Primarily, physiological ecology is autecology assessing the physiological traits of individual plants or species in relation to ecological performance. Conversely, synecol-ogy covers larger vegetation units, ecosystems, or biomes and is mainly based on floristic, phytosociological, and phytogeographical approaches. However, physiological ecology can also develop to synecology when larger data sets on physiological reactions for different plants composing the vegetation can be obtained. This is increasingly facilitated in the physiological ecology of photosynthesis due to miniaturization of equipment for measuring gas exchange (CO2 and water vapour) and parameters of photosynthetic electron transport. The former is assessed by infrared gas analysis (IRGA). The latter is particularly easy to achieve by measurements of chlorophyll fluorescence. When discussing the above the various ways of energy dissipation of activated chlorophyll, fluorescence has not been mentioned yet. In fact, a small part of the energy not used for photochemical work can be released again by emission of light, that is, fluorescence, which is readily recorded using miniaturized pulse amplitude-modulated fluorometers. In addition, appropriate sampling for analyses of metabolic compounds and also stable isotopes (mainly 2H or deuterium, 13C, 18O, 15N) provides a wealth of information. There are several isotope effects in metabolism in general and in photosynthesis in particular. For example, the discrimination of RubisCO against the rare 13C isotope in the substrate CO2 as compared to the abundant C isotope is much larger than that of PEPC, and thus, with the appropriate precautions mass spectrographic analyses of carbon isotope ratios in dried plant material allows to distinguish C3, C4, and CAM plants.
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