Effects of Salt on plants

[Degenerate]

If you germinate plants in water with some salt concentration. Why do they grow slower? what is affecting them? I know that osmosis has to do with something. Does salt prevent certain reactions? I love botany myself but cant quite work out why plants wither or don't germinate in salty conditions. I know some plants like mangroves can tolerate salt as they can either filter out salt or expell salt.

SO in short, how do salt effect plant growth? Are their any good links?

Thank you.

 

[Rilescat]

If I recall correctly, the salt in the water causes the water concentration to lower outside the plant cells forcing water to diffuse out of the cells. (I know that's it for animal cells, but am not absultely certain for plant cells - given cell walls).

The diffusion lowers the plants water intake and hence makes it grow slower, or wilt...depending on the stage of the plant.

Link? Possibly this will help: http://www.ussl.ars.usda.gov/answers/cellroot.htm

 

[PowerMacG5]

The reason the plant will grow slowly in a salt solution is because the salt removes water from the plant cells. In an ideal situation, the concentration of water outside of the cell would be slightly greater than inside so to allow the osmosis process to continue. When salt is added it draws water away from the cell. It is just like putting salt on a slug, it draws all of the water out and it will shrivel up. The cell wall in a plant is just cellulose, it only stiffens the plant to allow it to grow upright. The cell wall is not a membranse and does not offer protectiveness from outside things, this is why a plant cell has both a cell membrane and a cell wall. But to answer your question, again, salt causes reverse osmosis, it causes the water to flow from an area of low concentration, to an area of high concentration (much like active transport, but does not require energy to be added). When the is removed, the osmosis process will start again, flowing the water from an area of high concentration to an area of low concentration. I A'ced my Bio SATII so if you want anymore information about something to do with Biology just post it.

 

[rgwalt]

The chemical reactions that take place in cells are meant to occur under specific PH and ionic strength conditions. A change in these conditions will cause proteins to unfold, denature, or break down. So, the presence of a large salt concentration in the water the plant has available will can cause water to be drained from the plant in order to balance out the chemical potentials. Some plants have adapted to tolarate or even demand a higher salt concentration in the water in their cells, so the plant can still extract water from solutions that are highly saline.

Osmosis all works because of the cell trying to balance the chemical potentials on either side of the cell wall. In general, this means that the cell trys to equilibriate the concentrations. This is why if you take a salt water fish and drop it into a tank of fresh water, it will swell and die.

Ryan

 

[Belegost]

I think what everyone was trying to describe is the effect of osmotic pressure.

As an experiment, try to gain access to some of the membrane they use for reverse osmosis. Place it in a water proof box, about a third of the way down the length, make sure its sealed to the sides of the container so water can't go around it. On the short side add a saline solution, and on the other add pure water (distilled). Make sure you fill the to the same height, over a period of time the saline side will rise to a level higher than that of the pure water. (the smaller the saline side the more noticeable the height change, it's best when the waline is stuck in a tube.) Make sure you try it, because its hard to believe if you just hear it.

The pressure of the saline being held up then is equal to the osmotic pressure. To explain this we consider what happens at the membrane, the membrane only allows small molecules such as water to pass, whereas the larger salt ions cannot. So, the water molecules on the pure side have more opportunity to pass through the membrane, while the solution side has fewer opportunities, since there are fewer water molecules per unit volume, and the salt ions tend to obstruct them. Furthermore, the forces that exist between ions and dipoles are much stronger than those between two dipoles (water, being polar, has a dipole and is held together by dipole-dipole forces) So there is an attraction of water molecules to the salt ions. This of course fits with free energy considerations, no appreciable heat is required or produced by the process, but the lower concentration on the saline side is favored by entropy.

This explains the behaviour of your plants, the roots of a plant contain such a semi-permeable membrane, and the osmotic pressure (as well as the capillary effect in the small tubes) is used to passively distribute the water to the top of the plant. However, when the water in the soil has a salt concentration it lowers the osmotic pressure, making it more difficult for water to get to the top of the plant.

As an example of how large this pressure can be, a .15M solution of table salt (sodium chloride) in water (about 8.8 grams of salt per liter of water) at 25C when placed in a situation with pure water will produce an osmotic pressure of approximately 7.3 atm. This could hold up a saline column around 250 ft high.

 

[Degenerate]

Firstly. Thank you all for your help

Now..


<< As an example of how large this pressure can be, a .15M solution of table salt (sodium chloride) in water (about 8.8 grams of salt per liter of water) at 25C when placed in a situation with pure water will produce an osmotic pressure of approximately 7.3 atm. This could hold up a saline column around 250 ft high. >>

Here are you saying that the salt solution produces a larger pressure than the pure water? or the other way around. Logically, the pure water should produce more pressure since the salt solution 'draws' water form the plants'.. Can you please confirm that for me? After all you did say that the addition of salt lowers the pressure so yeah..

Also. Okay. now that i understand that the osmosis side of it when salt solution is given to plants, what about liquid fertilisers? Some come in fine crystals and you dissolve it in the reccomended amounts. I believe that you are adding nutrients in the form of ions right? So why dosent this make the plant wither? It is because that the ions are in relatively low concentrations? Or, are the advantages to the plants to benificial in the long run since plants need these ions.

Lastly: generally, would different concentrations of salt affect the growth rate in a linear pattern at the start and sor ot flatten out near the end as the plant dies eventually when given too much salt.?

thank you all again.

 

[Degenerate]

Please people

 

[rgwalt]

The osmotic pressure is caused by fresh water being drawn into the salt water side of the membrane. So, his explanation is indeed correct. About liquid fertilizers... you may or may not know that if you over-fertilize a plant, it will die. Try quadrupiling the amount of crystals used in a batch of fertilizer (it might take more to see an effect though). If you use a highly concentrated solution of fertilizer, it will burn/wilt the plants.

Ryan

 

[PowerMacG5]

In low concentration, the fertilizer is good for the plants because it will draw water from the ground and near the fertilizer. As you increase the amount of fertilizer, yes the plant is getting more nutrients from it, but now it will draw water from the plant as well as from the ground.

 

[Macro2]

Some plants grow quite well in saltwater. Coconut palms and mangroves for example.
In less salt tolerant plants, brown leaf tips are indicative of too much salt. If a plant is in a pot you can flush it with water. In the ground and a period of watering will help.

Mac

 

[Degenerate]

thanks all again