Water’s Role in Plant Life: Properties, Processes, and Quality

Posted on Feb 20, 2025 in Biology

Water’s Vital Role in Plant Life

Water’s Functions:

  • Nutrient Transport: Facilitates the movement of nutrients from the roots to the leaves via the ascent of sap.
  • Specific Heat: Regulates cell temperature, protecting the cytoplasm from drastic temperature changes.
  • Osmosis: Enables the movement of solvent from a solution of lower concentration to one of higher concentration at a constant temperature.

Physiological Processes Involving Water

  • Constituent: Makes up 80-90% of fresh fruit weight.
  • Solvent: Dissolves and transports plant nutrients.
  • Reactant: Participates in chemical reactions with nutrients.
  • Turgor: Maintains cell firmness, preventing wilting. Cells absorb water and expand.

Water’s Physical Properties

  1. Physical state: Solid, liquid, and gas
  2. Color: Colorless
  3. Taste: Bland
  4. Odor: Odorless
  5. Density: 1 g/cc at 4°C
  6. Freezing point: 0°C
  7. Boiling point: 100°C
  8. Critical pressure: 217.5
  9. Critical temperature: 374°C

Water’s Chemical Properties

  1. Reacts with acidic oxides
  2. Reacts with basic oxides
  3. Reacts with metals
  4. Reacts with nonmetals
  5. Forms salt hydrates

Irrigation Water Quality

  • Chemical Quality: Concentration of dissolved salts, relative sodium concentration, carbonates and bicarbonates, and the amount of toxic elements.
  • Agronomic Quality: Soil type (physicochemical characteristics), salt content, crop type (tolerance to salinity, concentration of toxic elements), and irrigation methods.

Toxic Elements in Water

  • Boron
  • Chlorine
  • Sodium

Soil Components

  1. Mineral material
  2. Organic matter
  3. Air
  4. Water

Soil Density and Porosity

  • Actual Density: Mass of soil solids relative to the volume occupied, regardless of pore space (2.65 g/cm³).
  • Density: Weight of dry soil divided by total volume, including all pores.
  • Porosity: Proportion of soil volume not occupied by solids, but by air and/or water. Ep = 100 – (Da/Dr x 100)

Soil Drainage and Water Classification

  • Soil Drainage: The soil’s capacity to remove excess water.
  • Depth: A key factor affecting root system development.

Classification of Water in Soil

  • Microscopic: Water held tightly by soil particles, not available to plants.
  • Capillary: Water retained by soil particles through surface tension.
  • Gravitational: Water held at tensions under 3 atmospheres.

Transpiration

Water loss as vapor through stomata, cuticles, and periderm.

Water Absorption and Transportation

Water and salts are absorbed by the roots and transported up the stem via tracheids and xylem vessels. Sugars and other organic materials are transported mainly in the phloem sieve tubes. This process is influenced by environmental factors such as soil composition, rainfall, sunlight, and heat.

Factors Affecting Stomatal Opening and Closing

Water availability, carbon dioxide concentration, light, and temperature. Stomata generally open with light and close in darkness.

Water’s Journey Through the Plant

Soil-root-stem-leaf. Water enters through root hairs and can take three paths:

  1. Transmembrane route: Direct travel through cortex cells to the endodermis.
  2. Apoplast: Journey through the apoplast (without crossing membranes).
  3. Symplast: Journey through the symplast via intercellular connections (plasmodesmata).

Water enters endodermal cells, passes into the vascular cylinder, and enters the xylem, then travels to the stems and leaves.

Water’s Role in the Cell

Mechanical support, osmotic regulation, metabolic processes, cell division, and growth.

Water Potential

Represents the measure of free water energy per unit volume, expressed in units of energy. Pure liquid water is the reference point.

Importance of Water Potential

  1. Determines water movement through membranes.
  2. Measures water status in plants.

Techniques to Measure Transpiration

Fitometros and potometros.