Photosynthesis is the process in which the energy of sunlight is used by plants and other organisms to synthesise carbohydrates from carbon dioxide and water. Most forms of photosynthesis release oxygen as a byproduct, which is, of course, good for humans and other animals because we require oxygen to breathe. The rate of photosynthesis is not constant, however, and there are a number of factors that limit it.
Because sunlight is such an important factor in photosynthesis, low light intensity has been found to decrease photosynthesis. The reverse has been found as well, however. Once light intensity reaches 10,000 lux (the unit for measuring light intensity), the rate of photosynthesis no longer increases. In fact, high intensity light can actually decrease photosynthesis.
Carbon Dioxide Concentration
Reduced carbon dioxide in the atmosphere can significantly limit photosynthesis. Typically, our atmosphere consists of about .03 to .04 per cent carbon dioxide, which is interesting when you consider that when the rates of carbon dioxide have been higher in the atmosphere, the rate of photosynthesis has increased. This is why greenhouses are used: They can artificially increase carbon dioxide levels. As a result, bigger and better-yielding crops have been grown.
Water is another of the most important factors that limits photosynthesis. Because photosynthesis involves synthesising carbohydrates from water, when there is a lack of water in an organism, rates of photosynthesis can only decrease. You can see this when you don't water your plants. Although you don't want to overwater your plants, when you don't water them at all, they die very quickly.