[Campbell Biology P.684] Based on the provided data and additional information, evaluate how... | Practice Question

Based on the provided data and additional information, evaluate how nitrogen availability in northern forests changes with successional age, considering both Pleurozium nitrogen fixation and atmospheric deposition.

  • A: Nitrogen availability remains relatively constant across all successional ages due to consistent atmospheric deposition.
  • B: Nitrogen availability primarily decreases after 170 years as *Pleurozium* fixation declines significantly.
  • C: In younger forests (e.g., <100 years), atmospheric deposition is the primary source of new nitrogen, but in older forests, *Pleurozium* fixation becomes much more significant.
  • D: *Pleurozium* consistently contributes more nitrogen than atmospheric deposition across all successional ages.

Explanation

By adding the atmospheric deposition of 1 kg N/ ha·yr to the Pleurozium fixation rates, we can see the total nitrogen input. In young forests e.g., 35-41 years , Pleurozium contributes only 0.001-0.005 kg N/ ha·yr , making atmospheric deposition the primary source. However, in older forests e.g., 170+ years , Pleurozium fixation rates are much higher 1.3-3.0 kg N/ ha·yr , surpassing atmospheric deposition and becoming the more significant contributor to nitrogen availability.