In the context of ecosystem production and efficiency, gross primary productivity (GPP) of an ecosystem is best defined as:

• A. The amount of energy available to decomposers after all trophic levels have respired
• B. The total energy transferred from primary producers to herbivores per unit time (secondary productivity)
• C. The total rate at which primary producers capture and store chemical energy via photosynthesis before accounting for cellular respiration
• D. The rate of biomass accumulation by primary producers after subtracting energy used in respiration (net primary productivity)

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of Gross Primary Productivity (GPP). GPP refers to the total amount of chemical energy produced by primary producers (like plants) through photosynthesis in a given time period, before any energy is used for their own respiration.
2. Step 2: Differentiate GPP from Net Primary Productivity (NPP). NPP is the energy remaining after primary producers use some of the GPP for their own cellular respiration. Mathematically, NPP = GPP - Respiration by primary producers.
3. Step 3: Recognize that GPP represents the total energy captured and stored as organic molecules by photosynthesis, which forms the base energy input for the entire ecosystem.
4. Step 4: Understand that energy available to decomposers or energy transferred to herbivores (secondary productivity) are subsequent steps in the energy flow and are not definitions of GPP.
5. Step 5: Conclude that the best definition of GPP is the total rate at which primary producers capture and store chemical energy via photosynthesis before accounting for cellular respiration.