Asahi SL stimulates plant’s vital processes like growth and development, affects physiology and biochemistry, what often leads to increased biomass accumulation and yield. However, common is opinion that application of this preparation could be beneficial only, when treated plants are grown under unfavorable conditions. Therefore the aim of this work was the assessment of the stimulatory effect of Asahi SL on Arabidopsis thaliana L. and ornamental amaranth plants grown under optimal conditions. Plants treated with Asahi SL were higher and more advanced in development, particularly generative. Biomass accumulation was greater after biostimulator application mainly due to better photosynthetic apparatus efficiency, which was manifested by (i) greater leaf area, (ii) higher total chlorophyll content and (iii) increased intensity of photosynthesis. Effect of Asahi SL on chlorophyll a fluorescence was marginal. Despite of higher transpiration and lowered stomatal resistance the RWC was almost unchanged in biostimulator treated plants what was attributed to increased water uptake. Obtained results clearly showed that Asahi SL applied on plants can also be effective and beneficial when they are grown under optimal conditions.

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