Chlorophyll Fluorescence Imaging and Other Imaging Approaches to Estimate the Vitality of Plants

Chlorophyll fluorescence is a now well-established technique for the analysis of photosynthesis in plants and algae. Fluorescence transients (Kautsky curves), exhibited by photosynthetic organisms under different conditions provide detail information about the structure, conformation and function of the photosynthetic apparatus, especially of photosystem II. The analysis of the so-called OJIP-curve and of the pulsed-amplitude-modulated fluorometry in conjunction with the saturation pulse method has been very successful. In recent years, the versatility of these techniques has increased by the development of imaging systems. High resolution systems make it possible to investigate the photochemical efficiency of individual cells in a leaf or individual algal cells in a mixed population. Lower resolution systems can be used to analyze heterogeneous patterns of photosynthetic performance across leaves. Fluorescence imaging systems nowadays can be used to screen large numbers of plants or to record continuous fluorescence traces from multiple leaves or algal cells. Furthermore, ground monitoring of vegetation has been made possible due to recent developments of LIDAR-based fluorescence techniques. Also, passive detection of chlorophyll fluorescence based on the FLD-principle has been reported. A major problem is the proper analysis of images. Several approaches have been already applied in analyzing the impact of environmental factors on the vitality of plants and crops. The first phase in image processing consists of background subtraction, intensity correction and masking. To select the interveinal zones, different combinations of morphological operations are applied. For further statistical analysis, each image is reduced to a set of selected features followed by techniques used in texture analysis. In this paper, a range of examples will be provided to illustrate how chlorophyll a fluorescence can be used in physiological investigations and what it can contribute to analyze agricultural and horticultural crops in greenhouses and in the field.