Nitrogen deficiency strongly influences crop photosynthetic performance and biomass production. In this study, we applied rapid, non-invasive records of chlorophyll a fluorescence kinetics for evaluation of wheat (Triticum aestivum L.) leaf photosynthetic performance. Plants were grown during the whole season in big pots filled with the soil substrate and they were supplied by different doses of nitrogen nutrition. The plant nitrogen and leaf chlorophyll content as well as the plant aboveground

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... biomass were analyzed after chlorophyll fluorescence records in three growth stages. Our results confirmed that the maximum quantum yield of photochemistry frequently used in previous studies was almost insensitive to nitrogen treatment, if measured in young, non-senescent leaves. On the contrary, the performance index was much more responsive. The performance index values derived from parallel measurements in the youngest and third leaf from the top were used to calculate performance index leaf ratio, which correlated well with the plant nitrogen content. Moreover, this parameter was not sensitive to midday depression, which significantly affected the values of other chlorophyll fluorescence parameters. Although the optimum performance index leaf ratio values decreased continuously in the second part of the growing season, the optimum and critical values for each growth stage can be easily identified. Thus, we suggest performance index leaf ratio as the simple parameter for the rapid evaluation of the wheat photosynthetic performance and an early indicator of insufficient nutrition level. Unlike some other approaches, suggested method seems to be useful also in conditions of a moderate nutrient deficiency.