There is an extensive history of measuring plant photosynthetic processes and water relations. However, a major impediment has been the impossibility of actually determining the light distribution over the entire surface of a particular plant during a physiological experiment; plant geometry is just too complex. While much useful information has been obtained in spite of this, other, important questions have gone begging. Information of this type would contribute to the understanding of (1) the partitioning of biomass among plant components and its relationship to photosynthesis; (2) examination of subtle morphological differences between species and subspecies; (3) influence of photobiology on morphology and phenology (e.g., elongation, heliotropism); (4) plant morphological responses to chemical and environmental factors (e.g., water stress, temperature, and CO2); and many others. This project seeks to develop a laboratory instrument capable of measuring transient photosynthetic and transpiration rates of a plant while simultaneously determining the complete 3D structure of its canopy. The instrument will combine elements of machine vision and stereophotogrammetry with traditional methods of gas exchange monitoring and online sap flow measurement. The basic design will involve a gas tight, transparent chamber containing the experimental plant with connections to CO2/H2O gas analyzers. Sap flow sensors will be attached to the plant. All outputs will be monitored by microcomputer. Illumination will be controlled and the plants will be photographed at various angles by a robotically operated camera. Machine vision techniques will be used to separate the plant from the background and then segment it into leaves, stems, etc. Multiple images will be combined through stereophotogrammetry to obtain a solid, 3D computer model of the plant. The plant surface illumination distribution can then be calculated using standard radiosity imaging software. Given the num ber of plant scientists who make laboratory measurements of photosynthesis and transpiration, there is a large potential audience for this device. There is also good reason for confidence that the effort will be successful. One PI has already developed a stereophotogrammetry system which computes and images 3D plant models from manually digitized photos. The team also includes machine vision expertise and examples of segmenting digital plant images exists in the literature. The physiological techniques are well established and three PI's are versed in their use. Team members also have experience with data acquisition system design and general engineering. Finally, appropriate radiosity codes are available in the public domain.
