In terrestrial ecosystems, what is Net Primary Productivity (NPP), and how is it mathematically related to Gross Primary Productivity (GPP)?

Answer and explanation

Correct answer: C. NPP = GPP - R (where R represents respiratory losses by the autotrophic plants)

  1. Step 1: Gross Primary Productivity (GPP) is the total rate at which solar radiant energy is captured and converted into organic biomass through photosynthesis by autotrophs per unit area over a given time interval.
  2. Step 2: Autotrophic plants use a substantial fraction of this captured energy for their own cellular maintenance and cellular respiration ().
  3. Step 3: Net Primary Productivity (NPP) is the remaining biomass stored in plant tissues that is available for consumption by heterotrophic herbivores and decomposers: .
Answer
NPP = GPP - R (where R represents respiratory losses by the autotrophic plants)
Why not the others: 'NPP = GPP + R...' erroneously adds respiratory loss to gross production; 'NPP = GPP / R...' is dimensionally and mathematically incorrect; 'NPP = R - GPP...' would yield a negative value since gross photosynthetic production exceeds respiratory losses.

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