title: Effects of CO2elevation on canopy development in the stands of two co-occurring annuals.
abstract: Elevated CO2may increase dry mass production of canopies directly through increasing net assimilation rate of leaves and also indirectly through increasing leaf area index (LAI). We studied the effects of CO2elevation on canopy productivity and development in monospecific and mixed (1:1) stands of two co-occurring C3annual species, Abutilon theophrasti, and Ambrosia artemisiifolia. The stands were established in the glasshouse with two CO2levels (360 and 700 μl/l) under natural light conditions. The planting density was 100 per m2and LAI increased up to 2.6 in 53 days of growth. Root competition was excluded by growing each plant in an individual pot. However, interference was apparent in the amount of photons absorbed by the plants and in photon absorption per unit leaf area. Greater photon absorption by Abutilon in the mixed stand was due to different canopy structures: Abutilon distributed leaves in the upper layers in the canopy while Ambrosia distributed leaves more to the lower layers. CO2elevation did not affect the relative performance and light interception of the two species in mixed stands. Total aboveground dry mass was significantly increased with CO2elevation, while no significant effects on leaf area development were observed. CO2elevation increased dry mass production by 30-50%, which was mediated by 35-38% increase in the net assimilation rate (NAR) and 37-60% increase in the nitrogen use efficiency (NUE, net assimilation rate per unit leaf nitrogen). Since there was a strong overall correlation between LAI and aboveground nitrogen and no significant difference was found in the regression of LAI against aboveground nitrogen between the two CO2levels, we hypothesized that leaf area development was controlled by the amount of nitrogen taken up from the soil. This hypothesis suggests that the increased LAI with CO2elevation observed by several authors might be due to increased uptake of nitrogen with increased root growth.
authors.affiliation: Biological Institute, Graduate School of Science, Tohoku University, Aoba, 980-77, Sendai, Japan.
authors.forename: Tadaki
authors.initials: T
authors.lastname: Hirose
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, 02138, Cambridge, MA, USA.
authors.forename: David D
authors.initials: DD
authors.lastname: Ackerly
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, 02138, Cambridge, MA, USA.
authors.forename: M Brian
authors.initials: MB
authors.lastname: Traw
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, 02138, Cambridge, MA, USA.
authors.forename: Fakhri A
authors.initials: FA
authors.lastname: Bazzaz
keywords: Abutilon theophrasti; Ambrosia artemisiifolia; CO2 elevation; Canopy; Nitrogen