ASSIMILATION, STOMATAL CONDUCTANCE, SPECIFIC LEAF-AREA AND CHLOROPHYLL RESPONSES TO ELEVATED CO2 OF MARANTHES CORYMBOSA, A TROPICAL MONSOONRAIN-FOREST SPECIES
D. Eamus et al., ASSIMILATION, STOMATAL CONDUCTANCE, SPECIFIC LEAF-AREA AND CHLOROPHYLL RESPONSES TO ELEVATED CO2 OF MARANTHES CORYMBOSA, A TROPICAL MONSOONRAIN-FOREST SPECIES, Australian journal of plant physiology, 20(6), 1993, pp. 741-755
Seeds of Maranthes corymbosa Blume, a monsoon rain forest species of n
orthern Australia, were sown under ambient or elevated CO2 concentrati
ons in tropical Australia. Seedlings were grown under conditions of ph
oton flux density, temperature and atmospheric vapour pressure deficit
which followed ambient variations as closely as possible. Specific le
af area, chlorophyll, stomatal density, stomatal conductance and assim
ilation responses to photon flux density were measured after 30 weeks
growth. Gas exchange characteristics were divided into morning and aft
ernoon data sets and analysed separately. Stomatal density decreased a
nd leaf area:dry weight ratio decreased in response to elevated CO2. I
n contrast there was no effect of elevated CO2 upon chlorophyll (total
or ratio of a:b). Apparent quantum yield and rates of light saturated
assimilation (A(max)) increased in response to elevated CO2. There wa
s a significant decline in apparent quantum yield for both treatments
between morning and afternoon. Stomatal conductance (g(s)) declined in
response to elevated CO2. There was no significant difference in g(s)
between morning and afternoon for ambient grown trees, but g(s) decli
ned significantly between morning and afternoon for elevated CO2 grown
trees. Instantaneous transpiration efficiency (ITE) was higher for el
evated CO2 grown trees compared with control trees. There was a signif
icant increase in ITE between morning and afternoon data for ambient g
rown trees; in contrast a significant decline in ITE was observed for
elevated CO2 grown trees between morning anf afternoon data sets. The
slope of the regression between assimilation rate and stomatal conduct
ance increased for plants grown under elevated CO2. These data are dis
cussed and compared with the responses of plants adapting to different
photon flux densities.