According to weather reports, the 100 degree heat is supposed to break starting today with temperatures a more normal ninety or so degrees with chances for rain. We cope with heat through air-conditioning, drinking plenty of fluids, dressing appropriately, finding shade, and sweating. But have you ever wondered how crop plants cope with excessive temperatures or why plants wilt? They can’t hide or sweat but within limits they have very effective coping mechanisms. Please keep in mind this is the Readers’ Digest version.
• Plants can’t regulate their temperature as mammals do, however they do have certain mechanisms that help. The water that plants need for their cells and to produce sugars during photosynthesis enter through young actively growing parts of roots and root hairs. They are transported up to the rest of the plant through the xylem part of the vasculature system. What drives this is movement out of the plant through pores called stomata. These pores may be open or closed. When they are closed transpiration (water movement through the plant) ceases. As long as the plant roots can move enough water to maintain this stream, the stomata stay open and the plant maintains turgor pressure. If soil moisture is inadequate or the difference in humidity between the inside of the plant and the outside air is too great (low humidity, high temperatures, winds), the cells surrounding the stomata close the pore and transpiration ceases to protect the plant. When conditions are more favorable the stomata reopen and transpiration resumes. This helps protect the plant.
• Wilting is, believe it or not, a coping mechanism. When conditions are unfavorable, plants can protect themselves by wilting and leaf curling. Under what conditions this occurs depends on the species (corn wilts under less harsh conditions than grain sorghum). The soil moisture and conditions this happens at is the wilting point. Overnight as conditions improve, the plant will return to normal. If the unfavorable conditions still exist, it will wilt again. It isn’t that this is “good” for the plant but it does protect it and allow it to complete its life cycle and produce a seed crop. If conditions don’t improve, eventually the crop will not recover overnight and you have reached the PWP, the permanent wilting point and the plant is essentially toast.
• Other coping mechanisms include a variety of strategies. Grain sorghum can essentially go into neutral and wait for conditions improve and then resume its life cycle. Corn is totally driven by heat accumulation and simply tries to go ahead and produce grain no matter what the conditions. Corn can adjust the number of kernels set on the ear or the number that fill to insure some seed production. A field of corn can also adjust the number of ears/plants to fit conditions. Soybeans, drop pods and will only fill those they can support.
• Are these mechanisms foolproof – Of course not. But these mechanisms help the plant insure the survival of the species.
It is not that yield isn’t hurt with these strategies but they allow producers to produce crops under fairly extreme conditions.