Estimating Leaf CO2 Assimilation in C3 Plants Using a Handheld Porometer With Chlorophyll Fluorometer in Field Conditions.

Gas exchange measurement is the gold standard method for determining leaf CO2 assimilation rate (An). However, conventional systems for measuring An often require time and/or effort to collect numerous samples in the field owing to their high weight and large size. Here, we present an efficient and convenient method for estimating An using a handheld porometer with a chlorophyll fluorometer, facilitating on-the-go assessment of An in the field. This porometer-fluorometer method integrates the measured stomatal conductance and quantum yield of photochemistry in PSII into a biochemical photosynthesis model, incorporating model uncertainties into a single calibrated parameter. Using this method, we successfully estimated An variations in 12 species under field conditions, with a root mean square error of 2.0 μmol m-2 s-1, despite using the common parameter set. In contrast, without calibration (i.e., with the often-assumed parameter value), this method greatly overestimated An. These results highlight the importance of appropriate calibration depending on prevailing conditions, particularly the light source. In summary, this method demonstrates the potential for accessible, high-throughput, and accurate estimation of An in diverse plants, thereby addressing a key bottleneck in field-based phenotyping of photosynthesis. However, further studies are required to reduce the uncertainties imposed on the calibrated parameter.