PHOTOSYNTHETIC RESPONSES TO TEMPERATURE, LIGHT FLUX-DENSITY, CO2 CONCENTRATION AND VAPOR-PRESSURE DEFICIT IN EUCALYPTUS TETRODONTA CROWN UNDER CO2 ENRICHMENT
D. Eamus et al., PHOTOSYNTHETIC RESPONSES TO TEMPERATURE, LIGHT FLUX-DENSITY, CO2 CONCENTRATION AND VAPOR-PRESSURE DEFICIT IN EUCALYPTUS TETRODONTA CROWN UNDER CO2 ENRICHMENT, Environmental pollution, 90(1), 1995, pp. 41-49
Seeds of Eucalyptus tetrodonta were sown under ambient or CO2 enriched
(700 mu l litre(-1)) conditions in tropical Australia. Four sets of m
easurements were made, the first two after 12 months, on trees growing
either in pots or planted in the ground. The third and fourth set wer
e made after 18 and 30 months exposure to CO2 enrichment, on trees gro
wing in the ground After 12 months exposure to CO2 enrichment, the rat
e of light-saturated assimilation (A(max)) of plants growing in the gr
ound was determined. Responses of CO2 assimilation to variations in le
af temperature, leaf-to-air vapour,pressure deficit (LAVPD), Eight flu
x density and CO2 concentration were also measured in the laboratory u
sing plants growing in large pots. There was no significant difference
in A(max) between pot and ground located plants. Assimilation of E. t
etrodonta was relatively insensitive to changes in LAVPD for both ambi
ent and CO2 enriched plants but the temperature optimum of assimilatio
n was increased in plants grown and measured under CO2 enrichment. Pla
nts grown with CO2 enrichment had an increased rate of light-saturated
assimilation and apparent quantum yield I-vas significantly inn eased
by CO2 enrichment. rn contrast, carboxylation efficiency was decrease
d significantly by CO2 enrichment. After 18 months growth with CO2 enr
ichment, there was no sign of a decline in assimilation I ate compared
to measurements undertaken after 12 months, At low LAVPD values, assi
milation rate was not influenced by CO2 treatment but at moderate to h
igh LAVPD, plants grown under CO2 enrichment exhibited a larger assimi
lation rate than control plants. Specific leaf area and chlorophyll co
ntents decreased in response to CO2 enrichment, whilst foliar soluble
protein contents and chlorophyll a/b ratios were unaffected by CO2 tre
atment. Changes in soluble protein and chlorophyll contents in respons
e to CO2 enrichment did not account for changes in assimilation betwee
n treatments. After 30 months exposure to CO2 enrichment, the rate of
light-saturated assimilation was approximately 50% larger than control
s and this enhancement was larger than that observed after 18 months e
xposure to CO2 enrichment.