Fræðaþing landbúnaðarins - 16.02.2007, Side 14

12 • Fræðaþing landbúnaðarins 4, 2007
Inter- and intra-specific response of grassland
vegetation to elevated atmospheric CO,
A. Luscher1, K.A. Stinson2 and J. Connolly3
1 Forage Production and Grassland Systems, Research Station Agroscope Reck-
enholz-Tánikon ART, Reckenholzstrasse 191, CH-8046 Zurich, Switzerland
2Organismic and Evolutionary Biology, Harvard University, Harvard Forest,
PO Box 68, Petersham, MA 01366, USA
3Department of Statistics and Actuarian Science, University College Dublin,
Belfield, Dublin 4, Ireland
Introduction
Global atmospheric change consists of (i) an increase of the main greenhouse gases
- carbon dioxide (C02,), methane (CH4,), and nitrous oxide (N20); and (ii) transient
changes in temperature, precipitation and other climatic elements over the coming
decades and centuries. Using general circulation models, global projections of the
earth’s climate have been developed for a set of emission scenarios related to a range of
assumptions regarding future socio-economic development (IPCC, 2001). The average
increase of atmospheric C02 concentration has been about 1.5 ppm (0.4%) per year over
the past two decades. The IPCC in its 3rd assessment report (IPCC, 2001), projects C02
concentration may rise up to between 540 and 970 ppm by 2100 (depending on future
global socio-economic development and associated emission pattems). Since the increase
in atmospheric C02 is the most reliable aspect of global atmospheric change (Ltischer et
al., 2005), this paper focuses on the response of plant stands, plant species and genotypes
to elevated C02 and on methodological aspects how to assess these responses.
Effects of elevated C02 on grassland vegetation
Physiological effects
The physiological effects of elevated CO, are well known (Long et al., 2004).
Drake et al. (1997) reviewed 60 studies where plants were grown separately under
controlled conditions with ample nutrient supply, and reported an average increase in
leaf photosynthesis of 58% when grown at approximately double the pre-industrial
concentration of C02. These increases in photosynthesis translate into increased dry
matter production of about 30% (Newton, 1991). However, when plants are grown in
communities in the field, competition and limiting growth resources restrict the plant’s
response to elevated C02. These differences have prompted researchers to design
experimental systems that more effectively simulate an increase in atmospheric C02
concentration without altering natural conditions. The most advanced systems for this
work use a technology called Free Air Carbon Dioxide Enrichment (FACE), which does
not require any enclosures and, so does not alter the microclimate of the experimental