Comparing approaches for fast estimation of photosynthesis parameters

The maximum carboxylation rate (Vcmax) and maximum electron transport rate (Jmax) are key parameters characterizing the photosynthetic performance of plants. To inform modelling efforts and improve our understanding of spatiotemporal variations of these key plant traits, it is important to increase measurement efforts. However, measuring these parameters is challenging due to the expensive gas exchange equipment involved as well as the time needed for the response curve measurements. While there have been recent advances in faster measurement/estimation protocols such as the one-point method and other estimation approaches based on spectral reflectance measurements, direct comparisons of these approaches have not been reported. Furthermore, there appears to be untapped potential using chlorophyll fluorescence-based approaches. Key aspects for comparing methods beyond the accuracy of estimation include the speed and cost of measurement instruments.

Here, we evaluate and compare approaches based on gas exchange, chlorophyll fluorescence and spectral reflectance measurements for estimating Vcmax and Jmax parameters using data from 37 broadleaf tree species grown in an arboretum. We found that active chlorophyll fluorescence had the best performance for Jmax, while for Vcmax, single point gas exchange measurements could be used in ways that considerably improve over the one-point method. The spectral reflectance-based approach had comparable performance as the conventional one-point method.