Browsing by Subject "transpiration"

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  • Rufelt, Henry; Wiese, Björn (Suomen metsätieteellinen seura, 1981)
  • Hari, Pertti; Kanninen, Markku; Kellomäki, Seppo; Luukkanen, Olavi; Pelkonen, Paavo; Salminen, Raimo; Smolander, Heikki (Suomen metsätieteellinen seura, 1979)
  • Salmon, Yann; Torres-Ruiz, Jose M.; Poyatos, Rafael; Martinez-Vilalta, Jordi; Meir, Patrick; Cochard, Herve; Mencuccini, Maurizio (2015)
    Understanding physiological processes involved in drought-induced mortality is important for predicting the future of forests and for modelling the carbon and water cycles. Recent research has highlighted the variable risks of carbon starvation and hydraulic failure in drought-exposed trees. However, little is known about the specific responses of leaves and supporting twigs, despite their critical role in balancing carbon acquisition and water loss. Comparing healthy (non-defoliated) and unhealthy (defoliated) Scots pine at the same site, we measured the physiological variables involved in regulating carbon and water resources. Defoliated trees showed different responses to summer drought compared with non-defoliated trees. Defoliated trees maintained gas exchange while non-defoliated trees reduced photosynthesis and transpiration during the drought period. At the branch scale, very few differences were observed in non-structural carbohydrate concentrations between health classes. However, defoliated trees tended to have lower water potentials and smaller hydraulic safety margins. While non-defoliated trees showed a typical response to drought for an isohydric species, the physiology appears to be driven in defoliated trees by the need to maintain carbon resources in twigs. These responses put defoliated trees at higher risk of branch hydraulic failure and help explain the interaction between carbon starvation and hydraulic failure in dying trees.
  • Hallman, Erkki; Hari, Pertti; Räsänen, Pentti K.; Smolander, Heikki (Suomen metsätieteellinen seura, 1978)
  • Marshall, John D.; Laudon, Hjalmar; Makela, Annikki; Peichl, Matthias; Hasselquist, Niles; Nasholm, Torgny (2021)
    Forests pass water and carbon through while converting portions to streamflow, soil organic matter, wood production, and other ecosystem services. The efficiencies of these transfers are but poorly quantified. New theory and new instruments have made it possible to use stable isotope composition to provide this quantification of efficiencies wherever there is a measurable difference between the branches of a branchpoint. We present a linked conceptual model that relies on isotopes of hydrogen, carbon, and oxygen to describe these branchpoints along the pathway from precipitation to soil and biomass carbon sequestration and illustrate how it can be tested and generalized. Plain Language Summary The way a forest works can be described in terms of carbon and water budgets, which describe the ways that carbon and water flow through the forest. The paths of such flows are frequently branched and the branches are often different in their stable isotope composition. This means that stable isotopes can be used to describe the branching events. We present isotopic methods of quantifying several such events, then link them in a chain that begins with the evaporation of water and ends with biomass production.
  • Smolander, Heikki (Suomen metsätieteellinen seura, 1984)
    Measurements were made of temporal and spatial microvariations in irradiance in a small part of the canopy of a 20-yr-old Scots pine stand. Linear integration of the variations gave biased estimates; second order Taylor series approximations were satisfactory only for a low curvature response; two-point distribution approximations were applicable to high and low curvature response but presupposed that the mean and variance were known. It is suggested that a light measuring method in which first power (mean) and second power (variance) of irradiance are integrated resolves these problems; the method takes into account the geometry of the shoot and can also be used in transpiration studies.
  • Korpilahti, Eeva (Suomen metsätieteellinen seura, 1988)
    Data were collected over 3 yr during the growing season in a 20-yr-old stand at the Forestry Field Station of the University of Helsinki, Finland, to study the relations of photosynthesis and transpiration to environmental factors (irradiance, temperature, water content of soil and air) and metabolic processes.
  • Paljakka, Teemu (Helsingfors universitet, 2013)
    In consequence of transpiration vast amounts of water moves from tree roots to the atmosphere via stem and leaves. Water does not only move directly from roots towards canopy. It is essential element in the maintenance of cells and fuel to solute transport in phloem. Movement of water inside the tree is caused by differences in water potential between cells and tissues. Water moves towards lower pressure potential in the xylem. Pressure is the main component of water potential in the xylem. Phloem transport is also driven by hydrostatic pressure gradient. Water moves from xylem to the phloem when the water potential is lower in the phloem than xylem. Osmotic potential is the main component of phloem water potential. Osmotic potential, practically the osmotic strength, of a cell is related to the soluble sugar and water content in the phloem. Therefore, the main components of tree water potential are pressure and the osmotic strength of a cell. Phloem is the transport pathway of sugars and other important compounds many which role is yet unknown. The dynamics of water and sugar transport is still an enigma for researchers. Understanding of water and sugar transport is vital because they appear to affect other physiological functions in trees, i.e. the function of stomata and cell growth. The research of phloem is very challenging because phloem content is easily contaminated when collected. Phloem cells have several defend reaction when disturbed. Some methods are in use in phloem research but these methods can only be used in laboratory conditions or with specific tree species. Especially few research is been carried out in situ due to its damaging effect when collecting phloem samples. Promising method to assess phloem transport is to utilize diameter measurements. Modeling of phloem transport with xylem diameter data does not disturb the function of phloem. Essential missing piece of information is quantitative data of osmotic strength in the phloem. The topic of this thesis is to examine the diurnal changes of the main components of tree water potential. Emphasis is on examining the osmotic strength of phloem and the testing of new method for studying osmotic strength of phloem. The measurements are mainly carried out with scots pine (Pinus sylvestris L.) and test evaluations are carried out with pillar black alder (Alnus glutinosa F. pyramidalis). The measurements are made with phloem pieces collected from different heights of the tree examined and with leaves from the canopy. Also the leaf water potential is measured which is related to diameter changes of the xylem. The former are compared to the osmotic strength of phloem pieces and leaves. The method used in this thesis is apparently not used in literature. The difference with methods in the literature is the freezing and thawing of phloem pieces before sampling with sentrifuge. Method brings out similar results of phloem osmotic strength found in the literature. The values might be slighlty underestimated due to the method used. According to these results the water potential of phloem are closely related to the xylem water potential with scots pine. The strongest relation with the xylem is in the phloem beneath the canopy and weakest in the phloem collected in the base of a trunk. The phloem water potential of a branch was most difficult to intepret. The osmotic strength and water content of needles were strongly related to the needle water potential. The results support the idea of a strong interaction between phloem and xylem.
  • da Costa, Antonio C. L.; Rowland, Lucy; Oliveira, Rafael S.; Oliveira, Alex A. R.; Binks, Oliver J.; Salmon, Yann; Vasconcelos, Steel S.; Junior, João A. S.; Ferreira, Leandro V.; Poyatos, Rafael; Mencuccini, Maurizio; Meir, Patrick (2018)
    Transpiration from the Amazon rainforest generates an essential water source at a global and local scale. However, changes in rainforest function with climate change can disrupt this process, causing significant reductions in precipitation across Amazonia, and potentially at a global scale. We report the only study of forest transpiration following a long-term (>10 year) experimental drought treatment in Amazonian forest. After 15 years of receiving half the normal rainfall, drought-related tree mortality caused total forest transpiration to decrease by 30%. However, the surviving droughted trees maintained or increased transpiration because of reduced competition for water and increased light availability, which is consistent with increased growth rates. Consequently, the amount of water supplied as rainfall reaching the soil and directly recycled as transpiration increased to 100%. This value was 25% greater than for adjacent nondroughted forest. If these drought conditions were accompanied by a modest increase in temperature (e.g., 1.5°C), water demand would exceed supply, making the forest more prone to increased tree mortality.