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Das Jena Trockenstress Experiment - warum sterben Bäume wenn das Wasser knapp wird ?

Das Jena Trockenstress Experiment - warum sterben Bäume wenn das Wasser knapp wird ?. Henrik Hartmann Waldemar Ziegler Susan Trumbore. Outline. Henrik Hartmann? I ntroduction Forests and the carbon cycle Effects of drought on trees

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Das Jena Trockenstress Experiment - warum sterben Bäume wenn das Wasser knapp wird ?

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  1. Das Jena Trockenstress Experiment-warumsterbenBäumewenn das Wasserknappwird? • Henrik Hartmann • Waldemar Ziegler • Susan Trumbore

  2. Outline • Henrik Hartmann? • Introduction • Forests and the carbon cycle • Effects of drought on trees • Potential mechanisms of drought-induced tree mortality • Research hypotheses • Experimental design • First results • Scientific conclusion • Non-scientific conclusions • Questions and discusssion

  3. Henrik Hartmann * Haiger, Hessen (1968) Immigration to Canada (1992) B.ForSci, Edmundston, N.B. (2003) Ph.D. Forest ecology, Montreal (2008) Postdoc, Jena (2009 - )

  4. …

  5. Sugar maple mortality following partial harvest Do disturbances from partial harvest cause physiological stress strong enough in residual trees to kill them? Nope! What caused mortality? – Malacosomadisstria (forest tent caterpillar)

  6. Forests in the modern world • Forests cover ~ 30% of land surface (4 billion ha) and are “essential to economic development and maintenance of all life forms” (UNO 1992) • They foster the bulk of terrestrial biodiversity and are a major driving force of the cycling of life-supporting elements (e.g., carbon) (Gaston 2000, FAO 2007) • Forests contain ~90% of living biomass and ~2/3 of atmospheric carbon (Körner 2003)

  7. Forests and the carbon cycle • Forests circulate about 8% of atmospheric CO2 back and forth into the biosphere every year (Malhi et al. 2002) • Forest net carbon uptake is the small difference between two large fluxes – photosynthesis and respiration (Litton et al. 2007) • However, forest mortality from disturbances and environmental change liberates large amounts of stored carbon into the atmosphere (Kurzet al. 2008) • … and thus can fuel feedback loops between atmospheric CO2 concentrations and climate change

  8. Forests and the carbon cycle

  9. Forest and drought • Anthropogenic GHGs, mainly CO2, have been linked to climate change … • ... which is predicted to cause alterations in precipitation patterns (IPCC 2007) • Frequencies of severe and extreme drought events have increased during the last decades of the 20th century and… • … the area affected by extreme drought events will further increase (from 3% to ~ 30%) and drought events will be more frequent and longer-lasting (Burke et al. 2006) • Elevated temperatures and drought have been linked to tree and forest mortality in many parts of the world (Allen et al. 2010)

  10. Weltweites Baum- und Waldsterben Source: Allen et al. 2010

  11. A model tree • Main processes of tree carbon and water cycle Transpiration Photosynthesis CO2 Respiration O2 O2 CO2 Carbohydrate translocation Water transport Water uptake

  12. Drought impacts on main processes • Carbon gain vs. water loss • Xylem and phloem transport • Respiration vs. temperature

  13. Linking water and carbon cycle

  14. Hydraulic framework

  15. Experimental evidence

  16. The Jena Drought Stress Experiment Field experiment: 2 seasons, 2 species (P.abies, P.sylvestris), rainroof, WTC Treatment: water availability Greenhouse experiment: 3 seasons, 3 species (P.abies, P.sylvestris, T.occidentalis), above- and belowground chambers Treatments: water and CO2 availability

  17. Hypotheses 1. Trees ‘dry out’ • Water potential decreases below specific threshold and causes hydraulic/symplastic failure 2. Trees starve to death after depleting all stored carbon • Trees respire all stored carbon 3. Trees starve to death because they cannot access stored carbon • Trees respire local carbon stores but decreasing water potential empedes long-distance carbon translocation

  18. Measurements

  19. Custom-made equipment

  20. Custom-made equipment

  21. First results (pre-experiment) • Strong decrease in sapflow, maybe even cavitation, after < 2 weeks of drought

  22. First results (pre-experiment) • Pronounced stem shrinking from drought stress • Reduced phloem hydration lower C-translocation capacity

  23. First results (pre-experiment) • Higher C-investment in root turnover

  24. First results (pre-experiment) • C-balance negative after < 2 weeks of drought stress

  25. First scientific conclusions • Drought • Creates very low water potential in xylem and maybe even cavitation • Increases C-expenditures due to higher fine root turnover • Cause a rapid decline of NPP • All 3 hypotheses are supported by our data  We‘re on the right way but mortality has not occured yet.

  26. Non-scientific conclusions • Technical equipment has been costom-made to serve our needs and to reduce costs • Purchase of equipment has to follow low-bidding rules • More collaboration between suppliers and customers would facilitate research and may be economically intersting for both sides

  27. Thank you!!

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