Roots, rhizomes and other plant organs usually obtain sufficient oxygen for aerobic respiration directly from gaseous spaces in the soil. However, the diffusion of O2 from the air into the soil can be effectively blocked when soil becomes flooded or waterlogged. In such cases, the respiratory consumption by plant roots, soil fauna and microorganisms can totally deplete the oxygen. Periods of oxygen deficiency can trigger functional and developmental responses that promote acclimation to hypoxic or anoxic conditions. Low oxygen concentrations lead to long-term morphological adaptations such as developing aerenchyma in roots.
I would think sclerenchyma development as more associated with lignin strength in intertidal zone whereas growth of aerenchyma for air (oxygen) storage, as well as transport (up and down). Another factor may be the water temperature, as less oxygen dissolves in warmer water. The cycles of respiration and transpiration change depending on daylight hours, so roots and leaves switch metabolic roles daily. Since aerenchyma also transport carbon dioxide, the pH of aquatic environment may influence the biology. As mangrove adaptation has occurred one would prefer to look at the episome for pectin synthase as well as the lignin biosynthetic route.
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