Citrate test

[Ray]

Aquatic systems and soils are entirely different environments from most orchid media. I fail to see how there would be a problem with the use of citric acid. Let's not forget that both MSU formulas and K-Lite contain it to increase solubility.

I also don't see how the use of a strong acid favors algae.

 

[Secundino]

Of course the environment is different. I was not speaking about environments. I was speaking about water, precisely water bodies. If you water an orchid - in whatever a soil, soil-substrate, hidroponic methods - there is a water body in touch with that substrate and the roots. This water body may be continuous or intermittent (to our eyes), but it is there and the physics and chemical process' are essentially the same. The way an acid changes the pH is identical, and the way substrate maintains the buffer system of the water is identical. I did not say that the buffer system is the same for each and every body of water, I do say that the buffering system works accordingly.

In one of the spanish orchid forums there are momentaneously praising the benefits of watering with sugar water. Well, the effect is just the same: the glucose boosts the microbial community in the substrate which in turn results in more metabolites available for the plant roots.
evil: Waiting for the complaints about ants and pathological fungi which benefit equally!)

I strongly feel I shouldn't have compared to my aquaria (orthodox orchidist are very huffy with this things), I just wanted to try to explain this observation Rick had made: The crazy part is that the first application was only 24 hours prior to taking picture #2. And (you are free to believe it) lemon juice is very quickly metabolised.

And I don't know HOW mineral acids favour algae growth; though I've an idea; I just can tell that this are my observations.

 

[naoki]

Lime/Ca induced Fe deficiency?

It seems a bit far-fetched that the color changes in 24 hours, but if you look at the p.9 of the following, there are some experiments of acid foliar application to re-green Fe deficient leaves.

https://www.researchgate.net/profil..._L.)_trees/links/0fcfd50b77f3de7c31000000.pdf

One hypothesis is that physiologically inactive Fe pools in the leaf apoplast (outside of the cells in the cell walls) get remobilized by the lower pH of apoplast (from the intro of the paper).

 

[Stone]

I used citric acid for years to bring water pH down from 10 to 6.
Works fine.

 

[gonewild]

The greening effect is probably not related to pH but rather to some form of chelation. Since lemon juice contains both citric and salicylic acids this study may explain the foliar application result.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215826/

It's possible that the acid combination chelated iron within the leaf and the iron allowed for more chlorophyll production in a fast 24 hour period.... maybe.

I don't think that a pH change would cause the leaves to get greener in 24 hours.

 

[myxodex]

Interesting result and discussion. I second Rick's comment that these TCA cycle have special roles in metabolism. Both plants and fungi excrete organic acids into their substrates. Malic, citric, succinic and fumaric acids have been detected in forest leaf litter in some studies.

For me the most curious effect of these acids is that discovered in the 1970's in the plant tissue culture setting. Oddly, NH4 is used rather poorly as a sole N source for plant cells in tissue culture. This can be boosted by adding one of the TCA organic acids to the medium; succinic and alpha-ketoglutaric are the most effective, but both citric and malic acids have an effect. Sorry I didn't copy the link to this but the reference is below.
Behrend,J. and Mateles, R.I. (1976) Plant Physiol 58: 510 - 512

Another intriguing study by the same group indicates that the use of nitrate as the sole N source can be inhibited by adding single amino acids to the medium, all that is except arginine (and possibly alanine) which also can counter the inhibitory effect of the others when added together.
Behrend,J. and Mateles, R.I. (1975) Plant Physiol 56: 584 - 589

 

[Rick]

I was out of town all last week and my wife didn't give any lemon juice the entire time. But progress in general continues. I've restarted the lemon juice at ~1/8 tsp per gallon of fertigation water.

 

[Rick]

The greening effect is probably not related to pH but rather to some form of chelation. Since lemon juice contains both citric and salicylic acids this study may explain the foliar application result.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215826/

It's possible that the acid combination chelated iron within the leaf and the iron allowed for more chlorophyll production in a fast 24 hour period.... maybe.

I don't think that a pH change would cause the leaves to get greener in 24 hours.

There's also some evidence that plants can use organic acids as a source of carbon for respiration (which ultimately is the whole point of photosynthesizing in the first place).

 

[gonewild]

There's also some evidence that plants can use organic acids as a source of carbon for respiration (which ultimately is the whole point of photosynthesizing in the first place).

If lemon juice is providing needed carbon, wouldn't this indicate a shortage of carbon in the atmosphere?

 

[Secundino]

Yes, definitely. We'are out of CO2.

 

[Rick]

If lemon juice is providing needed carbon, wouldn't this indicate a shortage of carbon in the atmosphere?

No, but organisms are conservative. Why waste energy fixing carbon from CO2 if you can get prefixed food from other sources in the environment?

 

[cnycharles]

Could be other limiting factor restricting the normal carbon uptake, or the organic acids greening things up is like us eating white bread or soda and getting a boost


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[Rick]

Found a new cool paper

http://www.hindawi.com/journals/aag/2014/147278/

Gives doses too.

Note indications for use of both malic and citric acids which both found in lemon juice.

 

[Rick]

Could be other limiting factor restricting the normal carbon uptake, or the organic acids greening things up is like us eating white bread or soda and getting a boost


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http://www.docsdrive.com/pdfs/ansinet/pjbs/2004/187-196.pdf

Going full circle on the eco-relevance of organic acids to orchids. Mycorrhrizal fungi seem to be a pretty awesome source of citric and malic acid.

So maybe orchids never truly give up there dependence on mooching off the fungus after developing their own photosynthetic capacity.

 

[Rick]

http://link.springer.com/article/10.1007/s11676-012-0284-y

Crazy Aspergillus flavus and other citric acid producing fungus were common endophytes in a vanda a bulbo species.

I also found an article on the full scale production of citric acid (which uses A. flavus).

 

[terryros]

Rick - I have been wondering if you have found any evidence for an adverse effect from excess lemon juice, assuming that the pH in the root zone is not dropped too low? I really want to use the lemon juice to acidify my fertigation solution enough to overcome a pretty alkaline growing media. You have come down on the amount that you use in your environment, but I am wondering about adverse effects of using more than 5 mL (1 teaspoon) per gallon?


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[Rick]

Rick - I have been wondering if you have found any evidence for an adverse effect from excess lemon juice, assuming that the pH in the root zone is not dropped too low? I really want to use the lemon juice to acidify my fertigation solution enough to overcome a pretty alkaline growing media. You have come down on the amount that you use in your environment, but I am wondering about adverse effects of using more than 5 mL (1 teaspoon) per gallon?


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I found a paper that indicated root damage would occur (very quickly) at low pH, but the detrimental pH level was based on the calcium concentration (i.e. more calcium = more safety at a given pH).

So after a couple of shots at a tablespoon per gallon I got scared and went to 6-8 drops per gallon (watering every day). pH is around 5.5 to 5.9 Root growth is still great after 2+ months.


Coming up with a way to dose optimally is not going to be easy.

I hope you poked through some of those papers I linked.

The upshot is that orchids contain endphytic fungi species that supply organic acids like citrate and malate. One species of orchid endophyte Aspergillis niger is what is commercially used to make citric acid for soft drinks like Coca Cola!

 

[abax]

Any differences in lime juice as opposed to lemon juice?

 

[Rick]

Any differences in lime juice as opposed to lemon juice?

Don't know with regards to orchid culture. I found a paper on the citrate content of various citrus juices and concentrates, and there are subtle differences between lemon vs lime.

But don't know if it will make any difference to orchids.

 

[consettbay2003]

Would bottled lemon juice be acceptable or do you recommend freshly squeezed?