Estimating Leaf CO Assimilation in C Plants Using a Handheld Porometer With Chlorophyll Fluorometer in Field Conditions.

Gas exchange measurement is the gold standard method for determining leaf CO assimilation rate (A). However, conventional systems for measuring A 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 A using a handheld porometer with a chlorophyll fluorometer, facilitating on-the-go assessment of A 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 A variations in 12 species under field conditions, with a root mean square error of 2.0 μmol m s, despite using the common parameter set. In contrast, without calibration (i.e., with the often-assumed parameter value), this method greatly overestimated A. 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 A 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.