Transport and logistics inside the plant

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.
http://st0ney0.tripod.com/efoto4.jpg

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.
http://st0ney0.tripod.com/efoto5.jpg

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.

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