Photosynthetic and related traits in variety-specific drought acclimation of soybean

This study evaluated the acclimation of eight soybean varieties to water deficit through changes in photosynthetic performance and physiological, biochemical, and epigenetic traits. Plants were grown under controlled conditions in two treatments: control (80% water-holding capacity; WHC) and drought (40% WHC). Water status was assessed using relative water content and osmotic potential, while photosynthetic performance was evaluated using gas exchange, water use efficiency, maximum quantum efficiency of photosystem II, chlorophylls, and carotenoids. Total flavonoid content, reducing power, proline accumulation, and 5-methylcytosine content were determined. Water deficit induced marked variety-specific changes across traits. The varieties Hana and Atacama maintained higher relative water content (RWC), less negative leaf osmotic potential (Ψs), and more favourable photosynthetic performance under drought, while the variety Atlas showed a favourable profile in several other traits. In contrast, the varieties Dornburg, York, and Impala showed a less favourable response, whereas the varieties Labrador and Zaria occupied intermediate positions depending on the trait evaluated. Multivariate and correlation analyses showed that photosynthetic performance was closely associated with plant water status, while stronger biochemical and epigenetic responses were more evident in less favourable or intermediate profiles. These results indicate that soybean acclimation to water deficit is coordinated and variety-specific and cannot be assessed using a single parameter.