Alpine treelines in a CO2-rich and warm world
Delivery of CO2.
Photo: Frank Hagedorn.
Treeline ecosystems are enriched with CO2 using the FACE approach.
Photo: Frank Hagedorn.
We are experimentally
increasing atmospheric CO2 concentrations (+200 ppm) and soil temperatures
(+4K) at the alpine treeline and study the response of plant growth and soil
processes. First results indicate that elevated CO2 affects the C cycling
rates rather than the C pools in plants and soils. Warming has increased the
rate of soil organic matter decomposition and turned the ecosystem into a CO2
The strong increase
in atmospheric CO2 is changing ecosystems either directly through
the CO2-effects on plant growth, or indirectly through its impact on
temperatures. It is likely that high altitude soils will be particularly
sensitive to the ongoing atmospheric and climatic changes. The temperature
sensitivities of most biogeochemical processes are greater at a low temperature
range. Since alpine and montane soils contain large pools of labile C, they
play an important role in the response of the overall ecosystem’s C balance to
the changing environment and in feedbacks at the ecosystem level.
With our studies, we aim to
how and why tree and dwarf shrub growth and physiology change in response to increasing
temperatures and CO2 concentration.
how elevated CO2 and warming affect the competition between trees,
dwarf shrubs, and grasses, and therefore the vegetation structure and composition.
if elevated CO2 and increased soil temperature alters plant
sensitivity to frost events during the growing season
the response of C fluxes (soil respiration, DOC leaching, accumulation in
different SOM pools, aboveground biomass) and nutrient status.
how composition of the soil microbial community responds to elevated CO2
whether the new plant-derived rapidly cycling soil C fraction or the older
slower cycling soil C fraction responds more sensitive to climatic warming.
if warming alters the partitioning of recent assimilates between plants and
the transfer of carbon and nutrients between plants and mycorrhiza.
- test for the effect of atmospheric and climate
change on seedling emergence and survival.
In our project, we
are experimentally increasing atmospheric CO2 concentrations (+200
ppm) and temperatures (+4K) at the alpine treeline at the research site of Stillberg, Davos.
Larch and mountain pine trees that were planted slightly above treeline in the
course of an afforestation experiment in 1975 have been exposed (along with the
natural understorey layer of dwarf shrubs, forbs, and grasses) to elevated CO2
concentrations since 2001 using the FACE approach (n=20; Hättenschwiler et al.,
2002). The added CO2 originates from fossil fuel burning and
is depleted in 13C as compared to normal air (-30‰ vs. -8‰). This allows
us to trace the isotopic signal through the plant and soil system. For the
warming experiment, we laid out 26 m of heating cables in spirals on the ground
surface in the 1.1 m2-plots. Soil and the air around the dominating dwarf shrubs
and grasses have been heated by 4K since 2007.
- Dawes MA, Hagedorn F,
Handa IT, Streit K, Ekblad A, Rixen C, Körner C, Hättenschwiler C (2013) An
alpine treelines in a CO2-rich world: synthesis of a nine year free
air CO2 enrichment study. Oecologia 171, 623-637.
- Dawes, MA, Hättenschwiler S, Bebi P, Hagedorn F, Handa IT, Körner C, Rixen
C (2011). Species-specific
tree growth responses to nine years of CO2 enrichment at the alpine
of Ecology 99: 383–394.
- Dawes MA, Hagedorn F,
Zumbrunn T, Handa IT, Hättenschwiler S, Wipf S, Rixen C (2011). Growth and community response of alpine dwarf
shrubs to in situ CO2 enrichment and soil warming. New Phytologist 191: 806-818
W, Vicca, S., Dijkstra F, Hagedorn F, Hovenden M, Larsen K, Morgan J, Volder A, Beier C,
Dukes J, King J, Leuzinger S, Linder S, Oren R, Tingey D, Hoosbeek M, Lup Y, Janssens I (2012) Simple additive effects are rare: a quantitative review of plant
biomass and soil process responses to combined manipulations of CO2
and temperature. Global Change Biology 18, 2681-2693. doi: 10.1111/j.1365-2486.2012.02745.x
- Hagedorn F,
Hiltbrunner D, Streit K, Ekblad A, Lindahl B, Miltner A, Frey B, Handa IT,
Hättenschwiler S (2013) Nine years of CO2 enrichment at the Alpine
treeline stimulates soil respiration but does not alter soil microbial
communities. Soil Biology
and Biochemistry 57, 390-400.
- Hagedorn F, Martin M, Rixen C, Rusch S, Bebi P, Zürcher A,
Siegwolf RTW, Wipf S, Escape C, Roy J, Hättenschwiler S (2010) Short-term
responses of ecosystem carbon fluxes to experimental warming at the Swiss
alpine treeline. Biogeochemistry 97,
- Hagedorn F, van Hees
PAW, Handa IT, Hättenschwiler S (2008) Elevated atmospheric CO2 fuels leaching of old dissolved
organic matter at the alpine treeline. Global
Biogeochemical Cycles 22. GB2004,
- Hagedorn F, Machwitz M
(2007) Controls on dissolved organic matter leaching from forest litter grown
under elevated atmospheric CO2. Soil
Biology and Biochemistry 39, 1759-1769
- Handa, I.T., Hagedorn, F.,
und S. Hättenschwiler 2008. No stimulation in root production in response
to four years of in situ CO2 enrichment at the Swiss treeline. Functional Ecology 22, 348-358.
- Martin M, Gavazov K, Körner
C, Hättenschwiler S, Rixen C (2010) Reduced early growing season freezing resistance in alpine
treeline plants under elevated atmospheric CO2. Global Change Biology 16, 1057-1070.
- Müller M, Alewell C, Hagedorn
F (2009) Effective
retention of litter-derived dissolved organic carbon in organic layers. Soil Biology and Biochemistry 41, 1066-1074.
- Rixen C, Dawes MA, Wipf S, Hagedorn F (2012) Evidence of enhanced freezing damage in
treeline plants during six years of CO2 enrichment and soil warming.
- Streit K, Rinne KT, Hagedorn F, Dawes MA,
Saurer M, Hoch G, Werner RA, Buchmann N, Siegwolf RTW (2013) Tracing fresh
assimilates through Larix deciduas exposed to elevated CO2 and soil
warming at the alpine treeline using compound-specific stable isotope analysis.
New Phytologist 197, 838-849.
Links and downloads
Experimental station Stillberg
Project description of University of Basel (PDF, 840KB)
The treeline (PDF in German, 481KB)
||alpine soils, elevated CO2, climate change , carbon, nutrients, DOC, respiration, soil chemistry, stable isotopes, temperature, organic layers, plant ecology, dendroecology, treeline, tree growth