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Cause of death?

idris

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As I understand it, plant leaves die when :
- "converting" from emersed to submerged.
- "converting" from submerged to emersed.
What is this "conversion" and why do the leaves die?
 

Bobtastic

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BigTom said:
I started typing a reply and then realised that Darrel or Ceg will undoutedly be along shortly and will do a much better job than I can :p
Just cos the gods will come down and "educate" the heathens is no reason for the heathen to give it ago!

As I understand it, from my limited biological knowledge, there is differences it leaf structure depending on whether it grows in or out of the water. It will most likely be to do with allowing air/water to access the internal structure of the leaf for Co2 exchange and the requirement for greater structural rigidity out of water.
 

ghostsword

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I believe that submerge leaves have bigger pores to absorb co2 than the emersed ones, also they will need to get more clorophyl so that they can make a better use of the light.

Also due to the water presure their capillary is different from emerge leaves.

Open to be educated, *duck* :)


.
 

ceg4048

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Bobtastic said:
Open to be educated, *duck* :)
How about some Peking Duck? :p
As Bob mentions, emergent leaves are fundamentally equivalent to terrestrial leaves because they live in air and therefore must be optimized for that environment.

35_18-LeafAnatomy-L.jpg


Since there is no hope of being buoyant in air, the leaf must have structure to support itself, so it uses rigid veins for structural support. These veins are subdivided into the Xylem (used to transport water and it's nutrient solutes) and the Phloem (used to transport food energy.)

Terrestrial leaves also have a system of intracellular air gaps which form a network of channels in order to distribute and to exchange gasses such as O2 and CO2.

Venting and introduction of these gasses are facilitated by holes on the surface of the leaf known as the stoma (plural stomata).

The terrestrial leaves also produce a waxy waterproof coating on the surface of the leaf called the cuticle. This coating helps protect the leaf from insects, bacteria and other forms of damage.

In many species, the orientation of the chloroplasts are towards these intracellular air spaces because that's where the CO2 is routed.

Clearly, when the leaf is flooded the terrestrial morphology fails miserably. The intracellular air spaces become flooded. The source of CO2 and O2 now shifts from theses channels to the entire area surrounding the leaf. The waxy cuticle, so effective at waterproofing now becomes a real liability in a water environment. Gas exchange between the plant and the environment is severely hampered when plants are submerged because gas diffusion in water is approximately 10,000 times slower than in air. This immediately leads to massive oxygen, CO2 and energy deficits.

The new leave that grow submerged must therefore have significant adaptations in order for the plant to survive. The vascular structure containing the Xylem/Phloem no longer needs to be as rigid. The waxy cuticle is reduced in thickness and in some species disappears entirely. To further enhance gas and nutrient diffusion, the upper epidermal cells are reduced to only a few cells thickness. The leaf which was once waterproof now must be a semi-permeable membrane and as a result of increase internal availability of CO2, the chloroplasts rearrange themselves so that they are oriented towards the epidermis instead of towards the air channels which no longer function as they did.

There are many other morphological and biochemical changes to enhance underwater photosynthesis. It's hardly surprising therefore that many leaves die when the plant is submerged. Unless flow, CO2 and nutrients are enhanced, the plant suffers terribly until it can grow new leaves adapted to the new environment.

Cheers,
 

idris

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Thanks Ceg. Very informative! :)

So if i may cross polinate my own threads, my plants have had about 2 weeks emersed, and a high percentage of leaves have died, yet there are signs of new growth. Are the new healthier young leaves likely to already be terrestrial or if I flooded now, are they young enough that they could continue to grow as aquatic leaves?
 

niru

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So now we know why Mr. Anderson is THE Mr. Anderson, and only the chosen ones can crack the Matrix! Its 21st May tomorrow, so good that I read it all today!

cheers
 

niru

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Ceg, does this also implies that only those plants which manage to change their leaf internal wirings to suit the under water flooding can grow in the tank, and others will simply rot/decay? One never sees a rose garden in a tank?? Is this the sole/primary reason for this? And are there genetic engineering methods to modify this available?
 

Bobtastic

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I think there, basically, three main types of plants. One type that will only live out of water, another type that can only live in water and the final type that can adapt, by changing their leaves, and will grow both in and out of water.

There are clearly lots of fine details missing from the above but that is the basic of basic explanation.
 

dw1305

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Hi all,
I think there, basically, three main types of plants. One type that will only live out of water, another type that can only live in water and the final type that can adapt, by changing their leaves, and will grow both in and out of water.
Pretty much it, the only thing to add is that some plants which may predominately terrestrial, but live in conditions where flooding is an occasional or seasonal events, may be able to live permanently submerged if we give them extra C02, more PAR etc. These are the plants that will usually only grow with CO2 addition.

cheers Darrel
 

ceg4048

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idris said:
Thanks Ceg. Very informative! :)

So if i may cross polinate my own threads, my plants have had about 2 weeks emersed, and a high percentage of leaves have died, yet there are signs of new growth. Are the new healthier young leaves likely to already be terrestrial or if I flooded now, are they young enough that they could continue to grow as aquatic leaves?
Well, really it's not clear exactly what the sequence of events are in your setup. It's very easy to misdiagnose unless we have a precise understanding of what, where and when.

In this tank where the DSM is being performed where did you get the plants? Were they pulled from an established submerged environment and then placed in a dry tank? If so this was a fatal error. Dry start is meant to use emmersed growth in an emmersed environment to minimize the need for adaptation, and it's function is primarily for the establishment of carpet plants and for the mineralization of Nitrogen (to lower ammonia production) by development of a healthy microbial community in the sediment. DSM's main goal is for sediment maturation. There is really no point putting large rosette plants in the tank because they are difficult to grow unless the humidity is kept very high. These plants have very little difficulty in transitioning to submersed when the tank is flooded, unlike carpet plants, which are notorious for their inability to adapt. That's why, typically, a DSM setup focuses on the planting and nurturing of the carpet, and the large plants are put in the tank only on the same day of flooding. Of course this general rule isn't handed down by Parliament, or anything like that, it's just a best practice, least stressful sort of thing.

Placing submersed leaves in an emmersed environment simply results in desiccation of the leaves. Either way therefore one is bound to have trouble with large leaved plants until the original leaves die back and are replaced by adapted leaves - if the plant manages to survive the transition.

Any new growth is adapted to the conditions present at the time of growth, therefore, new leaves in a DSM will typically be emergent growth. When you flood the tank they will face adversity, no question about it. As I mentioned previously, if flow, nutrients and CO2 are adequate, and if the lighting is not so high as to cause nuclear meltdown, then these new leaves can survive long enough under flooded conditions for new submerged growth. But this is what makes it pointless for these types of plants to be in a DSM. The tissue loss and subsequent re-growth mitigates any advantage, although I suppose you only have to arrange the scape once, so that part's already done.

In any case, if the plants you put in the tank were emmersed and if they leaves died, then this simply means that the humidity in the tank is less controlled, and probably significantly lower than it was in the nursery, or wherever they originated.
niru said:
Ceg, does this also implies that only those plants which manage to change their leaf internal wirings to suit the under water flooding can grow in the tank, and others will simply rot/decay? One never sees a rose garden in a tank?? Is this the sole/primary reason for this? And are there genetic engineering methods to modify this available?
Yes, well as noted, it's less a matter of what plants "manage" to accomplish than which plants have been programmed by evolutionary forces in this type of environment. It's also worth noting that not only the leaves have to make this transition, but the roots have to adapt to flooding as well. Within the root structure are cells which are programmed to die and rot. When the cells decay and collapse this forms a network of voids (spaces) called "Aerenchyma". This is a super-important adaptation because this is the only way that Oxygen, produced by the leaves, can be transported to the roots, which nourishes the roots and then which escapes out into the sediment to help support the aerobic bacteria. This is sometimes why we can see the sediment pearling under high CO2/light/nutrient conditions. This Aerenchyma formation technique is the definitive behavior of amazingly tall trees in the Amazon Basin. This is how trees like Mahogany survive 6 months of flooding in the rain forrest. Terrestrial plants simply aren't programmed to make these changes, so the entire plant rots away when flooded. That's what happens when you overwater your house plants or garden plants.

People don't realize how thoroughly profound the adaptations are to a flooded environment. Also, it's noteworthy that aquatic plants do not necessarily "like" to be flooded. These are highly specialized adaptations that allow them to survive a hostile environment. Most aquatic plants do their very best to grow up out of the water to gain better access to CO2. As far as genetic engineering to enable non-aquatics to perform these amazing feats, well, I don't think we'll see that any time soon...

I think people have a skewed vision of aquatic environments. We look at incredibly beautiful and verdant Amano scapes and often describe the scene as looking so "natural". Nothing could be further from the truth. Aquatic environments are more often than not, hot, choking, nutrient/CO2 starved, dreary places for a plant. In some waterways, which are fed by natural springs containing high levels of CO2, plants do well, but the opposite is more typical, like this grove of Bacopa struggling to keep their heads out of water. The green parts are above water while the brown parts are submerged sections of the plant. This is the brutal reality. What you see in an Amano tank is a dream world.
8398051744_b8d7df6a07_c.jpg


Cheers,
 

idris

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Thanks again Ceg.
You have highlighted a fundamental lack of understanding on my part - that DSM is primarily of worth for carpet plants. This has not been particularly apparent from my reading to date.

In the light of new learning I shall flood the tank for the sake of the crypts and swords. Quite where this will leave me WRT the Hair Grass may require some more research (and/or supliments).
 

ceg4048

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Hi Idris,
Well didn't you say that on the plants which have dying leaves you detected new shoots? If this is the case then there is no point in flooding the tank now. The dying of the old leaves is a transition in this sense, but the fact that new leaves are growing means that the plant has survived.

Many people grow emmersed crypts and swords. This is not a big deal. The real problem everyone has is keeping carpet plants such as Glosso or HC from either floating out of the sediment or incurring massive die back. Since these plants are expensive, the hobbyist usually only purchases a few pots, so the total mass is quite low. This leaves a very narrow margin of error if the plant decays. With DSM Glosso and HC will develop a more extensive and stable root structure, which will prevent them floating away, and will substantially increase their mass, giving you a broader margin of error for leaf die back when the tank floods.

The thing about DSM though, is that it will not save you from yourself if you are not good at growing aquatic plants generally. This is another misconception. DSM cannot not save you from poor flow/distribution. It cannot save you from poor CO2 techniques in a CO2 injected tank. It cannot save you from poor nutritional habits. And it certainly won't save you from excessive lighting. You can get just as much algae after flooding a DSM tank if your submersed technique is poor. However, the added biomass of the plants may give you the opportunity to fix the mistakes before they they are completely decimated.

In Barr's DSM introductory post The Dry Start Up Method for Planted Aquariums it is clearly indicated that although swords and crypts are not excluded from this technique the focus is on biomass enhancement, therefore the priority is on those low biomass plants. I'm not sure where you've read about DSM but this is the definitive summary. Also, just because something is easy, it doesn't mean that it is not subject to failure.

This method is rather simple, it’s simply terrarium horticulture for the first 2-6 weeks and then the planted aquarium is filled with water after the plants are grown in and well rooted. Generally this method is most suited for lawns of HC, Glossostigma, Crypts, some stem plants, swords, dwarf clover, dwarf hygro and the like. It is particularly useful for iwagumi style rock layouts using low growing plants. Such tanks with low total plant biomass can be challenging to start up and established. While terrariums and emergent dry aquariums is hardly a new hobby, applying this to the start up phase of a submersed approach is new.

The goal of this method is avoid such labor. By starting a new tank out “dry”, with only the sediment fully saturated with water. We avoid water changes, there’s none to change (this saves us several intensive weeks of water changes and dosing carefully)! Dosing? There are no nutrients to dose. Bacteria? It’s cycling in the root zone just fine. We only need to buy a small amount of HC to make a nice lawn of foreground plants in a few weeks; these are also very well rooted. Roots add O2 to the sediment and the O2 helps increase bacterial cycling. Upon adding the water and submersing the aquarium, the bacteria will be ready, the plants will be ready and adding CO2 (or not) and dosing (or not) is all that’s needed from this point on. However, this method however will not save someone who’s not very good at keeping submersed plants to begin with, but it will give anyone an upper leg up on a new tank start up.

Some plants will adapt better than others to submersed culture. The biggest issue for plants going through this process is gas exchange. So adding plenty of CO2 and current will help. Ethylene is a gas as well as a plant hormone that is generally considered a senescence hormone. Ethylene is no long able to diffuse out easily and causes some species to melt and rot back, but the new growth will have a much better chance and already have a nice strong root system to draw on for growth of new shoots above the sediment, whereas am emergent plant from an aquatic nursery will have both the roots and shoot being transplanted and experience the shock of the tank’s water, the light, the CO2, and bacteria changes. This Dry Start Method avoids all of that. So what are the problems with this method? Folks do not want to wait 2-6 weeks for the tank to grow in well first is perhaps the biggest issue, but seeing their small clump of HC or Gloss grow in and spread, no water changes and other very helpful, less costly and labor intensive advantages might convince them.

Cheers,
 
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