In an aquatic ecosystem, which factor generally least influences the rate of photosynthesis (primary production) compared with light intensity, nutrient availability, and temperature?

• A. Salinity (within the normal tolerance range of the photosynthetic organisms present)
• B. Availability of limiting nutrients such as nitrogen or phosphorus
• C. Light intensity (photosynthetically active radiation)
• D. Water temperature affecting enzyme activity in photosynthesis

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the main factors that influence photosynthesis in aquatic ecosystems. These typically include light intensity, nutrient availability, temperature, and salinity.
2. Step 2: Recognize that light intensity directly affects the energy available for photosynthesis, making it a critical factor.
3. Step 3: Note that nutrient availability, especially limiting nutrients like nitrogen and phosphorus, is essential for building the molecules needed for photosynthesis and growth.
4. Step 4: Consider temperature, which influences enzyme activity and thus the rate of photosynthetic reactions.
5. Step 5: Evaluate salinity, which generally has less impact on photosynthesis rate within the normal tolerance range of the organisms, making it the least influential factor compared to the others listed.