Palynology on lake sediments from the Pyrenees

A multi-proxy palaeoecological investigation including pollen, plant macrofossil, radiocarbon and sedimentological analyses, was performed on a small mountain lake in the Eastern Pyrenees. This has allowed the reconstruction of: (1) the vegetation history of the area based on five pollen diagrams and eight AMS14C dates and (2) the past lake-level changes, based on plant macrofossil, lithological and pollen analysis of two stratigraphical transects correlated by pollen analysis. The palaeolake may have appeared before the Younger Dryas; the lake-level was low and the vegetation dominated by cold steppic grasslands. The lake-level rose to its highest level during the Holocene in the Middle Atlantic (at ca. 5060±45 b.p.). Postglacial forests (Quercetum mixtum and Abieto-Fagetum) developed progressively in the lower part of the valley, while dense Pinus uncinata forests rapidly invaded the surroundings of the mire and remained the dominant local vegetation until present. The observed lowering of the lake levels during the Late Atlantic and the Subboreal (from 5060 ± B.P. to 3590±40 b.p.) was related to the overgrowth of the mire. The first obvious indications of anthropogenic disturbances of the vegetation are recorded at the Atlantic/Subboreal boundary as a reduction in the forest component, which has accelerated during the last two millennia.

Kritische untersuchungen über die sogenannten wasserspalten. Von dr. Anton Nestler ...

"Eingegangen bei der Akademie am 2.februar 1893."

Physiological responses to water stress in Eucalyptus cloeziana and E-argophloia seedlings

Effects of water stress duration and intensity on gas exchange and leaf water potential were investigated in 7-month-old seedlings of a humid coastal provenance (Gympie) and a dry inland (Hungry Hills) provenance of E. cloeziana F. Muell. and in a dry inland (Chinchilla) provenance of E. argophloia Blakely supplied with 100% (T-100), 70% (T-70), 50% (T-50) of their water requirements, or were watered only after they were wilted at dawn (T-0). Seedlings of E. argophloia had the highest midday net photosynthetic rate (A), stomata] conductance (g(s)), stomatal density and predawn leaf water potential (Psi(pd)) in all treatments. The E. cloeziana provenances did not differ in these attributes. The T-70 and T-50 treatments caused reductions in A of 30% in E. argophloia, and 55% in the E. cloeziana provenances. Under the T-0 treatment, E. argophloia maintained higher rates of gas exchange at all levels of water stress than E. cloeziana provenances. The estimates of Psi(pd) and midday water potential (Psi(md)) at which plants remained wilted overnight were respectively: -2.7 and -4.1 MPa for E. cloeziana (humid), -2.8 and -4.0 MPa for E. cloeziana (dry) and, -3.7 and -4.9 MPa for E. argophloia. Following stress relief, both A and g(s) recovered more quickly in E. argophloia and in the dry provenance of E. cloeziana than in the humid provenance. We conclude that E. argophloia is more drought tolerant and has a potential for cultivation in the humid and semi humid climates, whilst E. cloeziana has greater potential in the humid subtropical climates.

Localization and movement of mineral oil in plants by fluorescence and confocal microscopy

Fluorescence and confocal laser scanning microscopy were explored to investigate the movement and localization of mineral oils in citrus. In a laboratory experiment, fluorescence microscopy observation indicated that when a 'narrow' distillation fraction of an nC23 horticultural mineral oil was applied to adaxial and opposing abaxial leaf surfaces of potted orange [Citrus x aurantium L. (Sapindales: Rutaceae)] trees, oil penetrated steadily into treated leaves and, subsequently, moved to untreated petioles of the leaves and adjacent untreated stems. In another experiment, confocal laser scanning microscopy was used to visualize the penetration into, and the subsequent cellular distribution of, an nC24 agricultural mineral oil in C. trifoliata L. seedlings. Oil droplets penetrated or diffused into plants via both stomata and the cuticle of leaves and stems, and then moved within intercellular spaces and into various cells including phloem and xylem. Oil accumulated in droplets in intercellular spaces and within cells near the cell membrane. Oil entered cells without visibly damaging membranes or causing cell death. In a field experiment with mature orange trees, droplets of an nC23 horticultural mineral oil were observed, by fluorescence microscopy, in phloem sieve elements in spring flush growth produced 4-5 months and 16-17 months after the trees were sprayed with oil. These results suggest that movement of mineral oil in plants is both apoplastic via intercellular spaces and symplastic via plasmodesmata. The putative pattern of the translocation of mineral oil in plants and its relevance to oil-induced chronic phytotoxicity are discussed.

Ecophysiology and biomechanics of Equisetum giganteum in South America

Equisetum giganteum L., a giant horsetail, is one of the largest living members of an ancient group of non-flowering plants with a history extending back 377 million years. Its hollow upright stems grow to over 5 m in height. Equisetum giganteum occupies a wide range of habitats in southern South America. Colonies of this horsetail occupy large areas of the Atacama river valleys, including those with sufficiently high groundwater salinity to significantly reduce floristic diversity. The purpose of this research was to study the ecophysiological and biomechanical properties that allow E. giganteum to successfully colonize a range of habitats, varying in salinity and exposure. Stem ecophysiological behavior was measured via steady state porometry (stomatal conductance), thermocouple psychrometry (water potential), chlorophyll fluorescence, and ion specific electrodes (xylem fluid solutes). Stem biomechanical properties were measured via a 3-point bending apparatus and cross sectional imaging. Equisetum giganteum stems exhibit mechanical characteristics of semi-self-supporting plants, requiring mutual support or support of other vegetation when they grow tall. The mean elastic moduli (4.3 Chile, 4.0 Argentina) of E. giganteum in South America is by far the largest measured in any living horsetail. Stomatal behavior of E. giganteum is consistent with that of typical C3 vascular plants, although absolute values of maximum late morning stomatal conductance are very low in comparison to typical plants from mesic habitats. The internode stomata exhibit strong light response. However, the environmental sensitivity of stomatal conductance appeared less in young developing stems, possibly due to higher cuticular conductance. Exclusion of sodium (Na) and preferential accumulation of potassium (K) at the root level appears to be the key mechanism of salinity tolerance in E. giganteum. Overall stomatal conductance and chlorophyll fluorescence were little affected by salinity, ranging from very low levels up to half strength seawater. This suggests a high degree of salinity stress tolerance. The capacity of E. giganteum to adapt to a wide variety of environments in southern South America has allowed it to thrive despite tremendous environmental changes during their long tenure on Earth.

Biossistemática do complexo Cryptanthus zonatus (Vis.) Beer

The taxonomic delimitation at the species level in plants is not an easy task due to the large polymorphism of plants. In this project we aimed to evaluate three morphotypes (forms) of Cryptanthus zonatus (Vis.) Beer ( Bromeliaceae, Bromelioideae ) described in the literature using fl oral biology and phenology, as well as flo ral morphology and leaf anatomy . These studies were conducted in the Parque Estadual das Dunas de Natal, Rio Grande Norte (RN) and Private Reserve of Natural Patrimony Mata Estrela , in the municipality of Ba í a Form osa. The survey of the phenology of the morphotypes involved monthly specimen observation in the field, during one year. In each visit, we observed the status of flowering and fruiting phenophases of the population of the three forms of C. zonatus . For flo ral biology we sought to evaluate data like: observed floral visitors, nectar volume and concentration, time of anthesis and closing of flowers . Flowers of the three fo rms were collected in the field , analyzed by stereomicroscope, and measurements of the f loral pieces were made with the help of a caliper . Transversal and paradermal sections of the leaves of the three forms were stained and then examined under an optical microscope. Observations of the epidermis under scanning electron microscopy were also conducted. The three m orphotypes could not be sepated based on all evidence investigated. Thus, we conclude that there is not evidences to support the recognition of C. zonatus morphotypes as taxonomic entities, and also that the tools of phenology, anatomy, biology and floral morphology were not useful to delimit these three forms . Yet to characterize better the Flora of Bromeli aceae of RN, the leaf anatomy of Orthophytum disjunctum was also studied. Orthophytum is the sister genus to Cryptanthus and only recently documented in the semiarid of RN. The anatomical comparison between Cryptanthus and Orthophytum allowed the separatio n of both genera based on the arrangement of stomata and thickness of aquiferous parênquima . During the fieldwork, it was still possible to document the first occurrence of Aechmea muricata in RN, inside the Mata Estrela preserve, aiding the understanding of the distribution of the taxon that is currently threatened with extinction.