Détail de l'auteur
Auteur E. Beck |
Documents disponibles écrits par cet auteur (2)
trié(s) par (Pertinence décroissant(e), Titre croissant(e)) Affiner la recherche
Titre : Cold tolerance in tropical alpine plants Type de document : texte imprimé Auteurs : E. Beck Importance : pp. 77-110 Langues : Anglais (eng) Résumé : "Summer every day and winter every night’ (Hedberg 1964) is a brief but succinct characterization of the tropical alpine climate, pointing to the fact that the amplitude of the daily temperature oscillation by far exceeds that of the monthly mean values. Although cloudiness exerts a mitigating effect on the daily temperature extremes during the rainy seasons, nocturnal frost may occur throughout almost all of the year at altitudes above 4000 m. Therefore tropical alpine plants must maintain mechanisms of permanent frost hardiness which differ considerably from those providing the overwintering plants of temperate climates with seasonal frost resistance. Whereas, for example, in Norway spruce the frost-hardy state is characterized by a high proportion of unsaturated fatty acids in the membrane lipids (Senser 1982), by a shift from photosynthetic starch formation to the production of sucrose and its galactosides (Kandler et al 1979), by a reduced capability of photosynthetic electron transport (Senser & Beck 1979) and by a suspension of growth activity, tropical alpine plants must combine physiological features providing frost resistance with continuously high rates of photosynthesis and growth." (source : auteur) Type de publication : article de livre Référence biblio : Beck E., 1994 - Cold tolerance in tropical alpine plants. In : 1994 - Tropical alpine environments : plant form and function. Cambridge University Press, 77-110. ID PMB : 7615 Permalink : http://www.cbnbrest.fr/catalogue_en_ligne/index.php?lvl=notice_display&id=7615 Exemplaires(0)
Disponibilité aucun exemplaire
Titre : Turnover and conservation of nutrients in the pachycaul Senecio keniodendron Type de document : texte imprimé Auteurs : E. Beck, Auteur Importance : pp. 215-221 Langues : Anglais (eng) Catégories : [Espèces (in biblio)] Senecio Résumé : "Pachycaul senecios from the upper Afroalpine zone produce stems up to 11 m tall which are coated with marcescent leaves. Each stem or branch is terminated by a huge leaf rosette composed of 30–120 leaves which surround the central cone-shaped leaf-bud. During the course of a year about 50–60 leaves are produced from the bud (Beck et al. 1980) and in principle the same number of mature leaves at the outer periphery of therosette become senescent and die. The leaves are up to 50 cm long and 15–20 cm wide. Senescence commences at the tip which becomes yellow and subsequently necrotic. Yellowing of the lamina spreads from the tip downwards to the base. A senescing leaf, the upper part of which was already partially necrotic, was found to be still capable of photosynthesis in the lower part (E. Beck, unpublished data). This mode of gradual senescence suggests that a substantial portion of the nutrients can be mobilized and exported from the leaf before it dies. Table 11.1 shows the disappearance of nitrogen in the senescing leaf. The plant was located at 4200 m elevation in the Teleki Valley, Mount Kenya. The prolonged viability of the midribs presumably facilitates this mobilization. This type of internal recycling of nitrogen and other nutrients is common in higher plants. However, unlike the majority of the higher plants the pachycaul groundsels do not shed the dead leaves but maintain them as a dense collar around the stem." (source : auteur) Type de publication : article de livre Référence biblio : Beck E., 1994 - Turnover and conservation of nutrients in the pachycaul Senecio keniodendron. In : 1994 - Tropical alpine environments : plant form and function. Cambridge University Press, 215-221. ID PMB : 7608 Permalink : http://www.cbnbrest.fr/catalogue_en_ligne/index.php?lvl=notice_display&id=7608 Exemplaires(0)
Disponibilité aucun exemplaire
