Plant Nutrition and Soil

Plant Nutrition and Soil

• About 95% of a plant's dry weight is composed of carbon, hydrogen, and oxygen
• These elements are fundamental in building organic compounds like carbohydrates
• Primary nutrients for plants include carbon dioxide and water
• Carbon dioxide provides carbon, while water delivers hydrogen and oxygen
• A mineral is an inorganic substance containing two or more elements
• A nutrient is essential if it plays an identifiable role, cannot be substituted by another nutrient, and its deficiency leads to plant death.
• Essential nutrients are categorized into macronutrients and micronutrients, based on their concentrations in plant tissues.
• Macronutrients consist of carbon, hydrogen, oxygen, phosphorus, potassium, sulfur, calcium, and magnesium.
• Micronutrients consist of iron, boron, manganese, copper, zinc, chlorine, and molybdenum.

Determining Essential Nutrients

• Hydroponics involves cultivating plants by providing the required nutrients
• Plants can grow when supplied with the necessary nutrients
• Plants need sunlight, water, and minerals to grow
• Testing for nutritional deficiencies can be done by omitting a specific nutrient from a liquid medium and observing the effects on growth.
• Farmers and gardeners use fertilizer to prevent nutritional deficiency issues

NPK Ratio

• The NPK ratio denotes the weight percentage of nitrogen, phosphorus, and potassium in fertilizer.
• Nutrient deficiencies in plants can manifest as yellowing leaves and leaf shape deformities
• Fertilizer with a balanced NPK ratio promotes healthy growth

Soil Composition and Formation

• Soil comprises mineral particles, decaying organic matter, living organisms, air, and water
• It supports plant growth
• Soil formation starts with the weathering of rock
• Weathering can occur mechanically through wind, rain, ice, and grinding, or chemically via acid rain or degradation by lichens/moss
• Organisms are vital for soil formation
• Lichens and mosses contribute to soil development
• Humus is decaying organic material that enriches the soil

Soil Particles

• Soil is a combination of three particle types: sand, silt, and clay
• Sand ranges from 0.05 to 2.0 millimeters in diameter and facilitates water drainage
• Silt ranges from 0.002 to 0.05 millimeters in diameter
• Clay has a diameter less than 0.002 millimeters
• Clay has small spaces that retain water

Soil Health

• Loam soil balances sand aeration and mineral retention from silt and clay
• A healthy soil has balanced clay particles and humus

Humus Benefits

• A good soil concentration is 10 to 20% humus
• Humus reduces runoff and prevents leaching
• It increases positively charged minerals in the soil
• Organic matter breaks down into bacteria and fungi which is then returned to the plants

Organisms in Soil

• Small plants aids soil formation from rock
• Large plants can dominate ecosystems and their roots penetrate soil to bedrock, enabling water and air penetration
• Soil-dwelling animals helps to mix the soil
• Earthworms ingest soil particles and deposit them as worm casts and aerate soil
• Soil-dwelling ants create colonies and loosen/aerate the soil
• Microorganisms break down humus
• Bacteria helps to make nitrogen which plants use

Soil Ions

• Negatively charged clay and humus bind to positively charged minerals like calcium and potassium
• It prevents leaching of minerals

Cation Exchange

• Cation Exchange is a process by which hydrogen and other positive ions exchange with positively charged minerals
• It allows the root to take up nutrients
• Cation Exchange Capacity (CEC) reflects the negative charge sites available to bind positive cations

Soil Types

• The CEC of sandy soils is less than that of soils with clay and humus
• Soil profiles are vertical sections from the ground surface to unaltered rock
• Soil horizons are parallel layers within soil
  • The 'A' horizon (topsoil) consists of litter and humus
  • The 'B' horizon (subsoil) contains inorganic nutrients
  • The 'C' horizon (parent material) is made of weathered rock

Plant Nutrition Effects

• The soil profile can vary due to differing parent material and climate
• Soil erosion is when wind or water carries soil to a new location
• At least 40% of worldwide farmland faces serious degradation
• Fertile soil approximately the size of Texas is lost annually

Erosion Factors

• Poor land management contributes to high erosion levels
• Deforestation, or tree removal, contributes to erosion levels
• Desertification, caused by overgrazing and over-farming marginal lands, leads to increased deserts

Mitigation of Soil Erosion

• Mitigation strategies for soil erosion include crop rotation, reduced tillage, and companion crops
• Coastal Erosion has changed much of the landscapes in specific areas
• The presence of trees can prevent coastal erosion

Mineral and Water Uptake

• Water and minerals enter plant roots through identical pathways
• Water moves between porous cell walls to reach the endodermal cells through the Casparian Strip
• Absorption happens through root hairs, moving across the cortex and endodermis via cytoplasmic strands in plasmodesmata
• Water enters root cells when the cell's osmotic pressure is lower than the soil's
• Minerals actively absorbed by plant cells get transported through the xylem along with water

Mineral Transport

• Plants use passive or active mechanisms to obtain the minerals
• Cells actively use energy to absorb to mineral ions and concentrate them
• Casparian Strip stops minimizes mineral backflow allowing the root xylem to maintain a high mineral concentrate compared to outside soil
• Roots have the ability to concentrate minerals to concentration levels 10000 times greater than in the soil

Water Transport

• A plasma-membrane proton pump can transport hydrogen ions out of the cell
• Positively charged ions enter then cell via gradient
• Negatively charged mineral ions enter the cell via gradient

Chemiosmosis

• Mineral ion transport via chemiosmosis happens using an electrochemical gradient
• Minerals that enter the xylem are then transported into leaves
• Adaptations of roots for mineral uptake includes symbiotic relation ships
  • Rhizobium bacteria living in root nodules and fix atmospheric nitrogen
  • Host plants provide the bacteria with carbohydrates
  • Fungi increases the surface area for water and mineral uptake
    • Root provides the fungus with sugars

Plant Adaptations

• Parasitic plants may grow independently of soil mineral content
• Carnivorous plants can obtain nutrients in unconventional ways

Transport Mechanisms in Plants

• Vascular tissues are critical for moving water and nutrients
• Xylem delivers water and minerals
  • The xylem is composed of two conductive cell types known as Tracheids and Vessel Elements
  • Flows passively, shifting from areas of more intense water potential to areas of lesser water potential
• Phloem moves organic materials
  • Sieve-tube members are conducting cells in the phloem tissues that have companion cells to provide cellular proteins
  • End walls of the the phloem are sieve plates and contain strands of plasmodesmata

Xylem and Phloem Cells

• Xylem and pholem are series of cells acting as movement channels
• Water in xylem moves UP from the bottom
• Sucrose and other materials in pholem can move in any direction

Water Potential

• Water moves as the roots have more water and higher amount of osmosis
• Water moves as more water escapes through stomata with lower amounts of osmosis

Water Potential Properties

• Potential energy is stored
• Energy of moving water is measured by water potential
• Water passively moves through a membrane based on differing solute potential
  • Water pressure and solute concentrations affect this movement
• Osmosis occurs as water moves from high pressure / low concentrations of water solute to higher concentration levels
• Turgor pressure is the force that drives osmosis forward to equalize water transfer

Plant Needs

• Lower turgor pressure is an indication that a plant cell needs more water
• Higher turgor pressure means that plant cells are turgid
• Open xylem vessels serve an open pipeline to transfer water
• Water in tracheids is moved into other tracheids through pits
• Positive entry of water happens for root pressure
  • Root pressure forces fluids up the plants shoots
  • Guttation happens when roots pressure is responsible for forcing open vein ending which expels water along the leave edges

Water Control

• Cohesion-tension model explains passive xylem transports, driven by water's properties
  • Molecular forces holds water molecules together and is known a Cohesion
  • Adhesion is the polarity that help water interact with vessel walls
  • Combined forces, resulting in a continuous water column moving upwards during transpiration

Plant Properties

• Leaves help to transpire water and use waxy coatings to shut off water releases
• Stem acts as a vessel where xylem tensions pulls water upwards
• Roots passively permit osmosis by entering water xylem upward

Transportation by Stomata

• Each stoma in the leaf epidermis is guarded by guard cells.
• As light increases the stomata opens
• Active transport, causing water to enter through osmosis, opens stoma, which is increased by turgor pressure.
• The hormone abscisic acid (ABA) can causes stomata to close.
• A significant portion of the water is released into the atmosphere by plants
• Evaporative cooling cools the plants and affects climate
• Transpired water returns as rainfall

Phloem Sap Elements

• Sugar transports in the vessels of the pholem
• Sugar travels from origin to be dissolved
• Removal in areas below creates a high bark concentration of sugars
• Scientists can analyze pholem by collecting stylets from plant life

Transportation Types

• Sucrose loading is dependent on water and ions
• Ions pump into meophyll cells which creates sucrose production that moves into the sap
• Elevated levels of sucros increases h2o level which forces nutrients flow towards the weaker cells
• Pressure results in water and sugar transfer out of the higher concentrated nutrients to the weaker sink cells