Effects of Plant Growth Promoting Bacteria on chlorophyll a fluorescence parameters of Lolium perenne grown with microclover in drought conditions

Background Turf surface is a dominant element of green areas located within rural buildings or in cities. In recent years, mainly lawn varieties of grasses have been used to plant green areas, but microclover (Trifolium repens L.) has been increasingly popular. In addition, microclover can be effective in reducing irrigation costs. Drought is one of the main factors inhibiting the growth and development of plants. In modern agriculture some bacteria are used to promote plant growth and development ie. Plant growth promoting rhizobacteria (PGPR) increase systemic resistance of plants to biotic and abiotic stress. Chlorophyll fluorescence is used to measure the physiological condition and stress level of plants. Fluorescence analysis at O-J-I-P points (OJIP test) is a method used for the examination of plant vitality. Results The presence of microclover in the mixture contributed to the improvement of many chlorophyll a fluorescence parameters of Lolium perenne. Statistically, the maximum fluorescence (Fm), the maximum photochemical efficiency of PSII (Fv/Fm), and the maximum water-splitting efficiency on the donor side of PSII (Fv/Fo) increased significantly. The number of active reaction centers also increased, which translated into better energy flux absorbed by one reaction center (ABS/RC). In addition, there were upward tendencies of such parameters as the area above the induction curve (Area) and the density of reaction centers (RC/CSo). The use of Plant Growth Promoting Bacteria increased the maximum chlorophyll a fluorescence (Fm), the area above the induction curve (Area), and the density of reaction centers (RC/CSo). Conclusion Due to the above effects, microclover can be recommended to be used in lawn mixtures. The positive effect of the plant-promoting PGPB microbial vaccine on the Lolium perenne lawn variety suggests that more studies should be conducted on other plant species subjected to other kinds of abiotic stress. Growing plants exposed to drought stress with the substrate moisture level of 40% FWC did not affect the photosynthesis process. The parameter most sensitive to low substrate moisture was the rate of electron transport through one active reaction center (ETo/RC). Therefore, the ETo/RC parameter should be recommended for further research on drought stress.