Hymenaea courbaril L. (Fabaceae) seedlings maintain growth but weaken their stem under experimental flooding conditions

Abstract

Flooding is a frequent event in the development of seedlings in riparian forests and adjacent areas. Once flooded, seedlings can develop a broad range of morphoanatomical changes that enable their growth and survive in hypoxic soil. With flooding events increasing in frequency worldwide, understanding the response of seedlings to flooding is an essential issue in the management and restoration of flooding prone areas. Here, we investigated the effects of flooding on the growth rate, biomass, morphoanatomy and secondary xylem anatomical traits of 110-day-old Hymenaea courbaril L. (Fabaceae) seedlings. We maintained the seedlings for 70 days in a recirculating and stagnant water treatment. We applied linear models to verify the effects of flooding on the growth rate, biomass and stem secondary xylem anatomical traits. Flooded seedlings had similar growth rates and stem and leaf dry biomass to those of non-flooded seedlings. In addition, flooded seedlings had lower root biomass and secondary xylem with narrower vessels with thinner cell walls in a higher density, shorter vessel elements, thinner fibre walls, a lower vessels and fibres fraction and a higher axial parenchyma fraction than non-flooded seedlings. Our results showed that H. courbaril seedlings are tolerant to flooding, maintaining their growth rate and aboveground biomass under hypoxic soil. Experimental flooding induced the development of a secondary xylem for more secure water supply, but with lower mechanical support potential, resulting in the seedlings more susceptible to stem breakage and decay.