Certified Professional Horticulturist (CPH) Practice Exam

Water loss from plants, primarily through the process of transpiration, is significantly influenced by atmospheric conditions such as temperature, humidity, wind, and sunlight. Weather conditions directly affect the rate of evaporation from plant surfaces and soil, thereby impacting how much water is lost through transpiration. For instance, on hot, dry, and windy days, plants may lose water more quickly due to increased temperature and lower humidity levels leading to higher rates of evaporation.

While the other factors mentioned also play a role, their influence is often more indirect. Soil drainage affects how much water is available to plants but does not directly regulate the rate of water loss; rather, it influences the water supply. Competition from adjacent plants can lead to resource competition, but it is not a primary factor for the rate of transpiration for a single plant. Leaf surface area does influence transpiration rates—larger leaf areas can result in more significant water loss—but this is more of a physical characteristic of the plant itself rather than an environmental condition.

Thus, the environmental factors associated with weather patterns have the most profound and direct impact on water loss from plants due to their immediate effect on transpiration rates.