title: The response of fast- and slow-growing Acacia species to elevated atmospheric CO2: an analysis of the underlying components of relative growth rate.
abstract: In this study we assessed the impact of elevated CO2with unlimited water and complete nutrient on the growth and nitrogen economy of ten woody Acacia species that differ in relative growth rate (RGR). Specifically, we asked whether fast- and slow-growing species systematically differ in their response to elevated CO2. Four slow-growing species from semi-arid environments (Acacia aneura, A. colei, A. coriacea and A. tetragonophylla) and six fast-growing species from mesic environments (Acacia dealbata, A. implexa, A. mearnsii, A. melanoxylon, A. irrorata and A. saligna) were grown in glasshouses with either ambient (˜350 ppm) or elevated (˜700 ppm) atmospheric CO2. All species reached greater final plant mass with the exception of A. aneura, and RGR, averaged across all species, increased by 10% over a 12-week period when plants were exposed to elevated CO2. The stimulation of RGR was evident throughout the 12-week growth period. Elevated CO2resulted in less foliage area per unit foliage dry mass, which was mainly the result of an increase in foliage thickness with a smaller contribution from greater dry matter content per unit fresh mass. The net assimilation rate (NAR, increase in plant mass per unit foliage area and time) of the plants grown at elevated CO2was higher in all species (on average 30% higher than plants in ambient CO2) and was responsible for the increase in RGR. The higher NAR was associated with a substantial increase in foliar nitrogen productivity in all ten Acacia species. Plant nitrogen concentration was unaltered by growth at elevated CO2for the slow-growing Acacia species, but declined by 10% for faster-growing species. The rate of nitrogen uptake per unit root mass was higher in seven of the species when grown under elevated CO2, and leaf area per unit root mass was reduced by elevated CO2in seven of the species. The absolute increase in RGR due to growth under elevated CO2was greater for fast- than for slow-growing Acacia species.
authors.affiliation: Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, 0200, A.C.T., Australia e-mail: evans@rsbs.anu.edu.au, Tel.: +61-2-62494492, Fax: +61-2-62494919, , , , , , AU.
authors.forename: Owen K
authors.initials: OK
authors.lastname: Atkin
authors.affiliation: Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, 0200, A.C.T., Australia e-mail: evans@rsbs.anu.edu.au, Tel.: +61-2-62494492, Fax: +61-2-62494919, , , , , , AU.
authors.forename: Marcus
authors.initials: M
authors.lastname: Schortemeyer
authors.affiliation: Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, 0200, A.C.T., Australia e-mail: evans@rsbs.anu.edu.au, Tel.: +61-2-62494492, Fax: +61-2-62494919, , , , , , AU.
authors.forename: Nola
authors.initials: N
authors.lastname: McFarlane
authors.affiliation: Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, 0200, A.C.T., Australia e-mail: evans@rsbs.anu.edu.au, Tel.: +61-2-62494492, Fax: +61-2-62494919, , , , , , AU.
authors.forename: John R
authors.initials: JR
authors.lastname: Evans
keywords: Elevated CO2; Growth analysis; Key wordsAcacia; Nitrogen productivity; Relative growth rate