Techniques for photosynthesis phenomics: gas exchange, fluorescence, and reflectance spectrums

Photosynthesis represents the most important biological process on earth and generates food and energy for most living organisms. Increasing photosynthetic efficiency in crops is a feasible strategy to enhance grain yield. Canopy photosynthesis, the integral of photosynthesis of all photosynthetic tissues of an entire plant canopy, is intrinsically linked to biomass production and crop yield and is influenced by both photosynthetic efficiency at the tissue level and canopy architecture, which determines the light environment at that tissue. This review summarizes current methodologies for measuring photosynthesis via gas exchange, fluorescence, and reflectance spectrum at the field, canopy, and leaf levels. Gas exchange techniques include eddy covariance, canopy gas exchange chambers, and organ-level gas exchange methods, which can measure CO₂ and H₂O fluxes. Chlorophyll fluorescence methods include solar-induced fluorescence (SIF), laser-induced fluorescence transient (LIFT), pulse amplitude modulated (PAM) fluorescence, and light induced chlorophyll a fluorescence rise (OJIP transient), which can be used to evaluate photosynthetic efficiency and plant stress responses. One of the commonly used reflectance spectrum methods for studying photosynthesis is the hyperspectral reflectance technique, which can estimate photosynthesis-related traits. High-throughput crop photosynthesis phenotyping can be performed with different combinations of these techniques. This review aims to provide a one-stop resource for researchers working in plant physiology, agronomy, and environmental science and working on either crop management or genetic enhancement to address either food security or the response of plants to global climate change.