A COMPOSITE BIOCHAR-BASED BIOFERTILIZER WITH A HALOTOLERANT PGPR PSEUDOMONAS SP. MITIGATES NACL-INDUCED STRESS IN SUNFLOWER

Soil salinization is one of the global problems. Therefore, it is of particular importance to identify the mechanisms of salt resistance in cultivated plants. The effect of composite biofertilizer (CBF) based on wood biochar and halotolerant growth-stimulating rhizobacteria (PGPR Pseudomonas sp. STF13) on the growth and physiological and biochemical parameters of sunflower (Helianthus annuus L.) of the Yenisei cultivar was studied in normal conditions and under sodium chloride salination. The vegetation experiment included 4 options: control substrate (CS); CS with the addition of CBF (2.5 % by volume); CS with watering of 80 mM NaCl; CS with the combined use of CBF + NaCl. The plants were grown for 5 weeks in natural light and at room temperature. It was found that CBF significantly improved the morphometric parameters of plants, increasing the raw biomass of roots and leaves by 11 and 33 %, respectively, compared with CS. The addition of NaCl suppressed root development, reducing their weight by 2 times. However, the use of CBF + NaCl almost completely eliminated this negative effect, stimulating the growth of root biomass to the control level. At the biochemical level, CBF also demonstrated a protective effect: under salt stress, the intensity of lipid peroxidation decreased (the content of malonic dialdehyde was 1.3 times lower than under the action of salt), and the release of electrolytes from tissues decreased by 1.4 times, which indicates a decrease in oxidative stress. The introduction of CBF also had a positive effect on ionic homeostasis, increasing the K⁺/Na⁺ ratio in plant organs under salinization conditions by 1.7 times on average and preventing Na+ translocation into leaves. Salinization caused a 14-fold increase in the specific electrical conductivity of soils in comparison with CS, however, CBF offset this effect, reducing its value by 27 %. The results obtained indicate the prospects of using composite biofertilizers based on biochar and PGPR to increase the salt resistance of crops and restore the fertility of saline soils.