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Dynamic measurements of Scots pine stem processes

Anni Vanhatalo1, Tommy Chan1, Juho Aalto1, Janne F. Korhonen1, Kaisa Rissanen1, Katerina Machácová2, Pasi Kolari1, Teemu Hölttä1, Eero Nikinmaa1, Jaana Bäck1
1 Department of Forest Sciences, University of Helsinki
2 CzechGlobe, Global Change Research Centre

P 3.22 in Fluxes between the atmosphere and ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

We measure several dynamic processes of Scots pine stems with different measurement techniques in field conditions at SMEAR II station, Finland. By combining these different datasets we are able to get hold on many processes going on inside tree stems and to find out how they are connected to each other. 

The stem gas exchange, including VOCs, is measured with custom-made chambers connected to a dynamic gas exchange measurement system including CO2 and H2O analysers and a PTR-MS. The chamber consists of a transparent and UV-permeable FEP foil wrapped around the Scots pine stem 2–3 times and tightened around the stem with binds on both ends. Inside the chamber, there is spiral of PE coated aluminium tube to maintain an air space between the foil and the bark, and an FEP tape covered aluminium brace for inlet and outlet connectors. The changes in stem diameters are measured with point-dendrometers with short time intervals. They are installed in twos so that the other is on inner-bark and the other on xylem. Diameter changes tell about tree growth and water use. The water balance of trees is followed with sap flow measurements done with Granier-sensors on both lower and upper stem. By combining these datasets with soil water content measurements and foliage transpiration, the transport of water all the way from soil to atmosphere can be followed. There are two separate closed pressure systems inside pine stems. Both are limited by elastic walls which may pass the pressure to the neighbouring system. The sap system is under a negative pressure due to transpiration whereas the resin system is under positive pressure which is important for damage repair. At our site, the resin pressure has been followed with a mechanic pressure gauge from time to time during the growing season.  

The measurements run 24/7 the year around so daily, seasonal and between years variation can be detected. Our measurements show low but continuous VOC emissions from pine stem, especially monoterpenes due to resin richness of pines. We have found interesting spring-time relations between monoterpene emissions and water-related variables measured on the same trees. Once the VOC data is set against flux data measured with micrometeorological techniques, we can distinguish different VOC sources inside ecosystem. Campaign-wise we have measured also CH4 and N2O fluxes from the basal part of the stem. Setting the water-related measurements (stem diameter, sap flow, stem transpiration) against defence-related parameters (resin pressure, VOC emissions) makes it possible to better understand the tree level processes as a whole.

Letzte Änderung 19.06.2014