Ontogenetic patterns of leaf CO2 exchange, morphology and chemistry in Betula pendula trees |
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Authors: | J Oleksyn R Żytkowiak P B Reich M G Tjoelker P Karolewski |
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Institution: | (1) Polish Academy of Sciences, Institute of Dendrology Parkowa 5, PL-62–035 Kórnik, Poland, PL;(2) University of Minnesota, Department of Forest Resources 115 Green Hall, 1530 Cleveland Avenue N., St. Paul, MN 55108–6112, USA e-mail: oleks001@gold.tc.umn.edu Tel.: +1-612-624-3671, Fax: +1-612-625-5212, US |
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Abstract: | In order to explore ontogenetic variation in leaf-level physiological traits of Betula pendula trees, we measured changes in mass- (A
mass) and area-based (A
area) net photosynthesis under light-saturated conditions, mass- (RSmass) and area-based (RSarea) leaf respiration, relative growth rate, leaf mass per area (LMA), total nonstructural carbohydrates (TNC), and macro- and
micronutrient concentrations. Expanding leaves maintained high rates of A
area, but due to high growth respiration rates, net CO2 fixation occurred only at irradiances >200 μmol photons m–2 s–1. We found that full structural leaf development is not a necessary prerequisite for maintaining positive CO2 balance in young birch leaves. Maximum rates of A
area were realized in late June and early July, whereas the highest values of A
mass occurred in May and steadily declined thereafter. The maintenance respiration rate averaged ≈8 nmol CO2 g–1 s–1, whereas growth respiration varied between 0 and 65 nmol CO2 g–1 s–1. After reaching its lowest point in mid-June, leaf respiration increased gradually until the end of the growing season. Mass
and area-based dark respiration were significantly positively correlated with LMA at stages of leaf maturity, and senescence.
Concentrations of P and K decreased during leaf development and stabilized or increased during maturity, and concentrations
of immobile elements such as Ca, Mn and B increased throughout the growing season. Identification of interrelations between
leaf development, CO2 exchange, TNC and leaf nutrients allowed us to define factors related to ontogenetic variation in leaf-level physiological
traits and can be helpful in establishing periods appropriate for sampling birch leaves for diagnostic purposes such as assessment
of plant and site productivity or effects of biotic or abiotic factors.
Received: 29 December 1998 / Accepted: 26 July 1999 |
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Keywords: | Betula pendula Photosynthesis Respiration Nutrients Leaf ontogeny |
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