Research on the effects of ultraviolet-B (UV-B) radiation on soybean seed quality is limited. The objective of this study was to quantify UV-B doses, 0, 5, 10 & 15 kJ •m –2 •d –1, on soybean growth and seed quality. The experiment was conducted in the Soil-Plant-Atmosphere-Research (SPAR) facility. Chambers located at the R.R. Foil Plant Science Research Facility of Mississippi State University, Mississippi, USA, were used. Each SPAR chamber consists of a steel soil bin to accommodate the root system, a Plexiglas chamber to accommodate plant canopy and a heating, and cooling system connected to air ducts that pass conditioned air to cause leaf flutter through the plant canopy. The SPAR units, supported by an environmental monitoring and control systems, are networked to provide automatic acquisition and storage of the data, monitored every 10 seconds throughout the day and night. Soybean cultivar Pioneer 93Y92 (maturity group IV, Roundup Ready) was used in the study. The desired UV-B radiation was supplied by square-wave UV-B supplementation systems under near ambient PAR and delivered to plants for eight hours, each day, from 08:00 to 16:00 h by eight fluorescent UV-313 lamps. The results showed that increased UV-B did not influence many of the growth parameters because the treatments were imposed at mid-fruiting period. Seed quality parameters that are important for seed industry and human and animal nutrition were all affected by UV-B. Protein and palmitic and oleic acids declined linearly, while oil and linoleic and linolenic acid contents increased with increased UV-B. Sucrose, stachyose, and stearic acid contents showed quadratic trends, increased to about 4 - 5 kJ of UV-B and declined at higher doses. Thus, both current and projected UV-B radiation levels can modify soybean growth and seed quality. The functional algorithms developed in this study could be useful to develop UV-B- specific sub-models for soybean farm management and in policy decision areas.
Soybean is an important source of protein, oil, carbohydrates, isoflavones, and other minerals [
For the past 10 plus years, the effect of enhanced UV-B radiation on soybean yield has been extensively studied because of the importance of intensity and quality of solar radiation intercepted by the canopy in determining soybean yield and yield components [
Soybean is mainly produced for oil and soymeal, and the quality of oil and the soymeal depends on the composition of fatty acids and protein, respectively. Soybean seed protein concentration ranges from 341 to 568 g∙kg−1 of total seed weight, with a mean of 421 g∙kg−1. Oil concentration ranges from 83 g∙kg−1 to 279 g∙kg−1 with a mean of 195 g∙kg−1 [
Understanding soybean responses to the increasing intensities of UV-B radiation is much needed to develop suitable management and cultural practices for the present and future climates. Some studies have been carried out either under greenhouse or under unrealistic solar radiation environments and results may not be portable to field situations. Studies have been conducted on other crops such as wheat [
The Soil-Plant-Atmosphere-Research (SPAR) chambers located at the R.R. Foil Plant Science Research facility of Mississippi State University (33˚28N, 88˚47W), Mississippi, USA were used for this study. Briefly, each SPAR chamber consists of a steel soil bin (1 m deep by 2 m long by 0.5 m wide) to accommodate the root system, a Plexiglas chamber (2.5 m tall by 2 m long by 1.5 m wide) to accommodate plant canopy and a heating and cooling system connected to air ducts that pass conditioned air to cause leaf flutter through the plant canopy. The SPAR units supported by an environmental monitoring and control systems are networked to provide automatic acquisition and storage of the data, monitored every 10 s throughout the day and night. Many details on the operation and control of SPAR chambers were described by others [
Soybean cultivar Pioneer 93Y92 (maturity group IV, Roundup Ready) seeds were planted on 5 July 2011 in pots (22 cm tall and 22 cm diameter) filled with fine sand and soil mixed in the ratio of 75:25. Seventy pots having planted with 3 seeds per pot were maintained in an outdoor environment. In each pot one healthy plant per pot was maintained a week after emergence. Twelve pots, 1 plant pot−1 and 3 plants row−1, were arranged in 6 rows in each of the 4 SPAR chambers on 27 August 2011. Plants were watered three times a day with half- strength Hoagland’s nutrient solution [
The desired UV-B radiation was supplied by square-wave UV-B supplementation systems under near ambient PAR. The UV-B radiation was delivered to plants for eight hours, each day, from 08:00 to 16:00 h by eight fluorescent UV-313 lamps (Q-Panel Company, Cleveland, Ohio, USA) powered by 40 W variable dimming ballasts. The lamps were wrapped with pre-solarized 0.07 mm cellulose diacetate film to filter UV-C (<280 nm) radiation. The cellulose diacetate film was changed at 3 - 4 d intervals. The UV-B energy delivered at the top of the plant canopy was checked daily at 09:00 h with a UVX digital radiometer (UVP Inc., San Gabriel, CA, USA) calibrated against an Optronic Laboratory (Orlando, FL, USA) Model 754 Spectroradiometer, which was used initially to quantify lamp output. The lamp output was adjusted, as needed, to maintain the respective UV-B radiation levels. A distance of 0.5 m from lamps to the top of plants was always maintained throughout the experiment. The actual biologically effective UV-B radiation was measured during the crop growth period at six different locations in each SPAR unit corresponding to the pots arranged in rows. The weighted total biologically effective UV-B radiation at the top of the plant canopy during the treatment period is presented in
Final harvesting was carried out on 13 October 2011 (100 DAS or 47 days after UV-B treatment). Plants were cut above ground and separated into roots, leaves, pods, and stems. Pods were kept outside under normal drying conditions while other plant parts were dried in oven at 75˚C until it weighed constant during a period of 72 h. The biomass parameters such as dry weight of leaf, stem, root and total per plant, number of pods and seeds per plant, number of seeds per pod as well as seed weight per seed were measured.
Treatments | Measured variables | |
---|---|---|
UV-B (kJ∙m−2∙d−1) | Mean temperature (˚C) | Chamber CO2 (µmol∙mol−1) |
0 | 29.6 ± 0.04 | 409 ± 2.2 |
5 | 29.7 ± 0.03 | 407 ± 3.1 |
10 | 29.3 ± 0.05 | 406 ± 2.3 |
15 | 29.6 ± 0.03 | 404 ± 2.7 |
Each value represents the mean ± SE (standard error of the mean) for one typical day for [CO2], and 27 August to 13 October 2011 for temperature.
Seed pooled from each row of plants were analyzed for protein, oil, fatty acids, sucrose, raffinose and stachyose. About 25 g of seed from each pot was ground using a Laboratory Mill 3600 (Perten, Springfield, IL). Analyses were conducted by near infrared reflectance [
To test the significance of UV-B radiation on growth and biomass components of soybean, analysis of variance was performed by using general linear model PROC GLM (SAS Institute Inc., Cary, NC, USA). Fisher protected LSD tests at P = 0.05 was used to determine significance of treatment effects. Regression analysis was performed between seed quality parameters and UV-B radiation using SAS (Sas Institute, Inc.) and SigmaPlot 11.0 (Systat Software Inc., San Jose, CA, USA) and best fit regression models were selected based R2 values. The graphical analysis was carried out using SigmaPlot.
The ultraviolet-B radiation treatments were very close to the set points (
Seed weight was negatively impacted by UV-B radiation. Chen et al. [
Stem and pod dry weight per plant were reduced by UV-B radiation up to 10 kJ∙m−2∙d−1, while it enhanced at 15 kJ∙m−2∙d−1, but the enhancement remained lower than control. The significant reduction in stem and pod dry weight at 10 kJ∙m−2∙d−1 were of the order of 30 and 12% over control, respectively, while reductions were close and comparable with 5 kJ∙m−2∙d−1. Decreased stem dry weight might be due to reduction in main stem and branch elongation rates upon enhanced UV-B radiation resulting more compact and shorter plants [
Biomass parameters | UV-B radiation, kJ∙m−2∙d−1 | F test | |||
---|---|---|---|---|---|
0 | 5 | 10 | 15 | ||
Leaf dry weight, g | 20.6bc | 24.2ab | 20.4c | 24.4a | 3.67 |
Stem dry weight, g | 30.3a | 29.5a | 23.2b | 30.1a | 4.27 |
Root dry weight, g | 18.4a | 16.8a | 17.7a | 17.7a | ns |
Pod dry weight, g | 75.8a | 68.1b | 67.5b | 69.3ab | 7.51 |
Total dry weight, g | 145.0a | 138.5a | 128.8a | 141.5a | ns |
Pods, no. plant−1 | 109.9a | 101.6b | 105.7ab | 107.8ab | 6.57 |
Seeds, no. plant−1 | 259.3a | 237.7b | 248.4ab | 258.8a | 16.19 |
Seeds, no. pod−1 | 2.36a | 2.34a | 2.35a | 2.41a | ns |
Seed weight, g∙seed−1 | 0.22a | 0.21ab | 0.21b | 0.20b | 0.013 |
mValues are means of four replicates; ns = Not significant at p = 5%; means within columns followed by the same letter are not significantly different at the 5% level.
44% and 28% [
Pod and seed number per plant were significantly decreased by UV-B radiation up to 5 kJ∙m−2∙d−1, exhibiting 8 and 9% reduction compared with control, respectively, where as it increased at 10 and 15 kJ∙m−2∙d−1, and the increases were maintained lower than control. UV-B radiation decreased average pod number per plant of three soybean cultivars by 34%. This suggests that UV-B radiation imposed during early flowering stage would change assimilates availability to the developing reproductive structures, influence flowering, and flower and pod abscission number with a resultant change in final pod number at harvest. Pod number per plant was the yield component most influenced by change in cultural and environmental conditions [
The attenuation of the stratospheric ozone has led to the enhanced UV-B radiation on the surface of land in recent decades [
Although crop yield and seed quality are important products of soybean crop, few studies addressed UV-B effects on seed quality parameters that are important to human and animal nutrition. Soybean seed protein reported in this study under various UV-B treatments, 407 to 440 g∙kg−1, is within the range, 340 - 570 g∙kg−1, reported in other studies (Wilson 2004). Seed protein content, however, declined linearly with increase in UV-B radiation, 2.21 g∙kg−1 UV-B−1 (
have affected both uptake and translocation of nutrients as reported in other studies under UV-B treatments in soybean and other plants under UV-B radiation [
Soybean seed oil is an important product with many industrial application. The seed oil content of found in this study ranges from 198 to 238 g∙kg−1, are with the ranges reported in the literature of about 83 to 279 g∙kg−1, depending on cultivar and growing season environment [
The inverse negative relationship between soybean seed protein and oil (y = 752 ? 1.6x; R2 = 0.88, where y = g∙kg−1 protein and x = g∙kg−1 oil) observed in our study when used all treatments and inverse relations with protein and yield [
Soybean oils contain about 16% saturated, 23% monosaturated and 58% polysaturated fatty acids and these fatty acid composition play important roles in oil stability and human and animal nutrition [
Growing season environment such as temperature [
This study reports the biomass and seed quality responses of soybean crop exposed to enhanced UV-B irradiance under sunlit controlled plant growth chamber conditions. Enhanced UV-B irradiance caused significant reductions in certain plant growth parameters, but the influence was not consistent as the treatments were
imposed during mid-fruiting period. The protein, oil, fatty acid and sugar contents in soybean plants are critical to soybean seed industry and human and animal nutrition. Increased UV-B radiation altered soybean seed quality. Seed protein declined linearly while oil content increased with increase in UV-B radiation. Changes in these two important seed quality parameters have implications for seed industry and animal and human nutrition. The negative correlation between seed protein and oil content and their opposite responses to increasing UV-B doses poses challenges for breeders to develop soybean cultivars better suited for human and animal nutrition in a changing climate. The desirable fatty acids such as oleic acid declined while the linoleic and linolenic acids increased with increase in UV-B radiation. Palmitic and stearic acids showed linear and quadratic trends with increasing UV-B doses. While lower levels of desirable sugars such as raffinose declined linearly while stachyose increased up to 4 - 5 kJ and declined at higher UV-B treatments will have positive effects on improved feed energy efficiency in non-ruminant animals. The declined sucrose content at higher UV-B doses compared to the levels typically seen in soybean growing areas (~5 kJ), will have serious implications for human consumption. The functional relationships between UV-B radiation and soybean seed quality parameters will be useful to develop seed quality-specific sub-models under optimal temperature and nutrient conditions. Models equipped with seed quality would be useful not only for production optimization of natural resources such as water and nutrients, but also useful in assisting planting dates in the current environment and in policy decisions for the hypothesized changes in global environmental change on soybean production in the future.
We thank Mr. David Brand for their technical assistance. This article is a contribution from the Department of
Plant and Soil Sciences, Mississippi State University, Mississippi Agricultural and Forestry Experiment Station, paper no. J-12658. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the Unites States Department of Agriculture (USDA). USDA is an equal opportunity provider and employer. This work was in part funded by the USDA-NIFA 2013-34263-20931, sub-award to Mississippi State University, G-7799-2. Funding for this research was also partially provided by USDA, Agricultural Research Service projects 6066-21220-012- 00D and 6066-21000-051-00D.
K. RajaReddy,HrusikeshPatro,SureshLokhande,NacerBellaloui,WeiGao, (2016) Ultraviolet-B Radiation Alters Soybean Growth and Seed Quality. Food and Nutrition Sciences,07,55-66. doi: 10.4236/fns.2016.71007