Does flooding affect the survival and primary and secondary metabolism of two species of Croton?

Abstract

Key message: Both Croton species survive flooding for a considerable period, changing primary and secondary metabolism; C. urucurana is more tolerant than C. floribundus. Native tropical species with a wide distribution are subject to environmental heterogeneity. Croton floribundus and C. urucurana, for example, occur in different forest formations, such as semideciduous seasonal forest and riparian forests, in well-drained or flooded soils. To explain possible adaptive strategies that allow this congeneric pair to occupy areas subject to flooding, we studied the effects of different times of exposure to flooding on species survival and metabolism and the potential for post-flood recovery. Unlike C. urucurana, the plants of C. floribundus survived flooding for only 60 days and the post-flood period; they did not survive flooding for 90 days. In both species, flooding reduced CO2 absorption rate, stomatal conductance, Rubisco carboxylation efficiency, photochemical efficiency of the photosystem II, and shoot and root biomass; however, there was a recovery of these parameters in post-flooding. Additionally, the flooding of Croton plants increased the content of alkaloids, total phenolic compounds, flavonoids, antioxidant activity, proline, and the activity of the enzymes guaiacol peroxide and superoxide dismutase. These responses were also observed in the post-flooding period. Thus, we conclude that C. floribundus is more sensitive to flooding compared to its congeneric pair. We also conclude that the mechanisms of adaptation to flooding are related to the phenotypic plasticity of both species, including the formation of hypertrophied stem lenticels and adventitious roots, changes in primary and secondary metabolism, and production of protective molecules such as proline.