Emerging approaches to measure photosynthesis from the leaf to the ecosystem

Abstract

Measuring photosynthesis is critical for quantifying and modeling leaf to regional scale productivity of managed and natural ecosystems. This review explores existing and novel advances in photosynthesis measurements that are certain to provide innovative directions in plant science research. First, we address gas exchange approaches from leaf to ecosystem scales. Leaf level gas exchange is a mature method but recent improvements to the user interface and environmental controls of commercial systems have resulted in faster and higher quality data collection. Canopy chamber and micrometeorological methods have also become more standardized tools and have an advanced understanding of ecosystem functioning under a changing environment and through long time series data coupled with community data sharing. Second, we review proximal and remote sensing approaches to measure photosynthesis, including hyperspectral reflectance- and fluorescence-based techniques. These techniques have long been used with aircraft and orbiting satellites, but lower-cost sensors and improved statistical analyses are allowing these techniques to become applicable at smaller scales to quantify changes in the underlying biochemistry of photosynthesis. Within the past decade measurements of chlorophyll fluorescence from earth-orbiting satellites have measured Solar Induced Fluorescence (SIF) enabling estimates of global ecosystem productivity. Finally, we highlight that stronger interactions of scientists across disciplines will benefit our capacity to accurately estimate productivity at regional and global scales. Applying the multiple techniques outlined in this review at scales from the leaf to the globe are likely to advance understanding of plant functioning from the organelle to the ecosystem.

Keywords: gas exchange; phenotyping; photosynthesis.

Figure 1.. Depiction of techniques and example data for gas exchange (A–C) and proximal/remote sensing (D–F) techniques used to measure photosynthesis.

(A) Leaf-level gas exchange with one measured representative photosynthetic CO₂ response curve. (B) Canopy photosynthesis chamber situated over a soybean field with representative diurnal Net Ecosystem Productivity (NEP) data (Image Credit: Anthony DiGrado). (C) Ecosystem-scale eddy covariance system situated over sorghum with representative Net Ecosystem Exchange (NEE; negative values signify downward flux from atmosphere toward land surface) partitioned into Gross Primary Productivity (GPP) and Ecosystem Respiration (ER). (D) leaf hyperspectral point sensor being used on the model crop tobacco and representative spectral reflectance measurements. (E) A hyperspectral imaging sensor measuring plots of the model crop tobacco and an example hypercube showing the visible surface and spectral information for each pixel with depth of image. (F) aircraft and satellite depicted over the earth surface and a map of GPP (public domain image courtesy of GeoEye/NASA SeaWIFS project). Other than where indicated, all images were taken by authors.