In a green house, there can be many factors responsible for the ultimate produce. These are small areas that are manmade and influenced to optimize plant production. Every plant needs abundant carbon dioxide, good soil and adequate sunlight to grow healthy and strong. Factors like humidity and warmth matter as well.
However, sometimes one factor becomes the limiting problem. In this case increasing the amount of that factor results in extra growth of the plant. In the problem, increasing the carbon dioxide concentration lead to increase in plant growth, hence it was the limiting factor in the green house set up.