Keeping Plants Cool for the Summer

You might love a warm summer, but heat is a big problem for plants. It dries out plants and causes them to slow down photosynthesis. Luckily, plants have adapted to heat, and there are things we can do to help them.

Fun Fact: Plants get most of their weight from the air. Air is where plants get carbon to make sugar and make cellulose.

Plants on a hot day

To get essential nutrients from the air like oxygen and carbon plants have stomata. Stomata are like noses for the plants, allowing them to breathe. Plants can open and close stomata depending on how much carbon they need. The problem with keeping stomata always open is that the plant loses water when the stomata are open. Plants are continually trading water for carbon. The hormone that closes stomata and tells the plant that there is a drought is abscisic acid. Abscisic acid also slows down photosynthesis, slow cell division and inhibits fruit ripening. It does this to reduce the amount of sugar and carbon the plant.

How is this helpful for us growers? We can apply abscisic acid to plants to tell them that there is a drought and to prepare for less water. In a way, we’re talking to plants.

So, the plants are in a balancing act of exchanging water for carbon to keep their stomata open. How can we help them on a hot day when the plant wants to close stomata and stop photosynthesis? We can water them. The problem might be then that we water them, but the water evaporates before it gets to the plant. How can we water plants without wasting water? One way is drip irrigation.

Drip Irrigation

Think about if you were an alien and you wanted to keep humans alive. You know humans need water, so you dump thousands of gallons of water in one place. Call it a day? Well, some humans will die of thirst while others will drown. We are the aliens, but instead of people, we take care of plants. We know that plants need water, but we might not be giving water to plants in the best way. Overhead irrigation is the standard way to water. It is cheap and gets the job done. However just like being a clueless alien, it causes problems: increases in diseases, wasting water, more soil erosion, and increase in weeds.

 

Drip irrigation fixes these problems and conserves water on hot summer days.
How modern drip irrigation works is it uses plastic tubing, a filter, a pump, and a micro spray head or dripper. These parts move the water to the plant and slowly release the water, or drip it onto the soil right next to the plant. Unlike animal cells, plant cells have a cell wall and are pressurized with water. When the plant loses water, the cell loses shape and the plant wilts. Giving water to plants on hot days keeps the cell turgid and in the correct shape. When plants are under drought stress, what do they do? How do they adapt?

Plants Adaptation to Heat and Drought

Plants have several mechanisms to adapt to drought stress. One strategy of plants are to flower. Plants will quickly flower and die, ensuring the survival of the next generation. You might think, great they flower then I can harvest, however flowering from drought stress causes a significant decrease in yield. Fruits have less sugar and are much smaller. Flowering is a last resort for plants, but what about for just one hot summer day?

For shorter drought periods plants close their stomata to prevent water from escaping. Doing this prevents carbon dioxide from being absorbed, so plants slow down photosynthesis.

On really sunny hot dry days plants aren’t doing much work. To keep their cells in the correct shape plants increase their salt concentration so they can hold onto more water in the cell. Don’t run and put table salt on your plants, as they will have a hard time absorbing it and will prevent them from absorbing water. Plants are continually optimizing scarce resources. If nutrients are scarce, they substitute them for another resource. Some plants use sugars instead of salts to regulate the water inside their cells. Great that plants adapt to drought stress, but what can we do to help them?

Nutrients to help plants

When plants are balancing their salt or sugar level to keep water in their cells, they also use other compounds to help.

    • Proline and glycine betaine has been shown to help the plant keep water and recover after a drought.
    • Silicon is the go-to nutrient for drought stress. Silicon helps reduce the number of other nutrients the plant needs to adapt to drought. Phosphorus also helps cells keep their water and shape.
    • High temperatures cause plants to dry out faster. Water is a critical resource of plants.

To conserve water plants close their stomata. By closing stomata, plants cannot absorb carbon dioxide and must slow down photosynthesis. Water is also used to maintain plant shape. Plants increase salts or sugars to keep water in the plants’ cells. Growers can help plants in hot or dry conditions by applying small concentrations of Abscisic acid before a drought or giving the plant proline, glycine betaine, silicon, or phosphorus to maintain water levels in the plant cells.

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