Biochemical Limitations to Carbon Assimilation in C3 Plants—A Retrospective Analysis of the A/Ci Curves from 109 Species

differences in the assimilation of atmospheric CO2 depends upon differences in the capacities for the biochemical reactions that regulate the gas-exchange process. Quantifying these differences for more than a few species, however, has proven difficult. Therefore, to understand better how species differ in their capacity for CO2 assimilation, a widely used model, capable of partitioning limitations to the activity of ribulose-l,5-W.sphosphate carboxylase-oxygenase, to the rate of ribulose 1,5-tophosphate regeneration via electron transport, and to the rate of triose phosphate utilization was used to analyse 164 previously published A/C, curves for 109 C3 plant species. Based on this analysis, the maximum rate of carboxylation, Vcmax, ranged from 6/umol m~2 s"1 for the coniferous species Picea abies to 194jj,mol m" 2 s"1 for the agricultural species Beta vulgaris, and averaged 64^mol m" 2 s"1 across all species. The maximum rate of electron transport, Jmx, ranged from 17/^mol m~2 s"1 again for Picea abies to 372/j.mol m~2 s"1 for the desert annual Mahastrum rotundifolium, and averaged 134fxmol m~2 s"1 across all species. A strong positive correlation between Vc^x and Jmax indicated that the assimilation of CO2 was regulated in a co-ordinated manner by these two component processes. Of the AjC{ curves analysed, 23 showed either an insensitivity or reversed-sensitivity to increasing CO2 concentration, indicating that CO2 assimilation was limited by the utilization of triose phosphates. The rate of triose phosphate utilization ranged from 4-9/xtnol m" 2 s"1 for the tropical perennial Tabebuia rosea to 20-1 /xmol m~2 s"1 for the weedy annual Xanthium strumarium, and averaged 101 ftmol m" 2 s"1 across all species. Despite what at first glance would appear to be a wide range of estimates for the biochemical capacities that regulate CO2 assimilation, separating these species-specific results into those of broad plant categories revealed that Vcmax and Jmax were in general higher for herbaceous annuals than they were for woody perennials. For annuals, Vc^^ and Jmax averaged 75 and 154ftmol m~2 s"1, while for perennials these same two parameters averaged only 44 and 97/xmol m~2 s"1, respectively. Although these differences between groups may be coincidental, such an observation points to differences between annuals and perennials in either the availability or allocation of resources to the gas-exchange process.