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CO 2 ELEVATION, CANOPY PHOTOSYNTHESIS, ANDOPTIMAL LEAF AREA INDEX
Author(s) -
Hirose T.,
Ackerly D. D.,
Traw M. B.,
Ramseier D.,
Bazzaz F. A.
Publication year - 1997
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(1997)078[2339:cecpal]2.0.co;2
Subject(s) - photosynthesis , canopy , leaf area index , abutilon , interception , photosynthetic capacity , botany , biology , environmental science , ecology , weed
We studied the effects of CO 2 elevation on leaf and canopy photosynthesis and optimal leaf area index (LAI) for stands of the annual species Abutilon theophrasti and Ambrosia artemisiifolia. Leaf photosynthesis was modeled as a function of photosynthetic photon flux density (PPFD) and nitrogen content per unit leaf area ( N L ). There was a curvilinear relationship between the light‐saturated rates of leaf photosynthesis ( P max ) and N L . CO 2 elevation significantly increased P max as a function of N L in both species. Dark respiration ( R d ) was linearly correlated with N L . CO 2 elevation slightly but significantly increased R d in Abutilon, while it had no significant effect on R d in Ambrosia. The initial slope of a light‐response curve was determined from quantum yield (φ abs ) multiplied by leaf absorptance and then calibrated against N L . Daily canopy photosynthesis, calculated by integration of leaf photosynthesis with the actual distribution of leaf area, leaf N, and PPFD within a canopy, showed fairly good agreement with the canopy photosynthesis estimated from growth analysis. CO 2 elevation increased canopy photosynthesis by 30–50%. Based on the leaf photosynthesis model for Abutilon, we calculated daily canopy photosynthesis for a given LAI and N availability, in which N was assumed to be distributed optimally within a leaf canopy to maximize daily canopy photosynthesis. An optimal LAI to maximize daily canopy photosynthesis was obtained for each level of N availability and this optimum increased with increasing N availability. Contrary to the often predicted increase in LAI with CO 2 elevation, the optimum LAI did not increase at high CO 2 when N availability was limited. Two factors were suggested to be involved in counteracting the increase in LAI in a high‐CO 2 world. One is the higher φ abs of plants grown in elevated CO 2 , which makes leaves in the canopy more N limited, favors higher N L and thus lowers optimal LAI. The other is the higher R d in elevated CO 2 , which leads to higher light compensation points, and lowers optimal LAI.