Carbon Assimilation and Productivity

Goals and Objectives:

  1. Be able to distinguish between Net and Gross Primary Productivity and why determining productivity is important (especially in agriculture).
  2. Be able to distinguish between growth respiration and maintenance respiration, and why manipulation of maintenance respiration would lead to improved plant productivity.
  3. Be able to describe how different environmental factors could influence plant productivity.

Study Questions
  1. The following is a list of the new terms in this chapter.  Define each of these terms:
  1. Which of the two Primary Productivity measures is the one that is most important to plant productivity?
  2. Why is plant productivity based on carbon gain, and not rate of the light reactions of photosynthesis or carbon fixation (C3, C4, CAM)?
Respiration and Carbon Economy
  1. When determining plant productivity, which of the following has the greatest affect and why?  Growth Respiration or Maintenance Respiration
  2. How does growth and maintenance respiration vary in a plant (i.e. between different plant tissues)?
  3. How might one control the amount of carbon lost by maintenance respiration?
Factors Influencing Photosynthesis and Productivity
  1. What is the light compensation point?  How does it vary between C3 and C4 plants?
  2. What is the light saturation point?  How does it vary between C3 and C4 plants?
  3. From these last two questions - what do your answers tell you about productivity in C3 and C4 plants?
  4. How do plants respond to light over a whole growing season?
Carbon Dioxide
  1. How do C3 and C4 plants differ in their utilization of CO2?
  2. How does CO2 affect stomatal conductance?
  3. What can occur in greenhouses with respect to CO2levels?
  1. What is Q10?
  2. How does temperature affect the photochemical reactions in the thylakoid membranes?
  3. How does temperature affect the enzymatic reactions of C3 and C4 plants?
  1. How does water potential affect productivity?
  1. How does mineral nutrition affect productivity?
  2. Which mineral nutrient effects productivity the greatest?
Leaf/Canopy Factors
  1. In what way does growth and maintenance respiration change over the life of a plant leaf?
  2. Why are evergreen leaves a compromise between not being deciduous and having a high maintenance respiration?
  3. How does canopy structure affect productivity?
  4. What is the Leaf Area Index?  What relationship exists between an increasing Leaf Area Index and biomass?  (Hint:  look at Figure 13.9)
  5. How can the angle of  leaf attachment affect productivity?
  6. How does heliotropism help a plant increase its productivity?
Primary Productivity on a Global Scale
  1. Why are terrestrial ecosystems more productive than aquatic ecosystems?
  2. What factors are presently affecting the productivity of agricultural ecosystems?