A test of the 'one-point method' for estimating maximum carboxylation capacity from field-measured, light-saturated photosynthesis

Abstract

<p> • Simulations of photosynthesis by terrestrial biosphere models typically need a specification of the maximum carboxylation rate (<i>V</i>_cmax). Estimating this parameter using <i>A–C</i>_i curves (net photosynthesis, <i>A</i>, vs intercellular CO₂ concentration, <i>C_i</i> ) is laborious, which limits availability of <i>V</i>_cmax data. However, many multispecies field datasets include net photosynthetic rate at saturating irradiance and at ambient atmospheric CO₂ concentration (A_sat) measurements, from which <i>V</i>_cmax can be extracted using a ‘one-point method’.</p> <p>• We used a global dataset of <i>A–C</i>_i curves (564 species from 46 field sites, covering a range of plant functional types) to test the validity of an alternative approach to estimate <i>V</i>_cmax from A_sat via this ‘one-point method’.</p> <p>• If leaf respiration during the day (<i>R_day</i>) is known exactly, <i>V</i>_cmax can be estimated with an <i>r ²</i> value of 0.98 and a root-mean-squared error (RMSE) of 8.19 lmol m^-2 s^-1 . However, <i>R_day</i> typically must be estimated. Estimating <i>R_day</i> as 1.5% of <i>V</i>_cmax, we found that <i>V</i>_cmax could be estimated with an <i>r ²</i> of 0.95 and an RMSE of 17.1 lmol m^-2 s^-1 .</p> <p>• The one-point method provides a robust means to expand current databases of fieldmeasured <i>V</i>_cmax, giving new potential to improve vegetation models and quantify the environmental drivers of <i>V</i>_cmax variation. </p>