Browsing by Subject "xylem diameter change"

As most conifers, pine trees produce and store oleoresin in their resin ducts. Oleoresin is a defensive secondary metabolite that protects trees mainly against bark beetles and herbivores. The oleoresin of pine trees consists of different hydrocarbons, such as terpenes and resin acids. Inside the resin ducts, the pressure of oleoresin varies from 3 to 12 bars depending on the tree species, individual tree and environmental conditions. Traditionally, oleoresin has been studied because of its defensive features, since it has an important role in preventing insect-induced damage in coniferous forest .The pressure of oleoresin in pine trees has been a subject for excessive studies especially in 1960s and 1970s due to large epidemics of bark beetles, for example Dendroctonus frontalis, in United States of America. As a result, oleoresin pressure has been linked to the water balance of a tree. Since the changes in the tension of water inside water conducting tracheids affect the diameter of xylem, the diurnal pattern of oleoresin pressure and the diameter of xylem have been recorded to be similar. The connections between oleoresin pressure and other physiological processes of a tree have nevertheless been neglected, although there may be a strong relation between the pressure of oleoresin and the BVOC (biogenic volatile organic compound) -emissions from the trunk of a tree. The constituents of oleoresin, for example monoterpenes, form a part of the BVOC emissions that pine forests emit. Estimating the BVOC emissions from tree trunks and from forests and understanding the mechanisms behind monoterpene emissions would be essential, because BVOCs have been detected to contribute to the cloud formation and thus to the climate. In addition, the studies on oleoresin pressure are relatively old and conducted mostly in Southern USA where the climate is mainly subtropical. In boreal forests of Northern Europe, the pressure of oleoresin has not been extensively studied before the summer of 2012, when the preliminary study for this study was conducted. The results of the preliminary study were contrary to the earlier studies conducted in Southern USA. The maximum pressures of oleoresin pressure were recorded in the afternoon and minimum pressures before sunrise, whereas according to the literature the pressure of oleoresin is highest in the early morning and lowest in the afternoon. Hence, in this study the diurnal variations in oleoresin pressure of Scots pine (Pinus sylvestris) are measured at the SMEAR II station in Southern Finland. A pressure gauge system similar to that of Vité (1961) and Perrakis (2008) is employed. The variations in oleoresin pressure are compared to environmental variables (temperature, VPD and PAR) and physiological variables (the diameter of xylem, transpiration and photosynthesis). Furthermore, the connection between oleoresin pressure and monoterpene emissions from a pine trunk is analysed by the means of EFRA - approach. The results on the diurnal pattern of oleoresin pressure are throughout the summer of 2013 similar to the results of the preliminary study. The pressure of oleoresin is highest during the warmest time of a day and lowest during the coldest time of a day. According to the results, temperature is the single variable that explains the changes in oleoresin pressure the best. However, temperature fails to explain all the changes in oleoresin pressure, so there appears to be other influences that are outshadowed by the effect of temperature. These influences could be generated by water balance and VPD, as explained in literature, since the diameter of xylem is the single variable that explains best the changes in temperature corrected oleoresin pressure. Furthermore, a relation between monoterpene emissions and oleoresin pressure is detected, although temperature appears to affect both the emissions of monoterpenes and the pressure of oleoresin.