CO2 ELEVATION, CANOPY PHOTOSYNTHESIS, AND OPTIMAL LEAF AREA INDEX

We studied the effects of CO2 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 photosyn- thetic photon flux density (PPFD) and nitrogen content per unit leaf area (NL). There was a curvilinear relationship between the light-saturated rates of leaf photosynthesis (Pmax) and NL. CO2 elevation significantly increased Pmax as a function of NL in both species. Dark respiration (Rd) was linearly correlated with NL. CO2 elevation slightly but significantly increased Rd in Abutilon, while it had no significant effect on Rd in Ambrosia. The initial slope of a light-response curve was determined from quantum yield (4gabs) multiplied by leaf absorptance and then calibrated against NL. 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. CO2 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 CO2 elevation, the optimum LAI did not increase at high CO2 when N availability was limited. Two factors were suggested to be involved in counteracting the increase in LAI in a high-CO2 world. One is the higher 4abs of plants grown in elevated C02, which makes leaves in the canopy more N limited, favors higher NL and thus lowers optimal LAI. The other is the higher Rd in elevated C02, which leads to higher light compensation points, and lowers optimal LAI.

[1]  William J. Campbell,et al.  Response of Soybean Canopy Photosynthesis to CO2 Concentration, Light, and Temperature , 1990 .

[2]  M. L. Williams,et al.  The effects of increased atmospheric carbon dioxide and temperature on carbon partitioning, source‐sink relations and respiration , 1991 .

[3]  C.J.T. Spitters,et al.  Separating the diffuse and direct component of global radiation and its implications for modeling canopy photosynthesis Part II. Calculation of canopy photosynthesis , 1986 .

[4]  Paul W. Leadley,et al.  Canopy photosynthesis of crops and native plant communities exposed to long‐term elevated CO2 , 1991 .

[5]  F. D. Vries,et al.  The cost of maintenance processes in plant cells , 1975 .

[6]  J. Coleman,et al.  Effects of CO_2 and Temperature on Growth and Resource Use of Co‐Occurring C_3 and C_4 Annuals , 1992 .

[7]  J. Goudriaan.  Optimization of nitrogen distribution and leaf area index for maximum canopy assimilation rate. , 1995 .

[8]  M. Monsi.  Uber den Lichtfaktor in den Pflanzengesellschaften und seine Bedeutung fur die Stoffproduktion , 1953 .

[9]  L. H. Allen,et al.  Acclimation of rice to changing atmospheric carbon dioxide concentration , 1991 .

[10]  J. Reynolds,et al.  The Influence of Carbon Dioxide and Daily Photon-flux Density on Optimal Leaf Nitrogen Concentration and Root: Shoot Ratio , 1991 .

[11]  James R. Ehleringer,et al.  Quantum Yields for CO2 Uptake in C3 and C4 Plants: Dependence on Temperature, CO2, and O2 Concentration , 1977 .

[12]  Tadaki Hirose,et al.  Canopy Development and Leaf Nitrogen Distribution in a Stand of Carex Acutiformis , 1989 .

[13]  I. Impens,et al.  Effects of rising atmospheric carbon dioxide concentration on gas exchange and growth of perennial ryegrass , 1988 .

[14]  H. Lambers.  Respiration in Intact Plants and Tissues: Its Regulation and Dependence on Environmental Factors, Metabolism and Invaded Organisms , 1985 .

[15]  M. Werger,et al.  Optimal leaf area indices in C3 and C4 mono‐ and dicotyledonous species at low and high nitrogen availability , 1995 .

[16]  C. Field,et al.  Allocating leaf nitrogen for the maximization of carbon gain: Leaf age as a control on the allocation program , 1983, Oecologia.

[17]  B. Strain,et al.  Growth and maintenance components of leaf respiration of cotton grown in elevated carbon dioxide partial pressure , 1993 .

[18]  Toshiro Saeki.  植物群落における葉量, 光分布, 全光合成の相互関係 , 1960 .

[19]  Ichiro Terashima,et al.  A model of the acclimation of photosynthesis in the leaves of C3 plants to sun and shade with respect to nitrogen use , 1995 .

[20]  C. Körner,et al.  Effects of elevated CO2 and increased nitrogen deposition on photosynthesis and growth of understory plants in spruce model ecosystems , 1996, Oecologia.

[21]  J. R. Evans,et al.  Nitrogen and Photosynthesis in the Flag Leaf of Wheat (Triticum aestivum L.). , 1983, Plant physiology.

[22]  S. Long,et al.  Effect of the Long-Term Elevation of CO(2) Concentration in the Field on the Quantum Yield of Photosynthesis of the C(3) Sedge, Scirpus olneyi. , 1991, Plant physiology.

[23]  H. Lambers,et al.  Causes and consequences of variation in growth rate and productivity of higher plants , 1990 .

[24]  A. Bloom,et al.  CO(2) Inhibits Respiration in Leaves of Rumex crispus L. , 1992, Plant physiology.

[25]  26 – CO2 Elevation and Canopy Development in Stands of Herbaceous Plants , 1996 .

[26]  Tadaki Hirose,et al.  Nitrogen use efficiency in instantaneous and daily photosynthesis of leaves in the canopy of a Solidago altissima stand , 1987 .

[27]  L. Ziska,et al.  Responses of Respiration to Increases in Carbon Dioxide Concentration and Temperature in Three Soybean Cultivars , 1996 .

[28]  C. Körner,et al.  Responses to elevated carbon dioxide in artificial tropical ecosystems. , 1992, Science.

[29]  H. Lambers,et al.  The effect of an elevated atmospheric CO2 concentration on growth, photosynthesis and respiration of Plantago major , 1988 .

[30]  B. Acock,et al.  Crop responses to carbon dioxide doubling: a literature survey , 1986 .

[31]  J. Berry,et al.  A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species , 1980, Planta.

[32]  W. Weerakoon,et al.  The Influence of Nitrogen on the Elevated CO2Response in Field-Grown Rice , 1996 .