Current issue: 57(2)
Under compilation: 57(3)
The interactive effects of water stress and temperature on the CO2 response of photosynthesis was studied in Salix sp. cv. Aquatica using the closed IRGA system. A semi-empirical model was used to describe the CO2 response of photosynthesis. The interactive effect of water stress and temperature was divided into two components: the change in CO2 conductance and the change in the photosynthetic capacity. The CO2 conductance was not dependent on the temperature when the willow plant was well watered, but during water stress it decreased as the temperature increased. The photosynthetic capacity of the willow plant increased along with an increase in temperature when well-watered, but during water stress temperature had quite opposite effect.
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The concept of tree class as indicated by dominant, codominant, intermediate and suppressed trees is analysed using empirical material representing 13 younger Scots pine (Pinus sylvestris L.) stands. The relative needle biomass, i.e. the needle biomass related to the maximum needle biomass in the stand, was closely related to the relative height of the tree and independent of the stand characteristics. Furthermore, the relative illumination of the crown system was related to the relative height of the trees as well as the relative photosynthetic capacity and tree-to-tree variation in growth. When calculated per needle biomass unit it appeared that height growth, radial growth, needle growth and other growth parameters were the highest in the suppressed trees. The suppressed trees thus appear to be more efficient in utilizing available resources than other tree classes. The ecologic significance of the results is discussed.
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The effect of nitrogen fertilizers on the photosynthetic capacity of conifers is assessed on the basis of literature. The review emphasizes the role of changes of needle mass as a factor affecting the result of nutrient application. In particular, the increase in needle mass results in a considerable increase in photosynthetic capacity. The effect of fertilization on the photosynthetic rate seems to be of minor importance. The effect on the photosynthetic rate is, however, poorly documented as is the case for the effect of fertilization on the respiration rate. There is evidence that proper application of nitrogen fertilizers may double the photosynthetic capacity of conifers, mainly as a result of increase in needle mass.
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Physiological studies of long-lived trees are particularly important at this time, especially in light of the need for trees to adapt to global climate change. The results of the present studies were obtained on an approximately 700-year-old Quercus robur L. – the ‘Bartek’ oak. The tree has to adapt to changing climatic conditions, starting from the transition between the Medieval Warm Period and the Little Ice Age, up to the present time of rapid global climate change. Tomograph imaging showed decay of the tree trunk interior and revealed that undamaged wood forms a thin layer around the trunk perimeter. Two series of experiments were carried out to assess the physiological state of the tree. The first concerned measurements related to photosynthetic capacity: chlorophyll a fluorescence, gas exchange (CO2 assimilation, transpiration), stomatal conductance and leaf water potential. The second series concerned xylem sap flow velocity and anatomical studies of stem wood. Photosynthetic capacity was within the limits reported for young healthy trees. The diurnal pattern of velocity of xylem sap flow was also typical for young vigorous trees and flow velocity correlated positively with solar radiation and negatively with air relative humidity. Anatomical observations of the outermost wood showed relatively narrow annuals rings with large diameter earlywood vessels. The results indicate that the veteran tree does not show signs of water stress probably due to a good balance of water flow and that leaf area of the canopy needs only the current ring of wood to feed transpiration of the canopy.