2-6: Soil-Vegetation-Atmosphere Modeling

Unit Objectives

• To understand how interactions among vegetation, soil, and atmosphere are included in global and regional climate models.
• To understand how plants regulate the flow of CO2 and moisture in and out of leaves.

Preparation for Online and Class Discussion

1. Read the summary information.

   Class images

2. Print for offline review.

3. Take the summary information quiz. Quizzes are available from your portfolio.

4. Additional Related Reading. Although you are not ultimately responsible for content listed in this section, we encourage you to fully explore the links in order to provide a better scope on the upcoming class discussion.

Online and Class Discussion

• Social Comments
• Knowledge-building Comments
• Ethical Comments

• Unit Problem to Ponder
• Unit exam questions from previous years
• Unit discussions from previous years

Unit Wrap-up Materials

• Group Discussion Summary: Summary prepared by: Jared Anderson, Don Miller and Bobbier Johnson

  Unit 2-6 Summary

  Both global and regional climate models need accurate input/output of energy transformations to perform properly. Soil-vegetative-atmosphere transfer models (SVATs) link global and regional climate models to these fluxes. SVATs have emerged due to:

  1. heat and moisture input to the atmosphere from the surface and how the surface takes these fluxes to make energy and momentum through friction.
  2. the need to determine how plants and plant communities respond to environmental conditions.

  The SiB model allows for the interactions between plants and the atmosphere through:

  1. Radiation absorption and reflection.
  2. Control of evapotranspiration through plant stomates and canopies.
  3. Momentum transfer by friction and turbulence caused by plants.
  4. Soil moisture availability as a function of root length.
  5. Insulation from plants shading of the surface.

  Terms are defined for plant and surface properties that affect atmospheric conditions as described by the SiB model. The areas affected are:

  1. Atmospheric boundary conditions including temperature, vapor pressure, wind speed, radiation and precipitation.
  2. Morphological parameters such as the two classifications of vegetation, and rooting zones.

  SVAT models are designed to describe the flow of energy, mass, momentum, trace gases, etc., between the atmosphere and the surface biosphere, all per unit time. Such flows are called fluxes, and the components are analogous to the potential, resistance, and current flow (flux) in an electric circuit. Stomates, which regulate plant water vapor and CO2 exchange, act as control valves, determining the flux of these gases between plants and the atmosphere. Equations are given describing conservation of energy and water substance and their interrelationship, allowing SVATs to describe both energy and moisture content in atmosphere and soil reservoirs, and their respective fluxes.

  Dialog:

  Bernard - questions whether plants can sufficiently cool themselves if global warming causes the stomates to constrict, allowing less water for evaporative cooling.
  Frundle - says alfalfa roots are not deep but are massive, drawing lots of surface moisture but not much deep moisture. Believes leaf area has a greater effect due to more stomata meaning greater water vapor release. Research shows greater CO2 concentrations cause smaller stomates but higher plant productivity.
  Bickert - says that if stomates control CO2 exchange then root systems do not matter.
  Kochen - does more transpiration change local weather conditions? Questions increased erosion with increased rainfall and atmospheric moisture content.
  Johnson - provides reference for rooting depths of plants and points out the distinction between the amount of moisture in the soil and the amount actually available to plants, based on different soil types.
  Salem - more roots mean more water transferred from soil through roots to the air.
  Kardell - increased available moisture in the atmosphere from plant sources can be expected to increase the number and severity of thunderstorms and other types of severe weather.
  Cillo - more plants growing puts more moisture into the atmosphere as evidenced by more rain in early summer than in late summer.
  Pederson - Longer roots mean better chance of survival for plants, especially in drought conditions.
  Anderson - deeper roots absorb more moisture and the plant puts more moisture into the air as a consequence.
  Johnson - provides a website describing root depths for various plants, including corn at rooting depths of 3 to 4 feet.
  

References

Soil, Water, and Crop Characteristics Important to Irrigation Scheduling