Question

In a stable ecosystem, the relationship between Gross Primary Productivity (GPP) and community respiration (R) is:

• A. GPP $<$ R
• B. GPP = R
• C. GPP $>$ R always
• D. GPP independent of R

Hint:

The P/R ratio (Production to Respiration) is a reliable indicator of ecosystem maturity.
In a stable climax community, the P/R ratio is always equal to $1$.
If P/R $>$ $1$, it is an autotrophic or successional system.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Gross Primary Productivity (GPP) is the total rate at which solar energy is captured by autotrophs to produce organic matter.
Community Respiration (R) is the total energy consumed by all organisms (producers, consumers, and decomposers) in the ecosystem for metabolic processes.
Stability in an ecosystem refers to a state of equilibrium, often achieved in a climax community.

Step 2: Detailed Explanation:
In a stable ecosystem, there is a balance between energy gain (production) and energy loss (respiration).
During the early stages of succession, GPP is typically greater than R, leading to an accumulation of biomass.
As the community reaches its stable climax stage, the rate of organic matter production (GPP) becomes almost equal to the rate of consumption (R).
This means the Net Ecosystem Productivity (NEP = GPP $-$ R) approaches zero.
If GPP were less than R, the ecosystem would lose its biomass and eventually collapse.
Thus, for long-term stability, GPP must be equal to R.

Step 3: Final Answer:
In a stable or climax ecosystem, the total production is balanced by total community respiration, resulting in the relationship GPP = R.

Answer 2

Think of a stable ecosystem as an account that must stay balanced over the long run: energy captured by autotrophs (Gross Primary Productivity, \(GPP\)) is the income, and energy consumed by all organisms for respiration (\(R\)) is the expenditure. Checking each option against this ledger shows which one can hold indefinitely.

1. \(GPP \lt R\): here the ecosystem spends more energy than it earns every single cycle. Such a deficit forces organisms to draw down stored biomass continuously, and a system that keeps losing capital eventually runs out of it and collapses, so this cannot describe a stable, self-sustaining ecosystem.
2. \(GPP = R\): income exactly matches expenditure, so the account neither grows nor shrinks. Net Ecosystem Productivity, \(NEP = GPP - R\), works out to zero, meaning biomass stored in the system stays constant year after year. This is exactly the condition of a balanced ledger and matches what stability means for an ecosystem.
3. \(GPP \gt R\) always: a permanent surplus means biomass keeps accumulating without limit. That describes a developing or early-successional system still building up standing crop, not one that has already reached a steady state; no real ecosystem can add biomass forever without hitting resource ceilings.
4. GPP independent of R: in every real ecosystem, respiration scales with the biomass and activity that photosynthesis itself supports, so the two quantities are tightly linked, not independent. Treating them as unrelated ignores the basic energy-flow coupling between production and consumption.

Only the balanced-ledger condition, where energy fixed equals energy spent, can persist indefinitely without the system either shrinking away or growing without bound.

Therefore, the correct answer is GPP = R.