Isotopenverhältnis Infrarot Spektroskopie von CO2 und Wasserdampf im Vergleich zu IRMS
Final Report Abstract
In research-oriented projects, the measuring system was first used within the framework of a cooperation with the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL; Birmensdorf, Switzerland) for a three-week measurement campaign as part of the long-term research project (17 years) "Pfynwald Irrigation Experiment" in Valais (Switzerland) with labelling of Scots pines (Pinus sylvestris) in a hundred-year-old stand with the stable carbon isotope 13C and the stable oxygen isotope 18O via the canopy (fumigation/spraying). The purpose of the experiment was to track (1) the incorporation of carbon assimilated by photosynthesis in the various compartments of the tree as well as the carbon transfer from the roots to the soil and its microbiome and (2) the 18O absorbed into the needles and branches via air humidity by spraying with water. The aim of the study was to test the response of the tree species to artificial irrigation in parts of the stand in comparison with the non-irrigated stand areas in the naturally very dry pine forest. The results should provide indications of the responses of the forestry-important tree species Scots pine to weather events in times of climate change. In the irrigated plots, the δ13C ratio in the CO2 respired by the stem and soil was higher than in the non-irrigated controls. In a period of low rainfall, the marker in respired CO2 was found 24 h earlier in the irrigation treatment than in the control plots. However, naturally occurring heavy rainfall led to a reduction in the differences between the treatments. Taken together, the results suggested an increased δ13C allocation to stems and belowground compartments and an increase in C transport rates due to water supply. The results show that metabolic activity in the rhizosphere and its modification by soil moisture drives carbon allocation in adult trees and forest ecosystems. Soil moisture in turn affects the incorporation of 13C and 18O into assimilates differently: In the irrigated pines, the incorporation of 13C but not of 18O into assimilates was significantly higher than in the non-irrigated parts of the stand. The lack of difference in 18O incorporation can be explained primarily by non-photosynthetic processes of 18O uptake. Overall, the findings show that even a relatively small increase in soil moisture has a rapid and significant effect on the tree-internal uptake and translocation of carbon and on soil functions. The results have been published in Proceedings of the National Academy of Sciences (PNAS) and Tree Physiology. In a master's thesis unpublished so far, the measuring system was used to show that plantations of young beech trees in a vegetation period with cool, humid weather are more of a source than a sink for CO2 due to the long-term restriction of stomatal conductivity.
Publications
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Effects of soil moisture, needle age and leaf morphology on carbon and oxygen uptake, incorporation and allocation: a dual labeling approach with 13CO2 and H218O in foliage of a coniferous forest. Tree Physiology, 41(1), 50-62.
Wang, Ao; Siegwolf, Rolf T. W.; Joseph, Jobin; Thomas, Frank M.; Werner, Willy; Gessler, Arthur; Rigling, Andreas; Schaub, Marcus; Saurer, Matthias; Li, Mai-He & Lehmann, Marco M.
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Rhizosphere activity in an old-growth forest reacts rapidly to changes in soil moisture and shapes whole-tree carbon allocation. Proceedings of the National Academy of Sciences, 117(40), 24885-24892.
Joseph, Jobin; Gao, Decai; Backes, Bernhard; Bloch, Corinne; Brunner, Ivano; Gleixner, Gerd; Haeni, Matthias; Hartmann, Henrik; Hoch, Günter; Hug, Christian; Kahmen, Ansgar; Lehmann, Marco M.; Li, Mai-He; Luster, Jörg; Peter, Martina; Poll, Christian; Rigling, Andreas; Rissanen, Kaisa A.; Ruehr, Nadine K. ... & Gessler, Arthur
