NaCl dosing?

[Goatman]

I'm more of a physiologist than chemist or botanist, but there has been one trend here that has been nagging at me. It seems that adding salt to your planted tank is to be avoided like the plague, and I'm just curious why. In all higher lifeforms (plants being considered "higher" for this purpose) there is a Na/K pump facilitating photo/oxidative phosphorilation, and action potentials. The specifics of the Na/K pump took about 6 hours of A&P lecutre last semester, so I'll spare the details to those that don't already know what it does. Plants undergo a lot of active transport funcions that require the Na/K pump to be used, so I guess my real question without the fluff, is why do people dose with K but not with Na? It seems that in cells of humans with Na there is K on the other side of the membrane.

[StLouisan]

OOH good question. I found this on the internet that I thought might give some insight http://www.bettersoils.com/water_testing.cfm

Salinity as an Osmotic Problem

Salinity is a qualitative term used for the state of saline water or saline soil that contain various amounts of salt. A salt is the combination of a cation (a positively charged metal ion) with an anion (a negatively charged ion such as ionized acids). For example, sodium bicarbonate and sodium hydroxide or lye react with hydrochloric acid forming sodium chloride or table salt. Many salts are possible such as sodium sulfate and calcium salts. As the salt level increases in water, the water molecules are held more firmly preventing the diffusion of water from the external solution into plant roots (this phenomenon is called osmosis). When the level of salinity is too high, the water is unavailable for the plantings and the water is unsuitable. Organic molecules such as sugar or the alcohol mannitol cause osmotic problems also.

Based off of this, organic molecules such as compounds in fertizers would cause the same? This would be another reason why regular partial water changes are important....

:huh:

[rrkss]

Osmosis is the main reason for this but also, Chloride inhibits Nitrogen uptake and Sodium Inhibits Potassium Uptake. Yes we do have the sodium potassium pump but given the high amount of sodium diffusing in and the relatively low nature of potassium in the water column, plants are affected adversely long term. Also ATP drives the Sodium Potassium Pump. Without adequete nitrogen the production of Adenosine (The A in ATP) is slowed down given the fact that nitrogen is a major component of it also the production of proteins, chlorophyll, and DNA are greatly inhibited. Also the osmotic stress of the saline reduces the turbidity of the cellular membrane and could affect cellular function.

[Goatman]

Thanks a bunch guys, that gave a lot of insight.