Based on the illustrated agroecosystem, which process directly returns CO2 to the atmosphere from soil and plant systems?

• Uptake

• Respiration

• Weathering of bedrock

• Nutrient inputs

Fill in the blank: In sustainable agriculture, soil microorganisms primarily facilitate _______ of organic matter to release nutrients for plant uptake.

Compare natural and anthropogenic nutrient sources in an agroecosystem. Explain one example from each category provided and describe how they contribute nutrients.

Which statement best explains why nutrient cycling is essential for sustainable agriculture?

• It maximizes chemical fertilizer usage.

• It ensures nutrients taken up by crops are returned to the soil through natural processes, maintaining soil fertility.

• It prevents decomposition by microbes.

• It eliminates the need for organic inputs.

Which statement best explains why atmospheric nitrogen (N2) must be transformed before plants can use it?

• Plants can absorb N2 directly through stomata.

• N2 is inert; soil microorganisms convert it into NH4+ and NO3− that plants can assimilate.

• N2 is toxic to plant roots unless converted into NO2−.

• N2 spontaneously becomes NH3 in soil without microbial action.

Fill in the blanks with the correct nitrogen transformation pathway: _______ converts atmospheric N2 into NH4+, _______ oxidizes NH4+ to NO2− and then to NO3−, and _______ reduces NO3− back to N2 in anaerobic conditions.

In a well-aerated agricultural soil rich in legume roots, predict the dominant nitrogen transformations and responsible microbes. Explain your reasoning based on environmental conditions and plant associations.

Identify the process by which microorganisms convert insoluble inorganic phosphate minerals (e.g., Ca3(PO4)2, FePO4, AlPO4) into forms available for plant uptake.

• Mineralization

• Immobilization

• Solubilization

• Precipitation

A flooded paddy soil relies on cyanobacteria such as Anabaena sp. and Nostoc sp. to improve phosphorus availability. Which mechanism is primarily involved?

• Nitrogen fixation increases P directly

• Secretion of organic acids that solubilize mineral phosphate

• Mycorrhizal symbiosis expands root surface

• Exopolysaccharide sorption immobilizes P

Which process directly removes atmospheric CO2 and incorporates it into plant biomass in the carbon cycle?

• Animal respiration

• Photosynthesis

• Root respiration

• Decomposition by microbes