Photosynthetic characteristics and their leaf-age dependence were examined to estimate ecophysiological effects on net primary production (NPP) of a polar willow (Salix polaris), a dominant dwarf shrub species in a polar semi-desert area of Ny-Ålesund, Svalbard. Leaves of S. polaris emerged just after snowmelt in early July in 2000; flowers were initiated within 1 week, and fruits in late July. Light-saturated rate of photosynthesis and stomatal conductance to water vapor increased rapidly to their maximum values within 1 week after leaf emergence and then decreased gradually. Depending on the leaf age, photosynthetic rates saturated at photosynthetically active photon flux density (PPFD) of 200-400 µmol·m -2 ·s -1 , which is the light level usually available in the natural habitat. Optimum leaf temperature of photosynthesis ranged from 10 to 18°C, while air temperature in the habitat ranged from 8 to 20°C. These light and temperature responses of photosynthesis of S. polaris would be suitable for efficient carbon gain in the natural habitat characterized by highly variable light and temperature conditions. Using the photosynthetic and respiratory characteristics, biomass distribution, and meteorological data, NPP of S. polaris in the current year was estimated to be 26.1 g C·m -2 . A model simulation of rising temperature conditions predicted a reduction of NPP because of a large increase in respiration. It was suggested that temperature condition and leaf phenological aspects strongly influence the carbon fixation by plants in the high arctic area studied.Résumé : L'étude porte sur un saule arctique (Salix polaris), une espèce d'arbre nain dominant dans une région polaire semi-désertique du Ny-Ålesund, Svalbard. Afin d'évaluer les effets de facteurs éco-physiologiques sur la production primaire nette (NPP) de cette plante, les auteurs en ont examiné les caractéristiques photosynthétiques et leur dépen-dance par rapport à l'âge des feuilles. Le S. polaris développe ses feuilles immédiatement après la fonte de la neige au début de juillet (2000), fleurit en moins d'une semaine et fructifie à la fin de juillet. Le taux de photosynthèse en lumière saturante et la conductance stomatale pour l'évaporation de l'eau augmentent rapidement et atteignent leurs valeurs maximales moins d'une semaine après l'émergence des feuilles, puis diminuent graduellement par la suite. Selon l'âge des feuilles, les taux photosynthétiques sont saturés à une densité de flux de photons photosynthétiquement actifs de 200-400 µmol·m -2 ·s -1 , ce qui est égal à l'intensité lumineuse prévalant naturellement dans leur habitat. La tempéra-ture optimale pour la photosynthèse va de 10 à 18°C, alors que la température de l'air dans cet habitat se situe entre 8 et 29°C. Ces réactions de la photosynthèse du S. polaris, en relation avec la lumière et la température, semblent convenir pour assurer un gain en carbone efficace dans cet habitat naturel caractérisé par des conditions de lumière et de température fortement variables. Sur la base des caract...

Summary• Evolution of dimorphic breeding systems may involve changes in ecophysiological traits as well as floral morphology because of greater resource demands on females. Differences between related species suggest that ecophysiological traits should be heritable, and species with higher female frequencies should show greater sexual differentiation.• We used modified partial diallel crossing designs to estimate narrow-sense heritabilities and genetic correlations of sex-specific ecophysiological and morphological traits in closely related gynodioecious Schiedea salicaria (13% females) and Schiedea adamantis (39% females).• In S. salicaria , hermaphrodites and females differed in photosynthetic rate and specific leaf area (SLA). Narrow-sense heritabilities were significant for stomatal conductance, SLA and inflorescence number in hermaphrodites, and for SLA and inflorescence number in females. Schiedea adamantis had no sexual dimorphism in measured traits; stomatal conductance, stem number and inflorescence number were heritable in females, and stem number was heritable in hermaphrodites. In both species, significant genetic correlations of traits between sexes were rare, indicating that traits can evolve independently in response to sex-differential selection. Significant genetic correlations were detected between certain traits within sexes of both species.• Low heritability of some ecophysiological traits may reflect low additive genetic variability or high phenotypic plasticity in these traits.

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Pre-dawn leaf water potential and parameters controlling water flow through a plant of five co-occurring plant species, Dodonaea viscosa Jacquin (Sapindaceae), Wikstroemia pseudoretusa Koidzumi (Thymelaeaceae), Ligustrum micranthum Zucc. (Oleaceae), Distylium lepidotum Nakai (Hamamelidaceae) and Hibiscus glaber Matsumura (Malvaceae) were compared in late April, early June and early September 1989. These species are common members of the scrub community found on shallow-soil ridges in the Bonin Islands, Japan. Mean pre-dawn leaf water potential during the dry period of early September was lowest in Dod. Viscosa growing on microsites with shallower soil on a ridge. Deeper rooted species, Dis. Lepidotum and H. glaber, had higher values of pre-dawn leaf water potential than shallower rooted species, L. micranthum and W. pseudoretusa. Anatomical and morphological characteristics, and physiological characteristics such as water relations of leaves suggested that W. pseudoretusa and H. glaber are less tolerant to drought than L. micranthum and Dis. Lepidotum, and that W. pseudoretusa and H. glaber might avoid severe stress by temporal leaf fall and dense deeper root, respectively. Relationships between leaf conductance and hydraulic conductance suggested different water use patterns among the five species growing in close proximity on xeric shallow-soil ridges in the Bonin Islands.

Boninia grisea is a woody species comprising two varieties that have adapted to habitats with different wind conditions. Boninia grisea var. grisea is a tree occurring in forests on mountain slopes, whereas B. grisea var. crassifolia is a shrub occurring at sites exposed to strong wind at forest edges and on mountain plateaus. The former has somewhat larger and thinner leaves than the latter. Despite the differences in habitat wind conditions and leaf morphology, plants of both taxa are found in a wide range of light environments from sunny to shady. We measured leaf morphological and photosynthetic traits for B. grisea plants of both taxa growing in the field and attempted to clarify the differences between them in terms of leaf morphological and photosynthetic acclimation to sun and shade. Boninia grisea var. crassifolia had a thicker leaf upper epidermis and a thicker spongy mesophyll layer with thicker cell walls than B. grisea var. grisea, suggesting that the former had mechanically tough leaves. Under sunny conditions, the stomatal conductance and area-based photosynthetic capacities of the two B. grisea taxa were comparable. Under shady conditions, B. grisea var. crassifolia had thicker leaves with a higher photosynthetic light saturation, area-based nitrogen content and stomatal conductance than B. grisea var. grisea, suggesting that the former was less acclimated to deep shade than the latter.