Question

How does decreasing light intensity affect rate of photosynthesis in vascular aquatic plants?

Answer 1

It affects it by the increase of light intensity it increases the rate of photosynthesis but after the light intensity reaches its certain level the plant reaches its maximum rate of photosynthesis and photosynthesis occurs in the chloroplast.

Answer 2

The rate of photosynthesis is proportional to the intensity of incident light (given that it is on appropriate wavelength)
lowering the intensity will decrease the rate, while rasing it will increase it

hope this helps