All organisms depend on chemical reactions for life. The speed of these reactions increases rapidly with increasing temperature. Some animals, such as ourselves, closely control internal heat regardless of the surrounding temperatures, and thus our metabolic reactions are stable. Most animals, though, lack internal controls. Instead, their body temperature depends on the surrounding temperature, and control is based on moving between warmer and cooler places.
Plants have a different problem. Stuck in place, they have few means of
control. Up to a point, things work—as our Chihuahuan Desert summer temperatures climb,
the chemical reactions of photosynthesis speed up and more food is manufactured,
outstripping the increased levels of other bodily processes. The difficulty is, that if
it gets hot and dry enough, plants have to seal off their leaves to save moisture. When
this happens, a raw material for food manufacture, carbon dioxide gas, becomes
unavailable, and photosynthesis stops while other chemical reactions continue.
Non-native plants that are not adapted to go into dormancy quickly deplete their food
supply—even to the point of death.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.