Do lower leaves in a scrog grow really take nutrients away from the re

[SpaceMonkey23]

I have a good resource for you to read it goes into detail about sinks vs sources in a plant. Which leaves are sinks and which are sources. How and why they do what they do etc. I just have to dig it up when I get home so bear with me

 

Thanks dude. I appreciate you making the effort to dig it out.

[forgetiwashere]

First of all, you will need to understand the concept of Source vs. Sink within a plant. Pretty self explanatory, a source is any part of the plant that generates more photosynthate (sugar) than it requires for growth, and a sink is any part of the plant that requires more photosynthate than it can produce (or is producing). What is key to understand with this is that a plant tissue can change from sink, to source, and back to sink all as part of the plants natural process. For example, a newly forming leaf (fan leaf or bud leaf) is always going to be a sink, requiring more sugar to grow than it is currently producing from photosynthesis. . . but once that leaf has reached close to its mature size, it is producing much more sugar than it requires because it is hardly growing at that point. . . .and then again as that leaf becomes older and cells start to get older, the chlorophyll will actually lose effeciency and although the leaf may still look green and healthy, it is no longer generating more photosynthate than it requires to stay alive, and therefore older leaves become sinks again!

There are also parts of the plant which will almost always be sinks. Those are things like the roots (obviously no way of producing photosynthate, but still require it), the flowers on most plants because most flowers contain very little to no chlorophyll compared to a leaf, and seeds are always going to be sinks (the strongest sink).

The important reason I am explaining the Source vs. Sink relationship is because when you have too many sinks and not enough sources, your yield goes down and the overall vigor of your plant is reduced. So to maximize yield and sugar content in the final product (the buds), growers should try to eliminate other sinks as much as possible, while maintaining as many strong sources as they can without risking poor airflow or reduced efficiency with too much shading.

Keeping all this in mind, you can guess that a leaf which is receiving less light (heavily shaded) is most likely going to be functioning as a sink in the plant, drawing sugar away from other sinks that you may be more concerned about such as the buds. Removing leaves above the shaded leaf may give it more light, and maybe enough to start generating more sugar than it needs, but the lower down the leaf, the sooner it will be past its highest efficiency and the closer it is to becoming a sink permanently because of photosynthetic efficiency loss. Therefore, I tend to remove older fan leaves (less efficient) first before I go removing mature newer leaves higher up on the stems because they are more efficient.

Now, once you have removed any leaves that are past their prime, you may still have some fan leaves shading other bud sites, which in cannabis do produce their own smaller bud leaves. The larger fan leaves are MUCH more efficient at producing photosynthate than the smaller bud leaves, and because they tend to be more exposed to air flow they will also transpire more, meaning they help more water and nutrients move through the plant compared to bud leaves which have much less surface area and transpire/photosynthesize much less. So, that means it is better to keep large fan leaves, even if they are shading a bud site or two, because they will function as a source for the bud site (sink) and send its excess sugar to the bud. If you remove the fan leaf, the bud is already functioning as a sink, and so will have to get the rest of the sugar it needs from a different fan leaf on the plant (different source required), meaning a different sink is now getting less than it was because it is sharing its sugar supply from its own fan leaf. . . . this kind of sharing and relocating of sugar pathways takes extra energy in itself, and is not beneficial even if the bud site is no longer being shaded and can produce slightly more sugar on its own from the small bud leaves.
 

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that isnt taken from a peer reviewed journal or anything but it is good information. i hope it helps. to be honest i thought it was from a peer reviewed paper but it was such a long time since i had looked it up i guess my memory was a little off.

 

if you want further information try google scholar that is the most reliable source of good information

[forgetiwashere]

http://link.springer.com/article/10.1007/s004420050229

[billygoat]

First of all, you will need to understand the concept of Source vs. Sink within a plant. Pretty self explanatory, a source is any part of the plant that generates more photosynthate (sugar) than it requires for growth, and a sink is any part of the plant that requires more photosynthate than it can produce (or is producing). What is key to understand with this is that a plant tissue can change from sink, to source, and back to sink all as part of the plants natural process. For example, a newly forming leaf (fan leaf or bud leaf) is always going to be a sink, requiring more sugar to grow than it is currently producing from photosynthesis. . . but once that leaf has reached close to its mature size, it is producing much more sugar than it requires because it is hardly growing at that point. . . .and then again as that leaf becomes older and cells start to get older, the chlorophyll will actually lose effeciency and although the leaf may still look green and healthy, it is no longer generating more photosynthate than it requires to stay alive, and therefore older leaves become sinks again!

There are also parts of the plant which will almost always be sinks. Those are things like the roots (obviously no way of producing photosynthate, but still require it), the flowers on most plants because most flowers contain very little to no chlorophyll compared to a leaf, and seeds are always going to be sinks (the strongest sink).

The important reason I am explaining the Source vs. Sink relationship is because when you have too many sinks and not enough sources, your yield goes down and the overall vigor of your plant is reduced. So to maximize yield and sugar content in the final product (the buds), growers should try to eliminate other sinks as much as possible, while maintaining as many strong sources as they can without risking poor airflow or reduced efficiency with too much shading.

Keeping all this in mind, you can guess that a leaf which is receiving less light (heavily shaded) is most likely going to be functioning as a sink in the plant, drawing sugar away from other sinks that you may be more concerned about such as the buds. Removing leaves above the shaded leaf may give it more light, and maybe enough to start generating more sugar than it needs, but the lower down the leaf, the sooner it will be past its highest efficiency and the closer it is to becoming a sink permanently because of photosynthetic efficiency loss. Therefore, I tend to remove older fan leaves (less efficient) first before I go removing mature newer leaves higher up on the stems because they are more efficient.

Now, once you have removed any leaves that are past their prime, you may still have some fan leaves shading other bud sites, which in cannabis do produce their own smaller bud leaves. The larger fan leaves are MUCH more efficient at producing photosynthate than the smaller bud leaves, and because they tend to be more exposed to air flow they will also transpire more, meaning they help more water and nutrients move through the plant compared to bud leaves which have much less surface area and transpire/photosynthesize much less. So, that means it is better to keep large fan leaves, even if they are shading a bud site or two, because they will function as a source for the bud site (sink) and send its excess sugar to the bud. If you remove the fan leaf, the bud is already functioning as a sink, and so will have to get the rest of the sugar it needs from a different fan leaf on the plant (different source required), meaning a different sink is now getting less than it was because it is sharing its sugar supply from its own fan leaf. . . . this kind of sharing and relocating of sugar pathways takes extra energy in itself, and is not beneficial even if the bud site is no longer being shaded and can produce slightly more sugar on its own from the small bud leaves.

 

.................................................................................................

 

that isnt taken from a peer reviewed journal or anything but it is good information. i hope it helps. to be honest i thought it was from a peer reviewed paper but it was such a long time since i had looked it up i guess my memory was a little off.

 

if you want further information try google scholar that is the most reliable source of good information

Way too stoned.... And difficult to do edited quotes on a mobile device.... But, that article seems to contradict itself a number of times...?

[SpaceMonkey23]

.................................................................................................

 

that isnt taken from a peer reviewed journal or anything but it is good information. i hope it helps. to be honest i thought it was from a peer reviewed paper but it was such a long time since i had looked it up i guess my memory was a little off.

 

It sure is good information, dude. Thank you so much for going to all that effort! That's exactly the sort of information that I wanted!

 

It's interesting, because my current plant has bud sites at the scrog screen level which are shaded by a few fan leaves which poke above the screen, and they are developing beautifully. I am wondering if they will develop good resin coatings without direct light on them, since I've heard that the resin is a kind of 'sunscreen' for the plant. I will see how they go.

 

What I've been thinking recently is that, for really good buds above the screen (ie. if you were concerned about quality rather than total yield), it might even be good to pinch off the buds below the screen and leave the fan leaves to generate energy for the bud sites above the screen. Since the lower buds (sinks) would be gone, any sugar generated from the lower fan leaves would eventually be redirected about the rest of the plant to its other sinks (ie. the buds above the screen).

[billygoat]

Or perhaps lights both sides of the screen ?

[forgetiwashere]

i found the exact study you need to check out only trouble is they want $38 dollars to view it the tight arses.

 

this is the abstract describing the study

 

"

An investigation was made of the usefulness of old leaves and of some effects of light and nutrition upon their senescence. Three experiments were carried out on plants of Cucumis sativus grown in growth rooms and in a glasshouse. In the first, the effects of removing and shading old leaves suggested that they serve a useful function, not as photosynthetic organs, but as sources of substantial quantities of mobile elements which can be exploited to greater advantage by leaves in more favourably illuminated positions. In the second experiment, plants were grown horizontally so that individual leaves could be shaded independently of their neighbours. Shading hastened senescence. In the third, the effects of light intensity, defoliation, and nutrient deficiency upon the senescence of lower leaves were measured. The effects of light seemed to dominate those of nutrition in influencing the speed of senescence.

The results are discussed in relation to the concept of the parasitism of lower leaves, the importance of redistribution of minerals, and the control of the course of senescence."

 

I dont have the money right now but i will probably look into this further later on.

 

here is the link if you decide to go down this path yourself you will just have to register to oxford journals which is free and then select pay per view

 

http://jxb.oxfordjournals.org/content/17/4/762.abstract

[SpaceMonkey23]

...

 

I dont have the money right now but i will probably look into this further later on.

 

here is the link if you decide to go down this path yourself you will just have to register to oxford journals which is free and then select pay per view

 

http://jxb.oxfordjournals.org/content/17/4/762.abstract

 

Wonderful info, thanks so much mate! This is great. It's almost worth paying for...!

 

So to me it seems like the takeaway point from that abstract is that the older leaves are useful, and when they stop receiving enough light the plant will 'retire' them itself at the appropriate point in time (what they mean by "senescence"). Would you guys say that's how you read it?

Edited April 16, 2014 by SpaceMonkey23

[louise]

senescence = biological process of ageing and death.

[forgetiwashere]

Wonderful info, thanks so much mate! This is great. It's almost worth paying for...!

 

So to me it seems like the takeaway point from that abstract is that the older leaves are useful, and when they stop receiving enough light the plant will 'retire' them itself at the appropriate point in time (what they mean by "senescence"). Would you guys say that's how you read it?

 

that is only an abstract so if you really wanted to gain something useful from it you would have to either pay for it or if you know someone who is going to uni get them to search the university library for that paper. uni students should be able to access it free.

 

if i was going to take anything from the abstract it is that deprivation of light is the number one cause of senescence in leaves, which as louise correctly pointed out is early ageing and death. you can probably take that, if a leaf isnt getting light and isnt usefull the plant will remove the usefull nutrients and shed the leaf. other causes of senescence are nutrient deprivation because wen u have a deficiency it will again draw from those reserves.

 

this is the part that i think would be most interesting to read "The results are discussed in relation to the concept of the parasitism of lower leaves" and it looks like they will keep that locked away in the paid section of course.