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Light Acquisition and Growth by Competing Individuals in CO2- Enriched Atmospheres: Consequences for Size Structure in Regenerating Birch Stands

P. M. Wayne and F. A. Bazzaz
Journal of Ecology
Vol. 85, No. 1 (Feb., 1997), pp. 29-42
DOI: 10.2307/2960625
Stable URL: http://www.jstor.org/stable/2960625
Page Count: 14
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Light Acquisition and Growth by Competing Individuals in CO2- Enriched Atmospheres: Consequences for Size Structure in Regenerating Birch Stands
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Abstract

1 To investigate how CO2-enriched atmospheres may influence plant competition and stand size structure in regenerating forests, experimental populations comprised of three maternal families of yellow birch (Betula alleghaniensis Britt.) were grown in both ambient (350 μ L L-1) and elevated (700 μ L L-1) CO2-concentrations in a controlled environment facility. Individual seedling growth, light acquisition, and stand size structure were monitored throughout the first year of growth. 2 Elevated CO2 increased average seedling biomass in stands by 14%, a value much lower than the average enhancement reported elsewhere for individually grown yellow birch seedlings. Maternal families within stands differed significantly in their growth responsiveness to elevated CO2 ranging from +51% to -16%. As a result, CO2 altered the genetic identity of dominants in regenerating stands. 3 Seedling size inequalities were generally lower in CO2-enriched environments, a result that contrasts with other studies that have reported increased size inequality with increased productivity in resource-rich environments. Distribution modifying functions relating initial seedling size and subsequent growth suggest that there was a relatively smaller advantage to being larger in elevated vs. ambient CO2 environments. Together, these results suggest that competition in CO2-enriched environments was less size-asymmetric. 4 Differences in stand size structure between CO2 treatments were related to competition for light. Empirical measures of seedling light acquisition per unit biomass suggest competition for light was less size-asymmetric in CO2-enriched environments. Decreased size-asymmetric competition for light was attributable both to differences in the CO2-use efficiency of high-light canopy dominants vs. low-light canopy subordinates, and to CO2-induced differences in plant allometry. 5 This study highlights the importance of stand-level competition studies in global change research, and more generally, the value of studies that combine phenomenological descriptions of stand development with physiological mechanisms of competition.

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