low potassium concept is not sustained by analysis

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I don't get that interpretation at all. In light of this article I see nitrate reductase and pH increase by K as competitive processes.

http://link.springer.com/article/10.1007/BF00383860

Some where you need some protons to knock down all the alkalinity produced by K and nitrate reduction to generate ammonia. Given the large amounts of N (as NH3 recommended for high pH pot applications) applied to pots relative to the amount the plant actually uses, it may be another case of nitrifying bacteria to the rescue as they release protons in the process of converting NH3 to NO3.

The algae paper is coming up with the hypothesis of proton/charge balance is maintined across the plasma and chloroplast membrane by counter- and co-transportation, isn't it? I think it's trying to say that K is not involved in this process.

While I do not know why high pH is required for rubisco (RuBP carboxylase), the text says that to achieve high pH in stroma, K+ is pumped in across the chloroplast envelop, and H+ is pumped out from stroma (Wu et al 1991; Plant Physiology 97: 580-587. So inside of the chloroplast, both K+ and nitrite (NO2-) is required to have smooth light+dark reaction, so this seems to be synergism, isn't it? The nitrate reductase (which converts NO3- to NO2-) is cytosomic enzyme (not in chloroplast), and nitrite (NO2-) is transported into chloroplast, where conversion to NH4+ occurs as a part of photosynthesis electron transport chain. With regard to the overall proton balance, isn't NADP/NADPH is involved in it?

I'm still learning this (and I'm not so good at chemistry), so I may be missing your points, but it's kind of fun to learn about plant physiology through a hobby.
 
Although lots of the Ca ends up in cell walls it also is used metabolically, and yes it is a poor intracellular transport (but obviously not 0 since it ends up in the plant to the greatest degree in wild plants). However its also odd that in the case of the Panamanian epiphytes, Mg (one of the "phloem-mobile" group) was not recycled at all, while while Ca was still recycled at the rate of 15-20%. Now from an evolutionary standpoint if Ca was limiting environmentally wouldn't it make sense to come up with an energetically feasible way to recover it (instead of wasting it with growth)?

The Na thing was postulated by Xavier. My textbook is too old too.

You are right, it ends up with the cost of recycling vs the requirement/availability ratio. Even the cost of recycling is high, once required elements are not available, they should evolve to have some mechanisms of recycle (if it is possible). Here in interior Alaska, we don't really recycle paper/aluminum/plastic/metal because the cost of transporting them to recycling plants is too high. But once some necessary stuff is scarce, recycling become cost effective. Some agriculture researchers are artificially selecting for genotypes with higher recycling (White and Brown 2010; Annals of Botany 105: 1073-1080), so natural selection should work in a similar way.
 
Keeping in mind this is leaf litter and research has shown that tropical plants variably recycle minerals out of the leaves before senescence. The highest rate of recycle was for P (60% recover in Panamanian epiphytes) with about 30-40% recycle of K and N. Ca and Mg were not readily reabsorbed. I have no information about internal re-absorption of anything other than NPK Ca Mg.

Recycle rates give you an idea about what is rare and what is important to the plant to recover.
Sorry Rick. I cannot simply accept that at face value.

It seems to me that material that were accumulated to a significant degree would be the ones most likely to remain in the leaf litter. How they are accumulated can vary from active to passive, with the passive absorption being related to concentration in the local environment and the relative ease of absorption. Those easiest to absorb are probably also the easiest to extract from the leaf litter, making them available to easily absorb by living creatures.

Important? Possibly. Merely easily absorbable? Also possible.




Ray Barkalow
Sent using Tapatalk
 
A high pH is needed for RUBISCO to function because of the organic chemistry it is catalyzing. The reactions take place only under a low proton concentration.

It is very dangerous generalizing from experiment to experiment. Plants are very diverse, biochemically speaking, and reactions that are occurring in one plant may not be occurring in another species. This is even more the case when it comes to cyanobacteria which are billions of years removed from plants.

Also, plants have a plethora of ion channels. Some are run by ion exchange (one ion in, another out), these are antiports. Then there are synports where two ions are imported together. These can be a cation/cation, cation/anion or anion/anion. There are also channels/pumps that are run on ATP or NADH supplied energy. Some pumps/channels are doing the same job but are expressed in different locations and are also expressed by different genes. The whole story gets very complicated fast as one genus may use pump A in the chloroplast while genus B won't have that pump but a different one doing a similar reaction. We can't generalize about plant metabolism when it comes to the specifics.

What does hold is the physics governing these pumps. This described by the Nernst Equation (taken from Wiki):
4c767eef648cf4f2007111d25fe5921d.png
. As you can see the major effectors are the internal/external ion concentrations, the difference in charge between the membranes and the permeability of the membrane to the ions. If the movement can't occur spontaneously, then a power source is needed to drive the movement. If you keep flooding the cell with K+ then the membrane will be less permeable to NH4+ and Ca2+ etc... and more power will be needed to import these against the electrochemical gradient. This holes equally true if there is an excess of Ca2+ or NH4+ inside the cell which would make it hard to import K+ etc...

How much the plants can vary the relative pump/channel concentrations in the membrane to transport specific ions is, in the case of Paphs, an unknown. If they can decrease K-channels and increase Ca-channels then the effect of K concentration may be of little importance... Each plant will have evolved to either cope with the change in ions in its environment by evolving the specificity of each ion to the channel or the amount of channels/available; or the plant (unable to evolve specificity or pump quantity) simply survives in a specialized niche which is just right for its delicate biochemistry. Generally, living organisms maintain their enzymes/pumps/channels etc... operating very far from the equilibrium point so organisms have a lot of flexibility to adapt to changes in the external or internal environment without bothering about changes in gene expression. I don't think we have any idea just how flexible our plants are... but the various medium and fertilizer experiment suggest that there is a range and it is not very robust.

Whether the issue is absolute K or NH4+ concentration, or how these concentrations affect the metabolism of other nutrients is very difficult to pry apart without large, well thought-out experiments. In the case of orchids these would be very expensive experiments as the plants are no as easy to work with as the normal experimental model plants that grow easily and whose roots and leaves are readily available for analysis.

I think the best we can say is whether the fertilizer/substrate method works or not. How it works will remain a mystery until you get an orchid growing president in the white house to set up the National Orchid Research Institute funded lavishly with tax-payer dollars to benefit Dutch commercial orchid producers. :p
 
Tyrone, thank you very much for the detailed explanation! After reading your earlier comment about the cation channel/transporter of K vs NH4, I was starting to read about it. These two molecules have similar size/property, so the same channel could be used, right? Also it was mentioned that in terms of transport from rhizosphere into root cells, NH4+ could compete against K uptake, but K doesn't inhibit NH4 uptake. This is partly due to gene expression regulation of a transporter genes by [NH4] but not by [K]. I thought that this is interesting, but again, as you mentioned, this may not be true in orchids. As I read more about these, I started to agree with Mike (Stone) that mixture of NO3 + NH4 seems to be the safest bet (although I have a suspicion that much higher concentration of NO3 than 50:50 is a safer bet after considering possible problems of NH4).
 
I started to agree with Mike (Stone) that mixture of NO3 + NH4 seems to be the safest bet (although I have a suspicion that much higher concentration of NO3 than 50:50 is a safer bet after considering possible problems of NH4).
I remember me have read someplace that ideal ratio NNH4 / Ntotal in hydroponic culture was 1/6 (83 % NNO3: 17 % NNH4). Reason is probably not physiological but chemical (pH stabilization due to both forms assimilation of nitrogen).
 
There are things that are, again, confirmed, like the Mn quantity being on a standard 10 times higher than the Iron. This fits most analysis of wild orchids, not only Phalaenopsis, where Mn is always much higher than Fe.

Xavier, This relationship between Mn vs. Fe is interesting. But what is going on? is the Mn (and B for that matter) far more common in the natural substrate (available) to the plant OR is the Fe at very low levels in the substrate compared to the Mn? You mentioned some species like the early sanderianums being very susceptible to Fe toxicity. Was this due to the Fe being supplied as chelate or was Mn level supplieid to low? Obviously if the pH is too low the Fe can become toxic but so can the Mn so it must not be a pH issue.
 
I remember me have read someplace that ideal ratio NNH4 / Ntotal in hydroponic culture was 1/6 (83 % NNO3: 17 % NNH4). Reason is probably not physiological but chemical (pH stabilization due to both forms assimilation of nitrogen).

The reason for the high nitrate in hydroponics is because of the very low cation exchange of the solid media so the risk of NH4 toxicity is higher. Also the main way to supply the Ca is from CaN03. I think pH is adjusted automatically in big commercial setups (but not sure)
 
Xavier, This relationship between Mn vs. Fe is interesting. But what is going on? is the Mn (and B for that matter) far more common in the natural substrate (available) to the plant OR is the Fe at very low levels in the substrate compared to the Mn? You mentioned some species like the early sanderianums being very susceptible to Fe toxicity. Was this due to the Fe being supplied as chelate or was Mn level supplieid to low? Obviously if the pH is too low the Fe can become toxic but so can the Mn so it must not be a pH issue.

In short, so far all the analysis I have ever seen of orchids from the wild and nurseries had always much higher levels of manganese than iron, though in some hydro setups, clearly the iron was supplemented at higher level. However, when the manganese was dropped by reducing the concentration, or iron pushed up heavily, the plants started to have very severe problems. I am certain it is normal for Mn to be much higher than iron for orchids ( and surprisingly some other crops).

There were some cases were Mn was twice Mg in fact, and the plants were superb. It occured on species from vastly different Asian countries, so there is something behind the Manganese that is not well understood... It could be more a 'macro' inside the plant, but needs to be supplemented at low rate to the plants. If Magnesium is a 'macronutrient', looking at some analysis, Manganese should be considered the same...
 
Could the reason of the high concentration of Mn be that those analyzed orchids are using nitrates than ammonium as the main source of N? Traditionally, Mo requirement is thought to strongly depend on the mode of N supply, right? One of the four known Mo-containing enzymes is Nitrate Reductase, and NO3 without Mo causes severe effects on growth but NH4 doesn't seem to depend on Mn.
 
The reason for the high nitrate in hydroponics is because of the very low cation exchange of the solid media so the risk of NH4 toxicity is higher. Also the main way to supply the Ca is from CaN03. I think pH is adjusted automatically in big commercial setups (but not sure)
Yes in tomatos production greenhouses, pH is regulated via remote regulation system: pH electrode/computer/fine metering pumps.
 
@Xavier
Now do you use the solution of micro-nutrients described in your publication " Paphiopedilum culture and distribution, concepts and guidelines "?
In this solution you have 0.4 ppm of Iron and nearly 1 ppm of Manganese.
 
@Xavier
Now do you use the solution of micro-nutrients described in your publication " Paphiopedilum culture and distribution, concepts and guidelines "?
In this solution you have 0.4 ppm of Iron and nearly 1 ppm of Manganese.

Yes indeed... I use that one still. But many hydro setups have up to 2-3 ppm of iron and 0.2-0.4 ppm of manganese, still the manganese is higher than iron in the foliar analysis... Cymbidium comes to mind. Though when I advise, I correct that quickly...
 
So does an epiphytic order, living attached to a tree branch, naturally see more nitrate or ammonium nitrogen? How about one living in the leaf litter, or in the sediment in between rocks?


Ray Barkalow
Sent using Tapatalk
 
@Xavier, thank you for your fast response.
Your values for Iron and Manganese (versus Klite or MSU) are very high but when I calculate the Total Nitrogen content of the solution with which you are feeding I find 180 ppm (NNO3 + NNH4). Probably its conductivity is around 800 µS ... very hight ... is this correct?
PS: I consider that the weights for AN, Potassium nitrate .... are also for one liter.
 
So does an epiphytic order, living attached to a tree branch, naturally see more nitrate or ammonium nitrogen? How about one living in the leaf litter, or in the sediment in between rocks?


Ray Barkalow
Sent using Tapatalk

According to this article which was mentioned before, it seems to be about 1:1 in this study (on the tree):

http://aob.oxfordjournals.org/content/75/1/5.short

and organic N is about half of NO3.

These orchids seem to show slight preference for NH4 over NO3 (according to Table 2). This paper is rather statistic-free, so the preference should be considered as just a "trend". The net absorption of organic-N was small or negative.

But I'm guessing that different host tree, region, proximity to human activity could influence the ration in stem flow. So the ones with high Mn in Xavier's study could be exposed to a different ratio.

On the ground, nitrification by bacteria could change the ratio toward NO3. Nitrification is generally rapid in warmer, well-aerated, less acidic soil. So, this is another factor.
 
The algae paper is coming up with the hypothesis of proton/charge balance is maintined across the plasma and chloroplast membrane by counter- and co-transportation, isn't it? I think it's trying to say that K is not involved in this process.

The issue missed is that plants have no way of regulating K. Plants don't have kidneys. The element is regulated via its low availability in the environment. In orchids K requirement forced adaptation of living with low carbohydrate production. Seeds and fruits with no starch storage, deceptive pollination flowers with no food rewards.....

In the algae paper K is mobilized well beyond its utilization capacity forcing pH beyond metabolic limits. In a related paper by the same author (I'm not sure if its one of the 3 or so all from the same series I linked to you), cellular pH is raised to metabolically lethal levels. This particular paper was rather detailed on the mechanisms of K inhibition on photosynthetic function.

These authors were/are planning on using K to eradicate these algae from places they are considered nuisance or detrimental. The K dose to control macrocystis would be somewhere between 200 to 300ppm. At those concentrations of K, that would also wipe out the bulk of the mollusc fauna in those waters (so sent a warning email to the authors of unintended consequences).:wink:
 
According to this article which was mentioned before, it seems to be about 1:1 in this study (on the tree):

http://aob.oxfordjournals.org/content/75/1/5.short

and organic N is about half of NO3.


Did anyone notice that the total of any one of these forms of N (ammonia, nitrate, "organo) was less than 2ppm!! Table 2 page 11

So what's going on when we apply these things at 10,50, 100, 200ppm?

You're just managing a cesspool, not growing orchids:poke:
 

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