well...that was a lot of theory... Bottom line: Magnesium a key nutrient in our fast growing plants.
The faster they grow, the more energy is required and more energy produced, the more Mg2+ is needed.
If you go to my litterature thread, you will find the text book Introduction to Plant Physiology. If you ever have passed Biology 101 or a course in general biochemistry, you are able to comprehend this book. I never studied plant biology at university, so I have to read up so I at least master a B.Sc. level of botany.