Moderate water is an important condition for plant growth. If there is too much or too little water, the growth will be affected by the following factors.
(1) Effects on plant morphology
Plants accumulate photosynthesis and dry matter through water supply, and the amount of accumulation is directly reflected in the dynamic changes of plant height, stem diameter, leaf area and yield formation.
Under water stress, the individual height of the plant was low, the area of photosynthetic leaves was significantly reduced, and the yield was reduced.
(2) The influence on the change of leaves
Leaf is the main site of photosynthesis and transpiration.
Mesophyll cell expansion and leaf growth are sensitive to water conditions. In order to keep the leaves upright, the support of cellulose and the higher swelling pressure in tissues are needed.
The phenomenon of wilting occurs when the plants are short of water, which is the manifestation of the decrease of swelling pressure.
(3) Effect on the Formation of Production
Crop yield is the accumulation of solar energy into chemical energy in crops.
Soil water status affects plant root water uptake and leaf transpiration, then affects dry matter accumulation, and ultimately affects crop yield.
(4) Effect of water on root cap development
Root system is the main organ of water absorption, and its development is affected by many aspects, but the main role is soil moisture and ventilation.
Soil water status affects the vertical distribution of roots.
When soil water content is high, the resistance of root diffusion to soil decreases, which is conducive to the formation of new roots and the development of roots.
When the soil is drought or water supply is insufficient, the root system absorbs limited water, first of all, it meets its own needs, and seldom transports water to the aboveground part.
The results show that water deficit in a certain period is beneficial to improve yield and quality.
(5) The effect of photosynthesis
Photosynthesis is the main source of energy for green plants.
The photosynthetic rate is closely related to the water status of plants.
The results showed that photosynthesis was the strongest when the water content of plant tissues approached saturation, and when excessive water content reached saturation, stomata closed passively and photosynthesis was inhibited.
The photosynthesis decreased due to water shortage, and decreased sharply or even stopped when the leaves withered due to severe water shortage.
(6) Effects on the transport of organic matter
With the decrease of water supply, leaf water potential decreases, and assimilative substances from source leaf to phloem decrease.
On the one hand, the decrease of leaf water potential and photosynthetic rate resulted in the decrease of sucrose concentration in mesophyll cells.
On the other hand, the decrease of the longitudinal velocity of the centrifugal flow in the sieve tube.
Usually, the fruit is short of water during the period of expansion or filling. Because of the obstruction of photosynthesis and transportation, the fruits and seeds can not accumulate enough organic matter and become dry and thin.
Therefore, under drought conditions, irrigation can accelerate the transport of organic matter.
However, excessive water is not conducive to the transport of organic matter, which is mainly due to excessive water, resulting in poor soil ventilation, affecting respiration and other metabolic processes.
(7) Effect on the Absorption and Transport of Mineral Elements
Mineral elements must be dissolved in water before they can be absorbed by plants.
However, the amount of water and mineral salts absorbed by plants is disproportionate, and the two kinds of water and mineral salts absorbed by plants vary greatly with the change of environment.
The absorption of water and minerals by plants is both related and irrelevant. Relatively, salt must be dissolved in water before it can be absorbed by plant roots, and with water flow into plant roots.
Water absorption is mainly passive water absorption caused by transpiration, while mineral absorption is mainly active absorption of metabolic energy.
(8) Effect on Seed Germination
Water absorption is the main condition for seed germination.
The physiological and biochemical effects related to germination can only begin gradually after the seeds have absorbed enough water.
This is because water can make the seed coat expand and soften, oxygen permeate easily, and enhance the respiration of the embryo.
At the same time, it makes the embryo easy to break through the seed coat. Water can change the protoplasm from the gel state to the sol state, and increase the metabolism.
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