Effects of enhanced UV-B radiation on the nutritional chemistry of forages and influences on mammalian herbivores.

摘要

Ozone depletion has caused ultraviolet-B (UV-B) radiation to rise in temperate latitudes of both hemispheres. Enhanced UV-B radiation can affect plant nutritional chemistry, but the effects of these changes on mammalian herbivores are unknown. Therefore, we measured nutritional and chemical constituents of 18 forages and related changes to in vitro dry matter digestibility, and intake and in vivo digestibility of five of these plants by a ruminant herbivore (blue duiker, Cephalophus monticola) and a specialist (pygmy rabbit, Brachylagus idahoensis ) and generalist (eastern cottontail, Sylvilagus floridanus ) hindgut-fermenter. Forages were irradiated for three months with ambient (1X) or supplemental (1.6X) UV-B radiation representing a 15% ozone depletion for Pullman, WA, USA. Enhanced UV-B radiation had minimal effects on the nutritional content and the tannin-binding capacity of forages. However, flavonoid compounds increased in seven of the 13 forbs, shrubs, and trees that were evaluated. Flavonoids were found to decrease only in yarrow ( Achilles millefolium). Blue duikers and both rabbit species preferred 1X or 1.6X UV-B grown plants equally. Likewise, they digested the dry matter, fiber, protein, and energy similarly. In vitro dry matter digestibility (IVDMD) differed between 1X and 1.6X UV-B grown plants in only three of the 18 plants and these differences were inconsistent. With supplemental UV-B radiation, IVDMD decreased in big sagebrush (Artemisia tridentata ), but increased in winterfat (Eurotia lanata) and mountain mahogany (Cercocarpus montanus). We conclude that expected increases in UV-B radiation from ozone depletion would have minimal effects on intake and digestion of mammalian herbivores.