As saltmarshes are regularly covered by water the soil is usually low in oxygen. Water fills the space between soil particles that are typically filled with air in other soils. Second, because the rate of diffusion of oxygen is much slower in water than in air the rate of movement from the water surface to the root zone is extremely slow.
Oxygen in the water in the soil is used up, often by the activity of decomposers like bacteria.
Marsh plants have air spaces (aerenchyma tissue) in their stems which allow oxygen to move from the leaves to the roots. They generally have thick roots with a corky layer and without root hairs. Other marsh plants are able to survive in low oxygen conditions by relying on anaerobic respiration (respiration that does not use oxygen).
Some halophytes are able to secrete salt through salt glands, whereas other plants have mechanisms for dealing with higher concentrations of salt in their cells, or can reduce the uptake of salt through their roots. Some plants have salt gland cells on the lower surface of the leaves and excrete the salt from their tissues.
Some marshes become dry enough seasonally or during drought periods that they are can be burned by fire. The extensive root system of most emergent marsh vegetation allows them to resprout following a fire.