Biochemical Limitations to Carbon Assimilation in C3Plants—A Retrospective Analysis of theA/CiCurves from 109 Species

Species-specific 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-1,5-bisphosphate carboxylase-oxygenase, to the rate of ribulose 1,5-bisphosphate regeneration via electron transport, and to the rate of triose phosphate utilization was used to analyse 164 previously published A/Ci, curves for 109 C3 plant species. Based on this analysis, the maximum rate of carboxylation, Vcmax, ranged from 6μmol m−2 s−1 for the coniferous species Picea abies to 194μmol m−2 s−1 for the agricultural species Beta vulgaris, and averaged 64μmol m−2 s−1 across all species. The maximum rate of electron transport, Jmax, ranged from 17μmol m−2 s−1 again for Picea abies to 372μmol m−2 s−1 for the desert annual Malvastrum rotundifolium, and averaged 134μmol m−2 s−1 across all species. A strong positive correlation between Vcmax and Jmax indicated that the assimilation of CO2 was regulated in a co-ordinated manner by these two component processes. Of the A/Ci 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 μmol m−2 s−1 for the tropical perennial Tabebuia rosea to 20·1 μmol m−2 s−1 for the weedy annual Xanthium strumarium, and averaged 10·1 μmol 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, Vcmax and Jmax averaged 75 and 154 μmol m−2 s−1, while for perennials these same two parameters averaged only 44 and 97 μmol 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.