D. Whitehead et al., PERFORMANCE OF LARGE OPEN-TOP CHAMBERS FOR LONG-TERM FIELD INVESTIGATIONS OF TREE RESPONSE TO ELEVATED CARBON-DIOXIDE CONCENTRATION, Journal of biogeography, 22(2-3), 1995, pp. 307-313
In preparation for an investigation of the effects of elevated carbon
dioxide (CO2) concentration on the two tree species Pinus radiata D. D
on and Nothofagus fusca (Hook. f.) Oerst, the environmental conditions
inside sixteen open-top chambers, of the design described by Heagle e
t al. (1989), were measured and compared with those outside. During a
period in late summer, both air temperature and air saturation deficit
were greater inside the chambers, with mean increases of 0.3 degrees
C and 0.1 kPa, respectively. The increases were closely related to sol
ar irradiance, reaching maximum differences for temperature and air sa
turation deficit of 4.3 degrees C and 0.8 kPa, respectively, when sola
r irradiance was greater than 1600 mu mol m(-2)s(-1). The mean (+/- st
andard deviation) CO2 concentrations for the ambient and elevated trea
tments were 362+/-37 and 654+/-69 mu mol mol(-1), respectively. Howeve
r, the CO2 concentration in the elevated treatment decreased as windsp
eed increased, owing to incursions of ambient air into the chambers. T
ransmittance of visible solar irradiance (400-700 nm) through the plas
tic wall material decreased by 7% after 1 year of exposure at the site
. In cloudy conditions the mean transmittance of solar irradiance into
the chambers was 81% and on clear days this decreased from 80% to 74%
with increasing solar zenith angle. The ratio of diffuse to total sol
ar irradiance in the chambers was 13% and 21% greater than that outsid
e for cloudy and clear conditions, respectively. The implications of t
hese differences on water use efficiency for the trees growing inside
and outside the chamber are discussed. A cost effective system, built
to separate the CO2 required for the experiment from waste biogas, is
described. This project is contributing to the Global Change and Terre
strial Ecosystems (GCTE) Core Research Programme by providing data on
the long-term effects of elevated CO2 concentration on the above and b
elow-ground carbon balance for the two tree species.