RESUMEN
Potassium (K) is the most abundant cation in plants, playing an important role in osmoregulation. Little is known about the effect of genotypic variation in the tolerance to osmotic stress under different K treatments in barley. In this study, we measured the interactive effects of osmotic stress and K supply on growth and stress responses of two barley cultivars (Hordeum vulgare L.) and monitored reactive oxygen species (ROS) along with enzymatic antioxidant activity and their respective gene expression level. The selected cultivars (cv. Milford and cv. Sahin-91Sahin-91) were exposed to osmotic stress (-0.7 MPa) induced by polyethylene glycol 6000 (PEG) under low (0.04 mM) and adequate (0.8 mM) K levels in the nutrient solution. Leaf samples were collected and analyzed for levels of K, ROS, kinetic activity of antioxidants enzymes and expression levels of respective genes during the stress period. The results showed that optimal K supply under osmotic stress significantly decreases ROS production and adjusts antioxidant activity, leading to the reduction of oxidative stress in the studied plants. The cultivar Milford had a lower ROS level and a better tolerance to stress compared to the cultivar Sahin-91. We conclude that optimized K supply is of great importance in mitigating ROS-related damage induced by osmotic stress, specifically in drought-sensitive barley cultivars.
RESUMEN
Soil amendments are known to promote several plant growth parameters. In many agro-ecosystems, water scarcity and drought induced phosphorus deficiency limits crop yield significantly. Considering the climate change scenario, drought and related stress factors will be even more severe endangering the global food security. Therefore, two parallel field trials were conducted to examine at what extent soil amendment of leonardite and humic acid would affect drought and phosphorus tolerance of maize. The treatments were: control (C: 100% A pan and 125 kg P ha-1), P deficiency (phosphorus stress (PS): 62.5 kg P ha-1), water deficit stress (water stress (WS): 67% A pan), and PS + WS (67% A pan and 62.5 kg P ha-1). Three organic amendments were (i) no amendment, (ii) 625 kg S + 750 kg leonardite ha-1 and (iii) 1250 kg S + 37.5 kg humic acid ha-1) tested on stress treatments. Drought and P deficiency reduced plant biomass, grain yield, chlorophyll content, Fv/Fm, RWC and antioxidant activity (superoxide dismutase, peroxidase, and catalase), but increased electrolyte leakage and leaf H2O2 in maize plants. The combined stress of drought and P deficiency decreased further related plant traits. Humic acid and leonardite enhanced leaf P and yield in maize plants under PS. A significant increase in related parameters was observed with humic acid and leonardite under WS. The largest increase in yield and plant traits in relation to humic acid and leonardite application was observed under combined stress situation. The use of sulfur-enriched amendments can be used effectively to maintain yield of maize crop in water limited calcareous soils.
Asunto(s)
Sequías , Sustancias Húmicas/análisis , Minerales/química , Fósforo/deficiencia , Suelo/química , Estrés Fisiológico , Azufre/química , Zea mays/fisiología , Fosfatasa Ácida/metabolismo , Adaptación Fisiológica , Antioxidantes/metabolismo , Biomasa , Catalasa/metabolismo , Clorofila/metabolismo , Electrólitos/metabolismo , Fluorescencia , Peróxido de Hidrógeno/metabolismo , Malondialdehído/metabolismo , Estrés Oxidativo , Peroxidasa/metabolismo , Hojas de la Planta/metabolismo , Brotes de la Planta/crecimiento & desarrollo , Superóxido Dismutasa/metabolismo , Agua , Zea mays/crecimiento & desarrolloRESUMEN
Soil amendment with biochar has received increased attention because of its potential to i) sequester carbon and ii) reduce N2O emission when applied to N fertilised soils. To study the effect of biochar origin on greenhouse gas emission in two contrasting soil types, we used a robotized continuous flow incubation system and δ13C stable isotope approach to compare four biochar types (feed stock: olive mill, corn cob, pistachio shell, cotton stalk) in an alkaline clay soil and two selected biochar types (feed stock: olive mill and corn cob) in an acidic sandy soil. Furthermore, high-throughput sequencing of 16S rRNA genes was performed at the end of the incubation to investigate the effect of different biochars on bacterial community structure in the two different soils. In the alkaline clay soil, all biochar types in conjunction with N fertiliser decreased CO2 emissions up to 12% compared to the N added control treatment causing negative priming, whereas no significant effect of biochar addition on N2O emissions was observed. In contrast, application of olive mill biochar to the acidic sandy soil significantly increased soil pH, CO2, and N2O fluxes, whereas no significant effect of corn cob biochar addition was observed. There was a significant linear relationship between the biochar induced increase in soil pH and the biochar induced increase in soil born N2O emission. Additionally, we detected a clear variation in bacterial community structure in the acidic sandy soil (phyla Acidobacteria, Nitrospirare, and Arthrobacter) with the olive mill biochar addition. Overall, the amendment of different biochars failed to mitigate N2O emissions in both soil types when mineral fertiliser was added. Furthermore, amendment of olive mill biochar stimulated both N2O and CO2 emissions in the low pH sandy soil and altered the bacterial community structure, which was possibly related to its liming effect.
Asunto(s)
Contaminantes Atmosféricos/análisis , Bacterias , Carbón Orgánico/análisis , Monitoreo del Ambiente , Gases de Efecto Invernadero/análisis , Microbiota , Suelo/química , Bacterias/clasificación , Fertilizantes/análisis , Alemania , Nitrógeno/administración & dosificación , TurquíaRESUMEN
Potassium (K) is crucial for crop growth and is strongly related to stress tolerance and water-use efficiency (WUE). A major physiological effect of K deficiency is the inhibition of net CO2 assimilation (AN) during photosynthesis. Whether this reduction originates from limitations either to photochemical energy conversion or biochemical CO2 fixation or from a limitation to CO2 diffusion through stomata and the leaf mesophyll is debated. In this study, limitations to photosynthetic carbon gain of sunflower (Helianthus annuus L.) under K deficiency and PEG- induced water deficit were quantified and their implications on plant- and leaf-scale WUE (WUEP, WUEL) were evaluated. Results show that neither maximum quantum use efficiency (Fv/Fm) nor in-vivo RubisCo activity were directly affected by K deficiency and that the observed impairment of AN was primarily due to decreased CO2 mesophyll conductance (gm). K deficiency additionally impaired leaf area development which, together with reduced AN, resulted in inhibition of plant growth and a reduction of WUEP. Contrastingly, WUEL was not affected by K supply which indicated no inhibition of stomatal control. PEG-stress further impeded AN by stomatal closure and resulted in enhanced WUEL and high oxidative stress. It can be concluded from this study that reduction of gm is a major response of leaves to K deficiency, possibly due to changes in leaf anatomy, which negatively affects AN and contributes to the typical symptoms like oxidative stress, growth inhibition and reduced WUEP.
Asunto(s)
Helianthus/fisiología , Fotosíntesis/efectos de los fármacos , Potasio/farmacología , Agua/metabolismo , Biomasa , Clorofila/metabolismo , Fluorescencia , Gases/metabolismo , Helianthus/efectos de los fármacos , Helianthus/crecimiento & desarrollo , Peróxido de Hidrógeno/metabolismo , Células del Mesófilo/efectos de los fármacos , Células del Mesófilo/metabolismo , Complejo de Proteína del Fotosistema II/metabolismo , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/fisiología , Raíces de Plantas/efectos de los fármacos , Raíces de Plantas/fisiología , Brotes de la Planta/efectos de los fármacos , Brotes de la Planta/fisiología , Factores de TiempoRESUMEN
Salt stress impairs global agricultural crop production by reducing vegetative growth and yield. Despite this importance, a number of gaps exist in our knowledge about very early metabolic responses that ensue minutes after plants experience salt stress. Surprisingly, this early phase remains almost as a black box. Therefore, systematic studies focussing on very early plant physiological responses to salt stress (in this case NaCl) may enhance our understanding on strategies to develop crop plants with a better performance under saline conditions. In the present study, hydroponically grown Vicia faba L. plants were exposed to 90 min of NaCl stress, whereby every 15 min samples were taken for analyzing short-term physiologic responses. Gas chromatography-mass spectrometry-based metabolite profiles were analysed by calculating a principal component analysis followed by multiple contrast tests. Follow-up experiments were run to analyze downstream effects of the metabolic changes on the physiological level. The novelty of this study is the demonstration of complex stress-induced metabolic changes at the very beginning of a moderate salt stress in V. faba, information that are very scant for this early stage. This study reports for the first that the proline analogue trans-4-hydroxy-L-proline, known to inhibit cell elongation, was increasingly synthesized after NaCl-stress initiation. Leaf metabolites associated with the generation or scavenging of reactive oxygen species (ROS) were affected in leaves that showed a synchronized increase in ROS formation. A reduced glutamine synthetase activity indicated that disturbances in the nitrogen assimilation occur earlier than it was previously thought under salt stress.
Asunto(s)
Nitrógeno/metabolismo , Prolina/biosíntesis , Especies Reactivas de Oxígeno/metabolismo , Tolerancia a la Sal , Cloruro de Sodio/metabolismo , Estrés Fisiológico , Vicia faba/metabolismo , Cromatografía de Gases y Espectrometría de Masas , Glutamina/metabolismo , Hojas de la Planta/metabolismo , Proteínas de Plantas/metabolismo , Raíces de Plantas/metabolismo , Prolina/análogos & derivadosRESUMEN
Legumes match the nodule number to the N demand of the plant. When a mutation in the regulatory mechanism deprives the plant of that ability, an excessive number of nodules are formed. These mutants show low productivity in the fields, mainly due to the high carbon burden caused through the necessity to supply numerous nodules. The objective of this study was to clarify whether through optimal conditions for growth and CO2 assimilation a higher nodule activity of a supernodulating mutant of Medicago truncatula (M. truncatula) can be induced. Several experimental approaches reveal that under the conditions of our experiments, the nitrogen fixation of the supernodulating mutant, designated as sunn (super numeric nodules), was not limited by photosynthesis. Higher specific nitrogen fixation activity could not be induced through short- or long-term increases in CO2 assimilation around shoots. Furthermore, a whole plant P depletion induced a decline in nitrogen fixation, however this decline did not occur significantly earlier in sunn plants, nor was it more intense compared to the wild-type. However, a distinctly different pattern of nitrogen fixation during the day/night cycles of the experiment indicates that the control of N2 fixing activity of the large number of nodules is an additional problem for the productivity of supernodulating mutants.
Asunto(s)
Medicago truncatula/metabolismo , Dióxido de Carbono/química , Dióxido de Carbono/metabolismo , Medicago truncatula/crecimiento & desarrollo , Nitrógeno/química , Nitrógeno/metabolismo , Fijación del Nitrógeno , Fósforo/química , Fósforo/metabolismo , Fotosíntesis , Brotes de la Planta/metabolismo , Nódulos de las Raíces de las Plantas/metabolismoRESUMEN
In this review we summarize factors determining the plant availability of soil potassium (K), the role of K in crop yield formation and product quality, and the dependence of crop stress resistance on K nutrition. Average soil reserves of K are generally large, but most of it is not plant-available. Therefore, crops need to be supplied with soluble K fertilizers, the demand of which is expected to increase significantly, particularly in developing regions of the world. Recent investigations have shown that organic exudates of some bacteria and plant roots play a key role in releasing otherwise unavailable K from K-bearing minerals. Thus, breeding for genotypes that have improved mechanisms to gain access to this fixed K will contribute toward more sustainable agriculture, particularly in cropping systems that do not have access to fertilizer K. In K-deficient crops, the supply of sink organs with photosynthates is impaired, and sugars accumulate in source leaves. This not only affects yield formation, but also quality parameters, for example in wheat, potato and grape. As K has beneficial effects on human health, its concentration in the harvest product is a quality parameter in itself. Owing to its fundamental roles in turgor generation, primary metabolism, and long-distance transport, K plays a prominent role in crop resistance to drought, salinity, high light, or cold as well as resistance to pests and pathogens. Despite the abundance of vital roles of K in crop production, an improvement of K uptake and use efficiency has not been a major focus of conventional or transgenic breeding in the past. In addition, current soil analysis methods for K are insufficient for some common soils, posing the risk of imbalanced fertilization. A stronger prioritization of these areas of research is needed to counter declines in soil fertility and to improve food security.
Asunto(s)
Productos Agrícolas/fisiología , Potasio/metabolismo , Microbiología del Suelo , Suelo/química , Productos Agrícolas/crecimiento & desarrollo , Exudados de Plantas/metabolismo , Raíces de Plantas/metabolismo , Estrés FisiológicoRESUMEN
The increasing input of anthropogenically derived nitrogen (N) to ecosystems raises a crucial question: how does available N modify the decomposer community and thus affects the mineralization of soil organic matter (SOM). Moreover, N input modifies the priming effect (PE), that is, the effect of fresh organics on the microbial decomposition of SOM. We studied the interactive effects of C and N on SOM mineralization (by natural (13) C labelling adding C4 -sucrose or C4 -maize straw to C3 -soil) in relation to microbial growth kinetics and to the activities of five hydrolytic enzymes. This encompasses the groups of parameters governing two mechanisms of priming effects - microbial N mining and stoichiometric decomposition theories. In sole C treatments, positive PE was accompanied by a decrease in specific microbial growth rates, confirming a greater contribution of K-strategists to the decomposition of native SOM. Sucrose addition with N significantly accelerated mineralization of native SOM, whereas mineral N added with plant residues accelerated decomposition of plant residues. This supports the microbial mining theory in terms of N limitation. Sucrose addition with N was accompanied by accelerated microbial growth, increased activities of ß-glucosidase and cellobiohydrolase, and decreased activities of xylanase and leucine amino peptidase. This indicated an increased contribution of r-strategists to the PE and to decomposition of cellulose but the decreased hemicellulolytic and proteolytic activities. Thus, the acceleration of the C cycle was primed by exogenous organic C and was controlled by N. This confirms the stoichiometric decomposition theory. Both K- and r-strategists were beneficial for priming effects, with an increasing contribution of K-selected species under N limitation. Thus, the priming phenomenon described in 'microbial N mining' theory can be ascribed to K-strategists. In contrast, 'stoichiometric decomposition' theory, that is, accelerated OM mineralization due to balanced microbial growth, is explained by domination of r-strategists.
Asunto(s)
Carbono/metabolismo , Nitrógeno/metabolismo , Microbiología del Suelo , Suelo/química , Sacarosa/metabolismo , Zea mays/químicaRESUMEN
RATIONALE: N2O isotopomer ratios may provide a useful tool for studying N2O source processes in soils and may also help estimating N2O reduction to N2. However, remaining uncertainties about different processes and their characteristic isotope effects still hamper its application. We conducted two laboratory incubation experiments (i) to compare the denitrification potential and N2O/(N2O+N2) product ratio of denitrification of various soil types from Northern Germany, and (ii) to investigate the effect of N2O reduction on the intramolecular (15)N distribution of emitted N2O. METHODS: Three contrasting soils (clay, loamy, and sandy soil) were amended with nitrate solution and incubated under N2 -free He atmosphere in a fully automated incubation system over 9 or 28 days in two experiments. N2O, N2, and CO2 release was quantified by online gas chromatography. In addition, the N2O isotopomer ratios were determined by isotope-ratio mass spectrometry (IRMS) and the net enrichment factors of the (15)N site preference (SP) of the N2O-to-N2 reduction step (η(SP)) were estimated using a Rayleigh model. RESULTS: The total denitrification rate was highest in clay soil and lowest in sandy soil. Surprisingly, the N2O/(N2O+N2) product ratio in clay and loam soil was identical; however, it was significantly lower in sandy soil. The IRMS measurements revealed highest N2O SP values in clay soil and lowest SP values in sandy soil. The η(SP) values of N2O reduction were between -8.2 and -6.1, and a significant relationship between δ(18)O and SP values was found. CONCLUSIONS: Both experiments showed that the N2O/(N2O+N2) product ratio of denitrification is not solely controlled by the available carbon content of the soil or by the denitrification rate. Differences in N2O SP values could not be explained by variations in N2O reduction between soils, but rather originate from other processes involved in denitrification. The linear δ(18)O vs SP relationship may be indicative for N2O reduction; however, it deviates significantly from the findings of previous studies.
Asunto(s)
Gases/análisis , Óxido Nitroso/análisis , Suelo/química , Silicatos de Aluminio/química , Dióxido de Carbono/análisis , Arcilla , Desnitrificación , Nitrógeno/análisis , Isótopos de Nitrógeno/análisis , Oxidación-Reducción , Dióxido de Silicio/químicaRESUMEN
The attribution of nitrous oxide (N(2)O) emission to organic and inorganic N fertilizers requires understanding of how these inputs affect the two biological processes, i.e. denitrification and nitrification. Contradictory findings have been reported when the effects of organic and inorganic fertilizers on nitrous oxide emission were compared. Here we aimed to contribute to the understanding of such variation using (15)N-labelling techniques. We determined the processes producing N(2)O, and tested the effects of soil moisture, N rates, and the availability of organic matter. In a pot experiment, we compared soil treated with biogas waste (BGW) and mineral ammonium sulphate (Min-N) applied at four rates under two soil moisture regimes. We also tested biogas waste, conventional cattle slurry and mineral N fertilizer in a grassland field experiment. During the first 37 days after application we observed N(2)O emissions of 5.6 kg N(2)O-N ha(-1) from soils supplied with biogas waste at a rate of 360 kg N ha(-1). Fluxes were ca. 5-fold higher at 85% than at 65% water holding capacity (WHC). The effects of fertilizer types and N rates on N(2)O emission were significant only when the soil moisture was high. Organic fertilizer treated soils showed much higher N(2)O emissions than those receiving mineral fertilizer in both, pot and field experiment. Over all the treatments the percentage of the applied N emitted as N(2)O was 2.56% in BGW but only 0.68% in Min-N. In the pot experiment isotope labelling indicated that 65-95% of the N(2)O was derived from denitrification for all fertilizer types. However, the ratio of denitrification/nitrification derived N(2)O was lower at 65% than at 85% WHC. We speculate that the application of organic matter in conjunction with ammonium nitrogen first leads to a decrease in denitrification-derived N(2)O emission compared with soil receiving mineral fertilizer. However, at later stages when denitrification becomes C-limited, higher N(2)O emissions are induced when the soil moisture is high.
Asunto(s)
Monitoreo del Ambiente/métodos , Fertilizantes/análisis , Nitratos/química , Óxido Nitroso/química , Suelo/análisis , Isótopos de Nitrógeno/análisisRESUMEN
The Broadbalk Wheat Experiment at Rothamsted Research in the UK provides a unique opportunity to investigate the long-term impacts of environmental change and agronomic practices on plants and soils. We examined the influence of manure and mineral fertiliser applications on temporal trends in the stable N ((15)N) and C ((13)C) isotopes of wheat collected during 1968-1979 and 1996-2005, and of soil collected in 1966 and 2000. The soil delta(15)N values in 1966 and 2000 were higher in manure than the mineral N supplied soil; the latter had similar or higher delta(15)N values than non-fertilised soil. The straw delta(15)N values significantly decreased in all N treatments during 1968 to 1979, but not for 1996-2005. The straw delta(15)N values decreased under the highest mineral N supply (192 kg N ha(-1) year(-1)) by 3 per thousand from 1968 to 1979. Mineral N supply significantly increased to straw delta(13)C values in dry years, but not in wet years. Significant correlations existed between wheat straw delta(13)C values with cumulative rainfall (March to June). The cultivar Hereward (grown 1996-2005) was less affected by changes in environmental conditions (i.e. water stress and fertiliser regime) than Cappelle Desprez (1968-1979). We conclude that, in addition to fertiliser type and application rates, water stress and, importantly, plant variety influenced plant delta(13)C and delta(15)N values. Hence, water stress and differential variety response should be considered in plant studies using plant delta(13)C and delta(15)N trends to delineate past or recent environmental or agronomic changes.