plant transport and nutrition

• Plants need nutrients from above and below ground
• Plants require:

  Light from the sun

  CO2 from the air

  Water, O2 and minerals from the soil
• Vascular system allows for transport of nutrients
• Resources move from 'sources' to 'sinks'
• Light and CO2


  • Harvested by leaves
• Ability of leaves to absorb light


  • Leaf area index

  Phyllotaxy

  Leaf size

  Leaf orientation
• Water and minerals


  • Harvested with roots
• Ability of roots to absorb resources


  • Surface area (root hairs; mycorrhizae)

  Concentration of resources in soil
• Roots can respond to local environment
• Water is pulled (not pushed) upward from roots in xylem sap
• Xylem sap


  Transport fluid consisting of water and dissolved minerals
• Transpiration


  Evaporation of water from a plant's surface; drives xylem sap flow
• Negative water pressure in leaves helps draw water up through the xylem
• Hydrogen bonding allows for capillary action
• Transpiration is regulated by stomata
• Stomata


  Pores in the leaf surface; allow CO2 and O2 exchange, but also transpiration
• Guard cells help balance water conservation with gas exchange for photosynthesis
• Sugar source


  Organ that is a net producer of sugar, such as mature leaves
• Sugar sink


  Organ that is a net consumer of sugar, such as a tuber or bulb (storage roots)
• Phloem sap


  Aqueous solution high in sugar that travels from source to sink
• In addition to CO2, light and water, plants require other nutrients:

  Nitrogen

  Calcium

  Potassium

  Phosphorus

  Sulfur

  Magnesium
• Plants absorb required nutrients from soil
• Soil


  A complex ecosystem with both biotic and abiotic parts
• Abiotic particles in soil


  • Mainly weathered rock (sand, silt and clay)
• Biotic parts of soil


  • Living organisms existing between soil particles

  Humus: decaying organic material on the surface of soil
• In human agriculture, the nutrients and minerals in soil get depleted faster than they would in more natural conditions. Humans constantly add fertilizer to soil to combat this loss.
• Plants do not develop properly in nutrient poor conditions

  
• Plant nutrition involves other organisms
• Mutualistic relationships between soil microbes and plants


  • Nitrogen fixing bacteria
• Mutualistic relationships between mycorrhizal fungi and plants


  • ectomycorrhizae

  arbuscular mycorrhizae
• Non-mutualistic relationships with other organisms


  • Epiphytes

  Parasitic plants

  Carnivorous plants