ESA Soil Science & Biogeochemistry Flashcards
6 cards from real ESA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 ESA Soil Science & Biogeochemistry flashcards as text
Which soil horizon is characterized by the accumulation of leached materials such as clay, iron oxides, and organic matter?
Answer: B horizon
The B horizon (subsoil) is the zone of illuviation where materials translocated from upper horizons accumulate.
The primary driver of nitrogen fixation in terrestrial ecosystems is:
Answer: Biological N2 fixation by diazotrophic microorganisms
Biological nitrogen fixation by diazotrophs (e.g., Rhizobium, free-living cyanobacteria) is the dominant pathway converting atmospheric N2 to bioavailable forms.
Cation exchange capacity (CEC) of a soil is primarily determined by:
Answer: Clay content, clay mineralogy, and organic matter content
CEC reflects the abundance of negatively charged sites on clay particles and organic matter surfaces that retain exchangeable cations.
Which process converts ammonium (NH4+) to nitrate (NO3−) in soils?
Answer: Nitrification
Nitrification is a two-step aerobic microbial process: ammonia-oxidizing bacteria convert NH4+ to NO2−, which nitrite-oxidizing bacteria then convert to NO3−.
Soil organic matter decomposition is primarily regulated by which set of factors?
Answer: Temperature, moisture, and substrate quality (C:N ratio)
Decomposition rates are controlled by temperature and moisture availability, which govern microbial activity, and by litter chemistry (C:N ratio, lignin content).
Which ectomycorrhizal adaptation allows host trees to access phosphorus in organic soil layers?
Answer: Production of phosphatase enzymes by fungal hyphae
Ectomycorrhizal fungi produce phosphatase enzymes that mineralize organic phosphorus, making it available for plant uptake.