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Effects of a basic solution on photosynthesis - (Feb/07/2008 )


I have (hopefully) a fairly straightforward question for you guys: what is the effect of a basic solution on photosynthesis? I've read through and, form my understanding, an increase of carbon dioxide dissolved in water makes it more acidic. But, what if we were to go the other way? What effect would that have on photosynthesis? Is that measurable?

Now, suppose I have sort of regular garden plant that likes a pH from 5-7. What if, instead of watering it with water (pH 7) but with, let's say, a Barium Hydroxide solution or Sodium Hydroxide solution (with a pH of 10), how would that effect the photosynthetic ability of the plant? I've been searching around on the 'net but there seems to be more info on acidic solutions rather that basic ones. Thanks for reading and I look forward to the responses.




Well, that article you mention talks about marine plants (and algae I suppose), which are kind of different from garden plants.
I don't know if the basic pH it will influence the photosynthesis per se. The plant uses the CO2 from the air and not from the solution it's watered with. If there is an influence on photosynthesis it could be due to some effects of barium or sodium (in this case salt stress).

One extra thing - the water with wich you water the plants hasn't pH = 7. Even if it is distilled water, if you leave it out in the open, it will incorporate CO2 and become acidic.


Thank you for the response. Hmm, I'd like to test this. What sort of plant do you recommend trying this out on? Thanks in advance.


Plants vary in their pH range where they grow. For example Deschampsia flexuosa grows mainly in acidic soils while many halophytes require alkaline conditions. In general slightly acidic pH 5.5 - 7 is the optimal for growth since lower pH makes it hard for plants to capture nutrients and higher pH favours plant pathogens. According to what plants you have in your garden and the pH of the soil you will have to choose the pH you will use. Just bear in mind that soils (the heavier the soil the highest the buffer potential - even in pure sand the pH is not that of the solution) have a huge buffer potential which means that in order to change pH you need to supply huge quantities of solution. If you want to retain the pH of your soil a pH around 7.0 will serve you pretty well but even if you use a solution with much higher pH I don't think there will be any problem.

Usually pH in nutrient solutions is of minor importance (NOT of course if they are planned to use in liquid cultures or pure snad). What is really important is the type of nutrients you will be adding and the amount of them. For example all micronutrients are necessary in small amounts but they can get very easily toxic. Addition of too much nitrogen may favour grasses so that if you are growing plants that do not need that much nitrogen you might want to add a minor amount..