Abstract
Alpine ecosystems are, similar to arctic ecosystems, characterized by a very long snow season. Previous studies investigating arctic or alpine ecosystems have shown that winter CO2 effluxes can dominate the annual balance and that the timing and duration of the snow cover plays a crucial role for plant growth and phenology and might also influence the growing season ecosystem CO2 strength and dynamics. The objective of this study was to analyze seasonal and annual CO2 balances of a grassland site at an elevation of 2440 m a.s.l in the Swiss central Alps. We continuously measured the NEP using the eddy covariance method from June 2013 to October 2014, covering two growing seasons and one winter. We analyzed the influence of snow melt date on the CO2 exchange dynamics at this site, because snow melt differed about 24 days between the 2 years. To this end, we employed a process-based ecosystem carbon cycling model to disentangle the co-occurring effects of growing season length, environmental conditions during the growing season, and physiological/structural properties of the canopy on the ecosystem carbon balance. During the measurement period, the site was a net sink for CO2 although winter efflux contributed significantly to the total balance. The cumulative growing season NEP as well as mean and maximum daily CO2 uptake rates was lower during the year with the later snow melt, and the results indicated that the differences were mainly due to differing growing season lengths.
Highlights
Long-term observations provide evidence that the earth’s climate is changing
Previous studies investigating arctic or alpine ecosystems have shown that winter CO2 effluxes can dominate the annual balance and that the timing and duration of the snow cover plays a crucial role for plant growth and phenology and might influence the growing season ecosystem CO2 strength and dynamics
The cumulative growing season net ecosystem production (NEP) as well as mean and maximum daily CO2 uptake rates was lower during the year with the later snow melt, and the results indicated that the differences were mainly due to differing growing season lengths
Summary
Long-term observations provide evidence that the earth’s climate is changing. For example, an increase in global average temperature, more frequent and intense extreme climate events, and decreases in snowpack and snow cover have been documented (IPCC 2013), locally these trends can be reversed especially at high latitudes or elevation (for example, Beniston and others2003). Long-term observations provide evidence that the earth’s climate is changing. An increase in global average temperature, more frequent and intense extreme climate events, and decreases in snowpack and snow cover have been documented (IPCC 2013), locally these trends can be reversed especially at high latitudes or elevation According to the IPCC, these changes can be attributed to increased anthropogenic emissions of greenhouse gases (GHG), carbon dioxide (CO2) being the most important of these GHGs. Terrestrial ecosystems and the climate system are closely coupled through the carbon (C) cycle. The IPCC (2013) estimates that an increase in the C land sink has accumulated about 30% of the anthropogenic CO2 emissions, reducing increases in the atmosphere by about 75 ppm between 1750 and 2011. To predict future changes in atmospheric CO2 and global climate, it is crucial to quantify net ecosystem exchange of CO2 (NEE) for different types of ecosystem and to understand how NEE is affected by CO2 and climate
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