Nearly all woody species respond to increases in the air's CO2 content by displaying enhanced rates of photosynthesis and biomass production. In this summary, we review some recently published responses of eucalyptus trees to atmospheric CO2 enrichment.
In the eight-month study of Roden et al. (1999), Eucalyptus pauciflora seedlings growing at 700 ppm CO2 displayed seasonal rates of net photosynthesis that were approximately 30% greater than those exhibited by their ambiently-grown counterparts. In another eight-month study, Palanisamy (1999) reported that well-watered Eucalyptus cladocalyx seedlings exposed to 800 ppm CO2 exhibited photosynthetic rates that were 120% higher than those observed in control plants growing at 380 ppm CO2. Moreover, after a one-month period of water stress, photosynthetic rates of CO2-enriched seedlings were still 12% greater than rates displayed by ambiently-grown water-stressed seedlings.
Because elevated CO2 enhances photosynthetic rates in eucalyptus species, this phenomenon should lead to increased biomass production in these rapidly growing trees. And so it does. In the eight-month experiment of Gleadow et al. (1998), for example, Eucalyptus cladocalyx seedlings growing at 800 ppm CO2 displayed 134 and 98% more biomass than seedlings growing at 400 ppm CO2 at low and high soil nitrogen concentrations, respectively. Similarly, Eucalyptus pauciflora seedlings growing at twice-ambient CO2 concentrations for eight months produced 53% more biomass than control seedlings (Roden et al., 1999).
In summary, as the CO2 content of the air increases, eucalyptus seedlings will likely display enhanced rates of photosynthesis and biomass production, regardless of soil moisture and nutrient status. Consequently, greater amounts of carbon will likely be sequestered by this rapidly growing tree species.
For more information on eucalyptus growth responses to atmospheric CO2 enrichment see Plant Growth Data: Sugargum (dry weight, photosynthesis), and Snow Gum (photosynthesis).
References
Gleadow, R.M., Foley, W.J. and Woodrow, I.E. 1998. Enhanced CO2 alters the relationship between photosynthesis and defense in cyanogenic Eucalyptus cladocalyx F. Muell. Plant, Cell and Environment 21: 12-22.
Palanisamy, K. 1999. Interactions of elevated CO2 concentration and drought stress on photosynthesis in Eucalyptus cladocalyx F. Muell. Photosynthetica 36: 635-638.
Roden, J.S., Egerton, J.J.G. and Ball, M.C. 1999. Effect of elevated [CO2] on photosynthesis and growth of snow gum (Eucalyptus pauciflora) seedlings during winter and spring. Australian Journal of Plant Physiology 26: 37-46.