Thomas A. (Tad) Day
Research
In our research we use physiological and ecological approaches to determine how environmental factors influence the performance and distribution of plants. Additionally, we often assess how these influences in turn alter the productivity and nutrient cycling at the whole-community or ecosystem level. Environmental factors which we have recently addressed include high levels of ultraviolet and visible light, extreme temperatures and water stress. Our investigations typically contain field work where we assess the importance of these factors in limiting plant performance under natural conditions, and are often complimented with laboratory experiments where we investigate the underlying mechanisms responsible for limitations. We focus on how these factors alter key processes such as photosynthesis, respiration, growth, reproduction, productivity, and nutrient cycling.
One area of our research examines how tundra ecosystems dominated by grasses and cushion plants along the Antarctic Peninsula are responding to climate change, particularly rising temperatures and altered precipitation regimes. One facet of this research involves monitoring existing plant populations and communities and examining how changes relate to year-to-year variations in climate. Another aspect of this research involves exposing these communities to manipulations such as warming or altered precipitation regimes and examining population and community responses. This work includes examining responses from the leaf level (e.g. photosynthesis) up to the ecosystem level (primary productivity and carbon sequestration). In addition to responses of plants, some of this work has also focused on the response of soil microinvertebrates and microbes to these climate manipulations.
Another area of our research examines how environmental factors, particularly UV and visible light, influence leaf or litter decomposition in the Sonoran Desert. The factors that control litter decomposition in deserts are not well understood. Understanding these factors has become increasingly important in the context of understanding climate change. For example, should climate change accelerate decomposition of plant material, this will likely release more carbon into the atmosphere, adding more greenhouse gases and contributing to further climate warming. Past work has shown that greater moisture and temperature, which promote microbial activity, usually accelerate leaf decomposition in many ecosystems. However, these factors are usually not strong predictors of decomposition in desert systems. We suspect that the high levels of sunlight, particularly UV light, in deserts have a strong influence on leaf decomposition, and also explain why factors such as moisture and temperature do not have strong effects. UV light is likely to accelerate decomposition because compounds that are prevalent in desert vegetation are prone to degradation by UV light. We also suspect that the high levels of UV light suppress microbial activity to the point that moisture and temperature have relatively little effect on decomposition.
Selected Publications
Day, TA, CT Ruhland & FS Xiong. 2008. Warming increases aboveground biomass and C stocks in vascular-plant dominated Antarctic tundra. Global Change Biology, 14: 1827-1843.
Day, TA, ET Zhang & CT Ruhland. 2007. Exposure to solar UV-B radiation accelerates mass and lignin loss of Larrea tridentata litter in the Sonoran Desert. Plant Ecology, 193:185-194.
Park, J, TA Day, S Strauss & CT Ruhland. 2007. Biogeochemical pools and fluxes of carbon and nitrogen in a maritime tundra near penguin colonies along the Antarctic Peninsula. Polar Biology, 30:199-207.
Morse, LJ, SH Faeth & TA Day. 2007. Neotyphodium interactions with a wild grass are driven mainly by endophyte haplotype. Functional Ecology, 21:813-822.
Neale, PJ, WE Helbing & TA Day. 2007. Symposium-in-print: UV effects in aquatic and terrestrial environments. Photochemistry and Photobiology, 83:775-776.
Park, JH & TA Day. 2007. Temperature response of CO2 exchange and dissolved organic carbon release in a maritime Antarctic tundra ecosystem. Polar Biology, 30:1535-1544.
Ruhland, CT, FS Xiong, WD Clark & TA Day. 2005. The influence of ultraviolet-B radiation on growth, hydroxycinnamic acids and flavonoids of Deschampsia antarctica during springtime ozone depletion in Antarctica. Photochemistry and Photobiology 81:1086-1093.
Mueller, EC & TA Day. 2005. The effect of urban ground cover on microclimate, growth and leaf gas exchange of oleander in Phoenix, Arizona. International Journal of Biometeorology 49: 244-255.
Coleman, RS & TA Day. 2004. Response of cotton and sorghum to several levels of subambient solar UV-B radiation: a test of the saturation hypothesis. Physiologia Plantarum 122:362-372.
Day, TA & PJ Neale. 2002. Effects of UV-B radiation on terrestrial and aquatic primary producers. Annual Review of Ecology and Systematics 33:371-396.
Convey, P, PJA Pugh, C Jackson, AW Murray, CT Ruhland, FS Xiong & TA Day. 2002. Response of Antarctic terrestrial microarthropods to long-term climate manipulations. Ecology 83:3130-3140.Day, TA, P Gober, FS Xiong & EA Wentz. 2002. Temporal patterns in near-surface CO2 concentrations over contrasting vegetation types in the Phoenix metropolitan area. Agricultural and Forest Meteorology 110:229-245.
Wentz, EA, P Gober, RC Balling & TA Day. 2002. Spatial patterns and determinants of winter atmospheric carbon dioxide concentrations in an urban environment. Annals of the Association of American Geographers 92:15-28.
Xiong, FS, Ruhland, CT & TA Day. 2002. Effect of springtime ultraviolet-B radiation on growth of Colobanthus quitensis at Palmer Station, Antarctica. Global Change Biology 8:1146-1155.
Morse, LJ, TA Day & SH Faeth. 2002. Effect of Neotyphodium endophyte infection on growth and leaf gas exchange of Arizona fescue under contrasting water availability regimes. Environmental and Experimental Botany 48:257-268.
Johnson, GA & TA Day. 2002. Enhancement of photosynthesis in Sorghum bicolor by ultraviolet radiation. Physiologia Plantarum 116:554-562.
Xiong, F & TA Day. 2001. Effect of solar ultraviolet-B radiation during springtime ozone depletion on photosynthesis and biomass production of Antarctic vascular plants. Plant Physiology 125:738-751.
Day, TA. 2001. Ultraviolet radiation and plant ecosystems. pp 80-117 In: Ecosystems, evolution and ultraviolet radiation. CS Cockell and AR Blaustein (editors). Springer-Verlag, NY.
Ruhland, CT & TA Day. 2001. Size and longevity of seedbanks in Antarctica and the influence of ultraviolet-B radiation on survivorship, growth and pigment concentrations of Colobanthus quitensis seedlings. Environmental and Experimental Botany 45:143-154.
Mantha, SV, GA Johnson & TA Day. 2001. Evidence from action and fluorescence spectra that UV-induced violet-blue-green fluorescence enhances leaf photosynthesis. Photochemistry and Photobiology 73:249-256.Day, TA, CT Ruhland, & F Xiong. 2001. Influence of solar ultraviolet-B radiation on Antarctic terrestrial plants: results from a 4-year field study. Journal of Photochemistry and Photobiology B: Biology 62:78-87.
Day, TA. 2001. Multiple trophic levels in UV-B assessments - completing the ecosystem. New Phytologist 152:183-186.