Week 14: Field capacity and soil water holding capacity. Characteristics of xerophytes and hydrophytes. Effect of precipitation on distribution of plants

Soil is a great reservoir of water. The principle source soil water is rain. The following types of water present in the soil.

  1. Run away water
  2. Gravitational water
  3. Soil holding water
  4. Hygroscopic water
  5. Capillary water
  6. Chemically combined water
  7. Water table

Field capacity:

Much of rain water is retained by the soil particle  which make the soil wet. The amount of water retained by soil after the removal of excess water by gravitation is called field capacity or the water holding capacity of soil.

Plants are distributed in nature according to amount of moisture available to them. Plants are divided into four groups in relation to moisture. These groups are 

  1. Hydrophytes
  2. Amphibiophytes
  3. Mesophytes
  4. Xerophytes

Hydrophytes are the plants grow in water reservoirs like ponds, lakes and rivers. These plants live in a habitat with abundance of water.

They may be submerged, leaf floating, fixed floating  hydrophytes. The submerged hydrophytes having the hydathodes instead of stomata. For example hydrilla

Xerophytes: The desert plants are called xerophytes. They face the extreme  short of water. They have certain adaptation to reduce the rate of transpiration.

  1. Small and thick leaves
  2. Thick waxy and leathery cuticle
  3. The stomata are sunken in the lower epidermis 
  4. They shed their leaves during the extreme dry season and the stem acts as a photosynthetic organs
  5. They are succulents

Precipitation includes rain, snow, hail and dew. The precipitation is the major source of moisture for the plants. Rain increases the humidity of air. Thus reduce the transpiration rate. The amount of rain determine the different vegetation zones. For example deserts, grass land and forests are formed due to different amount of rain.

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