Bleached leaves. Too much light or nutrition problem?

[Bjorn]

Bjorn Although expressed as CaCO3 equivalents, at the pH ranges and gas saturation levels we are working with, the predominat ion is bicarbonate (which I guess is what you are calling hydrogencarbonate, HCO3).

Calcium carbonate is esentially insoluble (until pH <<4.0) I can't get it to melt until pH 2.0 in a reasonable length of time. But if you want to generate measurable alkalinity fast, add some baking soda (NaHCO3) to some RO water, and the math is easy.

The conversion from alkalinity as CaCO3 to bicarbonate ion is just a factor of 1.22. So "alkalinity as CaCO3)"X1.22 will give you bicarbonate ion concentration.

I know that calcium carbonate essentially is insoluble, the use of it is again just a convention. Just like presenting NPK in the fertilisers. Nobody think that N is there as nitrogen and K is not there as metallic potassium.
The below link is describing many of these aspects in detail.
http://books.google.no/books?id=ytG...epage&q=nitrogen assimilation orchids&f=false

 

[Rick]

The end point of the titration is just a matter of convention. It was chosen so to represent a value to keep to doing quick tests on that matter. Making real titration curves gets very difficult as the point of equivalence gets smeared out due to all the other salts except calcium carbonate that sums up the alkalinity. As a curiosity can be mentioned monosilicic acid that is the silicon species that is absorbed by plants.

Sure, but at some point are we getting woried about a very small effect outside of the relevance to 90% of the world our plants live in?

The vast majority of life exists around water explained by only 7 major ions taking up 99% of the inorganic chemistry. Also the majority (certainly not all) of life opperates between pH 4-9.

Generally we don't need to get to the precision of finding the Higgs to figure out most of natures operations. (at least in my GH)

 

[Rick]

In soil, Bill Argos presentation is probably correct, if all ammonium gets oxidised, but I am uncertain whether it is applicable for orchids.

That could be the focus of the issue since for one there are 30,000 species of orchids in almost as many different habitats, and secondly we are trying to grow orchids in conditions more applicable to potted mums.

From the handful of papers I have been able to find/read on orchids. It looks like offering a diversity of relatively low concentrations of N source is desirable.

It doesn't take a lot of anything in particular. It seems like working at concentrations of N that are not environmentally relevant turn the exercise into a pot management exercise rather than a plant physiology exercise.

 

[Ray]

1) Bill's article may have been in the IPA journal, but his background is in terrestrial plant nutrition, so those reactiuons are far more applicable to soils.

2) I am beginning to think that frequent, low concentrations are the keys.

The solutions reaching the plants are verry dilute - I have seen numbers of 5 ppm TDS for throughfall, and 25 ppm for "trunk flow". It makes sense that the first to cascade through would be the most concentrated, hence the "gold vein" the orchids would try to harvest. No too suprisingly, velamen has sites the immediately capture ionic species - I envision them as being the "baleen filtering the krill from the sea water".

So once those sites are occupied, it is not very efficient to dump more ions on them. Then, as it will take some amount of time for the trapped ions to be absorbed, a later-, but still dilute solution wil replenish the velamen.

 

[Rick]

So once those sites are occupied, it is not very efficient to dump more ions on them. Then, as it will take some amount of time for the trapped ions to be absorbed, a later-, but still dilute solution wil replenish the velamen.

I was looking at another corn article that seemed to come up with similar conclusion. Pulsed low nitrate input was better than constant dose. The hypothesis was that root uptake was fast, but the enzyme pathway (in the leaf/shoot tissues) just gets clogged up (backlogged) relatively fast, and idles until stored nitrate goes down.

 

[Rick]

http://hortsci.ashspublications.org/content/27/6/680.6

If someone wants to buy the whole paper (or find it otherwise) this could be a good one.

These authors doubt the hypothesis that the bottleneck is the velamin, but indicate the relative low activity of the N utilizing enzymes in the tissues for the low uptake rates in orchids.

But its another paper that shows the importance of amino acid uptake in orchids as a significant source of N.

 

[eggshells]

http://hortsci.ashspublications.org/content/27/6/680.6

If someone wants to buy the whole paper (or find it otherwise) this could be a good one.

https://dl.dropbox.com/u/993342/680.6.full.pdf

 

[Ozpaph]

https://dl.dropbox.com/u/993342/680.6.full.pdf

If you'd be so kind as to summarize the 944 abstracts for me that would be appreciated :rollhappy::rollhappy::rollhappy:

 

[Stone]

1) Bil

2) I am beginning to think that frequent, low concentrations are the keys.

Yes all the chemistry is interesting (up to a point) but is will it grow better paphs? I don't think so A good p/mix and a bit of fertilizer in the correct moisture/environment. The simple method of sitting a few plants in a saucer of water did FAR FAR more than any combination of fertilizer ever could.

 

[Ray]

Yes all the chemistry is interesting (up to a point) but is will it grow better paphs? I don't think so A good p/mix and a bit of fertilizer in the correct moisture/environment. The simple method of sitting a few plants in a saucer of water did FAR FAR more than any combination of fertilizer ever could.

I think we may be ignoring the role of frequency of watering.

As Rick mentioned a while back, water and air are part of the makeup of the plant, too.

> C, O, H, & N are present at levels of 1-7% of the overall mass (C is about 50% of the dry mass)
> Ca, Mg, P, K, & S in the 0.1-1% level
> Everything else is ppm's.

Watering not only provides chemical building blocks for the plants, but it tends to flush fresh air through the media at a rate faster than natural diffusion. I think that plays a role in Rick's basket culture observations.


Ray Barkalow
Sent using Tapatalk

 

[Rick]

I think we may be ignoring the role of frequency of watering.

(C is about 50% of the dry mass)

Ray Barkalow
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Yes and since that carbon is hydrolized, the carbon products (i.e mostly celulose, sugars) make up about 95% of the dry mass. N is incorporated into carbon structures at 3% of the total dry mass.

 

[Rick]

http://www.ncbi.nlm.nih.gov/pubmed/16667499

Ok for the mechanistic folks.

This article shows that the optimal pH for Nitrate Reductase in spinach is 7.0, and is also suppressed by higher ionic strength (TDS).

Nitrate reductase is the enzyme pathway responsible for reducing nitrate to ammonia in plants so it can be used to make amino acids.

the article also contrasts the NR activity in spinach with that of a unicellular algae (which operates more efficiently at a higher pH and TDS).

This means that different plants can have different optimal pH/TDS conditions for nitrate use. Which should be based on the natural/ecological conditions they are evolved to be in. Orchids are generally found in low ionic strength environments, so I wouldn't expect their nitrate reductase system to operate more like chlorella than spinach.

Also these are cellular conditions in this paper, not pot conditions. But if pot conditions are extreme, its hard to meet cell conditions. If you add a bunch of bicarbonate to a pot its going to be hard for the cell conditions to stay maintain a pH of 7.