Botany
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Item Seasonal changes in organic carbon content of leaves of deciduous trees(Elsevier, 1991) Jayasekera, R.; Schleser, G.H.Changes in organic carbon content were investigated during the course of one growing season in the leaves of beech (Fagus sylvaticaL.) and oak (Quercus robur L.). Considerable alterations in leaf carbon content were found not only during the course of the growing season, but also as a function of tree height. Until about August, leaf carbon content of oak gradually increased and then showed a decline as the leaves yellowed in October. In beech sun leaves there was a gradual increase in organic carbon content with increasing foliage age, whereas shade leaves showed the opposite trend. The results demonstrate that leaf carbon content may vary during leaf ontogenesis, and that the character of ontogenetic changes in carbon content depends not only on plant species but also on canopy position.Item Seasonal changes in potential net photosynthesis of sun and shade leaves of Fagus sylvatica L.(Elsevier, 1988) Jayasekera, R.; Schleser, G.H.Sun and shade leaves of the deciduous tree, Fagus sylvatica, were investigated for their potential photosynthetic activity during the course of one growing season. During the initial period of leaf development and expansion, sun leaves exhibited relatively higher photosynthetic rates. After full expansion of leaves, shade leaves had a higher activity in potential net photosynthesis until about the end of August. Low diffusion resistance for CO2/O2 and higher activities of photosystems in shade leaves seem to be the main causes of their higher photosynthetic potential.Item δ13C - variations of leaves in forests as an indication of reassimilated CO2 from the soil(Springer-Verlag, 1985) Schleser, G.H.; Jayasekera, R.An attempt has been made to evaluate the contribution of soil respired CO2 to the total assimilation of a forest tree, by heeding the 13C-concentrations of CO2 from the free atmosphere and from mineralization processes within the soil respectively. An expression has been derived, according to which the assimilated fraction of CO2 from the soil at a particular height of a tree is given by the δ13C-value of the corresponding leaves, δ13C of atmospheric CO2, δ13C of soil respired CO2 and the physiological state of the leaves expressed as the ratio of total respiration over gross photosynthesis and internal over external CO2-concentration. In the particular case investigated, a δ13C-difference of 5‰ has been determined from bottom to top of a beech tree which results in a CO2 contribution from the soil of about 22% for the lower forest strata, while the total contribution of soil respired CO2 accounts for about 5% of the overall assimilation.