When the water availability of a plant's environment decreases, the plant can respond by closing its stomata. This reduces the amount of water that the plant loses through its leaves due to transpiration. Closing the stomata also reduces the amount of carbon dioxide that the plant can take in through its leaves, which will most likely result in
a decrease in the plant's photosynthetic rate. Photosynthesis is the process by which plants convert carbon dioxide and sunlight into glucose (sugar), using water as a raw material. Carbon dioxide is one of the essential components required for photosynthesis to occur. When the stomata close, the entry of carbon dioxide into the plant is restricted, causing a decrease in the rate of photosynthesis.
To understand why closing stomata reduces the availability of carbon dioxide, we need to know how plants obtain carbon dioxide. Plants take in carbon dioxide from the air through tiny openings on the surface of their leaves called stomata. Stomata allow carbon dioxide to enter the plant while also allowing water to escape through transpiration.
When water availability decreases in the plant's environment, such as during drought or hot weather, the plant closes its stomata to conserve water. The closure of stomata reduces the loss of water through transpiration, which helps the plant maintain its water balance. However, as a side effect, it also restricts the entry of carbon dioxide into the plant.
As a consequence, the reduced availability of carbon dioxide limits the plant's ability to carry out photosynthesis effectively. Photosynthesis requires a constant supply of carbon dioxide to produce glucose, which is the plant's source of energy. Without sufficient carbon dioxide, the plant's photosynthetic rate decreases, leading to altered growth, reduced production of sugars, and possibly even wilting or damage in severe cases.
It's worth noting that while closing stomata helps the plant conserve water in the short term, extended closure can have negative consequences in the long run, as it affects the overall health and growth of the plant.