Aims Flooding reduces soil oxygen content, and leads to oxygen deprivation in the root system of plants. Since oxygen is essential for mitochondrial respiration, this process cannot be maintained under anoxic conditions and must be replaced by other pathways. Our objective was to understand flooding adaptation mechanisms of baldcypress (Taxodium distichum), Chinese tallow tree (Sapium sebiferum) and pecan (Carya illinoensis) under waterlogged conditions.
Methods One-year seedlings of baldcypress, Chinese tallow tree and pecan were grown in pots, and three treatments were implemented: CK (control, common soil water content), WA (waterlogging, water level equal with soil surface) and FL (flooding, water level 8 cm above soil surface). Treatments lasted 65 days, and indexes of growth, porosity and root oxygen consumption were determined at different times after treatment.
Important findings We found that WA and FL treatments inhibited growth of both Chinese tallow tree and pecan, but biomass and biomass increment of baldcypress increased under WA condition, indicating that baldcypress was more tolerant to flooding. Root/shoot ratio of the three tree species increased significantly under WA and FL treatments, which was primarily due to the decrease of stem and leaf biomass. WA and FL treatments also stimulated aerenchyma formation in the roots, stems and leaves of the three tree species, thereby the porosity in the roots, stems and leaves of the three tree species increased significantly under WA and FL conditions. The aerenchyma formation and increased porosity enhanced O2 diffusion to roots and rhizosphere. Our results indicate that baldcypress, Chinese tallow tree and pecan exhibit several adaptive mechanisms in response to waterlogging, including formation of new roots, aerenchyma formation, increased porosity of the roots, stems and leaves, and increased O2 release into the rhizosphere.