@article{cheng_booker_burkey_tu_shew_rufty_fiscus_deforest_hu_2014, title={SOIL MICROBIAL RESPONSES TO ELEVATED CO2 AND O-3 IN A NITROGEN-AGGRADING AGROECOSYSTEM}, volume={6}, ISBN={["978-1-77188-021-3"]}, DOI={10.1371/journal.pone.0021377}, abstractNote={Climate change factors such as elevated atmospheric carbon dioxide (CO2) and ozone (O3) can exert significant impacts on soil microbes and the ecosystem level processes they mediate. However, the underlying mechanisms by which soil microbes respond to these environmental changes remain poorly understood. The prevailing hypothesis, which states that CO2- or O3-induced changes in carbon (C) availability dominate microbial responses, is primarily based on results from nitrogen (N)-limiting forests and grasslands. It remains largely unexplored how soil microbes respond to elevated CO2 and O3 in N-rich or N-aggrading systems, which severely hinders our ability to predict the long-term soil C dynamics in agroecosystems. Using a long-term field study conducted in a no-till wheat-soybean rotation system with open-top chambers, we showed that elevated CO2 but not O3 had a potent influence on soil microbes. Elevated CO2 (1.5×ambient) significantly increased, while O3 (1.4×ambient) reduced, aboveground (and presumably belowground) plant residue C and N inputs to soil. However, only elevated CO2 significantly affected soil microbial biomass, activities (namely heterotrophic respiration) and community composition. The enhancement of microbial biomass and activities by elevated CO2 largely occurred in the third and fourth years of the experiment and coincided with increased soil N availability, likely due to CO2-stimulation of symbiotic N2 fixation in soybean. Fungal biomass and the fungi∶bacteria ratio decreased under both ambient and elevated CO2 by the third year and also coincided with increased soil N availability; but they were significantly higher under elevated than ambient CO2. These results suggest that more attention should be directed towards assessing the impact of N availability on microbial activities and decomposition in projections of soil organic C balance in N-rich systems under future CO2 scenarios.}, number={6}, journal={CARBON CAPTURE AND STORAGE: CO2 MANAGEMENT TECHNOLOGIES}, author={Cheng, Lei and Booker, Fitzgerald L. and Burkey, Kent O. and Tu, Cong and Shew, H. David and Rufty, Thomas W. and Fiscus, Edwin L. and Deforest, Jared L. and Hu, Shuijin}, year={2014}, pages={277–307} }
 @article{cheng_booker_burkey_tu_shew_rufty_fiscus_deforest_hu_2014, title={Soil microbial responses to elevated CO2 and O-3 in a nitrogen-aggrading agroecosystem}, DOI={10.1201/b16845-14}, journal={Carbon Capture and Storage: CO2 Management Technologies}, author={Cheng, L. and Booker, F. L. and Burkey, K. O. and Tu, C. and Shew, H. D. and Rufty, T. W. and Fiscus, E. L. and Deforest, J. L. and Hu, Shuijin}, year={2014}, pages={277–307} }
 @article{matthews_fiscus_smith_heitman_2013, title={Quantifying Plant Age and Available Water Effects on Soybean Leaf Conductance}, volume={105}, ISSN={0002-1962}, url={http://dx.doi.org/10.2134/agronj2012.0263}, DOI={10.2134/agronj2012.0263}, abstractNote={Given the ever‐present threat of drought and the knowledge that water availability is the strongest limiting factor in vegetation growth, it is important to characterize the effect of water limitations on agricultural production. In this study, a small field plot technique for controlling soil moisture content suitable for physiological research in moist, humid areas was tested. We characterized the effect of water stress on total leaf conductance ( g l ) for two distinct determinate soybean [ Glycine max (L.) Merr.] genotypes. Based on these findings, a model of g l as a function of plant age and soil moisture content was formulated and validated. The dependency of g l on plant age was well represented by a parabolic function that increased throughout the vegetative period, peaked around anthesis, and decreased throughout the reproductive period and senescence. A sigmoidal function explained the relation of g l to plant‐available soil water content. This new empirical model effectively quantifies the response of g l to plant‐available soil water and plant age with a functional form similar to the abscisic acid related Tardieu–Davies model.}, number={1}, journal={Agronomy Journal}, publisher={Wiley}, author={Matthews, Jessica L. and Fiscus, Edwin L. and Smith, Ralph C. and Heitman, Joshua L.}, year={2013}, month={Jan}, pages={28–36} }
 @article{fiscus_booker_sadok_burkey_2012, title={Influence of atmospheric vapour pressure deficit on ozone responses of snap bean (Phaseolus vulgaris L.) genotypes}, volume={63}, ISSN={["1460-2431"]}, DOI={10.1093/jxb/err443}, abstractNote={Environmental conditions influence plant responses to ozone (O(3)), but few studies have evaluated individual factors directly. In this study, the effect of O(3) at high and low atmospheric vapour pressure deficit (VPD) was evaluated in two genotypes of snap bean (Phaseolus vulgaris L.) (R123 and S156) used as O(3) bioindicator plants. Plants were grown in outdoor controlled-environment chambers in charcoal-filtered air containing 0 or 60 nl l(-1) O(3) (12 h average) at two VPDs (1.26 and 1.96 kPa) and sampled for biomass, leaf area, daily water loss, and seed yield. VPD clearly influenced O(3) effects. At low VPD, O(3) reduced biomass, leaf area, and seed yield substantially in both genotypes, while at high VPD, O(3) had no significant effect on these components. In clean air, high VPD reduced biomass and yield by similar fractions in both genotypes compared with low VPD. Data suggest that a stomatal response to VPD per se may be lacking in both genotypes and it is hypothesized that the high VPD resulted in unsustainable transpiration and water deficits that resulted in reduced growth and yield. High VPD- and water-stress-induced stomatal responses may have reduced the O(3) flux into the leaves, which contributed to a higher yield compared to the low VPD treatment in both genotypes. At low VPD, transpiration increased in the O(3) treatment relative to the clean air treatment, suggesting that whole-plant conductance was increased by O(3) exposure. Ozone-related biomass reductions at low VPD were proportionally higher in S156 than in R123, indicating that differential O(3) sensitivity of these bioindicator plants remained evident when environmental conditions were conducive for O(3) effects. Assessments of potential O(3) impacts on vegetation should incorporate interacting factors such as VPD.}, number={7}, journal={JOURNAL OF EXPERIMENTAL BOTANY}, author={Fiscus, Edwin L. and Booker, Fitzgerald L. and Sadok, Walid and Burkey, Kent O.}, year={2012}, month={Apr}, pages={2557–2564} }
 @misc{booker_muntifering_mcgrath_burkey_decoteau_fiscus_manning_krupa_chappelka_grantz_2009, title={The Ozone Component of Global Change: Potential Effects on Agricultural and Horticultural Plant Yield, Product Quality and Interactions with Invasive Species}, volume={51}, ISSN={["1744-7909"]}, DOI={10.1111/j.1744-7909.2008.00805.x}, abstractNote={The productivity, product quality and competitive ability of important agricultural and horticultural plants in many regions of the world may be adversely affected by current and anticipated concentrations of ground-level ozone (O3). Exposure to elevated O3 typically results in suppressed photosynthesis, accelerated senescence, decreased growth and lower yields. Various approaches used to evaluate O3 effects generally concur that current yield losses range from 5% to 15% among sensitive plants. There is, however, considerable genetic variability in plant responses to O3. To illustrate this, we show that ambient O3 concentrations in the eastern United States cause substantially different levels of damage to otherwise similar snap bean cultivars. Largely undesirable effects of O3 can also occur in seed and fruit chemistry as well as in forage nutritive value, with consequences for animal production. Ozone may alter herbicide efficacy and foster establishment of some invasive species. We conclude that current and projected levels of O3 in many regions worldwide are toxic to sensitive plants of agricultural and horticultural significance. Plant breeding that incorporates O3 sensitivity into selection strategies will be increasingly necessary to achieve sustainable production with changing atmospheric composition, while reductions in O3 precursor emissions will likely benefit world food production and reduce atmospheric concentrations of an important greenhouse gas.}, number={4}, journal={JOURNAL OF INTEGRATIVE PLANT BIOLOGY}, author={Booker, Fitzgerald and Muntifering, Russell and McGrath, Margaret and Burkey, Kent and Decoteau, Dennis and Fiscus, Edwin and Manning, William and Krupa, Sagar and Chappelka, Arthur and Grantz, David}, year={2009}, month={Apr}, pages={337–351} }
 @article{qiu_huber_booker_jain_leakey_fiscus_yau_ort_huber_2008, title={Increased protein carbonylation in leaves of Arabidopsis and soybean in response to elevated [CO2]}, volume={97}, ISSN={["1573-5079"]}, DOI={10.1007/s11120-008-9310-5}, abstractNote={While exposure of C3 plants to elevated [CO2] would be expected to reduce production of reactive oxygen species (ROS) in leaves because of reduced photorespiratory metabolism, results obtained in the present study suggest that exposure of plants to elevated [CO2] can result in increased oxidative stress. First, in Arabidopsis and soybean, leaf protein carbonylation, a marker of oxidative stress, was often increased when plants were exposed to elevated [CO2]. In soybean, increased carbonyl content was often associated with loss of leaf chlorophyll and reduced enhancement of leaf photosynthetic rate (Pn) by elevated [CO2]. Second, two-dimensional (2-DE) difference gel electrophoresis (DIGE) analysis of proteins extracted from leaves of soybean plants grown at elevated [CO2] or [O3] revealed that both treatments altered the abundance of a similar subset of proteins, consistent with the idea that both conditions may involve an oxidative stress. The 2-DE analysis of leaf proteins was facilitated by a novel and simple procedure to remove ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from soluble soybean leaf extracts. Collectively, these findings add a new dimension to our understanding of global change biology and raise the possibility that oxidative signals can be an unexpected component of plant response to elevated [CO2].}, number={2}, journal={PHOTOSYNTHESIS RESEARCH}, author={Qiu, Quan-Sheng and Huber, Joan L. and Booker, Fitzgerald L. and Jain, Vanita and Leakey, Andrew D. B. and Fiscus, Edwin L. and Yau, Peter M. and Ort, Donald R. and Huber, Steven C.}, year={2008}, month={Aug}, pages={155–166} }
 @article{reid_fiscus_2008, title={Ozone and density affect the response of biomass and seed yield to elevated CO2 in rice}, volume={14}, ISSN={["1365-2486"]}, DOI={10.1111/j.1365-2486.2007.01472.x}, abstractNote={Tropospheric O3 reduces growth and yield of many crop species, whereas CO2 ameliorates the negative effects of O3. Thus, in a combined elevated CO2 and O3 atmosphere, seed yield is at least restored to that of charcoal-filtered (CF) air at ambient CO2. The CO2-induced yield increase in CF air is highly variable, suggesting other potential resource limitations. To understand such variability in response, we tested that (1) competition for resources precludes some of the CO2 enhancement on biomass and yield; and (2) O3 reduces competition in elevated CO2. We grew rice (Oryza sativa L.) at five densities in CF and O3-fumigated (+O3) air at ambient (A) and elevated [CO2] (+CO2) in 1997 and 1998. O3 reduced biomass by 25% and seed yield by 13–20% in A, but had little effect in +CO2. A competition model of biomass and yield response to density based on resource availability without competition showed that fewer resources were used for biomass in +O3 than in CF (average 53% vs. 70%) in A, while in +CO2 85% of resources were used for biomass regardless of O3 suggesting greater depletion of resources. The enhanced biomass response to CO2 with O3 is consistent with a 22% greater CO2 enhancement ratio [mass in +CO2 air/mass in A air; enhancement ratio (ER)] in +O3 than in CF air. For seed yield, few resources were used (average 17% and 25% for CF in 1997 and 1998, respectively), and ER was 13% greater in +O3. With competition the rate of change of individual plant biomass to density was not affected by +CO2 in CF air in 1997 but was increased 19% with more nutrients in 1998, indicating resource limitations with +CO2. The rate of change of individual plant yield to density was reduced with CO2 in 1997 and unchanged in 1998 showing a different response to resource limitation for reproductive biomass. The resource use in +O3-A suggested that increased density and soil fertility might compensate for pollutant damage. Although ambient [O3] can modulate the response to elevated CO2, resource limitation precludes the CO2 fertilization impact and both factors need consideration for better management and forecasts of future productivity.}, number={1}, journal={GLOBAL CHANGE BIOLOGY}, author={Reid, Chantal D. and Fiscus, Edwin L.}, year={2008}, month={Jan}, pages={60–76} }
 @article{sinclair_fiscus_wherley_durham_rufty_2007, title={Atmospheric vapor pressure deficit is critical in predicting growth response of “cool-season” grass Festuca arundinacea to temperature change}, volume={227}, ISSN={0032-0935 1432-2048}, url={http://dx.doi.org/10.1007/s00425-007-0645-5}, DOI={10.1007/s00425-007-0645-5}, number={1}, journal={Planta}, publisher={Springer Science and Business Media LLC}, author={Sinclair, Thomas and Fiscus, Edwin and Wherley, Ben and Durham, Michael and Rufty, Thomas}, year={2007}, month={Oct}, pages={273–276} }
 @article{dubois_fiscus_booker_flowers_reid_2007, title={Optimizing the statistical estimation of the parameters of the Farquhar-von Caemmerer-Berry model of photosynthesis}, volume={176}, ISSN={["1469-8137"]}, DOI={10.1111/j.1469-8137.2007.02182.x}, abstractNote={• The model of Farquhar, von Caemmerer and Berry is the standard in relating photosynthetic carbon assimilation and concentration of intercellular CO2. The techniques used in collecting the data from which its parameters are estimated have been the object of extensive optimization, but the statistical aspects of estimation have not received the same attention. • The model segments assimilation into three regions, each modeled by a distinct function. Three parameters of the model, namely the maximum rate of Rubisco carboxylation (Vc max), the rate of electron transport (J), and nonphotorespiratory CO2 evolution (Rd), are customarily estimated from gas exchange data through separate fitting of the component functions corresponding to the first two segments. This disjunct approach is problematic in requiring preliminary arbitrary subsetting of data into sets believed to correspond to each region. • It is shown how multiple segments can be estimated simultaneously, using the entire data set, without predetermination of transitions by the investigator. • Investigation of the number of parameters that can be estimated in the two-segment model suggests that, under some conditions, it is possible to estimate four or even five parameters, but that only Vc max, J, and Rd, have good statistical properties. Practical difficulties and their solutions are reviewed, and software programs are provided.}, number={2}, journal={NEW PHYTOLOGIST}, author={Dubois, Jean-Jacques B. and Fiscus, Edwin L. and Booker, Fitzgerald L. and Flowers, Michael D. and Reid, Chantal D.}, year={2007}, pages={402–414} }
 @article{flowers_fiscus_burkey_booker_dubois_2007, title={Photosynthesis, chlorophyll fluorescence, and yield of snap bean (Phaseolus vulgaris L.) genotypes differing in sensitivity to ozone}, volume={61}, ISSN={["0098-8472"]}, DOI={10.1016/j.envexpbot.2007.05.009}, abstractNote={Abstract Understanding the impact of pollutant ozone (O3) is a concern for agricultural production. This work was undertaken as the first comparative study of the effects of O3 on the photosynthetic processes and yield of three snap bean (Phaseolus vulgaris L.) genotypes with known differences in sensitivity to O3 (S156, R123 and R331). Previous information showed R123 and R331 to be tolerant and S156 sensitive. The purpose was to identify physiological subsystems that may mediate those differences in sensitivity. Plants were grown in environmentally controlled field chambers with four levels of O3 (0, 15, 30 and 60 nmol mol−1). Net assimilation (A) and fluorescence were measured throughout the growing season and yield data were collected at physiological maturity. All genotypes were tolerant of low O3 (}, number={2}, journal={ENVIRONMENTAL AND EXPERIMENTAL BOTANY}, author={Flowers, Michael D. and Fiscus, Edwin L. and Burkey, Kent O. and Booker, Fitzgerald L. and Dubois, Jean-Jacques B.}, year={2007}, month={Nov}, pages={190–198} }
 @article{burkey_miller_fiscus_2005, title={Assessment of ambient ozone effects on vegetation using snap bean as a bioindicator species}, volume={34}, ISSN={["0047-2425"]}, DOI={10.2134/jeq2004.0008}, abstractNote={Tropospheric ozone is an air pollutant that is toxic to plants, causing visible injury to foliage and a reduction in growth and yield. The use of plant bioindicators is one approach to assess the ozone impacts in diverse geographical areas. The objective of this study was to evaluate snap bean (Phaseolus vulgaris L.) as a potential bioindicator species. Three snap bean genotypes known to exhibit a range of ozone sensitivity were grown in pots under charcoal-filtered (CF) or nonfiltered (NF) treatments in open-top chambers, or under ambient air (AA) conditions. Treatment effects on biomass were not significant at 56 days after planting (DAP), but midseason foliar injury increased in the NF and AA treatments relative to CF controls. An increase in ozone from 25 to 30 nL L(-1) in CF controls to approximately 50 nL L(-1) in the NF and AA treatments was found to suppress final pod dry weight per plant by 40 to 60% in the most sensitive genotype S156. The same treatments suppressed final pod dry weight by 20 to 30% in a moderately sensitive genotype Oregon-91, and by 10% or less in a tolerant genotype R123. An S156 to R123 yield ratio of approximately one was observed under CF conditions. The S156 to R123 yield ratio declined to 0.6 to 0.7 in the NF treatment and declined further to 0.4 to 0.5 in the AA treatment, suggesting that ozone impact was underestimated in the open-top chambers. The results suggest that a snap bean bioindicator system has the potential to detect ambient ozone effects at present-day ozone concentrations.}, number={3}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Burkey, KO and Miller, JE and Fiscus, EL}, year={2005}, pages={1081–1086} }
 @article{booker_miller_fiscus_pursley_stefanski_2005, title={Comparative responses of container- versus ground-grown soybean to elevated carbon dioxide and ozone}, volume={45}, ISSN={["1435-0653"]}, DOI={10.2135/cropsci2004.0198}, abstractNote={In studies of CO2–enrichment effects on plants, the applicability of results derived from experiments using container-grown plants for predictions of future crop performance in a CO2–enriched atmosphere has been questioned. Concerns also have been expressed about plant growth studies with the air pollutant O3 in pot-grown plants. Further, since elevated CO2 and O3 co-occur, studies are required with the combination of gases. In this 2-yr experiment, soybean [Glycine max (L.) Merr.] plants grown in large pots (15 and 21 L) and in the ground were exposed to mixtures of CO2 and O3 in open-top chambers. The CO2 treatments were ambient and CO2 enrichment of approximately 337 μmol mol−1 added 24 h d−1 Ozone treatments were charcoal-filtered (CF) air (23 nmol mol−1) and approximately 1.5 times ambient O3 levels (71 nmol mol−1) given 12 h d−1 Relative effects of elevated CO2 and O3 on aboveground biomass and seed yield were quite similar for plants grown in pots compared with plants grown in the ground. Elevated CO2 increased total seed mass and O3 suppressed it to similar magnitudes in both rooting environments. Elevated CO2 also reduced the toxic effects of O3 Net photosynthesis (A) was similar while stomatal conductance (gs) was higher in pot-grown compared with ground-grown plants, possibly due to better soil moisture status. The results indicated that planting density and rooting environment affected plant morphology, but relative responses of seed yield to elevated CO2 and O3 were not fundamentally different between soybean plants grown in large pots and in the ground in open-top chambers.}, number={3}, journal={CROP SCIENCE}, author={Booker, FL and Miller, JE and Fiscus, EL and Pursley, WA and Stefanski, LA}, year={2005}, pages={883–895} }
 @misc{fiscus_booker_burkey_2005, title={Crop responses to ozone: uptake, modes of action, carbon assimilation and partitioning}, volume={28}, ISSN={["0140-7791"]}, DOI={10.1111/j.1365-3040.2005.01349.x}, abstractNote={The inhibitory effects of tropospheric O3 on crop photosynthesis, growth, and yield have been documented in numerous studies over the past 35 years. In large part, the results of this research supported governmental regulations designed to limit tropospheric O3 levels to concentrations that affected crop production at economically acceptable levels. Recent studies have brought into question the efficacy of these concentration-based O3 standards compared with flux-based approaches that incorporate O3 uptake along with environmental and biotic factors that influence plant responses. In addition, recent studies provide insight into the biochemical mechanisms of O3 injury to plants. Current interpretations suggest that upon entry into the leaf intercellular space O3 rapidly reacts with components of the leaf apoplast to initiate a complex set of responses involving the formation of toxic metabolites and generation of plant defence responses that constitute variably effective countermeasures. Plant species and cultivars exhibit a range of sensitivity to O3, evident as heritable characteristics, that must reflect identifiable biochemical and molecular processes that affect sensitivity to O3 injury, although their exact makeup remains unclear. Ozone clearly impairs photosynthetic processes, which might include the effects on electron transport and guard cell homeostasis as well as the better-documented effects on carbon fixation via decreased Rubisco activity. Translocation of photosynthate could be inhibited by O3 exposure as well. Further, the influence of tropospheric O3 needs to be considered when assessing potential effects of rising concentrations of atmospheric CO2 on crop production. Advances in O3 flux modelling and improved understanding of biochemical and molecular effects of O3 on photosynthetic gas exchange and plant defence processes are leading to more complete, integrated assessments of O3 impacts on crop physiology that continue to support the rationale for maintaining or improving current O3 air quality standards as well as providing a basis for development of more O3-tolerant crop lines.}, number={8}, journal={PLANT CELL AND ENVIRONMENT}, author={Fiscus, EL and Booker, FL and Burkey, KO}, year={2005}, month={Aug}, pages={997–1011} }
 @article{booker_prior_torbert_fiscus_pursley_hu_2005, title={Decomposition of soybean grown under elevated concentrations of CO2 and O-3}, volume={11}, DOI={10.1111/j.1365.2486.2005.00939.x}, number={4}, journal={Global Change Biology}, author={Booker, F. L. and Prior, S. A. and Torbert, H. A. and Fiscus, E. L. and Pursley, W. A. and Hu, Shuijin}, year={2005}, pages={685–698} }
 @article{booker_fiscus_2005, title={The role of ozone flux and antioxidants in the suppression of ozone injury by elevated CO2 in soybean}, volume={56}, ISSN={["0022-0957"]}, DOI={10.1093/jxb/eri214}, abstractNote={The projected rise in atmospheric CO2 concentration is expected to increase growth and yield of many agricultural crops. The magnitude of this stimulus will partly depend on interactions with other components of the atmosphere such as tropospheric O3. Elevated CO2 concentrations often lessen the deleterious effects of O3, but the mechanisms responsible for this response have received little direct examination. Previous studies have indicated that protection against O3 injury by elevated CO2 can be attributed to reduced O3 uptake, while other studies suggest that CO2 effects on anti-oxidant metabolism might also be involved. The aim of this experiment was to test further the roles of O3 flux and antioxidant metabolism in the suppression of O3 injury by elevated CO2. In a two-year experiment, soybean [Glycine max (L.) Merr.] was exposed from emergence to maturity to charcoal-filtered air or charcoal-filtered air plus a range of O3 concentrations in combination with ambient or approximately twice-ambient CO2 concentrations in open-top field chambers. Experimental manipulation of O3 concentrations and estimates of plant O3 uptake indicated that equivalent O3 fluxes that suppressed net photosynthesis, growth, and yield at ambient concentrations of CO2 were generally much less detrimental to plants treated concurrently with elevated CO2. These responses appeared unrelated to treatment effects on superoxide dismutase, glutathione reductase, and peroxidase activities and glutathione concentration. Total ascorbic acid concentration increased by 28–72% in lower canopy leaves in response to elevated CO2 and O3 but not in upper canopy leaves. Increasing concentrations of atmospheric CO2 will likely ameliorate O3 damage to many crops due to reduced O3 uptake, increased carbon assimilation, and possibly as yet undetermined additional factors. The results of this study further suggest that elevated CO2 may increase the threshold O3 flux for biomass and yield loss in soybean.}, number={418}, journal={JOURNAL OF EXPERIMENTAL BOTANY}, author={Booker, FL and Fiscus, EL}, year={2005}, month={Aug}, pages={2139–2151} }
 @article{burkey_eason_fiscus_2003, title={Factors that affect leaf extracellular ascorbic acid content and redox status}, volume={117}, ISSN={["1399-3054"]}, DOI={10.1034/j.1399-3054.2003.1170106.x}, abstractNote={Leaf ascorbic acid content and redox status were compared in ozone-tolerant (Provider) and ozone-sensitive (S156) genotypes of snap bean (Phaseolus vulgaris L.). Plants were grown in pots for 24 days under charcoal-filtered air (CF) conditions in open-top field chambers and then maintained as CF controls (29 nmol mol−1 ozone) or exposed to elevated ozone (71 nmol mol−1 ozone). Following a 10-day treatment, mature leaves of the same age were harvested early in the morning (06:00–08:00 h) or in the afternoon (13:00–15:00 h) for analysis of ascorbic acid (AA) and dehydroascorbic acid (DHA). Vacuum infiltration methods were used to separate leaf AA into apoplast and symplast fractions. The total ascorbate content [AA + DHA] of leaf tissue averaged 28% higher in Provider relative to S156, and Provider exhibited a greater capacity to maintain [AA + DHA] content under ozone stress. Apoplast [AA + DHA] content was 2-fold higher in tolerant Provider (360 nmol g−1 FW maximum) relative to sensitive S156 (160 nmol g−1 FW maximum) regardless of sampling period or treatment, supporting the hypothesis that extracellular AA is a factor in ozone tolerance. Apoplast [AA + DHA] levels were significantly higher in the afternoon than early morning for both genotypes, evidence for short-term regulation of extracellular ascorbate content. Total leaf ascorbate was primarily reduced with AA/[AA + DHA] ratios of 0.81–0.90. In contrast, apoplast AA/[AA + DHA] ratios were 0.01–0.60 and depended on genotype and ozone treatment. Provider exhibited a greater capacity to maintain extracellular AA/[AA + DHA] ratios under ozone stress, suggesting that ozone tolerance is associated with apoplast ascorbate redox status.}, number={1}, journal={PHYSIOLOGIA PLANTARUM}, author={Burkey, KO and Eason, G and Fiscus, EL}, year={2003}, month={Jan}, pages={51–57} }
 @article{britt_fiscus_2003, title={Growth responses of Arabidopsis DNA repair mutants to solar irradiation}, volume={118}, ISSN={["0031-9317"]}, DOI={10.1034/j.1399-3054.2003.00062.x}, abstractNote={UV-B radiation damages a variety of cellular components. A plant's ability to resist the effects of UV is a product of its ability to reduce exposure (through the optimization of growth pattern and the production of UV absorbing pigments) and its ability to repair or replace damaged molecules. The expression of these UV resistance mechanisms is sensitive to the quantity and quality of ambient light. In the present study the significance of DNA repair as a UV resistance mechanism in Arabidopsis was investigated by comparing the effects of solar UV on the growth of a variety of repair-proficient and -deficient Arabidopsis lines grown under natural light, focusing on the effects of UV on the growth of well-established plants. It was found that solar UV had an inhibitory effect on the growth of wild-type plants, and that this effect is enhanced in repair-defective lines. Plants defective in the cyclobutane dimer photolyase are most sensitive to the effects of UV-B on plant height and rosette diameter growth, indicating that, at least in this Arabidopsis ecotype and at this stage of growth, this enzyme plays an important role in UV resistance. A mutant defective in nucleotide excision repair (NER), a non-specific repair pathway, also displayed a significant, though lesser, sensitivity to solar UV-B, suggesting that either the transcription-coupled repair of UV-induced dimers, or the repair of some other UV-induced lesion, is also important for optimal growth. The relatively mild enhancement of UV sensitivity in repair-defective Arabidopsis stands in dramatic contrast to the immediate, severe, and ultimately lethal effects of sunlight on repair-defective (XP) humans.}, number={2}, journal={PHYSIOLOGIA PLANTARUM}, author={Britt, A and Fiscus, EL}, year={2003}, month={Jun}, pages={183–192} }
 @article{fiscus_booker_2002, title={Growth of Arabidopsis flavonoid mutant is challenged by radiation longer than the UV-B band}, volume={48}, ISSN={["0098-8472"]}, DOI={10.1016/S0098-8472(02)00038-2}, abstractNote={Growth, seed yield and accumulation of ultraviolet (UV)-absorbing compounds were studied in chalcone isomerase-defective tt-5 mutant of Arabidopsis thaliana and its Landsberg erecta (Ler) progenitor under full-spectrum solar radiation and a series of filters which attenuated progressively larger portions of the UV-B and UV-A radiation bands. The purpose was to determine: (1) whether or not the tt-5 mutant could be induced to grow more or less normally, given adequate protection from damaging UV in the presence of high levels of photosynthetic active radiation (PAR) so that it could be used as a surrogate for mechanistic high UV studies; (2) whether the generalized plant action spectrum or the alfalfa DNA damage action spectrum would best describe the observed responses; and (3) if the traditional Mylar (polyester) filter provides an adequate control for UV damage studies. Maximum rosette diameter (MRD), plant height and fresh weight at harvest and seed yield were measured, along with absorbance of leaf extracts at 300 nm and accumulation of total phenolics before and after exposure to UV. Three types of UV filters were used: cellulose diacetate (CD), which non-selectively transmits all the UV reaching the earth's surface; Mylar, which cuts off UV below about 320 nm; and polyvinyl chloride (PVC) which cuts off UV below about 340 nm. Generally, Ler showed no significant growth effects under any of the treatments except for plant height which was reduced in Mylar and CD when compared to PVC. Conversely, tt-5 generally exhibited progressive decreases in all the measures of plant growth with PVC resulting in the best growth, Mylar treatments showing significant reductions and CD treatments even greater reductions. It was clear that even under these circumstances: the disruption to secondary metabolism in tt-5 makes it unsuitable for mechanistic studies of high UV-B damage; the alfalfa DNA action spectrum seemed the best correlated with observed responses and suggests a significant damaging radiation band which is not affected by stratospheric ozone; and since the damaging radiation extends beyond the Mylar cut-in, this material will not provide an adequate control for UV damage studies.}, number={3}, journal={ENVIRONMENTAL AND EXPERIMENTAL BOTANY}, author={Fiscus, EL and Booker, FL}, year={2002}, month={Dec}, pages={213–224} }
 @article{reid_fiscus_burkey_1999, title={Effects of chronic ozone and elevated atmospheric CO2 concentrations on ribulose-1,5-bisphosphate in soybean (Glycine max)}, volume={106}, ISSN={["1399-3054"]}, DOI={10.1034/j.1399-3054.1999.106404.x}, abstractNote={Ribulose-1,5-bisphosphate (RuBP) pool size was determined at regular intervals during the growing season to understand the effects of tropospheric ozone concentrations, elevated atmospheric carbon dioxide concentrations and their interactions on the photosynthetic limitation by RuBP regeneration. Soybean (Glycine max [L.] Merr. cv. Essex) was grown from seed to maturity in open-top field chambers in charcoal-filtered air (CF) either without (22 nmol O3 mol−1) or with added O3 (83 nmol mol−1) at ambient (AA, 369 μmol CO2 mol−1) or elevated CO2 (710 μmol mol−1). The RuBP pool size generally declined with plant age in all treatments when expressed on a unit leaf area and in all treatments but CF-AA when expressed per unit ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) binding site. Although O3 in ambient CO2 generally reduced the RuBP pool per unit leaf area, it did not change the RuBP pool per unit Rubisco binding site. Elevated CO2, in CF or O3-fumigated air, generally had no significant effect on RuBP pool size, thus mitigating the negative O3 effect. The RuBP pools were below 2 mol mol−1 binding site in all treatments for most of the season, indicating limiting RuBP regeneration capacity. These low RuBP pools resulted in increased RuBP regeneration via faster RuBP turnover, but only in CF air and during vegetative and flowering stages at elevated CO2. Also, the low RuBP pool sizes did not always reflect RuBP consumption rates or the RuBP regeneration limitation relative to potential carboxylation (%RuBP). Rather, %RuBP increased linearly with decrease in the RuBP pool turnover time. These data suggest that amelioration of damage from O3 by elevated atmospheric CO2 to the RuBP regeneration may be in response to changes in the Rubisco carboxylation.}, number={4}, journal={PHYSIOLOGIA PLANTARUM}, author={Reid, CD and Fiscus, EL and Burkey, KO}, year={1999}, month={Aug}, pages={378–385} }
 @article{fiscus_philbeck_britt_booker_1999, title={Growth of Arabidopsis flavonoid mutants under solar radiation and UV filters}, volume={41}, ISSN={["0098-8472"]}, DOI={10.1016/S0098-8472(99)00011-8}, abstractNote={Growth of the chalcone isomerase defective tt-5 mutant of Arabidopsis thaliana and its Landsberg erecta progenitor were compared under a variety of full spectrum solar radiation conditions to determine if the tt-5 mutant could serve as an adequate subject for studies of the mechanisms of damage by UV-B radiation. An experiment was conducted in the fall of 1995 under open field filter frames using cellulose diacetate and Mylar filters to transmit and exclude natural UV-B irradiation, respectively. Even though growth under these conditions was slow and erratic owing to lack of temperature control, growth suppression as indicated by rosette diameter and harvest fresh weights provided a sensitive indicator of UV-B stress. This experience led to development of temperature-controlled Teflon-covered field chambers that admit up to 88% of the total daily PAR and about 85% of ambient UV-B, omit predators, and provide a generally stable environment for quantitative plant growth studies. The chambers were designed to facilitate the addition of optical filters and/or shade cloth and to accommodate control of the gaseous environment for pollutant and climate change studies and to provide clean air for other experiments. Three additional experiments were conducted in these chambers. Measurements of rosette diameter, weights of various aboveground plant parts, and plant height were evaluated as potential methods of comparing growth sensitivities of the tt-5 mutant to UV-B radiation. The weight of the reproductive parts (flowers and siliques) as a fraction of the total (e.g. harvest index) was consistently and negatively affected by solar UV-B, as was simple plant height. However, in no case, even in the virtual absence of UV-B, was growth of tt-5 comparable to that of Ler. We conclude that the disruption of secondary metabolism in tt-5 has growth implications far beyond the lack of UV-B protection, making it unsuitable as a surrogate for high UV-B experimentation.}, number={3}, journal={ENVIRONMENTAL AND EXPERIMENTAL BOTANY}, author={Fiscus, EL and Philbeck, R and Britt, AB and Booker, FL}, year={1999}, month={Jun}, pages={231–245} }
 @article{reid_fiscus_burkey_1998, title={Combined effects of chronic ozone and elevated CO2 on Rubisco activity and leaf components in soybean (Glycine max)}, volume={49}, ISSN={["1460-2431"]}, DOI={10.1093/jexbot/49.329.1999}, number={329}, journal={JOURNAL OF EXPERIMENTAL BOTANY}, author={Reid, CD and Fiscus, EL and Burkey, KO}, year={1998}, month={Dec}, pages={1999–2011} }
 @article{reid_fiscus_1998, title={Effects of elevated [CO2] and/or ozone on limitations to CO2 assimilation in soybean (Glycine max)}, volume={49}, ISSN={["1460-2431"]}, DOI={10.1093/jexbot/49.322.885}, number={322}, journal={JOURNAL OF EXPERIMENTAL BOTANY}, author={Reid, CD and Fiscus, EL}, year={1998}, month={May}, pages={885–895} }
 @article{reid_tissue_fiscus_strain_1997, title={Comparison of spectrophotometric and radioisotopic methods for the assay of Rubisco in ozone-treated plants}, volume={101}, ISSN={["0031-9317"]}, DOI={10.1034/j.1399-3054.1997.1010221.x}, number={2}, journal={PHYSIOLOGIA PLANTARUM}, author={Reid, CD and Tissue, DT and Fiscus, EL and Strain, BR}, year={1997}, month={Oct}, pages={398–404} }
 @article{fiscus_reid_miller_heagle_1997, title={Elevated CO2 reduces O-3 flux and O-3-induced yield losses in soybeans: Possible implications for elevated CO2 studies}, volume={48}, ISSN={["0022-0957"]}, DOI={10.1093/jxb/48.2.307}, abstractNote={Soybeans were grown for three seasons in open-top field chambers to determine (1) whether elevated CO2 (360 versus 700 μmol mol−1) alleviates some of the yield loss due to pollutant O3, (2) whether the partial stomatal closure resulting from chronic O3 exposure (charcoal-filtered air versus 1.5 × ambient concentrations) is a cause or result of decreased photosynthesis, and (3) possible implications of CO2/O3 interactions to climate change studies using elevated CO2. Leaf conductance was reduced by elevated CO2, regardless of O3 level, or by exposure to O3 alone. As.a result of these effects on conductance, high CO2 reduced estimated midday O3 flux into the leaf by an average of 50% in charcoal-filtered air and 35% in the high O3 treatment. However, while exposure to O3 reduced seed yields by 41% at ambient CO2 levels, the yield reduction was completely ameliorated by elevated CO2. The threshold midday O3 flux for yield loss appears to be 20–30 nmol m−2 s−1 in this study. Although elevated CO2 increased total biomass production, it did not increase seed yields. A/Ci curves show a large reduction in the stomatal limitation to photosynthesis due to elevated CO2 but no effect of O3. These data demonstrate that (1) reduced conductance due to O3 is the result, and not the cause, of reduced photosynthesis, (2) 700 μmol mol−1 CO2 can completely ameliorate yield losses due to O3 within the limits of these experiments, and (3) some reports of increased yields under elevated CO2 treatments may, at least in part, reflect the amelioration of unrecognized suppression of yield by O3 or other stresses.}, number={307}, journal={JOURNAL OF EXPERIMENTAL BOTANY}, author={Fiscus, EL and Reid, CD and Miller, JE and Heagle, AS}, year={1997}, month={Feb}, pages={307–313} }
 @article{booker_reid_brunschonharti_fiscus_miller_1997, title={Photosynthesis and photorespiration in soybean [Glycine max (L.) Merr.] chronically exposed to elevated carbon dioxide and ozone}, volume={48}, ISSN={["0022-0957"]}, DOI={10.1093/jexbot/48.315.1843}, number={315}, journal={JOURNAL OF EXPERIMENTAL BOTANY}, author={Booker, FL and Reid, CD and BrunschonHarti, S and Fiscus, EL and Miller, JE}, year={1997}, month={Oct}, pages={1843–1852} }
 @article{fiscus_booker_miller_1996, title={Response of soybean bulk leaf water relations to ultraviolet-B irradiation}, volume={148}, ISSN={["0176-1617"]}, DOI={10.1016/S0176-1617(96)80295-1}, abstractNote={Summary Erosion of the stratospheric ozone layer by anthropogenic emission of halogenated compounds may lead to increased UV-B radiation at ground level. In 1990 soybeans ( Glycine max (L.) Merr. cv. Essex) were grown in open-top field chambers with 3 levels of UV-B replicated 3 times. UV-B treatments corresponded to changes in the total column ozone thickness of15% (low), -20% (medium) and -35% (high). Leaves were sampled during four intervals of the growing season and subjected to pressure-volume (P-V) analysis to determine symplastic volume (V o ); maximum turgor pressure ( p MAX), symplastic solute content (N s ), tissue elasticity coefficient (z), and the potential at turgor loss (TLP). Leaf conductance, average specific leaf weight (SLW), and area per leaf were measured several times during the season. During the second sampling period at 58 days after planting (DAP), V o was significantly decreased at the highest UV-B level but was not affected by UV-B treatments again. Also during the second sampling period the elasticity coefficient, z, in the medium and high UV-B treatments was significantly less than in the low UV-B treatment. In the fourth sampling period (100 DAP), z again was significantly affected by UV-B treatment; in this case, however, while z was lower in the high than the medium UV-B treatment, it did not diffet from the low UV-B treatment. The relative symplastic volume at the turgor loss potential (RSV TLP ) was the only other parameter to show a significant UV-B effect, but only at the highest treatment level and only near the end of the season. Generally, the significant changes in all P-V parameters with plant age were much larger than any treatment effects. There were no significant differences in leaf conductance, leaf area or SLW, indicating that, although the leaf P-V relationships were noticeably altered, these sporadic treatment effects had little real influence on leaf water balance.}, number={1-2}, journal={JOURNAL OF PLANT PHYSIOLOGY}, author={Fiscus, EL and Booker, FL and Miller, JE}, year={1996}, month={Apr}, pages={63–68} }
 @article{fiscus_booker_miller_reid_1995, title={RESPONSE OF SOYBEAN LEAF WATER RELATIONS TO TROPOSPHERIC OZONE}, volume={73}, ISSN={["0008-4026"]}, DOI={10.1139/b95-053}, abstractNote={Tropospheric O 3 and water stress cause significant reductions in crop growth and yield. The effects of chronic O 3 exposures on leaf water relations have been less thoroughly studied. Soybeans were grown in two years in open-top field chambers equipped to control O 3 . The seasonal mean O 3 concentrations for the charcoal-filtered controls and supplemental O 3 treatments were 24 and 83 nL∙L −1 for the first year (1990) and 20 and 99 nL∙L −1 for the second year (1992). In 1990 leaves were sampled during four intervals of the 106-d growing season and subjected to potential–volume analysis. In 1992, leaves were sampled over a 3-week period, centered on 49 days after planting for potential–volume analysis as well as for midday xylem pressure potentials and leaf conductance. Ontogenetic changes in most of the parameters were large compared with treatment effects. O 3 treatment consistently caused decreased symplastic volume, specific leaf mass, and tissue elasticity. In 1992, these effects were accompanied by decreased leaf conductances with no discernable change in xylem pressure potential, although midday turgor increased by 32% and stomatal competency was maintained. Tissue elasticity decreases may be related to O 3 -induced changes in cell wall structure during leaf expansion and may result in decreased symplastic volume. Key words: Glycine max, ozone, leaf water relations, pressure–volume analysis, elasticity, elastic modulus.}, number={4}, journal={CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE}, author={FISCUS, EL and BOOKER, FL and MILLER, JE and REID, CD}, year={1995}, month={Apr}, pages={517–526} }
 @article{fiscus_alam_hirasawa_1991, title={FRACTIONAL INTEGRATED STOMATAL OPENING TO CONTROL WATER-STRESS IN THE FIELD}, volume={31}, ISSN={["1435-0653"]}, DOI={10.2135/cropsci1991.0011183X003100040032x}, abstractNote={The usefulness of totally automated irrigation control systems is well established. Mass‐flow porometers can be used as the sensing and feedback elements to implement such a system for the experimental control of water stress in the field. This study was conducted to determine if consistent relationships could be established between the mass‐flow readings and other water‐related physiological parameters. A range of stress conditions were imposed on plots of corn ( Zea mays L.) by the system during the 1986 and 1987 field seasons in Greeley, CO. Midday leaf xylem water potential, leaf diffusive conductance, and year‐end grain yields were measure during both years. In 1987, additional measurements were made of the infrared canopy temperature for calculating the Crop Water Stress Index (CWSI), and individual kernel weights and numbers, to determine the components of the grain yield predictions observed in 1986. Reductions in the number of kernels produced per unit land area were associated with stress‐induced delays of silking relative to pollen shed. Additional yield reductions in some treatments were attributable to reduced weight per kernel. Significant correlations were found between the mass‐flow sensors and grain yield and CWSI. The relationship between grain yield and stomatal conductance was consistent over both years, suggesting that the cumulative mean conductance may be useful as a yield predictor.}, number={4}, journal={CROP SCIENCE}, author={FISCUS, EL and ALAM, ANMM and HIRASAWA, T}, year={1991}, pages={1001–1008} }