Plant Nutrition and Soil

4/23/2024 Plant Nutrition and Soil Why is soil important? – – – – A lot of the plants we rely on grow best in soil Carbon sequestration (nutrient cycling) We need the foundation! Habitat for organisms What impact have humans had on soil? – – – Failing to rotate crops Overusing the land Turning it into brick for construction Macronutrients – those that plants require in large quantities – Carbon, hydrogen, nitrogen, oxygen, magnesium, potassium Micronutrients – plants require these in small quantities (you guessed it) – Chlorine, iron, copper, zinc, boron Soil – compilation of water, minerals and organic material that create distinct layers Formation of soil: – – – Mechanical weathering Chemical weathering Biological processes (animals) Soil Properties – – – – – – Particle size Mineral composition Abundance of organic matter Color Texture Bulk density Humus – decomposed material Soil Horizons – – A horizon: topsoil B horizon: subsoil – – C horizon: soil base Bedrock Conifer forests have acidic soil Loam – equal amounts sand, silt & clay – – – – Sand o o o Silt o o o Clay o o o Loam o o Visible particle size Contains some nutrients High aeration and water drainage More water drainage than sand More nutrients that sand Fertile Smallest particle size Poor nutrient content Poor drainage (best at retaining water) All the nutrition! Fertile Nitrogen Cycle – – – – – – Nitrogen gas in the atmosphere Lightning or bacteria converts nitrogen gas to ammonia Nitrification turns ammonia into nitrates Plants assimilate the nitrogen from the nitrates in the soil Animals eat plants and take up the nitrogen Erosion/leaching of nutrients return nitrogen to the atmosphere 4/25/2024 Movement of Water and Solutes in Plants How does water get from roots to the leaves? – – – Xylem Capillary action Cohesion tension theory Movement of Water into the Root: – – – Apoplastic route: around the protoplasts via the cell walls (gets stopped at the Casparian strip outside of the pericycle) Symplastic route: from protoplast to protoplast via plasmodesmata Transcellular route: from cell to cell, across the plasma membranes & tonoplasts Pericycle – produces branch roots Stomatal transpiration Environmental factors affecting transpiration: – – – Light/temperature (the stomata close at around 30oC) Humidity (if there is water in the air, the plant will not release a lot of water – and vice versa) Air currents (wind blows away water vapor) Water enters root hairs —- is conducted upwards thru xylem —- goes out thru stomata Sapwood vs. heartwood Sapwood is the outermost part of the inner bark (whose xylem and phloem are still actively conducting) Heartwood is the innermost part (secondary xylem that no longer conducts) Phloem loading Phloem gets sugars either through the symplastic route (via companion cells & plasmodesmata) or the apoplastic route (via carrier proteins) Making Maple Syrup! 1. Why is the xylem tapped? This is where the sap is found! Sugar is stored in the roots during the winter, and in the spring sugar water (sap) travels up the plant through the xylem towards the leaves 2. Why is it tapped in the spring? The pressure builds up in the tree during the winter, and when the xylem is tapped in the spring, the pressure is released and the sap starts flowing. 3. What is in large excess in the sap that must be minimized by boiling to make syrup? Water (sap is only 2% sucrose and 98% water)