Which condition limits photosynthetic rate when rubisco enzyme concentration in leaf cells remains constant?

💡 Explanation

When rubisco is constant, photosynthetic rate limiting factor shifts to substrates; decreasing CO2 diffusion reduces substrate availability because rubisco's carboxylation activity becomes limited despite sufficient enzyme levels. Therefore reduced CO2 diffusion limits photosynthesis rate, rather than water availability, nutrient uptake, or respiration which affect different processes.

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