Yellowing is not neccessarily a lack of N.

[Mr. Greengenes]

Very good read, thanks Mr. Fista for starting this. Amazing points all around the table. In VG's first post, he mentioned that genetics can affect how much plants leaves turn yellow in late flowering. I've seen the same thing, and in very extreme amounts. Some plants will still have very dark green leaves when they reach advanced flowering, others will have lower sunleaves turning all colors of the rainbow. It seems to me that most plants that show fall foliage colors are later finishing and ones that are dark green are fast finishers, but not entirely. Another trait that (somewhat) seems to be related is what I call 'canopy' or total leaf area in relation to the plant size. Plants with few, small leaves and long internodes don't block much light. These seem more likely to hold their lower leaves until they turn colors, while plants with heavy canopy seem more likely to drop lower leaves even before they turn. Anyone else notice this kind of thing?

 

[Clackamas Coot]

Cation exchange Capacity (CeC)

Cation exchange Capacity (CeC)

i am pretty convinced that, in addition to the 'plant led' unlocking of nutrients from organic matter and ferts, there is also microbial process working independently from root exudates throughout the soil. the reasons i conclude this are that it is possible to burn plants using organic additives - and it is unlikely that the plant wound engineer it's own downfall in this way.

so i am suggesting that, alongside the nutrients that the plant generates with it's root exudates, there are also other nutrients in the organic soil that have been unlocked in total independence to what the plant 'asks for'

sorry for the unscientific approach. im just trying fit all the things that can happen into a bunch of processes, and i dont think that everything can be explained by just 'plant led' feeding.

i have more but lets find out what you think of the show so far

VG.

VerdantGreen

I've been studying the soil science behind the CeC (Cation exchange Capacity) of a living soil.

In a healthy soil about 50% of the cations (ions) will be elemental Calcium (C++), Magnesium (Mg++), Potassium (K) and Sodium (Na+) on the base alkaline side and Hydrogen (H) and Aluminum (Al+++) on the base acid side.

These cations are held in place by the soil's humus (humic acid) and clay particles - both of which hold negative charges.

Calcium which carries 2 'extra' exchange sites (i.e. Ca++) can exchange it's cations with 2 hydrogen cations (H) and hydrogen being a base acid that will raise the pH in the soil is now held to the humus and/or clay particles.

What got me trying to figure this out are the claims that the addition of humic acid can and will lower the pH of a soil - whatever that means. The way that it works is that humic acid carries a negative charge as I mentioned before meaning that as it is absorbed by the soil particles it can now begin to grab the floating cations that have been released by the microbial activity and other things like watering. Water is H2O (duh!) and the microbes being aerobic need the oxygen to live and grow releasing the hydrogen into the rhizosphere.

Humic acid stabilizes a soil's pH in another way - by ridding the clay particles of a positive charge if it exists. Clay particles are microscopic in size and are platelets in structure. They hold a negative charge but salts from a number of sources can create a positive charge around the edges forming a 3-way structure that blocks the CeC of the soil. Humic acids remove that positive charge returning the platelets to a negative charge thereby freeing up the compaction of the soil.

Plant roots exude hydrogen cations and are attached to the root hairs. These hydrogen cations are a medium of exchange, i.e. hydrogen plays a very minor role in plant health and overall development. So the hydrogen cation on the root is exchanged for a cation that is available on the exchange sites of the humus and clay.

How phosphorus or nitrogen is either absorbed or adsorbed is not something I know much about. The above is only relative to the specific elements cited in a soil's Base Saturation.

CC

 

[VerdantGreen]

hey MM i agree with what you say, and that was pretty much as i understood it (as far as i do understand these things)
the only thing i would disagree on is that i do believe that organic ferts (not just ionic salts within) can burn plants. surely if the microbes multiply and process an overferted soil then the ions they create can burn the plant. - however i notice you slipped in the caveat 'used properly' in which case you would be right - because if your organic ferts are burning your plants then you havent used them properly

going back to mr F's example in the OP, is it possible that a new (vegging) plant in a pot will be more 'focused' on 'encouraging' the microbes to make N available and thus it can get N from the soil that a flowering plant would not be focused on ?

so basically a flowering plant has prioritized getting P and K (and necessary micronutrients) from the soil, and unless there is an abundance of N fert in the soil there will be little available to the plant from the soil, whearas a vegging plant is tweaking it's rhizosphere to get N that wouldnt necessarily be available to a flowering plant (unless there was more N fert in the soil and it was available to the plant without it having to influence the microbes especially to produce it?)

Mr G - i have totally seen the kind of thing of which you speak
the fan leaves under my scrog screens will be sucked dry and die off very early in the grow when there is no shortage of ferts in the soil. i have stopped bothering to remove branches under the screen as the plant seems to recycle them of it's own accord ( and occasionally those wispy lower branches can provide some reveg cutting material that allows me to save genetics that have turned out to be promising and not been backed up previously.

VG

 

[Microbeman]

VG, Sorry I just don't have time for endless back and forth. If you or others are interested, my thoughts on this are outlined on my webpage (where there are citations to follow which lead to other citations) and elsewhere in this forum.

 

[MrFista]

I'm loving this conversation.

The Nitrate NO2- that plants preferentially take up actually gets converted back to ammonia in the plant (go figure). The Nitrate ion is charged and so a proton gradient in the rhizosphere would set up conditions for active transport of this ion. The means by which a plant selectively uptake molecules is active transport. - "In plants, the uptake of nitrate from the soil is a critical process controlled by complex regulatory networks that target nitrate transporters in the roots. Phosphorylation of the CHL1 nitrate transporter allows the plant root to sense and respond to different nitrate concentrations in the soil" - This is wee proteins embedded in the cell membrane that only allow certain molecules in or out. By this means a plant may police the levels of inputs.

If the ion concentration in the soil is too high it will force the plants via osmosis to start losing water molecules to correct osmotic balance. A plant raises it's osmotic potential overnight by pumping in ions to the roots and when daylight hits the water follows the ions in to restore balance. If you do the opposite, ie: add lots of ions to the soil, the osmotic gradient is reversed and water will exit the plant.

The phyllotaxy indeed plays an important role in senescence. Leaves in shade are always the first to go as they are less useful to the plant (can pick up the remaining far red light but not much else left to them).

The longer finishers display more senescence or colours. I agree with this observation too. Even strains with same finish time but one's a bit more sativa leaning = more colour.

 

[Tropic]

This reminds me of a grow, where I had no other substrate but equal parts rich compost/rabbit manure (quite N heavy). Plants grew very well, and by the end of flower, senescence was obvious. However, after harvesting, I reused the substrate, and as MrFista described in his 1st post, the younger plants took off real good.
First thing that comes to mind is "something is preventing the plant from uptaking all this available N".

Like others, I first thought about root exudates and their interactions with microbes. I didn't find much, but after some research, I came across this article, which deals with senescence in annuals:
http://www.socrtwo.info/senescence.htm

It is a (very) long but interesting read for anyone trying to understand what happens in a plant at that crucial time, I strongly suggest the read. It outlines important physiological changes taking place, at plant level and at cell level. In annuals, flowering induces a nutrient sink to the seeds, which results in plant senescence, for different reasons. Part of this article focuses on seeds sucking nutrients, however it dates back to 1984, deals with annuals in general, and we're growing sinsemilia in most cases. But without a flower there is no seed, so I guess the nutrient sink applies to the flower too. But that alone wouldn't explain the observed senescence by the end of flowering even in N rich soils. The article explains how senescence kills the plant, but not what triggers it.

I also came across this post (in French, but a translator helps), which states that after the early flower stretch (during which great amounts of N are uptaken), the Cannabis plant can uptake significantly less N from the soil, because of the reduced efficiency of N transporters in the roots (in other words, the roots will uptake way less N after stretching is done):
http://fcf.cannaweb.org/fcf/viewtopic.php?f=53&t=53328&sid=332acd77ae62788b1e995b77bacc44ad

Now my question is why do the roots lose that efficiency to uptake N? According to the above post (which cites its sources at the end), the important uptake of N during the stretch phase "tires" the roots, more specifically the N transporters. Thus, the plant will lose most of its ability to uptake N after the stretch. However, it has plenty of N stored in its stems, petioles, and leaves, which will later be used as the flowers become the main nutrient sink in the plant. It also outlines that during a reveg, it is, in most cases, more beneficial to restore a healthy root system before adding any N to the soil, I found it to make sense.

Just a side note, when we say that a plant is yellowing too early, or too late in flowering, we must not forget that we are judging things from our Cannabis consumer point of view. Ideal time for senescence is not necessarily the same for the smoker and for the plant.

 

[Microbeman]

Just a side note, when we say that a plant is yellowing too early, or too late in flowering, we must not forget that we are judging things from our Cannabis consumer point of view. Ideal time for senescence is not necessarily the same for the smoker and for the plant.

there are triggers built into plants which cause an early fruiting brought on by a variety of events or environmental swings, which may account for your 'early' yellowing.

Good insight my friend

 

[MrFista]

Interesting article. I think the author might consider that annuals might not be adapted to survive aseasonally hence they are annuals. Pure survival. Annuals have not adapted themselves to produce cold/heat shock proteins or whatever other aseasonal adaptations they require to survive averse conditions. Annuals will become perennial in the right conditions, meaning, with conditions suited to the adaptations the plant currently has it does not need to die. I've seen a few wild revegged 'annuals' in my time. Plants 'choose' to flower and die as the other option is death without reproduction. Perhaps...

I like this bit "explanation b, that senescence ensures more rapid transport of nutrients and minerals to the seeds than would otherwise occur. This points directly to a mechanism of frost avoidance. If the seeds were still in development (because of a longer development time produced by not senescing) and frost hit they would be killed."

This is helpful to explain a few anomalies growers get - "Death by aging always produces a bell shaped death curve, with a few dying young and a few dying old and most dying at an intermediate age."


Reveg - replace 'depodding' with 'harvesting your buds'...
"Molisch found that depodding treatments greatly delayed senescence. This suggested to him that the pods were killing the leaves by draining needed nutrients from the seeds. Careful work by Leopold (1959) confirmed these results in soybeans and showed that depodding delayed senescence in spinach as well, though "to much lesser extent. Once spinach plants had bolted, senescence was unstoppable."

I have a 2 year old spinach plant. it bolted, it hit the gutter of the roof. I cut the top off for seed and left about a metre of the plant there. It's still alive the next year, I'm eating greens off it. If the conditions are favourable the annual doesn't have to die.

The mystery hormone made in the leaves that he talks about is auxin. Auxin travels from cell to cell hence is not affected by cutting off the vascular tissue. Auxin signals ethylene in the senescence process, ethylene is a gas and diffuses outwards from it's source, no petiole manipulation will halt this process.

LOL - ok he got to auxin eventually...

The auxin has several roles determined by photosensitivity eg de-etiolation. The photoperiod will trigger it all off. Nice find on the zeatin being catabolized, that explains a lot of why I'm still confused how cytokinin:auxin gradients work - damn gradient doesn't mean dick if another molecule is destroying the hormones. So the zeatin (cytokinin) gets taken out in senescing organs thus auxins build up. YAY! That's why clones from reveg root so well. I just finished a cytokinin experiment and the control (cotyledons with plant produced auxins no root system so no cytokinins) senesced lightly and threw out loads of roots while the cytokinin culture had no roots, and no senescence, but did a lot of cell division (52% increase in size in 2 weeks).

IAAX - what is that a halophile on a hormone?

The stretch is also related to auxins and one other hormone. The photoperiod must induce an even flow of auxins (in even light conditions) across the meristem to enact the upright growth we see occuring. This is rapid cell elongation.

"When a cell is dead, it can obviously no longer actively transport." -This is just plain wrong. Sclerenchyma cells are functional when deceased. Plants in flooded conditions kill off root cells making tubes for gas exchange. In the context of a leaf cell - it depends on which cell it is!

And I love a wee bit of backup... to delay senescence " if the final senescence hormone works by breaking down CK and IAA then exogenously (externally) apply these hormones to the plants."

Like I've said earlier - don't put seaweed on your flowers unless you want them late.

 

[VerdantGreen]

awesome posts from fista and tropic - really set me thinking, and ive been pondering all this as ive stripped out some under-performing ornamentals from one of my client's borders this morning.

some further possibilities/thoughts in addition to what has already been said.

most of my thoughts ultimately lead back to genetics. as has been mentioned earlier in the thread, shorter flowering plants (indicas and indica dom) tend to senesce more convincingly than longer flowering ones (sativas and sativa dom)
i think that two factors will play into this and the general N conundrum. Sativa roots tend to grow for much longer into flowering than indica roots, and because Nitrogen is made available by microbial action, then as soon as those roots stop growing their ability to take up nitrogen is going to be diminished as they deplete what is available in the existing rootzone- this can be seen easily when a plant gets rootbound, N is the first thing to go short. P on the other hand can be transported to the roots by fungal hyphae so P from the soil mass in general can be delivered to the roots by an efficient process even if the roots have stopped growing. i guess N ions (in the soil but not the rootzone) may move around a little by diffusion and physical movement of the water in the soil by watering but i think that would be much more limited.
senescence is a pretty complex process in that it has (from my research and observation) quite a few triggers - and quite a few genes that will contribute to the overall effect.
cold weather is a major trigger to senescence in general and here again genetics will come into play. sativas, especially the tropical ones, will not necessarily be triggered into senescence by cold in the same way as indicas - because their genetics will not be programmed for it (the cold may still damage them though of course)
certain ornamental plants of tropical progeny - although not annuals - will basically flower and flower until the first frosts kill their top growth overnight - they just dont know that they should start to go into dormancy when the weather gets colder. examples would be dahlias, gaura, verbena bonariensis and many more.

following on from this i would say that senescence is much more pronounced outdoors anyway -particularly in temperate regions.
another likely trigger would be the lengthening of the dark period.
indoors you have more even temps, unchanging dark period once you have gone to 12/12. in these cases getting your plants to yellow towards the end may be more of a challenge - especially if you are growing sativas - and i strongly believe it is in these conditions that the amount of N ferts/amendments in the soil is of much more importance.

what really interests me is the question of how much influence we have over a plant growing in organic soil. obviously the plant is in the driving seat to a large extent but as someone who weighs out the nutrient sources in my soil by the gram - trying to tailor them for each strain i grow (often over and over again) i know for sure that this, along with many other factors, will influence the final outcome.

VG

 

[Microbeman]

Just a quick note to stimulate more research/thought. N is not just delivered by bacteria/archaearotozoa cycling but also by fungi.
Protozoa and bacteria can travel quite long distances in the soil provided there is moisture and porosity.

 

[DARC MIND]

heres a good read on plant growth regulators
http://www.biology-online.org/11/10_growth_and_plant_hormones.htm
some might find: seasonal responses, photoperiodism,fall colors & response to lenght of day/night to be a good read.

to me, it seems that genetic and environmental factors play the ultimate role w/ senescence.
i find that most of all the sats(that ive grown), fade just fine with amended soil,mulch & ACT program. since they arnt big feeders, i go really light on amendmening media and let the quality compost and casting support the soil/plant needs.
mulch and or ACT but i agree w/ VG, much easier OD and i think its from the slow change to 12/12 plus temps.

 

[MrFista]

The plant seems to dictate the terms allright. Much like it uses hormonal cues to determine an individual cells roles it uses environmental cues to determine the role of the plant entire. In the case of senescence, the cue is phototropism. A set series of responses take place, the severity of which are determined by individual environmental factors and genetics.

MM - N from fungi too. The carnivorous fungi I understand, is there a second symbiosis or is it just nutrient cycling from fungal predation? What search terms should I use in the data bases, which journals do you prefer for food web type content? Sorry bout all the questions I know you are a busy man.

 

[Mr. Greengenes]

Whoo, cool thread, very fun read.

 

[MrFista]

Tropic - where can I find a freeware translator that is trustworthy, scuse me ignorance. There's a hot french girl at uni, maybe if I drag her home...

 

[Clackamas Coot]

MrFista

You might want to give Scirus.com a run for searching. It's a science-only web search engine meaning that you seldom get a blog or a manufacture's web site but rather peer-reviewed studies from around the world.

I think you'll find it helpful.

CC

 

[Microbeman]

Mr Fista,

When doing a search for anything concerning fungal nutrient transfer, it is always good to include David Douds in the search term.

http://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=171448

Citation: Jin, H., Pfeffer, P.E., Douds, D.D., Piotrowski, E.G., Lammers, P.J., Shachar-Hill, Y. 2005. The form of nitrogen stored and transported by the extraradical hyphae of an arbuscular mycorrhizal symbiosis. New Phytologist. 435. pp. 819-823.

Interpretive Summary: Arbuscular mycorrhizal (AM) fungi can help deliver nitrogen to crop plants, thus lowering the need for excessive amounts of synthetic fertilizers. Presently little is known about the preferred source of nitrogen taken up by these fungi nor is there any knowledge of how it is transported to the host plant. We have pursued the process of how ammonium is used in the delivery of nitrogen in the symbiotic and germination phases of the AM life cycle. The fungus readily takes up ammonium in the symbiotic state and quickly converts it to arginine, which is transported to the host root. The amino acid, arginine acts as a store of nitrogen and moves it in both directions between the fungus and plant. It remains intact within the hyphae until the fungus becomes nitrogen limited. Arginine is easily taken up by the roots but uptake is limited in the associated hyphae and spores. Arginine is principally a 'mover' of nitrogen from fungus to the host. These findings give us insight into how AM fungi take up and transport nitrogen to their host crop plants. This information will allow us to determine the most efficient methods for utilizing AM fungi for low input nitrogen utilization.

http://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=170877

Citation: Govindarajulu, M., Pfeffer, P.E., Jin, H., Abubaker, J., Douds, D.D., Allen, J.W., Bucking, H., Lammers, P.J., Shachar-Hill, Y. 2005. Nitrogen transfer in arbuscular mycorrhizal symbiosis. Nature Magazine. 435. pp. 819-823.

Interpretive Summary: The uptake by plants of mineral nutrients from the soil is greatly aided by associations with mycorrhizal fungi which grow into and extend out of their roots. As well as benefiting plants by aiding phosphorus uptake from the soil, AM fungi can take up and transfer substantial amounts of N (the availability of which frequently limits plant growth) to their host plants. However despite the identification in AM fungi of enzyme activities and genes identities of primary nitrogen assimilation and catabolism we know very little about how nitrogen is moved from fungus to plant. In particular we do not know the form in which nitrogen is translocated within the fungus from the hyphae in the soil (extraradical mycelium) to the fungal structures within roots (intraradical mycelium) or the form transferred to the plant. This ignorance limits our understanding both of underground nitrogen movement worldwide and of nutrient exchange in what is arguably the world's most important symbiosis. In this study we have established that nitrogen is transported from the external fungus to the internal fungus located in the roots of the plant as the amino acid arginine. Final transfer of nitrogen to the plant cells is made in the form of ammonium. This information is critical to our understanding of how and in what form to supply nitrogen to mycorrhizal plants to optimize nitrogen utilization and plant production.

In the following they used Glomus intraradices which is one of the two (known) fungi to be mycorrhizal with cannabis.

http://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=167259

Citation: Jin, H., Pfeffer, P.E., Shachar-Hill, Y., Douds, D.D., Piotrowski, E.G., Lammers, P.J. 2004. The form of nitrogen stored and transported to the ri t-dna carrot root by the extradical hyphae of am fungi. Meeting Abstract #581.

Technical Abstract: We studied the form of nitrogen stored and transported by the fungal partner in the arbuscular mycorrhizal (AM) symbosis. The AM fungus Glomus intraradices was cultured in association with transformed roots of Daucus carota L. in petri dishes with two compartments. [15N]-NH4Cl, [guanido-15N]arginine, [15N413C6]arginine were added to the fungal compartment. Free amino acids of the extraradical mycelium and mycorrhizal root compartment tissue were analyzed with GC-MS after 1,3 or 6 wks of exposure. After exposure to [15N]-NH4 the main free amino acid in the extraradical mycelium was arginine, which had 99% enrichment in 15N. The concentration of arginine was about 200 nmol g-1 d.wt of hypha, and represented more than 90% of the total nitrogen in free amino acids. [guanido-15N] or [15N413C6] labeled arginine added to the fungal compartment, was observed intact in the free amino acids of the colonized root tissue. This indicated that arginine can be taken up directly by extraradical hyphae and transported to the colonized roots. Thus arginine is one form of nitrogen stored and transported to the root host by the extraradical hypha of AM fungi. Moreover, the arginine transported to the mycorrhizal compartment was broken down into ornithine and urea, consistent with our previous hypothesis that the urea cycle might be active in nitrogen transport in the AM symbiosis.

You will find this list interesting;

http://www.ars.usda.gov/pandp/people/people.htm?personid=1437

 

[Clackamas Coot]

Just an observation about a bagseed strain that I grow - the 'T.O.' deal. It never, ever turns yellow. You could run this strain until each and every trichome was the color of root beer and the leaves will stay green.

Even with professional growers running hydroponics and at least 3 different 'nute programs' cannot get the plant to yellow off.

Probably a sign of inferior genetics is what I'm thinking.

CC

 

[Mr. Greengenes]

My White Wizard strain is mostly W. Widow but I smacked it up for 6 generations or so. I noticed the fall foliage colors early on and tried to preserve, even amplify that trait. I guess you could say that I don't really pay much attention to cultivational methods for removing leaf color. I probably should, but since it's always been my habit to fix stuff through breeding, I guess I just went that route instead.

I'm still not totally convinced that plants that stay dark green until harvest taste any worse, though. I'm thinking of one cut we have in particular, the 'J7'. J7 is an F1 hybrid of a common Jack Herer clone mom and some of my WW males. A few commercial growers near me are running it now, and everyone loves it to death. No one, to my knowledge has ever got the J7 cut to turn yellow before harvest, yet it's grapefruity smell and taste are one of it's most desirable features. I think it's probable that you're more of a connoisseur than us southlanders Coot, but I'm pretty sure you'd give the thumbs up to a bowl of J7 if you were here now. Maybe not. Maybe you'd say, "Man, why din't you guys flush this first?"

 

[VerdantGreen]

some strains are like that.
grow them in soil so weak you have to sit up with it all night
and still they stay green

edit - as mr g says though they dont necessarily taste green

i have a handful of mr. G's white wizard that im itching to grow. sometimes i wish i wasnt such a wuss and had the balls to do a bigger grow...

 

[VerdantGreen]

the other massive factor in how much food your plants need (and thus if they yellow or not) is light levels. the more light, the more food they eat because the bigger they get.

so many variables...