Submitted to: Photochemistry and Photobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2003
Publication Date: 3/10/2004
Citation: King, J.Y., Milchunas, D., Mosier, A.R., Moore, J., Quirk, M., Morgan, J.A., Slusser, J. 2004. Uv radiation effects on plant growth and forage quality in a shortgrass steppe ecosystem. Photochemistry and Photobiology. 97:404-410. Interpretive Summary: Predictions of changes in UV-B radiation due to reduced stratospheric ozone (O3), increased tropospheric O3, and increased air pollution motivate current research interests in the effects of UV radiation on ecosystem processes. It is recognized that enhanced UV-B radiation can affect plant productivity and species composition, tissue chemistry, and decomposition and nutrient cycling in ecosystems. Efforts have concentrated on understanding changes at high latitudes because the largest changes in stratospheric O3 have occurred there. However, the intensity of UV radiation is greatest at mid-latitudes and increases in air pollution and changes in cloud cover associated with global climate change raise questions concerning UV effects in other systems as well. The focus of this research is to examine the influence of UV-B radiation on the decomposition of shortgrass steppe vegetation under controlled field conditions and, furthermore, to assess the importance of UV-B radiation as an abiotic control on decomposition compared to moisture and biotic controls on decomposition. Initial results indicate that UV-B radiation tended to increase plant decomposition but did not affect plant digestibility.
Technical Abstract: We initiated a study in winter 2000 in a Colorado shortgrass steppe to investigate effects of altered ultraviolet-B (UVB) radiation and altered precipitation on plant growth, plant tissue decomposition, and litter faunal activity. In the field, open-air structures were constructed of solid plastic sheet material that either passed all wavelengths of solar radiation or passed only wavelengths greater than 400 nm (UVB =280-315 nm). Preliminary results indicate decreases in warm-season grass production under UVB radiation and drought conditions. Analysis of fiber constituents shows some significant seasonal and UVB treatment effects. The results of in vitro digestible dry matter analyses show significantly higher digestibility with UVB. Simulated grazing increased plant production, but there were no UVB by grazing interactions. Litter decomposition was affected by UVB exposure, the CO2 growing conditions, and precipitation level. Under dry conditions, UVB radiation tended to increase litter decomposition, as measured by mass loss. There were no clear initial effects of UVB treatment on soluble and fiber constituents of litter. Exclusion of UVB resulted in reduced fungal hyphae counts in ambient CO2-grown litter collected in fall 2002. Preliminary results indicate that litter arthropod density was lower with exposure to UVB and also lower under drought conditions.