Transport and logistics inside the plant

Everybody knows that a plant needs water in order to survive. Without it, it goes weak, dries out and dies. It is also well known that the plant sucks up water through the roots, along with the nutrients. It all seems simple and logical, but in fact this is a complex process.

If we take a closer look, we will find that all climate-related factors, such as light, light-duration, humidity and temperature are closely related to the watering process.

A plant consists of three parts: Root, Stem and Leaf

Summarized, the transport inside the plant works as follows:
The roots absorb the water from the soil. Then, the water and it’s nutrients are converted into new parts of plant. These are mostly large, organic molecules, which are used all around the plant (for example, as a growth substance in the roots). The engine boosting the production inside the leaves, is photosynthesis. http://st0ney0.tripod.com/efoto1.jpg
Water and solved nutrients continually have to go up, and the newly produced molecules have to go down. So we are not just dealing with the transport of water and nutrients, but also with that of ‘large’ organic matter. How this functions and why there are no traffic-jams, we will discuss that later. Let’s start with the roots. http://st0ney0.tripod.com/efoto2.jpg

Water transport inside the roots
A root has different functions. Aside from taking in the water, they provide stability of the plant. In balance with it’s top-soil counterpart, a root has to grow (ad synthesize new root-parts), and carry partial responsibility for the storage of reserve-nutrients. They are also the production facility for very specific molecules (like nicotine for the tobacco-plant)

Roots give the plant stability
The roots hold a plant down in the ground, or other substance. They have the specific structure needed for this job. Both the guiding and the supportive plants of root form the axial strain. This helps the plant achieve great flexibility, as well as a good cable-structure. It also enlarges the available root surface.

The principle structure of a root is very visible with a seedling
The central branch of a root-structure is the primary-root, which drills itself into the ground right after germinating. When the primary root has taken a strong hold and water supplies have been secured, the first leaves may be directed towards the light to achieve photosynthesis. http://st0ney0.tripod.com/efoto3.jpg Then side-roots sprout from the primary root, increasing it’s surface and stability. All roots grow in one direction, enabling the out-growing hair-roots to anchor into the soil.


Root-growth, and the short-life span of the hair vessels
A root mostly grows at it’s tip. Close up to the newly formed cells is the root-unit, which controls the new-cell build up: a regular little root-factory. This production unit (meristern), moves forward along with it’s growth. Behind these tips, the newly formed cells are stretched out (cell-stretching). This part is followed by the hair-region, which is only a small part of the whole root. Still, the latter is the only part where water and nutrients are taken in.

Because roots continuously grow at the tip, the root-hair region shifts along with it. In effect, this means the hairs have to be built up and broken down every few days.
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Water transport inside the roots

The hair-vessels are of a delicate structure, and are surrounded by thin shells, through which water and unsolved nutrients may easily pass. The resistance to water here is minimal. The outer surface is increased enormously by branching out. In the middle of the root we find the central cylinder: the highway up. Water flows here from the hair-vessels. This section has the largest resistance to water, for many membranes have to be passed through here. In the hair-root region, the plant has an enormous force outer surface, which has intensive contract with it’s environment.

Clearly visible here, is the narrow contact between hair-vessels and soil-particles. Absorbing water does not come from active transport, but could well be compared to the cotton of an oil-lamp continuously sucking up oil towards the place of combustion (towards the flame).

The intake of water by the roots is controlled through it’s suction. This has to be lower than that of the soil (otherwise water would flow from the roots into the soil). With extremely dry soil this may actually happen!). this water-suction is dependant on the amount of resistance water encounters in penetrating the root. The resistance is among other factors, influenced by the soil-temperature. This on account of the fact that water’s viscosity (it’s toughness) rises when the temperature drops (the water becomes thick). If the bottom is warm, this means low water resistance, but if it is cold, resistance becomes high.

The second, and largest driving force behind water absorption is perspiration (the evaporation of water from the leaves). When much is evaporated, the suction in the roots grows larger (like with a fungus). Evaporating water from the leaves is in tune with the air-humidity (low R.H. = much evaporation, and vice versa) inside the room.
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The following drawing depicts an experiment which proves that perspiration of the leaves causes suction (negative water-pressure) even greater than the force of regular air-pressure.
http://st0ney0.tripod.com/efoto6.jpg Demonstration of the suction which can only be achieved through leaf-perspiration. The plant may pull the mercury up higher as would air-pressure inside a barometer. This experiment proves that perspiration is the driving engine behind water absorption into the roots.

Plants can experience water stress
If ground temperature and air-humidity are both low, much water leaves the leaves through perspiration, but the roots can’t keep up, due to high water resistance. Symptoms: weak or dead leaves on wet soil, and decaying roots, of fungi will soon follow.

Before we continue with more facts, let’s put this in practice. The plant-medium can’t be constantly dry or wet. Plants cannot actively absorb water, and never more than the amount which is perspired by the leaves. Don’t water ‘for storage’. This activity should be taken care of by your soil (perhaps by adding perlite). This achieves a water-buffer capacity. Hydro-systems should drop little but often, this imitating the water-buffer (not too wet and not too dry). The plant-medium should posses sufficient solidity in order to anchor the supportive roots, but it should also be soft enough to let the root-tubes through.

Grow zone

The microbiologic balance in the root-zone
The microbiologic balance is a simple way of describing this very complex society of micro-organisms. These micro organisms have a big influence to the growing and blooming of the plant. It is very important for the serious grower to understand the balance in the plant and, if possible, to control it. A healthy microbiologic life always leads to an optimal macro-biologic life (grow and bloom). This is also known in the regular and professional gardening. This year many researches about the biologic balance started. Many research-institutes in Holland are investing millions of guilders in these researches. The Highlife grow-school gathered the most important facts and definitions for again an informative grow-school for the serious grower.

The root-medium is a very complex thing, which is influenced constantly by the grower and factors of the outside. The grower influences by giving water, maturing of the plant, the choice of the substrate, the influence of temperature and light, the height of the pH etc. The most important outside factor is the separation out of the roots, also called root-exudates. Micro-organisms can be good or bad (they then cause diseases). When there are more good than bad micro-organisms in a plant and this situations is stable, then we are talking about a positive balance.

There are a few facts, which can influence a balance:

Tap-water
Tap water also contents micro-organisms. Every time you make water for the plants there are also micro-organisms in it. This influences the biological balance.

Substrate
The most occurred substrates are inert (it means that these don’t react with nutrition and roots), examples of these are rock-wool, PU-foam, oasis and Mapito (a mix of rock-wool and PU-foam). There are also organic substrates like coco and earth-mixes. The inert substrates do not influence micro-life very much. These are often that sterile that these hardly contain microbiologic life. This can be changed with biological means. Organic substrates on the contrary do have a lot of microbiologic life. Most of the times it is a positive balance, the quality-mixes for sure.

Root-temperature
The presence of a micro-organism and the quantity of it, depends on the temperature in the root-zone. Every micro-organism has its own optimum.

EC (solved salt-concentration)
The complete salt-concentration is important for the fact that the micro-organisms can survive. The separate nutrition-elements can influence the growth of certain micro-organisms.

Light
Roots don’t like light at all. Micro-organisms that live in the root-zone also don’t like light. Organic substrates have a natural dark colors, so the root-zone is also dark. Inert substrates are often packed in plastic material, which does not let through the light.

pH
Fluctuations of pH influence the composition of micro-organisms. The more stable the value of the pH (5.5 – 5., the more stabled the microbiologic balance will be.

Bio-means
Biologic, bio mineral, organic means and means on the base of plant-extracts all influence micro-organisms. The newest means in gardening are bio-stimulators. The bio-stimulator influence directly the micro-flora. So can the bio-stimulators directly restrain influences of the disease-producing micro-organisms, so the good organisms can develop better.

Chemical insecticides
These synthetic means kill more than only mite or white fly. If the residue of the insecticides drips from the leaves into the root-zone, they also kill the positive micro-life. Also these means are not recommended because of the damage they can do to your health.

Oxygen
The type of substrate, how thick the layer of the system is and how often the plants get nutrition influence the amount of oxygen in the root-zone. If there is a lot of oxygen, other micro-organisms will develop then when there is a lack of oxygen.

Root-exudates
Besides the enumerated factors which can influence the grower, there are processes in the root-zone, which are influenced by the plant itself. These are the so-called root-exudates. These separation-products can consist sugars, amino acids, phenols, phenol-acids or other organic combinations. Sugars and amino acids can serve as nutrition for the plant, so they can play a grow-stimulating role. Phenol-combinations and certain organic acids can restrain the growth of the plant if the strength is too high. Also bio-stimulators can be a part of it. Bio-stimulators can break down all kind of organic combination so the plant can absorb it.

That is why I advise the serious grower to check the micro-climate of his plants… it can make a lot of difference…

Too Hot, Too Cold

Water temperature is another important factor. If your solution is too cold, seeds won't germinate, cuttings will not root and plants will grow slowly - or stop growing and die. If it's too hot, the same seeds won't germinate, cuttings won't root and plants will die from oxygen deficiency or simply from temperature stress. Most plants prefer a root zone temperature range of between 65 degrees (18 C) and 80 degrees (27 C), cooler for winter crops, warmer for tropical crops. When adding water to your reservoir, it is a good idea to allow it to come to the same temperature as the water in the reservoir.

Remember, plant roots have evolved in a soil environment, where temperature changes occur slowly, tempered by the thermal mass of the earth.

Plants do not like rapid temperature changes, especially in the root zone!

Great thread, subscribed

edit: sorry for bringing up an old thread ;S didn't see the date. But it's an informational one, so new users probably will get something from it =D

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