Natural Shortwave UV-B Radiation Increases UV absorbing pigments levels in Texas native grasses Chasmanthium latifolium and Bouteloua curtipendula

Plants are routinely exposed to UV-B radiation (280-315 nm) as a natural component of incident solar radiation. UV-B radiation is relevant to plants as both a source of damage and as a photomorphogenic cue, but the relative impacts of different wavelengths within the UV-B waveband are largely unresolved. Previous studies indicate that the full spectrum of solar UV-B radiation elicits unique responses in model plants under laboratory conditions compared to photons within the longwave UV-B band (300-315 nm), but the impacts of shortwave UV-B radiation (SW-UVB; 280-300 nm) remain unknown in a field environment. In this study, we examine the impact of shortwave UV-B radiation on the pigmentation and morphology of C3 shade-adapted inland sea oats (Chasmanthium latifolium) and C4 sun-adapted side-oats grama (Bouteloua curtipendula) in field conditions. We characterized the responses of these grasses to SW-UVB radiation by placing UV-naive individuals under SW-UVB excluding or transmitting filters at three field sites in Central Texas and measuring their responses through leaf pigment extract absorbance, leaf surface reflectance, and whole leaf chlorophyll and flavonoid content. We found that both species exhibited changes to their UV-B associated traits following exposure to the field environment, which were influenced by field site location, maximum daily temperature, and SW-UVB exposure. In particular, C. latifolium increased the ratio of its maximum to minimum absorbance in response to SW-UVB, while B. curtipendula exhibited higher flavonoid content in response to SW-UVB exposure. We believe this is the first time that the effects of SW-UVB radiation have been documented in a field environment.