Summary• The hydraulic plumbing of vascular plant leaves varies considerably between major plant groups both in the spatial organization of veins, as well as their anatomical structure.• Five conifers, three ferns and 12 angiosperm trees were selected from tropical and temperate forests to investigate whether the profound differences in foliar morphology of these groups lead to correspondingly profound differences in leaf hydraulic efficiency.• We found that angiosperm leaves spanned a range of leaf hydraulic conductance from 3.9 to 36 mmol m 2 s − 1 MPa − 1 , whereas ferns (5.9 -11.4 mmol m − 2 s − 1 MPa − 1 ) and conifers (1.6 -9.0 mmol m − 2 s − 1 MPa − 1 ) were uniformly less conductive to liquid water. Leaf hydraulic conductance (K leaf ) correlated strongly with stomatal conductance indicating an internal leaf-level regulation of liquid and vapour conductances. Photosynthetic capacity also increased with K leaf , however, it became saturated at values of K leaf over 20 mmol m − 2 s − 1 MPa − 1 .• The data suggest that vessels in the leaves of the angiosperms studied provide them with the flexibility to produce highly conductive leaves with correspondingly high photosynthetic capacities relative to tracheid-bearing species.
The Atacama and Peruvian Deserts form a continuous belt for more than 3500 km along the western escarpment of the Andes from northern Peru to northernmost Chile. These arid environments are due to a climatic regime dominated by the cool, north-flowing Humboldt (Peruvian) Current. Atmospheric conditions influenced by a stable, subtropical anticyclone result in a mild, uniform coastal climate nearly devoid of rain, but with the regular formation of thick stratus clouds below I 000 m during the winter months. Where coastal topography is low and flat, the clouds dissipate inward over broad areas with little biological impact. However, where isolated mountains or steep coastal slopes intercept the clouds, a fog-zone develops. This moisture allows the development of plant communities termed lomas formations. These floristic assemblages function as islands separated by hyperarid habitat devoid of plant life. Since growth is dependent upon available moisture, an understanding of climatic patterns is essential in efforts to interpret present-day plant distributions. Topography and substrate combine to influence patterns of moisture availability. The ecological requirements and tolerances of individual species ultimately determines community composition. Species endemism exceeds 40% and suggests that the lomas formations have evolved in isolation from their nearest geographic neighbors in the Andes. While the arid environment is continuous, there appears to be a significant barrier to dispersal between 18° and 22"8 latitude in extreme northern Chile. Less than 7o/o of a total flora, 2 ALISO estimated at nearly 1000 species, occur on both sides ofthis region. Viable hypotheses concerning the age and origins of these desert floras will require continued study of the ecology and biogeography of their component species.
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The lomas formations of the Peruvian and Atacama deserts are characterized by both climatic and floristic spatial heterogeneity, as well as non-contiguous pockets of relatively distinct flora. We examined two distinct types of communities in Parque Nacional Pan de Azúcar in Chile, the low-elevation arroyo and bajada community, and the high-elevation fog-zone community. We determined the distribution with elevation of the dominant perennial plant species in a single arroyo community, as well as the distribution of associated climatic characteristics. Climatic conditions (including air temperature, relative humidity, and wind speed and direction) were recorded from June, 1999, to March, 2001, for the arroyo, as well as for a medium-elevation inland site with little vegetation, and a high-elevation fog-zone site with copious vegetation. The fog layer, or camanchaca, derived from the marine inversion layer ubiquitous to the Peruvian and Atacama deserts was found to be more persistent, though weaker, during the summer months and somewhat more condensed and shallower in the winter months, with uncharacteristically dry air and high temperatures occurring at and above 400 m elevation during the late fall and early winter of 2000. The reduction or increase in the maximum elevation of the camanchaca or a change in the rainfall regime of the park may have broad implications for the distribution or even presence of certain species in Parque Nacional Pan de Azúcar. Vegetation patterns appear to be strongly dependent on inversion layer development, and perhaps on its subsidence during the winter. A number of species prevalent at low-elevation sites may have little advantage at a highelevation foggy site, whereas the consistently high humidity at low elevations would be a boon to any desert plant accustomed to low precipitation. If we are to successfully assess the effects of changes in southern Pacific weather patterns, it will become necessary to more closely examine the local variation in climate and plant distribution in these regions, on sets of species with known distributions and in environments whose climatic conditions are particularly well-characterized.Key words: Pan de Azúcar, meteorology, plant, distribution. RESUMENLas "lomas", formaciones de los desiertos Peruano y de Atacama, se caracterizan por su heterogeneidad climática y florística, así como también por la discontinuidad de una vegetación relativamente distintiva y particular. Se investigaron dos grupos distintos de comunidades vegetales en el Parque Nacional Pan de Azúcar en Chile, las comunidades de baja elevación "arroyo" y "bajada", y la comunidad de la zona de niebla a mayor elevación. Se determinó la distribución altitudinal de las especies de plantas perennes dominantes en un arroyo, así como la distribución de las características climáticas asociadas. Las variables climáticas (incluyendo la temperatura ambiental, la humedad relativa, y la velocidad y dirección del aire) fueron registradas desde el mes de junio de 1999 hasta marzo de 2001, en...
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