In respiration, plants use oxygen to break down an energy source such as carbohydrates, proteins, and fats into CO2 and water. In the field, this water is replaced by water taken up through roots.
Harvest cuts off the link to roots, and the plant instantly loses water.
Produce breathes like people do, and like a person, it breathes harder and loses more water on a hot day than on a cool day. The higher the respiration rate, the faster you lose water. For ex., asparagus and peas are very high, leaf lettuce is in the middle, and potatoes and celery are very low. Cooler temperatures slow down respiration. Some vegetables are chilling sensitive.