The Science

The gold-standard method for measuring the capacity for photosynthetic carbon dioxide (CO₂) assimilation is time consuming. A rapid method to mathematically estimate this capacity from a single measurement rather than a full curve has been celebrated in the literature, but there are several key limitations to the effectiveness of this rapid method, including acclimation to light.

The Impact

The accurate estimation of the capacity for photosynthetic CO₂ assimilation is critical for the parameterization of climate models. Employing a rapid “one-point” method can improve model parameterization but only if the results are accurate. Deepening the scientific understanding of the limitations of this method allows appropriate use of the technique.

Summary

The maximum carboxylation capacity of photosynthesis (V_c,max) is usually obtained using a gold-standard photosynthetic CO₂ response curve. A rapid one-point method mathematically estimates V_c,max from a single-point measurement of photosynthesis rather than a full response curve, taking only a fraction of the time. Scientists from Brookhaven National Laboratory evaluated the practical application of the one-point method in six species measured both under standard conditions and under conditions that would increase the likelihood of successful estimation of V_c,max. Under standard measurement conditions, the one-point method significantly underestimated V_c,max in four of the six species, providing estimates 21% to 32% below fitted values. They identified three factors that can limit the effective use of the one-point method to accurately estimate V_c,max: (1) limitation of photosynthesis by carboxylation, when the measurement is taken; (2) acclimation of leaves to saturating light conditions prior to measurement; and (3) accurate estimation of leaf respiration. Most critical of these is the requirement for acclimation to saturating light. The requirements vary among species, meaning that the one-point method requires a species-specific understanding of its application and must be used with caution.

Principal Investigator

Angela Burnett
Brookhaven National Laboratory
aburnett@bnl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This work was supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science, under Contract No. DE-SC0012704 to Brookhaven National Laboratory and received partial support (e.g., some of the data collection) from the Next-Generation Ecosystem Experiments (NGEE)–Arctic project, which is supported by DOE BER.

Related Links

• Next-Generation Ecosystem Experiments (NGEE)–Arctic

References