Progress 09/01/09 to 08/31/10
Outputs
OUTPUTS: This past year was largely spent analyzing data, developing manuscripts for publication, and conducting field experiments/measurements during summer 2009. Significant findings included in our work this past year including the following. 1. We conducted non-destructive measurements of plant leaf epidermal UV transmittance (Tuv) on a variety of species, primarily crops and garden plants, but also included some woody shrubs and trees. Our results indicate that a) Tuv declined midday as compared to predawn for most species; b) variation in the magnitude of diurnal changes in Tuv appears related to variation in the base-line (predawn) levels of UV shielding (greater diurnal changes in Tuv when predawn values of Tuv are low); c) younger leaves in appear to show larger midday changes in Tuv than older ones; d) diurnal changes may be greater in for rapidly growing (with high turnover) leaves vs. slow growing, long-lived leaves; e) diurnal changes appear to follow a general pattern: forbs > grasses > shrubs/trees; and the link between midday changes and protective pigments extracted from leaves is still unclear. 2. We began a synthesis of our work of the past few years related to diurnal fluctuations in leaf epidermal transmittance for UV radiation. With a significant accumulation of information on the occurrence of this phenomenon, we are developing general patterns for this phenomenon. In addition, we are developing simple algorithms that can be used to aid in dose calculations for leaves exposed to UV radiation. PARTICIPANTS: Ronald J. Ryel, Associate Professor, Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT; Stephan D. Flint, Research Associate, Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT; Paul W. Barnes, Professor, Department of Biological Sciences, Loyola University New Orleans, New Orleans, LA; Wei Gao, Director of USDA UV-B Monitoring Research Program and Center of Remote Sensing and Modeling for Agriculture Sustainability, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO TARGET AUDIENCES: Crop researchers, crop producers, plant ecologists PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This research is designed to provide input to the USDA UV-B Monitoring and Research Program, program of the US Department of Agriculture's Cooperative State Research, Education and Extension Service (CSREES). The program provides information on the geographical distribution and temporal trends of UVB (ultraviolet -B) radiation in the United States. This information is critical to the assessment of the potential impacts of increasing ultraviolet radiation levels on agricultural crops and forests. In addition, the monitoring program supports research that increases our understanding of the factors controlling surface UVB irradiance and provides the data necessary for assessing the impact of UVB radiation on human health, ecosystems and materials. We propose to further examine how plants modulate their primary line of UV-B defense in response to varying climatic conditions, including solar radiation and drought. Findings from this research will enhance our mechanistic understanding of UV-B protection which is necessary to parameterize crop simulation models to account for UV acclimation. These findings will further allow us to better predict the interactive effects of changes in solar UV and other climate change variables, such as precipitation, on crop productivity and yield.
Publications
- Ryel RJ, Flint SD, Barnes PW 2010. Solar UV-B Radiation and Global dimming: Effects on plant growth and UV-shielding. UV Radiation in Global Change: Measurements, Modeling and Effects on Ecosystems, 370-394.
- Flint SD, Ryel RJ, Hudelson TJ, Caldwell MM 2009. Serious complications in experiments in which UV doses are effected by using different lamp heights.. Journal of Photochemistry and Photobiology B: Biology 97:48-53.
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Progress 09/01/08 to 08/31/10
Outputs
OUTPUTS: This past year was largely spent analyzing data, developing manuscripts for publication, and completing field experiments/measurements. Significant findings included in our work this past year including the following: 1. The accumulation of UV-absorbing compounds in epidermal leaf tissue of higher plants reduces the epidermal transmittance of solar UV radiation and therefore, plays a fundamental role in protecting underlying tissue from UV injury. In a previous study on several plant species growing at a high elevation site in Hawaii, we demonstrated that epidermal UV transmittance (TUV) varied over the course of a day, decreasing at midday and then increasing at night. In the present study, we tested the generality of this phenomenon by screening 52 taxa representing 37 species and 18 families of monocots and dicots (25 forbs, 5 grasses, 3 vines and 4 woody species of cultivated and wild species) grown in four locations spanning a gradient of ambient solar UV and climate (Hawaii, Utah, Idaho and Louisiana). Non-destructive measurements of adaxial TUV were made at predawn and midday under clear summer skies using a UV-A PAM fluorometer, which determines TUV based on the ratio of chlorophyll fluorescence induced by UV and blue-green (BG) radiation. Across all species, significant (P<0.05) midday decreases in TUV were detected in 23 of the 37 species tested (62%) with species in all life forms exhibiting this phenomenon. The mean magnitude of the diurnal TUV change was 3.1%, however interspecific variation was great, ranging from 0 in corn (Zea mays) to 31% for okra (Abelmoschus esculentus). Plants grown in Louisiana tended to show larger diurnal changes than those in the other three locations, and across all taxa, the magnitude of the diurnal TUV changes increased with increasing predawn TUV values (R2 = 0.74 for linear regression). Results indicate that diurnal changes in TUV 1) are widespread among higher plants at various locations; 2) vary both within and among species; 3) are highest in species with the lowest baseline levels of UV shielding, 4) tend to be greater in magnitude for plants growing in warm rather than cool environments; 5) diurnal changes appear to follow a general pattern: forbs > grasses > shrubs/trees; 6) the link between midday changes and protective pigments extracted from leaves is still unclear; 7) a consistent response of midday changes in TUV to drought condition of plants was not found; and 8) the pattern of diurnal changes in TUV may more closely follow the diurnal course of UB-B than visible light. PARTICIPANTS: Ronald J. Ryel, Associate Professor, Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT Stephan D. Flint, Research Associate, Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT Paul W. Barnes, Professor, Department of Biological Sciences, Loyola University New Orleans, New Orleans, LA Wei Gao, Director of USDA UV-B Monitoring Research Program and Center of Remote Sensing and Modeling for Agriculture Sustainability, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO. TARGET AUDIENCES: Crop researchers, crop producers, plant ecologists PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This research was designed to provide input to the USDA UV-B Monitoring and Research Program, program of the US Department of Agriculture's Cooperative State Research, Education and Extension Service (CSREES). This program provides information on the geographical distribution and temporal trends of UVB (ultraviolet-B) radiation in the United States; information critical to the assessment of the potential impacts of increasing ultraviolet radiation levels on agricultural crops and forests. In addition, the monitoring program supports research that increases our understanding of the factors controlling surface UVB irradiance and provides the data necessary for assessing the impact of UVB radiation on human health, ecosystems and materials. This project examined how plants modulate their primary line of UV-B defense in response to varying climatic conditions, including solar radiation and drought. Findings from this research have enhanced our mechanistic understanding of UV-B protection which is necessary to parameterize crop simulation models to account for UV acclimation. These findings will further allow us to better predict the interactive effects of changes in solar UV and other climate change variables, such as precipitation, on crop productivity and yield.
Publications
- No publications reported this period
- Ryel, R. 2010. Solar UV-B Radiation and Global dimming: Effects on plant growth and UV-shielding. UV Radiation in Global Change: Measurements, Modeling and Effects on Ecosystems, 370-394
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Progress 09/01/08 to 08/31/09
Outputs
OUTPUTS: This past year was largely spent analyzing data, developing manuscripts for publication, and designing field experiments for summer 2009. Significant findings included in our work this past year including the following. 1. We conducted non-destructive measurements of plant epidermal UV transmittance (Tuv) on several herbaceous plant species growing in various solar UV environments (sun/shade; tropical, subtropical and temperate habitats). 2. We conducted an experiment in the high-UV environment of Mauna Kea, Hawaii to compare the effects of UV-B reduction with a simulation of global dimming (accomplished with 13% shading). PARTICIPANTS: Ronald J. Ryel, Associate Professor, Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT; Stephan D. Flint, Research Associate, Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT; Paul W. Barnes, Professor, Department of Biological Sciences, Loyola University New Orleans, New Orleans, LA; Wei Gao, Director of USDA UV-B Monitoring Research Program and Center of Remote Sensing and Modeling for Agriculture Sustainability, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO. TARGET AUDIENCES: Crop researchers, crop producers, plant ecologists PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
With respect to the non-destructive measurements of plant epidermal UV transmittance (Tuv) on several herbaceous plant species growing in various solar UV environments (sun/shade; tropical, subtropical and temperate habitats), our results indicate that a) Tuv tracks solar radiation on a diurnal basis in sun and shade leaves on full sun days; b) variation in the magnitude of diurnal changes in Tuv appears related to variation in the base-line (predawn) levels of UV shielding (greater diurnal changes in Tuv when predawn values of Tuv are low); c) disruption of the solar radiation regime by clouds or experimental shading alters diurnal patterns of Tuv; d) diurnal changes in Tuv are not clearly linked to diurnal changes in whole-leaf concentrations of UV-absorbing compounds; and e) results suggest plants actively control diurnal changes in UV shielding and these changes occur in response to signals other than solar UV. Regarding the experiment in the high-UV environment of Mauna Kea, Hawaii to compare the effects of UV-B reduction with a simulation of global dimming (accomplished with 13% shading), using fava beans, (Vicia faba), we found: a) structural differences due to the treatments were minimal in this high light environment; b) most surprising was the minimal effect of UV-B on plant growth given the high UV-B environment, however, both UV-B and shading significantly influenced epidermal UV transmittance; and c) additional experiments suggest that the change in epidermal transmittance due to shading would most likely occur with foliage in high-shade environments. Such changes in secondary chemistry have the potential to affect herbivory, nutrient cycling, and plant response to pathogens. While there are few experimental studies that specifically address possible reductions in radiation due to global dimming, many UV reduction experiments have been conducted in recent decades. Attempts to generalize latitudinal responses from these studies, however, are frustrated by a number of factors. Chief among them are different methodologies (reduction of different UV wavebands in different experiments) and a lack of reporting UV irradiance levels. This research is designed to provide input to the USDA UV-B Monitoring and Research Program, program of the US Department of Agriculture's Cooperative State Research, Education and Extension Service (CSREES). The program provides information on the geographical distribution and temporal trends of UVB (ultraviolet -B) radiation in the United States. This information is critical to the assessment of the potential impacts of increasing ultraviolet radiation levels on agricultural crops and forests. In addition, the monitoring program supports research that increases our understanding of the factors controlling surface UVB irradiance and provides the data necessary for assessing the impact of UVB radiation on human health, ecosystems and materials. We propose to further examine how plants modulate their primary line of UV-B defense in response to varying climatic conditions, including solar radiation and drought. Findings from this research will enhance our mechanistic understanding of UV-B protection.
Publications
- Kanaga, M.K., Ryel, R.J., Mock, K.E., Pfrender, M.E. 2008. Quantitative-genetic variation in a phenotypically diverse dominant tree species. Canadian Journal of Forest Research 38:1690-1694.
- Barnes, P.W., Flint, S.D., Slusser, J.R., Gao, W., Ryel, R.J. 2008. Diurnal changes in epidermal UV transmittance of plants in naturally high UV environments. Physiologia Plantarum 133:363-372.
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