind speed conditions. We investigated the within-crown variation of nine vegetative traits of a tree species (Olea europaea subsp. guanchica) in six populations that represented a gradient of wind speed exposures. Wind-exposed twigs in outer-canopy layers had smaller leaves; thinner, lighter, and shorter internodes; and a larger internode cross-sectional area to leaf area ratio. Comparison between field and greenhouse trials revealed that field differences among populations were mediated by phenotypic plasticity. Outer-canopy twigs expressed plastic responses in populations exposed to high wind speeds, whereas inner-canopy twigs displayed high phenotypic convergence among populations. In addition, phenotypic integration increased with wind exposure (outer canopy > inner canopy > greenhouse) and was consequently affected by canopy openness. We conclude that exposure to wind above a certain speed threshold in this woody species elicits a plastic response that is associated with increased integration among traits and involves mechanical and hydraulic rearrangements in more exposed parts of the trees.

Temporal matching among diurnal photosynthetic patterns within the crown of the evergreen sclerophyll Olea europaea L

Trees are modular organisms that adjust their within-crown morphology and physiology in response to within-crown light gradients. However, whether within-plant variation represents a strategy for optimizing light absorption has not been formally tested. We investigated the arrangement of the photosynthetic surface throughout one day and its effects on the photosynthetic process, at the most exposed and most sheltered crown layers of a wild olive tree (Olea europaea L.). Similar measurements were made for cuttings taken from this individual and grown in a greenhouse at contrasted irradiance-levels (100 and 20% full sunlight). Diurnal variations in light interception, carbon fixation and carbohydrate accumulation in sun leaves were negatively correlated with those in shade leaves under field conditions when light intensity was not limiting. Despite genetic identity, these complementary patterns were not found in plants grown in the greenhouse. The temporal disparity among crown positions derived from specialization of the photosynthetic behaviour at different functional and spatial scales: architectural structure (crown level) and carbon budget (leaf level). Our results suggest that the profitability of producing a new module may not only respond to construction costs or light availability, but also rely on its spatio-temporal integration within the productive processes at the whole-crown level.

Simplifying data acquisition in plant canopies‐ Measurements of leaf angles with a cell phone

Summary 1. Canopies are complex multilayered structures comprising individual plant crowns exposing a multifaceted surface area to sunlight. Foliage arrangement and properties are the main mediators of canopy functions. The leaves act as light traps whose exposure to sunlight varies with time of the day, date and latitude in a trade-off between photosynthetic light harvesting and excessive or photoinhibitory light avoidance. To date, ecological research based upon leaf sampling has been limited by the available technology, with which data acquisition becomes labour intensive and time-consuming, given the overwhelming number of leaves involved. 2. In the present study, our goal involved developing a tool capable of measuring a sufficient number of leaves to enable analysis of leaf populations, tree crowns and canopies. We specifically tested whether a cell phone working as a 3D pointer could yield reliable, repeatable and valid leaf angle measurements with a simple gesture. We evaluated the accuracy of this method under controlled conditions, using a 3D digitizer, and we compared performance in the field with the methods commonly used. We presented an equation to estimate the potential proportion of the leaf exposed to direct sunlight (SAL) at any given time and compared the results with those obtained by means of a graphical method. 3. We found a strong and highly significant correlation between the graphical methods and the equation presented. The calibration process showed a strong correlation between the results derived from the two methods with a mean relative difference below 10%. The mean relative difference in calculation of instantaneous exposure was below 5%. Our device performed equally well in diverse locations, in which we characterized over 700 leaves in a single day. 4. The new method, involving the use of a cell phone, is much more effective than the traditional methods or digitizers when the goal is to scale up from leaf position to performance of leaf populations, tree crowns or canopies. Our methodology constitutes an affordable and valuable tool within which to frame a wide range of ecological hypotheses and to support canopy modelling approaches.

Field patterns of temporal variations in the light environment within the crowns of a Mediterranean evergreen tree (Olea europaea)

Key messageThere are specific diurnal light variation patterns and negligible seasonal variation within tree crowns. Crown-mediated regulation of temporal light regimes can be important for whole plant function in Mediterranean evergreens.AbstractThe light environment within a tree crown can be characterized by specific variation patterns arising from the structural features of the crown. Within-crown light variation patterns can be important for plant productivity, but this has yet to be assessed in natural settings. The spatio-temporal variations of direct and diffuse photosynthetic photon flux density (PPFD), their proportions and sunfleck frequency within the crowns of isolated adult wild olive trees (Olea europaea L.) were investigated. Trees growing in contrasting Mediterranean conditions (continental vs. coastal) at the same latitude were compared. Instantaneous diffuse and total PPFD were measured with sunshine sensors in three crown layers (outer-, middle- and inner-crown) in the south-facing part of the crown, at two points of the diurnal (mid-morning and midday) and seasonal (summer and winter) cycles. Direct PPFD and the proportion of direct to total PPFD vary diurnally within the crown as a result of an increase in sunfleck frequency during midday and in self-shading during mid-morning, in both summer and winter conditions. Conversely, the lack of seasonal variation in the three light attributes is better explained by a greater average crown transmittance in winter conditions. The interplay between crown architecture heterogeneity and varying solar position renders identifiable patterns of temporal variations in the light environment within tree crowns. These patterns suggest that trees can benefit from the light heterogeneity typical of Mediterranean environments by developing conservative architectural layouts.

The expression of light-related leaf functional traits depends on the location of individual leaves within the crown of isolated Olea europaea trees.

BACKGROUND The spatial arrangement and expression of foliar syndromes within tree crowns can reflect the coupling between crown form and function in a given environment. Isolated trees subjected to high irradiance and concomitant stress may adjust leaf phenotypes to cope with environmental gradients that are heterogeneous in space and time within the tree crown. The distinct expression of leaf phenotypes among crown positions could lead to complementary patterns in light interception at the crown scale. METHODS We quantified eight light-related leaf traits across 12 crown positions of ten isolated Olea europaea trees in the field. Specifically, we investigated whether the phenotypic expression of foliar traits differed among crown sectors and layers and five periods of the day from sunrise to sunset. We investigated the consequences in terms of the exposed area of the leaves at the tree scale during a single day. KEY RESULTS All traits differed among crown positions except the length-to-width ratio of the leaves. We found a strong complementarity in the patterns of the potential exposed area of the leaves among day periods as a result of a non-random distribution of leaf angles across the crown. Leaf exposure at the outer layer was below 60 % of the displayed surface, reaching maximum interception during morning periods. Daily interception increased towards the inner layer, achieving consecutive maximization from east to west positions within the crown, matching the suns trajectory. CONCLUSIONS The expression of leaf traits within isolated trees of O. europaea varies continuously through the crown in a gradient of leaf morphotypes and leaf angles depending on the exposure and location of individual leaves. The distribution of light-related traits within the crown and the complementarity in the potential exposure patterns of the leaves during the day challenges the assumption of low trait variability within individuals.

Intraindividual variation in light-related functional traits: magnitude and structure of leaf trait variability across global scales in Olea europaea trees

Key messageLight-related leaf traits variation is structured among individuals and within individuals in a latitudinal pattern from the equator (high variation) toward the poles (lower variation).AbstractIntraspecific variation in leaf functional traits can play a crucial role at multiple ecological scales. However, our understanding of leaf functional trait variation (FV) across spatial scales is limited. Moreover, the influence of FV in specific responses to the environment remains poorly assessed. We investigated FV across multiple nested ecological scales in a set of leaf traits related to light interception and photosynthetic performance in eight populations of Olea europaea trees distributed over a wide latitudinal gradient (~60°). Specifically, we measured SLA, leaf shape, leaf’s spatial position (leaf angles) and leaf’s potential exposure to direct sunlight (silhouette area of the leaf blade and silhouette to area ratio of the leaf blade). The variability in leaf traits revealed two main patterns depending on the considered trait. Differences among sites absorbed >50% of the trait variation related to leaf shape and structure. Conversely, traits related to leaf position and exposure to direct light varied mostly within individuals among crown positions. The variation within trees for multiple traits ranged from 4 to 14%. Trees of equatorial populations had wider, thinner and more exposed leaves to direct light than trees of the remaining populations. The FV for multiple leaf traits at the tree scale was spatially structured within the tree crown and was higher for populations at the equator than for populations located in other latitudes. The differences among traits and scales in the magnitude of FV revealed a complex structure that could be linked to local adaptation.

Unusual positional effects on flower sex in an andromonoecious tree: Resource competition, architectural constraints, or inhibition by the apical flower?

PREMISE OF THE STUDY Two, nonmutually exclusive, mechanisms-competition for resources and architectural constraints-have been proposed to explain the proximal to distal decline in flower size, mass, and/or femaleness in indeterminate, elongate inflorescences. Whether these mechanisms also explain unusual positional effects such as distal to proximal declines of floral performance in determinate inflorescences, is understudied. METHODS We tested the relative influence of these mechanisms in the andromonoecious wild olive tree, where hermaphroditic flowers occur mainly on apical and the most proximal positions in determinate inflorescences. We experimentally increased the availability of resources for the inflorescences by removing half of the inflorescences per twig or reduced resource availability by removing leaves. We also removed the apical flower to test its inhibitory effect on subapical flowers. KEY RESULTS The apical flower had the highest probability of being hermaphroditic. Further down, however, the probability of finding a hermaphroditic flower decreased from the base to the tip of the inflorescences. An experimental increase of resources increased the probability of finding hermaphroditic flowers at each position, and vice versa. Removal of the apical flower increased the probability of producing hermaphroditic flowers in proximal positions but not in subapical positions. CONCLUSIONS These results indicate an interaction between resource competition and architectural constraints in influencing the arrangement of the hermaphroditic and male flowers within the inflorescences of the wild olive tree. Subapical flowers did not seem to be hormonally suppressed by apical flowers. The study of these unusual positional effects is needed for a general understanding about the functional implications of inflorescence architecture.