Die saisonale Dynamik von Photosynthese und Kohlenhydratmetabolismus immergrüner Nadelbäume

2001

S. 31-46

67 Lit. Ang.

Unselbständiges Werk

200084561

In evergreen conifers a dynamic pattern of the source-sink relations occurs, caused by seasonal changes in the carbon demands of the various sinks which follow the annual cycle of the developmental phases. In spring, buds and new shoots represent the major sinks. In evergreen conifers, the carbon supply for bud sprouting is provided more or less exclusively by the photosynthetic production in the older leaves, while reserve material deposited during autumn of the previous year is of minor importance. Meristems of the roots and the axial systems also represent active sinks that compete for stored reserves and currently produced assimilates. In the course of the year the root acquires assimilates in early sping and in late autumn. During winter the root is by far the major carbon sink. Root growth activity as long as the soil is not frozen and the production of large amount of reserve starch cause the strong sink activity of the roots. In perennial plants carbon metabolism is stronlgy influenced by the environmental conditions. During frosthardening, accumulation of soluble carbohydrates, namely oligosaccharides of the raffinose-series occurs. Photosynthetic carbon assimilation of coniferous trees reveals a pronounced seasonal variation. During summer maximum rates of net photosynthesis were recorded which decrease in autumn due to a decrease in temperature, light intensity, and the daily photoperiod, and reach minimum values in mid winter. A reduction of the photosynthetic performance during winter is also caused by a reduction in the number of both photosystems indicated by a reduction of chlorophyll and chlorophyll-binding proteins during frosthardening of the trees. In many woody plants 30% to more than 60% of the daily photosynthetic production is dissipated by respiration. The rate of respiration of various organs and tissues varies seasonally in accordance with changes in physiological activity and temperature.