[Campbell Biology P.260] Tropical rainforests are estimated to be responsible for approximat... | Practice Question

Tropical rainforests are estimated to be responsible for approximately 20% of global photosynthesis, yet their consumption of large amounts of CO2 by living trees is thought to make little or no net contribution to the reduction of global warming. Which of the following best explains this paradox?

  • A: The high rates of decomposition in rainforests release all fixed carbon back to the atmosphere as CO2.
  • B: Rainforest trees primarily utilize C4 photosynthesis, which is less efficient at carbon capture.
  • C: The CO2 fixed by rainforests is mainly converted into glucose, which quickly undergoes cellular respiration by the trees themselves.
  • D: Large amounts of CO2 are released from the soil due to volcanic activity in tropical regions.

Explanation

While living trees in tropical rainforests absorb significant amounts of CO2 through photosynthesis, these ecosystems are often in a state of dynamic equilibrium. When trees die, their organic matter decomposes, and decomposers bacteria and fungi release CO2 back into the atmosphere through cellular respiration. In a mature, undisturbed rainforest, the amount of CO2 taken up by photosynthesis is roughly balanced by the amount released through respiration and decomposition, leading to little or no net contribution to atmospheric CO2 reduction.