Yunxia Wang

Yangzhou University, Chiang-tu, Jiangsu Sheng, China

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Publications (17)54.95 Total impact

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    [Show abstract] [Hide abstract] ABSTRACT: Rising tropospheric ozone concentrations in Asia affect the yield and quality of rice. This study investigated ozone-induced changes in rice grain quality in contrasting rice genotypes, and explored the associated physiological processes during the reproductive growth phase. The ozone sensitive variety Nipponbare and a breeding line (L81) containing two tolerance QTLs in Nipponbare background were exposed to 100 ppb ozone (8h per day) or control conditions throughout their growth. Ozone affected grain chalkiness and protein concentration and composition. The percentage of chalky grains was significantly increased in Nipponbare but not in L81. Physiological measurements suggested that grain chalkiness was associated with a drop in foliar carbohydrate and nitrogen levels during grain filling, which was less pronounced in the tolerant L81. Grain total protein concentration was significantly increased in the ozone treatment, although the albumin fraction (water soluble protein) decreased. The increase in protein was more pronounced in L81, due to increases in the glutelin fraction in this genotype. Amino acids responded differently to the ozone treatment. Three essential amino acids (leucine, methionine and threonine) showed significant increases, while seven showed significant treatment by genotype interactions, mostly due to more positive responses in L81. The trend of increased grain protein was in contrast to foliar nitrogen levels, which were negatively affected by ozone. A negative correlation between grain protein and foliar nitrogen in ozone stress indicated that higher grain protein cannot be explained by a concentration effect in all tissues due to lower biomass production. Rather, ozone exposure affected the nitrogen distribution, as indicated by altered foliar activity of the enzymes involved in nitrogen metabolism, such as glutamine synthetase and glutamine-2-oxoglutarate aminotransferase. Our results demonstrate differential responses of grain quality to ozone due to the presence of tolerance QTL, and partly explain the underlying physiological processes.
    Full-text · Article · Mar 2016 · Environmental Pollution
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    [Show abstract] [Hide abstract] ABSTRACT: Background: Rising atmospheric CO2 is accompanied by global warming. However, interactive effects of elevated CO2 and temperature have not been well studied on grain quality of rice. A japonica cultivar was grown in field by using a Free-Air CO2 Enrichment facility in combination with canopy-air-temperature increase system in 2014. The gas fumigation (200 μmolmol(-1) above ambient CO2 ) and temperature increase (1 °C above ambient air temperature) were performed from tillering until maturity. Results: Compared with the control (ambient CO2 and air temperature), elevated CO2 increased grain length and width, grain chalkiness, but decreased protein concentrations. In contrast, the increase of canopy air temperature showed less effects on these parameters except for grain chalkiness. The starch pasting properties of rice flour and taste analysis of cooked rice indicated that palatability of rice was improved by CO2 and/or temperature elevation, with the combination of two treatments showed the most significant changes compared with ambient rice. Conclusion: It is concluded that projected CO2 in 2050 may have larger effects on rice grain quality than the projected temperature increase. Although deterioration in the milling suitability, grain appearance and nutritional quality can be expected, the taste of cooked rice might be better in the future environment.
    Full-text · Article · Nov 2015 · Journal of the Science of Food and Agriculture
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    [Show abstract] [Hide abstract] ABSTRACT: Ascorbic acid (AsA) biosynthesis and its implications for stress tolerance and plant development were investigated in a set of rice knock-out (KO) mutants for AsA biosynthetic genes and their wild-types. KO of two isoforms of GDP-D-mannose epimerase (OsGME) reduced the foliar AsA level by 20-30 %, and KO of GDP-L-galactose phosphorylase (OsGGP) by 80 %, while KO of myo-inositol oxygenase (OsMIOX) did not affect foliar AsA levels. AsA concentration was negatively correlated with lipid peroxidation in foliar tissue under ozone stress and zinc deficiency, but did not affect the sensitivity to iron toxicity. Lack of AsA reduced the photosynthetic efficiency as represented by the maximum carboxylation rate of Rubisco (Vmax), the maximum electron transport rate (Jmax) and the chlorophyll fluorescence parameter ΦPSII. Mutants showed lower biomass production than their wild-types, especially when OsGGP was lacking (around 80 % reductions). All plants except for KO mutants of OsGGP showed distinct peaks in foliar AsA concentrations during the growth, which were consistent with up-regulation of OsGGP, suggesting that OsGGP plays a pivotal role in regulating foliar AsA levels during different growth stages. In conclusion, our data demonstrate multiple roles of AsA in stress tolerance and development of rice.
    Full-text · Article · Jul 2015 · Plant Molecular Biology
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    [Show abstract] [Hide abstract] ABSTRACT: Background Rising tropospheric ozone affects crop yield and quality. Rice protein concentration which is closely associated with eating/cooking quality is of critical importance to nutritional quality. The ozone effect on amino acids of rice grains were little known especially under different cultivation conditions. A hybrid rice cultivar Shanyou 63 was grown in 2010 and 2011 to investigate the interactive effect of ozone exposure and planting density on rice protein quality in a free-air ozone enrichment system.ResultsThe contents of protein, total amino acids (TAA), total essential (TEAA) and non-essential amino acids (TNEAA) in rice grain were increased by 12-14% with elevated ozone. Similar significant response to ozone was observed for the concentrations of the seven essential and eight non-essential amino acids. In contrast, elevated ozone caused a little but significant decrease in percentage of TEAA to TAA. The year effect was significant for all measured traits, however, interactions of ozone with year or planting density were not detected.Conclusion The study suggested that season-long elevation of ozone concentration to projected 2050 levels will increase protein and amino acids of Shanyou 63, and crop management such as changing in planting density might not alter the impacts.
    Full-text · Article · Jan 2015 · Journal of the Science of Food and Agriculture
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    [Show abstract] [Hide abstract] ABSTRACT: Tropospheric ozone concentrations are rising in parts of the world which rely heavily on rice as the major staple crop. Therefore, limiting ozone induced rice yield losses through the breeding of adapted varieties constitutes an important contribution to the food security of rice consumers. In this study we crossed two chromosome segment substitution lines (SL) containing individual ozone tolerance QTLs, OzT8 and OzT9, to obtain four lines with tolerance alleles at both loci. The OzT8/OzT9 lines were tested in a season long ozone fumigation experiment (100 nL L−1, 8 h per day, versus no ozone control) along with their sensitive parent Nipponbare, and SL46 (OzT8) and SL41 (OzT9) containing single QTLs. The OzT8/OzT9 lines showed significantly lower leaf bronzing than Nipponbare throughout the season, which was consistent with a significantly lower level of lipid peroxidation. In addition OzT8/OzT9 lines tended to have higher net photosynthetic rate despite lower stomatal conductance, and higher chlorophyll levels. These physiological advantages led to superior yield performance under ozone stress. Total biomass and shoot biomass yield were drastically reduced by 55% and 52% in Nipponbare, but for the OzT8/OzT9 lines reductions ranged only between 36-41% and 25-37%, respectively. Similarly the spikelet number/panicle and the spikelet number/plant were reduced by 35% and 46% in Nipponbare, but only by 15-18% and 29-34% in the OzT8/OzT9 lines. Overall, our data suggest that the pyramiding of OzT8 and OzT9 led to synergies resulting in superior yield performance under ozone stress.
    Full-text · Article · Aug 2014 · Environmental and Experimental Botany
  • [Show abstract] [Hide abstract] ABSTRACT: The effects of CO2 and/or O3 elevation on rice grain quality were investigated in chamber experiments with gas fumigation performed from transplanting until maturity in 2011 and 2012. Compared with the control (current CO2 and O3 concentration), elevated CO2 caused a tendency of an increase in grain chalkiness and a decrease in mineral nutrient concentrations. In contrast, elevated O3 significantly increased grain chalkiness and the concentrations of essential nutrients, while changes in starch pasting properties indicated a trend of deterioration in the cooking and eating quality. In the combination of elevated CO2 and O3 treatment, only chalkiness degree was significantly affected. It is concluded that the O3 concentration projected for the coming few decades will have more substantial effects on grain quality of Chinese hybrid rice than the projected high CO2 concentration alone, and the combination of two gases caused fewer significant changes in grain quality than individual gas treatments.
    No preview · Article · Mar 2014 · Environmental Pollution
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    [Show abstract] [Hide abstract] ABSTRACT: The effects of CO2 and/or O3 elevation on rice grain quality were investigated in chamber experiments with gas fumigation performed from transplanting until maturity in 2011 and 2012. Compared with the control (current CO2 and O3 concentration), elevated CO2 caused a tendency of an increase in grain chalkiness and a decrease in mineral nutrient concentrations. In contrast, elevated O3 significantly increased grain chalkiness and the concentrations of essential nutrients, while changes in starch pasting properties indicated a trend of deterioration in the cooking and eating quality. In the combination of elevated CO2 and O3 treatment, only chalkiness degree was significantly affected. It is concluded that the O3 concentration projected for the coming few decades will have more substantial effects on grain quality of Chinese hybrid rice than the projected high CO2 concentration alone, and the combination of two gases caused fewer significant changes in grain quality than individual gas treatments.
    Full-text · Article · Jan 2014 · Environmental Pollution
  • [Show abstract] [Hide abstract] ABSTRACT: Rising tropospheric ozone concentration is currently the most important air pollutant which suppresses plant growth and thus results in yield loss of agronomic crops. However little is known about ozone effects on grain quality of crops. Using a free-air gas concentration enrichment (FACE) facility for ozone fumigation in paddy rice (Oryza Sativa L.), a Chinese hybrid indica cultivar Shanyou 63 was exposed to either ambient or elevated ozone concentration (ca 23.5% above ambient) for two consecutive growth seasons from 2007 to 2008. Harvested grain samples were subjected to various quality tests. In both seasons, the brown, milled and head rice yield all reduced by elevated ozone concentration, with this reduction being greater in 2008 (17–22%) than in 2007 (8–19%). Ozone elevation caused small but significant decrease in brown rice percentage, but greatly increased head rice percentage by 8.8%. Chalky grain percentage increased (5.8%) due to ozone elevation, while chalkiness area and chalkiness degree remaining unchanged. Although the amylose concentration of rice grains was marginally reduced, starch pasting properties demonstrated that grains in elevated ozone concentration had lower breakdown (7.7%) and higher setback value (25.2%) and gelatinization temperature (0.9 °C) than those grown in ambient conditions. Nutrition evaluation indicated that ozone exposure tended to increase the concentrations of protein and all mineral elements analyzed (i.e., K, Mg, Ca, Fe, Zn, Mn and Cu), but the contents of protein and mineral elements in harvested grains were unchanged or reduced. For most traits of grain quality, the year effect was significant, however, its interaction with ozone was not detected. Our results suggested that long-term exposure to ozone-enriched atmospheres projected in the coming a few decades not only caused serious reductions in yield, but also tended to produce the deleterious effects upon grain quality of hybrid Shanyou 63 in terms of appearance and eating/cooking quality.
    No preview · Article · Apr 2012 · Field Crops Research
  • [Show abstract] [Hide abstract] ABSTRACT: This study investigated the impact of elevated ozone concentration ([O3]) on grain yield of rice in relation to the changes in spikelet formation, which plays a critical role in securing a sufficient number of spikelets per land area for a higher yield. Using a free air gas concentration enrichment (FACE) facility for O3 fumigation in China, two contrasting rice cultivars were exposed to either ambient (38 ppb) or elevated [O3] (47 ppb) from tillering stage to final harvest in 2008. A 23% increase in [O3] decreased grain yield of Yangdao6 and Shanyou63 by 6% and 27%, respectively. The yield loss was driven primarily by a decrease in the number of spikelets per panicle, rather than changes in the other yield components. The large reduction observed in panicle size of Shanyou63 under ozone stress resulted from both the inhibition of spikelet differentiation and promotion of spikelet degeneration, which was associated with decreased accumulation of nitrogen and biomass up to the heading stage. The results of this experiment indicated that the yield loss in rice under ozone exposure resulted primarily from negative effects on spikelet formation, and that a better understanding of spikelet formation process is indispensable for the assessment of rice yield response to future higher ground-level [O3].
    No preview · Article · Mar 2012 · Agriculture Ecosystems & Environment
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    Yunxia Wang · Michael Frei · Qiling Song · Lianxin Yang
    [Show abstract] [Hide abstract] ABSTRACT: Global atmospheric carbon dioxide concentration ([CO2]) is increasing rapidly. The Intergovernmental Panel on Climate Change estimated that atmospheric [CO2] has risen from approximately 280 μmol mol−1 in pre-industrial times to approximately 381 μmol mol−1 at present and will reach 550 μmol mol−1 by 2050. In the absence of strict emission controls, atmospheric [CO2] is likely to reach 730–1020 μmol mol−1 by 2100. Rising atmospheric [CO2] is the primary driver of global warming, but as the principal substrate for photosynthesis it also directly affects the yield and quality of crops. Food quality is receiving much more attentions recently, however, compared with grain yield, our understanding in the response of grain quality to elevated [CO2] is very limited. Rice (Oryza sativa L.) is one of the most important crops in the world and the first staple food in Asia, providing nutrition to a large proportion of the world’s population. Elevated [CO2] leads to numerous physiological changes in rice crops, such as changes in the photosynthesis and assimilate translocation, nutrient uptake and translocation, water relation, and altered gene expression and enzyme activity. These altered processes are very likely to affect the chemical and physical characteristics of rice grains. In this review, we first describe main characteristics of rice grain quality, and then summarize findings in literature related to the impact of elevated [CO2] on grain quality falling into four categories: processing quality, appearance, cooking and eating quality, and nutritional quality, as well as the possible mechanisms responsible for the observed impacts. Elevated [CO2] caused serious deterioration of processing suitability, in particular, head rice percentage was significantly decreased. In most cases, elevated [CO2] increased chalkiness of rice grains. The evaluation of physicochemical characteristics together with starch Rapid Visco Analyser (RVA) properties indicated no change or small changes in cooking and eating quality under elevated [CO2], and these changes could not be detected by sensory taste panel evaluation. Elevated [CO2] significantly decreased nitrogen or protein concentration in rice grains, while in most cases other macro- and micro-nutrients showed no change or decrease in concentration. In addition, the responses of rice quality to elevated [CO2] might be modified by varieties, applied fertilizer rates or gas fumigation methodologies. The available information in the literature indicates a clear tendency of quality deterioration and thus lower commercial value for rice grains grown under a projected high CO2 environment. Understanding the factors causing quality deterioration in rice and the related biological mechanisms might be the utmost important scientific theme in future research. Here we also discuss the necessity of formulating adaptation strategies for rice production in future atmospheric environments, nevertheless, the increase in yield, the improvement in quality and stress resistance of rice should be combined and integrated into the adaptation approaches. Compared with enclosure studies, the field experiments using Free-Air CO2 Enrichment (FACE) system provide sufficient experimental space and the most realistic mimic of a future high CO2 atmosphere, and give scientists perhaps the best opportunity to achieve multiple goals.
    Full-text · Article · Dec 2011 · Acta Ecologica Sinica
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    Yunxia Wang · Michael Frei
    [Show abstract] [Hide abstract] ABSTRACT: Abiotic environmental stresses negatively impact crop productivity and are major constraints to global food security. As a consequence of global change, certain stress factors such as heat, drought, salinity, tropospheric ozone, and excess UV radiation might become even more prevalent in the coming decades. While the negative impact of these stresses on crop yields is obvious, their effects on crop quality are less recognized. Exposure to environmental stress induces numerous physiological stress reactions in plants that can alter the chemical composition of crops and thus the quality of the harvested products. Literature on the impact of abiotic environmental stresses on crop quality falls into seven categories of quality parameters: protein, lipids, non-structural carbohydrates, minerals, antioxidants, feed value for ruminant herbivores, and physical/sensory traits. Apart from summarizing net effects on these quality parameters, this review intends to elucidate physiological mechanisms leading to the observed changes in crop quality. All categories of traits are significantly affected by abiotic environmental stresses, resulting in both positive and negative changes in crop quality. The overall effect of a certain stress factor is often dependent on numerous interacting factors such as the timing of stress application, the intensity of the stress, and the crop species. In spite of these confounding elements, this review identifies some common patterns of stress response, such as a tendency towards increasing concentrations in protein and antioxidants in stressed crops, and a loss in quality in terms of feed value, starch and lipid concentration, or physical/sensory traits. This information might help agronomists and crop breeders to develop strategies to produce higher quality crops in stress environments.
    Full-text · Article · May 2011 · Agriculture Ecosystems & Environment
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    [Show abstract] [Hide abstract] ABSTRACT: Zinc deficiency reduces rice growth and yield, and this is, in part, due to leaf damage caused by reactive oxygen species (ROS). The aim of this study was to identify biochemical mechanisms conferring tolerance to Zn deficiency-induced oxidative stress. A field experiment and three nutrient solution experiments were conducted with the intolerant genotype IR74 and recombinant inbred lines (RILs) derived from a cross between IR74 and the tolerant landrace Jalmagna. After 2 weeks of growth in low Zn soil, stress symptoms developed in leaves of IR74, but not in the tolerant RIL46. Activity of antioxidant enzymes showed clear treatment effects, but did not explain tolerance of RIL46. On the contrary, the intolerant IR74 showed higher activities of superoxide dismutase (SOD), guaiacol peroxidase (POX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) under Zn deficiency. This contrasted with a constitutively higher level of total and reduced ascorbic acid (AsA) in RIL46. Three further nutrient solution experiments focussed on enzymes and reducing substrates of the ascorbateglutathione cycle. The first experiment included the highly sensitive RIL76 in addition to the genotypes used in the field trial, to test whether the patterns of antioxidant response observed in the field were specific to the genotypes used. This genotype had similarly low AsA level as IR74, but did not respond to Zn deficiency with an increase in enzyme activity, leading to even more pronounced leaf symptoms. In a second experiment, co-segregation of AsA concentration and Zn deficiency tolerance was confirmed in five genotypes from the IR74/Jalmagna quantitative trait loci (QTL) mapping population. A third experiment was conducted to determine whether the observed patterns of antioxidant response were specific to Zn deficiency or would also apply to oxidative stress caused by iron deficiency. Although high AsA level apparently conferred tolerance under both types of stress, the enzymatic response to iron deficiency differed from that to Zn deficiency. In particular, APX activity showed a decrease instead of an increase under low iron stress. In conclusion, we suggest that a high AsA level is a promising target for developing rice genotypes with tolerance to oxidative stress.
    Full-text · Article · Jan 2010 · Functional Plant Biology
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    [Show abstract] [Hide abstract] ABSTRACT: Ozone is currently the most important air pollutant that negatively affects growth and yield of agricultural crops in most parts of the world, and rice is arguably the most important food crops on the planet. While a limited number of enclosure-based studies have examined the genotypic differences among rice (Oryza sativa L.) cultivars in response to increasing ozone concentration, no ozone experiment has been conducted to date under fully open-air field conditions to address this issue. In 2007, we conducted an experiment for the first time in the world with rice using free-air concentration enrichment (FACE) system at Xiaoji town, Jiangdu County, Jiangsu Province, China (119° 42′0″E, 32° 35′5″N). Four Chinese rice cultivars: Wujing 15 (WJ15, inbred japonica cultivar), Yangdao 6 (YD6, inbred indica cultivar), Shanyou 63 (SY63, three-line hybrid rice cultivar), Liangyoupeijiu (LYPJ, two-line hybrid rice cultivar), were grown at ambient or elevated (target at 50% above ambient) ozone concentration under nitrogen application rate of 15 g N m−2. The ozone enhancement strongly accelerated phenologycal development of WJ15 and SY63, with maturity being reached by 4 and 8 days earlier, respectively, but only 1 day earlier for YD6 and LYPJ. Elevated ozone concentration reduced the number of mainstem leaves (ca. by half a leaf) and plant height at maturity (ca. by 3–5 cm) of SY63 and LYPJ with no ozone effects detected in YD6 or WJ15. Among the cultivars tested, SY63 and LYPJ exhibited significant yield loss by exposure to ozone (−17.5%, −15%, respectively), while WJ15 and YD6 showed no responses. For all cultivars, no ozone effect was observed on panicle number per unit area as a result of no changes in both maximum tiller number or productive tiller ratio. However, the number of spikelets per panicle of SY63 and LYPJ showed a significant reduction due to ozone exposure, while those of WJ15 and YD6 remained unaffected. Meanwhile, ozone exposure also caused minor reductions in both filled spikelet percentage and individual grain mass. The results of this experiment indicated that yield loss due to ozone exposure differs among rice cultivars with hybrid cultivars (i.e., SY63 and LYPJ) exhibiting greater yield loss than inbred cultivars (i.e., WJ15 and YD6), which could be attributed to the suppression of spikelet formation in the hybrid cultivars under ozone stress.
    Full-text · Article · Jun 2009 · Agriculture Ecosystems & Environment
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    [Show abstract] [Hide abstract] ABSTRACT: Hybrid rice cultivar plays an important role in rice production system due to its high yield potential and resistance to environmental stress. Quantification of its responses to rising CO2 concentration ([CO2]) will reduce our uncertainty in predicting future food security and assist in development of adaptation strategies. Using free air CO2 enrichment (FACE), we measured seasonal changes in growth and nitrogen (N) uptake of an inter-subspecific hybrid rice cultivar Liangyoupeijiu grown under two levels of [CO2] (ambient and elevated by 200 μmol mol−1) and two levels of N fertilization in 2005–2006. Average across the 2 years, FACE increased crop growth rate similarly by 22%, 24% and 23% in the periods from transplanting to panicle initiation (PI), PI to heading and heading to maturity, which was mainly attributed to an increase in green leaf area index rather than the greater net assimilation rate. Grain yield increased greatly under FACE as a result of similar contributions by panicle number per unit area, grain number per panicle and individual grain yield. Final aboveground N acquisition showed a 10.4% increase under FACE, which resulted from enhanced N uptake at both vegetative and reproductive growth stages. Compared with previous FACE studies on final productivity of two inbred japonica cultivars, inter-subspecific hybrid cultivar appears to profit more from elevated [CO2], which mainly resulted from its greater enhancement in photosynthetic production during reproductive growth due to a lack of N limitations late in the season.
    Full-text · Article · Apr 2009 · Field Crops Research
  • [Show abstract] [Hide abstract] ABSTRACT: Hybrid rice (Oryza sativa L.) cultivars play an important role in rice production due to its heterosis, resistance to environmental stress and high yield potential. However, no attention has been given to its yield responses to rising atmospheric CO2 concentration ([CO2]). To address this need, we conducted a Free Air CO2 Enrichment (FACE) experiment at Yangzhou, Jiangsu, China, in 2004–2006. A two-line inter-subspecific hybrid rice variety Liangyoupeijiu, recently bred in China, was grown at ambient or elevated (c. 570μmolmol−1) [CO2] under two levels of nitrogen (N) application (12.5 and 25gNm−2). Elevated [CO2] slightly accelerated phenological development (1–2 days), and substantially enhanced grain yield (+30%). The magnitude of yield response to [CO2] was independent of N fertilization, but greatly varied among years. On average, elevated [CO2] increased panicle number per unit land area by 8%, due to an increase in maximum tiller number under FACE, while productive tiller ratio remained unaffected. Spikelet number per panicle showed an average increase of 10% due to elevated [CO2], which was also supported by increased plant height and dry weight per stem. Meanwhile, Elevated [CO2] caused a significant enhancement in both filled spikelet percentage (+5%) and individual grain mass (+4%). Compared with previous rice FACE studies, this hybrid cultivar appears to profit much more from elevated [CO2] than inbred japonica cultivars (c. +13%), not only due to its stronger sink generation, but also enhanced capacity to utilize the carbon sources in a high [CO2] environment. As sufficient intraspecific variation in yield response exists under field conditions, there is a pressing need to identify genotypes which would produce maximum grain yield under projected future [CO2] levels.
    No preview · Article · Jan 2009 · Agriculture Ecosystems & Environment
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    Yunxia WANG · Michael FREI · Matthias WISSUWA
    [Show abstract] [Hide abstract] ABSTRACT: Studies examining iron (Fe) toxicity and zinc (Zn) deficiency in rice have shown that screening experiments in nutrient solutions are of limited use because the rankings of genotypes as tolerant or intolerant can be very different from the results obtained in field-screening experiments. A possible reason for such deviation is that crucial rhizosphere processes cannot be reproduced in nutrient solutions. The objective of the present study was to evaluate the suitability of low-concentration agar nutrient solutions (ANS) as an alternative screening tool. Agar was dissolved in boiling water and mixed with nutrient solution to achieve a final agar concentration of 0.1% (w/v). Zinc deficiency was induced by supplying Zn at a low concentration (0.1 × 10−3 µmol L−1), while Fe toxicity was induced by supplying excess Fe2+ (200 mg L−1). Three-week-old seedlings were transplanted into this medium. Symptoms of Zn deficiency and Fe toxicity developed more rapidly in ANS compared with conventional nutrient solutions (CNS). For Zn deficiency this was probably because of the development of Zn depletion zones as a result of the reduced convection in the viscous agar medium. In the case of Fe toxicity we observed far less Fe precipitation in ANS compared with CNS. Genotypic comparisons showed that the tolerance rankings obtained in ANS were very similar to the field tolerance rankings, whereas this was not the case in CNS. This was particularly evident with regard to the considerable root growth inhibition detected in intolerant genotypes when stress treatments were imposed in ANS.
    Full-text · Article · Sep 2008 · Soil Science and Plant Nutrition
  • [Show abstract] [Hide abstract] ABSTRACT: Over time, the relative effects of elevated [CO2] on the aboveground photosynthesis, growth and development of rice (Oryza sativa L.) are likely to be changed with increasing duration of CO2 exposure, but the resultant effects on rice belowground responses remain to be evaluated. To investigate the impacts of elevated [CO2] on seasonal changes in root growth, morphology and physiology of rice, a free-air CO2 enrichment (FACE) experiment was performed at Wuxi, Jiangsu, China, in 2002–2003. A japonica cultivar with large panicle was exposed to two [CO2] (ambient [CO2], 370 μmol mol−1; elevated [CO2], 570 μmol mol−1) at three levels of nitrogen (N): low (LN, 15 g N m−2), medium (MN, 25 g N m−2) and high N (HN, 35 g N m−2). Elevated [CO2] increased cumulative root volume, root dry weight, adventitious root length and adventitious root number at all developmental stages by 25–71%, which was mainly associated with increased root growth rate during early growth period (EGP) and lower rate of root senescence during late growth period (LGP), while a slight inhibition of root growth rate occurred during middle growth period (MGP). For individual adventitious roots, elevated [CO2] increased average length, volume, diameter and dry weight early in the season, but the effects gradually disappeared in subsequent stages. Total surface area and active adsorption area per unit root dry weight reached their maxima 10 days earlier in FACE vs. ambient plants, but both of them together with root oxidation ability per unit root dry weight declined with elevated [CO2] during MGP and LGP, the decline being larger during MGP than LGP. The CO2-induced decreases in specific root activities during MGP and LGP were associated with a larger amount of root accumulation during EGP and lower N concentration and higher C/N ratio in roots during MGP and LGP in FACE vs. ambient plants. The results suggest that most of the CO2-induced increases in shoot growth of rice are similarly associated with increased root growth.
    No preview · Article · Apr 2008 · Global Change Biology