Q.What is primary productivity? Give brief description of factors that affect primary productivity.

Primary productivity is the rate at which autotrophic organisms (mainly green plants and photosynthetic bacteria) capture and store energy as organic matter in an ecosystem. It represents the amount of biomass or organic matter produced per unit area over a time period.

The gross primary productivity (GPP) is the total rate of organic matter production during photosynthesis, while net primary productivity (NPP) is what remains after plants use some energy for their own respiration. NPP is the actual biomass available to consumers in the ecosystem.

Several factors regulate primary productivity:

• Plant species and photosynthetic capacity – Different plants have different efficiencies in capturing and converting light energy.
• Availability of nutrients – Essential elements like nitrogen and phosphorus directly limit plant growth and productivity.
• Photosynthetic efficiency – The ability of plants to convert light energy into chemical energy varies with plant type and environmental conditions.
• Environmental factors – Sunlight intensity and duration, temperature, moisture, and water availability all influence the rate of photosynthesis and plant growth. …

Primary productivity lies at the foundation of every ecosystem's energy budget. It represents the speed at which producers—chiefly green plants, algae, and photosynthetic bacteria—convert radiant energy from the sun into chemical energy stored in organic compounds. This process, overwhelmingly driven by photosynthesis, builds the biomass that fuels all other trophic levels. Without primary productivity, there would be no food, no oxygen replenishment, and no energy flow through the living world.

We distinguish between gross primary productivity (GPP) and net primary productivity (NPP). GPP is the total rate of organic matter production during photosynthesis. But plants themselves respire, burning some of that newly made organic matter to power their own life processes. What remains after subtracting respiratory losses is NPP—the actual rate at which energy is stored as plant biomass available to herbivores and decomposers. In essence, NPP = GPP − respiration, and it is NPP that ecologists measure when assessing an ecosystem's capacity to support life.

Factors That Govern Primary Productivity

Several interacting factors determine how much organic matter an ecosystem can produce. No single factor acts in isolation; rather, they work together, and often the scarcest resource becomes the limiting factor.

Light is the ultimate energy source. In terrestrial ecosystems, canopy structure and latitude govern how much sunlight reaches photosynthetic surfaces. In aquatic systems, light penetration is critical—turbidity, depth, and dissolved particles all restrict the photic zone where photosynthesis can occur. Below a certain depth, darkness halts productivity entirely.

Temperature controls the rate of enzymatic reactions in photosynthesis and respiration. Tropical regions, with year-round warmth, sustain high productivity; temperate and polar zones see productivity drop sharply in winter. Each plant species has an optimal temperature range, and extremes—either freezing cold or scorching heat—depress photosynthetic efficiency.

Water availability is often the master limiting factor on land. Even with abundant light and warmth, a desert remains unproductive because moisture is scarce. Conversely, tropical rainforests, blessed with high rainfall, exhibit some of the planet's highest NPP. Water is both a raw material for photosynthesis and the medium for nutrient transport within the plant. …

List the governing factors as a single limiting-factor checklist (light, temperature, water, nutrients, photosynthetic capacity) and, for each ecosystem type mentioned, mark which ONE factor is scarcest there. Liebig's Law says that single scarcest factor alone s …