Foliage of Scots pine (Pinus sylvestris L.) and pedunculate oak (Quercus robur L.) was collected in a mixed pine/oak forest at canopy positions differing in radiation environment. In both species, chlorophyll (Chl) a/b ratios were higher in foliage of canopy positions exposed to higher irradiance as compared to more shaded crown layers. Throughout the growing season, pine needles exhibited significantly lower Chl a/b ratios than oak leaves acclimated to a similar photon availability. Hence, pine needles showed shade-type pigment characteristics relative to foliage of oak. At a given radiation environment, pine needles tended to contain more neoxanthin and lutein per unit of Chl than oak leaves. The differences in pigment composition between foliage of pine and oak can be explained by a higher ratio of outer antennae Chl to core complex Chl in needles of P. sylvestris which enhances the efficiency of photon capture under limiting irradiance. The shade-type pigment composition of pine relative to oak foliage could have been due to a reduced mesophyll internal photon exposure of chloroplasts in needles of Scots pine, resulting from their xeromorphic anatomy. Hence, the higher drought tolerance of pine needles could be achieved at the expense of shade tolerance. and U. Hansen, J. Schneiderheinze, B. Rank.
Pedunculate (Quercus robur) and sessile (Quercus patraea) oak, dominant species in European hardwood forests, are declining in many regions throughout Europe and extreme climatic events (summer drought, winter frost) are considered to be key factors contributing to this decline via a negative effect on wood formation. An extensive sampling of scattered oak trees within a landscape of small groves and flower meadows in the White Carpathians, a hilly chain in the warm south-eastern part of the Czech Republic, was undertaken in order to determine the association between growth in diameter and climate over the last 100 years. The association with climate was evaluated by comparing latewood, earlywood and total ring widths with monthly climatic data over the period 1900–2006, using a combination of response function and pointer year analyses. The two approaches clearly showed that late wood growth of oak trees, growing on deep calcium-rich soils, which dry out in summer, is mainly associated with rainfall in May–June, while early wood growth is associated with previous autumn and winter temperatures. Extreme growth years coincided with an abnormally wet or dry May–June periods, which are often associated with cool or hot Junes. Deficient water balances resulting from low rainfall and high temperatures during the summer period are negatively associated with late wood formation and hence total annual growth increment. The results provide support for a crucial role of climate change (decline in rainfall and increase in summer temperatures over the last three decades) among other external factors in the high number of oaks dying prematurely in the White Carpathian wooded grasslands. Prolonged periods of unfavourable climatic conditions cause attenuated trees to become prone to fungal attack and mistletoe hemiparasites, which predispose the oaks to damage or death, especially solitary pedunculate oaks.