Environmental factors constraining adventitious root formation during flooding of Solanum dulcamara

Flooding is a compound stress, imposing strong limitations on plant development. The expression of adaptive traits that alleviate flooding stress may be constrained if floodwater levels are too deep. For instance, adventitious root outgrowth is typically less profound in completely submerged plants than in partially submerged plants, suggesting additional constraints in full submergence. As both oxygen and carbohydrates are typically limited resources under submergence, we tested the effects of oxygen concentration in the floodwater and carbohydrate status of the plants on flooding-induced adventitious root formation in Solanum dulcamara L. Partially submerged plants continued to form adventitious roots in low-oxygen floodwater, whereas completely submerged plants developed hardly any roots, even in floodwater with twice the ambient oxygen concentration. This suggests that contact with the atmosphere, enabling internal aeration, is much more important to optimal adventitious root formation than floodwater oxygen concentrations. If plants were depleted of carbohydrates before flooding, adventitious root formation in partial submergence was poor, unless high light was provided. Thus, either stored or newly produced carbohydrates can fuel adventitious root formation. These results imply that the impact of an environmental stress factor like flooding on plant performance may strongly depend on the interplay with other environmental factors.