Light

Photosynthesis depends on the availability of light. Generally, as sunlight intensity increases, so does photosynthesis. However, for each plant species, there is a maximum level of light intensity above which photosynthesis does not increase. Many garden crops, such as tomatoes, respond best to maximum sunlight. Tomato production decreases drastically as light intensity drops, and only a few tomato varieties produce any fruit under minimal sunlight conditions.

Water

Water is one of the raw materials for photosynthesis. It is taken up into the plant by the roots and moved upward through the xylem.

Carbon dioxide

Photosynthesis also requires carbon dioxide (CO₂), which enters a plant through its stomata (Figure 25). In most plants, photosynthesis fluctuates throughout the day as stomata open and close. Typically, they open in the morning, close down at midday, reopen in late afternoon, and shut down for good in the evening.

 

Carbon dioxide is plentiful in the air, so it is not a limiting factor in plant growth. However, it is consumed rapidly during photosynthesis and is replenished very slowly in the atmosphere. Tightly sealed greenhouses may not allow enough outside air to enter and thus may lack adequate carbon dioxide for plant growth. Carbon dioxide generators are used to generate CO₂ in commercial greenhouses for crops such as roses, carnations, and tomatoes. In smaller home greenhouses, dry ice is an effective source of CO₂.

Temperature

Although not a direct component in photosynthesis, temperature is important. Photosynthesis occurs at its highest rate between 65° and 85°F and decreases at higher or lower temperatures.