Abstract
Autumn senescence of deciduous trees is characterized by chlorophyll degradation and flavonoid synthesis. In the present study, chlorophyll and flavonol contents were measured every morning and evening during the whole autumn with a non-destructive method from individual leaves of Sorbus aucuparia, Acer platanoides, Betula pendula and Prunus padus. In most of the studied trees, the chlorophyll content of each individual leaf remained constant until a phase of rapid degradation commenced. The fast phase lasted only ~1 week and ended with abscission. In S. aucuparia, contrary to the other species, the chlorophyll content of leaflets slowly but steadily decreased during the whole autumn, but rapid chlorophyll degradation commenced only prior to leaflet abscission also in this species. An increase in flavonols commonly accompanied the rapid degradation of chlorophyll. The results may suggest that each individual tree leaf retains its photosynthetic activity, reflected by a high chlorophyll content, until a rapid phase of chlorophyll degradation and flavonoid synthesis begins. Therefore, in studies of autumn senescence, leaves whose chlorophyll content is decreasing and leaves with summertime chlorophyll content (i.e. the leaves that have not yet started to degrade chlorophyll) should be treated separately.
Highlights
During autumn senescence, deciduous trees shed their leaves, remobilizing nutrients, mainly nitrogen and phosphorus, for winter storage
Rowan (S. aucuparia; ~5 m tall), Norway maple (A. platanoides; ~10 m), silver birch (B. pendula; ~15 m) and bird cherry (P. padus; ~1 m), growing in a small park (Turku, Finland, 60°N, 22°E), were chosen for the measurements, and individual full-grown leaves from each tree were marked before the measurements started
Chlorophyll contents of individual leaves of senescing trees remained stable until onset of rapid degradation Chlorophyll and flavonol contents of individual leaves of S. aucuparia, A. platanoides, B. pendula and P. padus were recorded with a non-destructive method twice a day from 23 August 2015 to 23 October 2015 (Figs 1‒4)
Summary
Deciduous trees shed their leaves, remobilizing nutrients, mainly nitrogen and phosphorus (for review, see Brant and Chen 2015), for winter storage. Senescence is a genetically controlled, energyconsuming process that leads to death of specific plant organs The course of autumn senescence in Populus tremula has been described by Keskitalo et al (2005). Photosynthesis declines while functional chloroplasts turn into gerontoplasts, and mitochondria become the main energy producers. Mattila et al – Autumn senescence in single leaves A small number of chloroplasts remain intact and some photosystem II (PSII) centres stay functional until almost the end of senescence (Keskitalo et al 2005; Moy et al 2015). Metabolic activity ceases, cytoplasm is degraded, the abscission zone forms and the leaf falls off
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