Background: The August 2005 hurricane (Katrina) affected five million acres of f
ID: 34098 • Letter: B
Question
Background: The August 2005 hurricane (Katrina) affected five million acres of forest across Mississippi, Louisiana and Alabama, with the immediate damage ranging from downed trees, snapped trunks and broken limbs to stripped leaves. In addition to the immediate damage caused by the hurricane, longer term consequences included a die-off of coastal trees for several years following the hurricane.
Your assignment: Use your knowledge of nutrient absorption, exclusion of unwanted ions, and osmosis and water potentials to hypothesize why the coastal trees that made it through the hurricane died over the following months/years. Hint: Seawater flooded the inland freshwater habitats during the hurricane. Seawater is ~99% sodium chloride. Your hypothesis should include a description of any plant physiological mechanisms referenced, and an explanation of how it might be related to the die-off of the coastal tress.
Explanation / Answer
Salts(NaCl) flooded with the sea water in the soil water of coastal area may inhibit plant growth for two reasons. First, the presence of salt in the soil solution reduces the ability of the plant to take up water, and this leads to reductions in the growth rate. This is referred to as the osmotic or water-deficit effect of salinity. Second, if excessive amounts of salt enter the plant in the transpiration stream there will be injury to cells in the transpiring leaves and this may cause further reductions in growth. This is called the salt-specific or ion-excess effect of salinity (Greenway and Munns, 1980). The definition of salt tolerance is usually the percent biomass production in saline soil relative to plants in non-saline soil, after growth for an extended period of time. For slow-growing, long-lived, or uncultivated species it is often difficult to assess the reduction in biomass production, so percent survival is often used.
As salinity is often caused by rising water tables, it can be accompanied by waterlogging. Waterlogging itself inhibits plant growth and also reduces the ability of the roots to exclude salt, thus increasing the uptake rate of salt and its accumulation in shoots.
The salt in the soil solution (the
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