Abscisic acid and biopreparations as markers of organic soybean adaptation to hydrothermal stress

Given the growing demand for organic soybeans and the need to mitigate the adverse effects of climate change, the study of biopreparations of various origins and their influence on plant adaptive mechanisms under stress conditions has become increasingly relevant. This study aimed to assess changes in abscisic acid (ABA) content under the influence of biopreparations in a multi-year field experiment and to analyse the relationship between ABA and the biochemical, physiological, and agronomic indicators of soybean adaptation to hydrothermal stress under organic farming conditions. The study involved the use of biological preparations based on mycorrhizal fungi, rhizosphere and nitrogen-fixing bacteria, as well as phytohormones. A range of field, laboratory (physiological and biochemical), and statistical methods was employed. The findings revealed the integration of molecular, biochemical, physiological, and agronomic stress resistance markers as a result of the enhanced adaptive potential of soybean following the application of biopreparations. Their effectiveness was evident through a comprehensive influence on key adaptive mechanisms, including: a 9.2%-36.3% reduction in ABA concentration, indicating alleviation of stress pressure; a 10.0%-27.6% increase in relative water content, contributing to the maintenance of optimal cellular water balance; a 19.2%-65.4% improvement in stomatal conductance, attributed to the optimisation of stomatal function; a 15.6%-41.8% reduction in lipid peroxidation levels (malondialdehyde), indicating effective membrane protection against oxidative stress; a 9.1%-46.6% increase in proline content, suggesting the activation of natural defence mechanisms and the maintenance of osmotic balance. Correlation analysis confirmed that the biopreparations facilitated a complex modulation of the plant stress response, optimising the balance between defence reactions and productivity, which led to a 12.3%-45.5% increase in yield even under adverse weather conditions. It was established that under water stress, the biological preparations modulated ABA biosynthesis and its regulatory role, contributing to coordinated changes in osmoprotective mechanisms, antioxidant defence, and the plant water regime. The most effective approach proved to be the triple combination of biopreparations, which ensured an optimal balance between phytohormonal regulation, physiological processes, and soybean productivity under hydrothermal stress. The results obtained may be recommended for the cultivation of organic soybeans to improve yield under climate-related challenges