The aim of this educational review is to provide practical information on the hardware, methodology, and the hands on application of chlorophyll (Chl) a fluorescence technology. We present the paper in a question and answer format like frequently asked questions. Although nearly all information on the application of Chl a fluorescence can be found in the literature, it is not always easily accessible. This paper is primarily aimed at scientists who have some experience with the application of Chl a fluorescence but are still in the process of discovering what it all means and how it can be used. Topics discussed are (among other things) the kind of information that can be obtained using different fluorescence techniques, the interpretation of Chl a fluorescence signals, specific applications of these techniques, and practical advice on different subjects, such as on the length of dark adaptation before measurement of the Chl a fluorescence transient. The paper also provides the physiological background for some of the applied procedures. It also serves as a source of reference for experienced scientists.

Perennial ryegrass (Lolium perenne L.) belongs to the common cultivated grass species in Central and Western Europe. Despite being considered to be susceptible to drought, it is frequently used for forming the turf in urban green areas. In such areas, the water deficit in soil is recognized as one of the most important environmental factors, which can limit plant growth. The basic aim of this work was to explore the mechanisms standing behind the changes in the photosynthetic apparatus performance of two perennial ryegrass turf varieties grown under drought stress using comprehensive in vivo chlorophyll fluorescence signal analyses and plant gas exchange measurements. Drought was applied after eight weeks of sowing by controlling the humidity of the roots ground medium at the levels of 30, 50, and 70% of the field water capacity. Measurements were carried out at four times: 0, 120, and 240 h after drought application and after recovery (refilling water to 70%). We found that the difference between the two tested varieties’ response resulted from a particular re-reduction of P700⁺ (reaction certer of PSI) that was caused by slower electron donation from P680. The difference in the rate of electron flow from Photosystem II (PSII) to PSI was also detected. The application of the combined tools (plants’ photosynthetic efficiency analysis and plant gas exchange measurements) allowed exploring and explaining the specific variety response to drought stress.

Chlorophyll content meters have been used successfully to estimate foliar chlorophyll content in various plant species in non-destructive way, especially to study stress physiology and abiotic stresses, such as nutrient deficiency. The main aim of this work was to compare the records of different chlorophyll content meters with the results obtained by the destructive method under the deficiency of main macronutrients in plants growth medium. Four devices (CL-01, SPAD-502, Dualex, and CCM-200) were used to estimate chlorophyll content in maize and tomato plants. In maize plants, all devices validated high accuracy for potassium and nitrogen deficiency and low accuracy for phosphorous and magnesium. In tomato, they showed a high degree of accuracy for calcium, potassium, and iron deficiencies, and low accuracy for phosphorus deficiency. All devices proved to be suitable to provide a reasonably estimation of chlorophyll content under optimal nutrient conditions. However, under nutrient deficiency conditions, tested devices showed different values for the same plant under the same nutrient deficiency. This suggest that, these devices should be validated by a sampling destructive method under such conditions.