diel

Diel is an adjective used in scientific literature to describe phenomena that follow a 24-hour cycle associated with the day–night cycle. In chronobiology, ecology, agriculture, and environmental science, diel patterns describe rhythms that repeat roughly every day and are often driven by light availability, temperature, and behavioral schedules.

Diel rhythms influence physiology and behavior. Many organisms show diel regulation of gene expression, metabolism, feeding, and movement, with peaks and troughs aligned to daylight. In plants, photosynthesis and stomatal conductance vary across the diel cycle; in animals, activity levels often rise during specific diel windows.

In ecology and oceanography, diel cycles are evident in phenomena such as diel vertical migration, where plankton and zooplankton ascend during nighttime and descend by day to avoid predation, and in primary production that follows light availability. Human activities, such as agriculture and fishing, also consider diel timing.

Terminology varies: diel is used to denote processes tied to the 24-hour day-night cycle and is often treated as synonymous with diurnal or daily in scientific writing, though some authors reserve diel for particular light-driven rhythms. The term is most common in scholarly sources rather than everyday language.