© 1993 Heron Publishing—Victoria, Canada
Effects of elevated carbon dioxide and drought on the growth and physiology of clonal Sitka spruce plants (Picea sitchensis (Bong.) Carr.)
John Townend
Division of Biological Sciences, Institute of Environmental and Biological Sciences, Lancaster University, Lancaster LA1 4YQ,
United Kingdom / Received March 25, 1993
Summary
Two-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) plants from four clones were grown in naturally lit growth chambers for 6 months at either ambient (350 ppm)
or ambient + 250 ppm (600 ppm) CO2 concentration. Plants were grown in large boxes filled with peat, in a system that allowed the roots of individual plants
to be harvested easily at the end of the growing season. Half of the boxes were kept well watered and half were allowed to
dry out slowly over the summer. Plants growing in elevated CO2 showed a 6.9% increase in mean relative growth rate compared to controls in the drought treatment and a 9.8% increase compared
to controls in the well-watered treatment, though there was considerable variation in response among the different clones
and water treatments. Rates of net CO2 assimilation were higher and stomatal conductances were lower in plants grown in elevated CO2 than in ambient CO2 in both the well-watered and drought treatments. Both of these factors contributed to the doubling of
instantaneous water use efficiency. The partitioning of biomass to roots was unaffected by elevated CO2, but the ratio of needle mass/stems + branches mass decreased. Together with reduced stomatal conductance, this probably
caused the observed increases in xylem pressure potentials with elevated CO2.
Keywords:
clonal differences, partitioning, rooting environment, water stress.
