Decrease in plant hydraulic conductance due to soil waterlogging suppresses the transpiration rate of Glycine max even during post-waterlogging reoxygenation

In humid regions, the transpiration rate is determined by transpiration demand because of the sufficiently moist soil. However, inhibition of plant water uptake capacity due to soil waterlogging can significantly constrain the transpiration rate even after drainage. This study aimed to evaluate plant hydraulic conductance during soil waterlogging and subsequent reoxygenation and its impact on whole plant transpiration.

Two experiments were conducted to assess the ecophysiological responses of soybeans during waterlogging (Experiment 1) and reoxygenation (Experiment 2). Transpiration rate, stomatal conductance, leaf water potential, and leaf area were measured. In addition, plant hydraulic conductance was calculated using the root water uptake equation. A simple transpiration model incorporating the response of plant hydraulic conductance to waterlogging was used to evaluate the impact of waterlogging on transpiration estimation.

Waterlogging for more than 3 days reduced plant hydraulic conductance, which persisted even during the post-waterlogging reoxygenation period. Furthermore, leaf water potential, stomatal conductance, and transpiration rate in waterlogging treatment exhibited a lower value than those in control during both waterlogging and reoxygenation. The constructed model effectively reproduced the responses of plant hydraulic conductance and transpiration rate, especially during reoxygenation.

Soil waterlogging significantly reduce the hydraulic conductance of soybean plants, resulting in leaf water stress and depression of transpiration, even during reoxygenation. Our results highlight the importance of integrating plant hydraulic responses with water dynamics models in the soil-plant-atmosphere system.