How roots navigate around obstacles in the soil

Ekka · 27th May 2008, 06:15 AM

Source: How Roots Find A Route Around Obstacles In The Soil

Quote:

ScienceDaily (Mar. 3, 2008) — Scientists at the John Innes Centre in Norwich have discovered how roots find their way past obstacles to grow through soil. The discovery, described in the forthcoming edition of Science, also explains how germinating seedlings penetrate the soil without pushing themselves out as they burrow.

"The key is in the fuzzy coat of hairs on the roots of plants" says Professor Liam Dolan. "We have identified a growth control mechanism that enables these hairs to find their way and to elongate when their path is clear."

Root hairs explore the soil in much the same way as a person would feel their way in the dark. If they come across an obstacle, they feel their way around until they can continue growing in an opening. In the meantime, the plant is held in place as the hairs grip the soil.

This ability is governed by a self-reinforcing cycle. A protein at the tip of root hairs called RHD2 produces free radicals that stimulate the uptake of calcium from the soil. Calcium then stimulates the activity of RHD2, producing more free radicals and further uptake of calcium. When an obstacle blocks the hair's path, the cycle is broken and growth starts in another location and direction.

"This remarkable system gives plants the flexibility to explore a complex environment and to colonise even the most unpromising soils," says Professor Dolan.

"It also explains how seedlings are able to grow so quickly once they have established."

In nutrient poor soils such as in parts of Australia and sub-Saharan Africa, plants have adapted by producing more root hairs. A better understanding of this adaptation will allow the development of crops able to grow in inhospitable environments.

wulkowicz · 28th May 2008, 07:56 PM

Quote:

Originally Posted by Ekka

Source: How Roots Find A Route Around Obstacles In The Soil

Well thank you very much Ekka. it is a much pleased and prideful Wulkowicz who responds to your post on roots meeting obstacles. I've argued for years about the poor science and misapplied thinking that went into claims that roots poked through concrete and brick walls, and generally vandalized our structures.

Here, from the glory days of 2001, is a snippet of the debate I had in Russ Carlson's Tree-Tech which includes the bolded statement that roots didn't push their way through much of anything. They don't have the strength.

The tip of a root is about the size of a period at the end of this sentence.The numbers bandied about as a pressure possible for a root tip were given in pounds per square inch, which is absolutely reasonable as a unit of discussion. The problem was no one really noticed that it took an awful lot of period-sized tips (500 microns) to make up that square inch.

In my clumsy grammar school arithmetic way, I calculated about 25,000 of the wee beasties all had to push at something at the same time with everything they had to generate the touted 145 psi. If herding cats is a problem, who's going to step forward and wrangle 25,000 root tips?

----------------------------------------------------

<Bob Wulkowicz>

Posted Tuesday August 28, 2001 12:34 PM
Reply to post by Russ Carlson, on August 24, 2001 at 22:24:48:

Bob, you pointed out that roots may be "on their way somewhere else" in some cases.

This is how a wall can be damaged The root tip will find its way into a tiny crack or crevice. It may be turned aside, yet still survive. The root tip that survives expands into a root, which grows laterally.

__________________

Russ,

Roots are notoriously on their way somewhere else. That is what accounts for root-bound plants in pots and girdling roots on trees. Roots search, explore, and exploit; indeed, it is a critical function of what they must do. Once past the buttress area where root sections serve a structural purpose, roots sick to the business of being the water and mineral transport mechanisms.

Encountering an obstacle is an everyday occurrence for roots and so wrestling for survival at an obstruction is rarely a consequence. When the path for an root apical meristem is blocked, the meristematic tissue further back simply creates a new apical point (obviously at right angle initially) and begins to grow in that direction. It is a wonderfully simple adaptive mechanism that works quite well. The root doesn't waste its time fighting, it goes somewhere else as a new lateral root.

__________________

This root then exerts a lateral pressure on the objects adjacent In most cases of damaged walls, curbs, etc. that I've inspected, the structure was defective in some way. It had cracks or crevices for the roots to enter.

This also implies a weakness at that point. So regardless of the compress or tension ratings of the concrete or other material, the structure's ability to withstand pressure at the defective point is less Roots can and do exert pressure.
____________________

I agree that the radial growth of roots creates a pressure, but again it is not in a range that can threaten concrete--even concrete weakened by other conditions. I also can't agree with your statement that compression or tension ratings adjacent to a crack or hole are somehow less at that defective point. The general integrity of the wall may change to some degree, but the strength of the surrounding concrete is essentially unaltered.

Mattheck estimated a possible pressure of over one mega-pascal (one million newtons per square meter). Now obviously, the root is pressing over a smaller area, but it's still a lot of force. Combined with other forces such as freeze/thaw cycles, slight shifting of the roots or soil due to tree movement, shrink/swell of the soil, etc., a wall with a weakness can be damaged.

You are aware that I am very troubled by many of Mattheck's pronouncements and the interpretations attributed to him. If I look in my conversion tables, the megapascal pressure you quote translates into 145 psi (1MPa). The water pressure from my pump at the cabin and at most city faucets is about 45 psi. This is not a big time pressure.

If I tripled the water pressure on my pump and held a garden hose nozzle against my foundation wall, does anyone think I would push a hole through the wall? I might blow a hole in the hose, but not the pump, the fittings, the nozzle or the concrete. That pressure attributed to the growing tips of roots is nowhere near the pressure necessary to affect concrete.

What is needed? Here's a typical rule of thumb today for cutting concrete: we find "a ratio of 3.5 psi. water pressure for every 1 psi. compressive strength of concrete is used to calculate optimal operation pressure. If a concrete core test indicated nominal compressive strength of the concrete to be 5,000 psi., a minimum water pressure of 17,500 psi. is indicated. "

This is what I mean about throwing the theoretical away in a second when presented with a practical consideration. A strength of 5000 psi is pretty close to residential foundation strengths and the 145 psi pressure from the tip of a root ain't beans to those walls.

The photo at the top of this piece is of a tree root showing the cap, the meristem, and the elongation zone. If you can see and count the cells, the structure is obviously microscopic. The force claimed for it are available only at its microscopic tip. This size is what enables it to slide through pore spaces and if it encounters a concrete wall, this is the area of pressure exerted against that wall.

Even if 100,000 root tips arrived at the wall at the same time, would they penetrate the wall? How many angels can dance on the head of a pin?.

________________________

Now, let's consider a lateral pressure as you suggest from roots growing horizontally and parallel in relation to a wall:

In a study sent to me, the authors attempted a compilation of papers on tree root pressures. I don't have it in front of me, but I remember a quoted primary growth forward pressure of 128 psi. The authors couldn't find a lateral growth pressure (secondary growth) anywhere, so they assumed a lateral pressure of at least the same 128 psi. The need to have both pri. and sec. answers for their paper prompts them to assume a number just to fill in the blank(?)! I don't find this great science, and I certainly don't find it a benchmark for pressures from diameter increases in roots adjacent to walls.

But let's use the Mattheck 145 psi. Even if it were true, this is even less likely a meaningful factor in distressing foundation walls. Our roots will probably exist mostly in the approximate 18" root zone that they occupy everywhere else. And even if they were laying right next to the wall, they would first compress the adjacent soil until it was incompressible before they would exert any subsequent pressure on the wall. The contact point of the root circle to the contact point of the next root circle against the wall will be determined by the root's diameters as an "automatic" spacing depending on root age that reduces the potential pressures..

I have only seen vertical and diagonal cracks in foundation walls, which would be consistent with vertical displacement and settlement. I have never seen horizontal fractures or cracks that would imply lateral pressure from lengths of pressure increasing structures like roots.

And if these roots went under a foundation and tried to lift it based on a 145 psi capacity, we're expecting a living expanding cylinder using its ability to divide cells to raise a foundation wall, the floor loads, the building contents, the framing, the roof timbers and the shingles? What pressure would that take? But more importantly, would the cells stay alive at that pressure to continue their division, expansion and subsequent growth.

I can crush the cells of a root or branch with a pair of pliers. I can impede radial growth in a woody cylinder with remarkably small counter pressures. I have hundreds of photographs illustrating the reluctance of meristematic cells to kill themselves in any kind of expansion that hardly approaches the pressures needed to lift a foundation and its vertical loads.

________________

It may not be the tree that caused it, but it certainly can contribute to the problem. In Mike's case, the foundation wall is probably new enough and well enough constructed that there will not be a problem. Old foundations with crumbling mortar would be an entirely different story, however.

________________

Trees really don't cause the problems--and in my judgment, don't really contribute either. A mega anything sounds big. The explanations seem plausible until they're examined more closely. Our prejudices and ignorance do not change the laws of physics or biology. Our deadly inclination to repeat myths and clichÃ©s will condemn more trees.

I keep sputtering. Please tell me where I'm wrong.

Bob Wulkowicz

------------------------------------------------------

"In all things it is a good idea to hang a question mark now and then on the things we have taken for granted." Bertrand Russell

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The root taking a sideways step.

http://www.sciencedaily.com/images/2...0228143543.jpg
A root growing vertically, with a root hair cell emerging horizontally. (Credit: John Innes Centre)

Ekka · 30th May 2008, 03:08 AM

You know I like reality shows.

It's debatable whether or not either structure was defective ... what is apparent is the lifting capacity of the roots. In both cases the roots have grown thicker in time and it must have been less resistance to lift the structure than depress into the ground.

So, what are the PSI capabilities of roots in such scenarios I wonder? How much weight can they lift?

newguy18 · 30th May 2008, 07:32 AM

Good read Eric.

reggie · 30th May 2008, 03:59 PM

I had a japanese maple and it was about 15yrs old,i decided to take it down as it was out of sink with the garden though now there are shoots coming up in the pavement in the street.I cant identify any major roots in the garden what should i do?

Ekka · 30th May 2008, 05:45 PM

Cut the shoots and poison with round-up ... it could kill any others in the area so only do it if all are expendable.

reggie · 31st May 2008, 01:08 AM

Quote:

Originally Posted by Ekka

Cut the shoots and poison with round-up ... it could kill any others in the area so only do it if all are expendable.

seems to be the only way,was think of digging up the space where the maple was to try and find the roots if find them i was gonna try and use round up on them,do you think it would be effective?

Ekka · 31st May 2008, 01:46 AM

Are you sure they're not seeds?

Trouble is that end might be the dead end and compartmentalized off ... gotta go to the "action end"

JohN Dee · 31st May 2008, 03:17 AM

We just completed this land clearing contract and this was a driveway in one of the yards where a camphor laurel had lifted the fence aswell as the driveway about 15-20 inches.

We were going to grind out the other side of the fence stump half, but found aspestos when raking it back so we let our client deal with the stumps being dug out and having the aspestos professionally removed. We did poison the stumps though, for the meantime.

This picture really doesn't do the justice of the destruction going on here.

This is a crappy edit by me trying to show the level ground, where it should be...

Sean Freeman · 31st May 2008, 04:38 AM

Bob, I really enjoy your writings, always have since I first read some in the early 2000's......i find you provoke positive questioning in my mind and hopefully in the minds of others.

Now I'm not absolutely confident about the relative pressures produced by roots under rigid slabs, so I will defer to the values you suggest, however clearly in the pics posted and in almost all the anecdotal experiences i have had with roots its dynamic leverage vs inflexible, flat concrete sheets lying over poorly prepared foundation layers.

It would be very hard to calculate just what pressures are being produced by the mass of roots that you would find under such slabs/sheets. But...what I would be confident in stating is that given a crow bar I could get movement in those slabs...the slads would probably crack at the point of leverage...the mass of roots have an advatage of spreading the loading...very clear in Erics 2nd pic...if you tried to lever up the slad at the red arrow it would crack but the proposed spread of lifting root mass (yellow lines) combined with the heaving of the soil beneath has little trouble moving the slab/sheet, and this does not surprise me at all.

The claims that are made against trees in relation to building foundations, are a different thing entirely, and I have written at some length about this on the forum previously....differential settlement of the subbase is very often the real cause for subsidence under buildings....correct foundation preparationand construction eliminates the direct physical role of roots.....moisture changes in the soil surrounding and below the foundation is effected by all vegetation but again correct foundations are not as vulnerable as the commonly held view suggests.

reggie · 31st May 2008, 09:42 AM

Quote:

Originally Posted by Ekka

Are you sure they're not seeds?

Trouble is that end might be the dead end and compartmentalized off ... gotta go to the "action end"

ahh,good point,cheers mate.:

Ekka · 31st May 2008, 03:53 PM

You're right Sean.

The tree roots only have to lift part the weight of the slab over the roots surface area, because they dont lift it off but tilt it. The slabs are just resting on the ground not anchored, be a whole different story if there were screw piers attached. Now if those slabs crack it makes it easier as it means less weight to lift.

In a recent exercise a guy was installing a 20,000L water tank near trees and worried about the weight on the roots. Here's my calculations.

Quote:

Water weighs 1kg/litre, so roughly a 20,000kg or 20 metric tons of weight.

Tree roots need air and having some 20ton weight on them over a large surface area will compact and reduce O2 levels in the soil.

You could pier and beam a foundation for it and not have it on the ground, that means only root interference would be the holes for the piers. Then you just need to address the "no rain" beneath the tank issue somehow.

This one here Tankmasta Water Tanks shows the dia as 3.63m so it would have 10.39m2 surface area. Use this tool to work it out. CIRCLE AREA, SPHERE AREA, SPHERE VOLUME, CYLINDER AREA AND CYLINDER VOLUME CALCULATOR

So you have 1924kg per m2 not including the weight of the tank.

Now if you think about this a bit the average large car weighs that and it's surface area is way smaller on tyres. My calculations show that the above tank would only exert 3psi pressure on the soil but it's the oxygen, water and nutrient factor that would destroy the roots ... not so much the weight.

So all of a sudden the weight of the water on the tree roots becomes insignificant.

Knowing what roots can exert in PSI before the cells die is the data we require. Like ole Bob says, the tree doesn't want to kill itself so there's going to be a force where cells under pressure no longer function.

Palm roots in retaining walls put side force on the wall and break it, seen that over and over.

Palms between a fence and pool, doubt the roots will push a concrete 40,000L pool so they do damage the other side if there's something there. In situations where there's say a block rendered wall with foundations and a pool and palms planted between in the 1m gap (like a huge pot) what happens? Over time the palms get root bound and start looking like crap, the under plantings look like crap as they get strangled with palm roots and robbed of resources. In effect the whole area becomes like a root bound pot.

reggie · 1st June 2008, 04:58 AM

Quote:

Originally Posted by reggie

ahh,good point,cheers mate.:

the garden centre recommended SKB as a root killer,though it dosent say how often to use it,after 24hrs the shoots still apear alive and well,should i use it daily for reinforcement or would it loose its effect?,thanks in advance

30th May 2008, 03:08 AM	#3 (permalink)
Ekka Admin - Dip Arb & Hort Join Date: Jan 2007 Location: Brisbane Posts: 7,734	Re: How roots navigate around obstacles in the soil You know I like reality shows. It's debatable whether or not either structure was defective ... what is apparent is the lifting capacity of the roots. In both cases the roots have grown thicker in time and it must have been less resistance to lift the structure than depress into the ground. So, what are the PSI capabilities of roots in such scenarios I wonder? How much weight can they lift? __________________ Arborist Training in Australia\| Your Free Helping Guide Free Tree and Green Industry Link Directory .... Yes, I also SEO (Optimize) and build websites that fly high in Google Qualified Brisbane Tree Lopping \| Stump Grinding and Stump Removal Brisbane Brisbane - Gold Coast Tree Care, Consulting, Developer, Tree and Arborist Reports Forum Sponsors

30th May 2008, 07:32 AM	#4 (permalink)
newguy18 Part of the Furniture Join Date: Jun 2007 Location: Dead twig Florida. Posts: 4,062	Re: How roots navigate around obstacles in the soil Good read Eric. __________________ Have your say join us today. I ship USA saws out of the USA "Everybody's hell on safety." G.f.beranek. www.atreestory.com

30th May 2008, 03:59 PM	#5 (permalink)
reggie Sappling Join Date: May 2008 Location: ireland Posts: 6	Re: How roots navigate around obstacles in the soil I had a japanese maple and it was about 15yrs old,i decided to take it down as it was out of sink with the garden though now there are shoots coming up in the pavement in the street.I cant identify any major roots in the garden what should i do?

30th May 2008, 05:45 PM	#6 (permalink)
Ekka Admin - Dip Arb & Hort Join Date: Jan 2007 Location: Brisbane Posts: 7,734	Re: How roots navigate around obstacles in the soil Cut the shoots and poison with round-up ... it could kill any others in the area so only do it if all are expendable. __________________ Arborist Training in Australia\| Your Free Helping Guide Free Tree and Green Industry Link Directory .... Yes, I also SEO (Optimize) and build websites that fly high in Google Qualified Brisbane Tree Lopping \| Stump Grinding and Stump Removal Brisbane Brisbane - Gold Coast Tree Care, Consulting, Developer, Tree and Arborist Reports Forum Sponsors

31st May 2008, 01:46 AM	#8 (permalink)
Ekka Admin - Dip Arb & Hort Join Date: Jan 2007 Location: Brisbane Posts: 7,734	Re: How roots navigate around obstacles in the soil Are you sure they're not seeds? Trouble is that end might be the dead end and compartmentalized off ... gotta go to the "action end" __________________ Arborist Training in Australia\| Your Free Helping Guide Free Tree and Green Industry Link Directory .... Yes, I also SEO (Optimize) and build websites that fly high in Google Qualified Brisbane Tree Lopping \| Stump Grinding and Stump Removal Brisbane Brisbane - Gold Coast Tree Care, Consulting, Developer, Tree and Arborist Reports Forum Sponsors