Photosynthetic responses to temperature, light flux-density, CO<inf>2</inf>concentration and vapour pressure deficit in Eucalyptus tetrodonta grown under CO<inf>2</inf>enrichment
- Publication Type:
- Journal Article
- Environmental Pollution, 1995, 90 (1), pp. 41 - 49
- Issue Date:
Seeds of Eucalyptus tetrodonta were sown under ambient or CO2enriched (700 μl litre-1) conditions in tropical Australia. Four sets of measurements were made, the first two after 12 months, on trees growing either in pots or planted in the ground. The third and fourth set were made after 18 and 30 months exposure to CO2enrichment, on trees growing in the ground. After 12 months exposure to CO2enrichment, the rate of light-saturated assimilation (Amax) of plants growing in the ground was determined. Responses of CO2assimilation to variations in leaf temperature, leaf-to-air vapour pressure deficit (LAVPD), light flux density and CO2concentration were also measured in the laboratory using plants growing in large pots. There was no significant difference in Amaxbetween pot and ground located plants. Assimilation of E. tetrodonta was relatively insensitive to changes in LAVPD for both ambient and CO2enriched plants but the temperature optimum of assimilation was increased in plants grown and measured under CO2enrichment. Plants grown with CO2enrichment had an increased rate of light-saturated assimilation and apparent quantum yield was significantly increased by CO2enrichment. In contrast, carboxylation efficiency was decreased significantly by CO2enrichment. After 18 months growth with CO2enrichment, there was no sign of a decline in assimilation rate compared to measurements undertaken after 12 months. At low LAVPD values, assimilation rate was not influenced by CO2treatment but at moderate to high LAVPD, plants grown under CO2enrichment exhibited a larger assimilation rate than control plants. Specific leaf area and chlorophyll contents decreased in response to CO2enrichment, whilst foliar soluble protein contents and chlorophyll a/b ratios were unaffected by CO2treatment. Changes in soluble protein and chlorophyll contents in response to CO2enrichment did not account for changes in assimilation between treatments. After 30 months exposure to CO2enrichment, the rate of light-saturated assimilation was approximately 50% larger than controls and this enhancement was larger than that observed after 18 months exposure to CO2enrichment. © 1995.
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