Because plant canopies are exposed to the sky, they constantly adjust their photosynthetic systems to balance the absorption of sunlight against their ability to use this absorbed light for carbon fixation, downregulating photosynthetic regulation under conditions of stress. The hypothesis of coordinate regulation states that it is makes economic sense for plants to regulate their pigment levels and activity to match their photosynthetic capacity, traditionally measured using gas exchange or Rubisco activity. Because of coordinate regulation, pigment levels and activity revealed through reflectance and fluorescence methods provide potent indicators of stress operating at different time scales.
Results/Conclusions
This presentation reviews the processes by which plant regulate photosynthesis, allowing optical remote sensing to be used as stress indicators under a variety of conditions, with a particular focus on pigment responses to moisture, temperature extremes. A key emphasis is on the relative amounts of chlorophyll, carotenoid, and anthocyanin pigments, and the different time scales of multiple plant responses, many involving adjustment of pigment levels and activity in concert with other plant responses. Particularly in combination with indicators of moisture or thermal status, a number of optical indicators of pigment status provide useful optical metrics of plant photosynthetic activity and stress. Many of these methods provide pre-visual detection, allowing early stress detection and assessment of changing photosynthetic phenology with remote sensing. Applications range from ecophysiology, biodiversity, and carbon cycle science to and precision farming and phenotyping.