Hot Weather & Your Trees

Most of us are familiar with the results of drought stress, but did you know that high temperatures alone can cause significant damage to the health of your plants? Given that many areas are recording rising temperatures, we should become aware of how warmer temperatures affect the physiology of plants.

High temperatures reduce photosynthetic rates faster than they reduce respiration rates. The result is an imbalance because the carbohydrates produced by photosynthesis are used faster than they can be replaced. Higher temperatures increase the loss of water through stomates in the leaves, and thereby increase demands on the root system to take up water to cool the tree via transpiration. (High temperatures are usually accompanied by low rainfall—adding insult to injury.) Cellular membranes also become unstable and result in ion leakage within the leaf cellular structure.

sun rays through trees leaves
Sun rays through trees leaves

So how do plants cope with high temperatures? One way is through the formation of heat-shock proteins (HSPs). Found in humans and other animals as well, HSPs perform the same function in both animals and plants: maintain the integrity and function of proteins in high heat. HSPs form in response to rising temperatures and help to stabilize proteins to ensure cell functioning; they help to moderate metabolic reactions that would otherwise speed up and cause an imbalance of metabolites and acidification in cellular tissue. Calcium also plays a critical role in temperature stress adaptation by modulating enzyme activity and stabilizing membranes. There are physical adaptations as well, such as increasing leaf hairs and waxes, changing leaf morphology to reduce light interception, and changing leaf orientation.

Preparing plants for heat stress consists of the horticultural basics: plant properly in high-quality soil, manage soil fertility, and irrigate properly. Soil sampling to assess soil nutrition (particularly calcium) and physical properties is also important so that fertilization can be customized to optimize the soil environment and enhance plant health.

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