When outside temperature increases, plant growth normally increases if moisture is available. What condition is required for this to happen?

• A. Soil pH is neutral
• B. Light intensity is high
• C. Moisture is available
• D. CO2 levels rise

Answer: (C)

Water availability is the factor that must be in place for increased temperature to boost growth. When temperatures rise, a plant’s metabolic rate and demand for water increase, but growth can proceed only if water is available to keep cells turgid, to transport nutrients, and to allow stomata to remain open for CO2 uptake and photosynthesis. If moisture is lacking, stomata close to conserve water, reducing CO2 entry and slowing photosynthesis, so growth does not rise with temperature. The other factors—soil pH, light intensity, and CO2—affect growth as well, but they don’t directly ensure that higher temperature will promote growth; without moisture, the temperature-driven growth boost cannot occur.