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See detailTesting biostimulants for validating the claims: a multi-level analysis
Quievreux, Martin ULiege; Falesse, Wiliam; Lengrand, Salomé et al

Poster (2021)

Plant biostimulants are placed on the market on the basis of their intended effects on crop plants, referred to as ‘claims’. In the EU, standardized protocols will be required to validate the claims of ... [more ▼]

Plant biostimulants are placed on the market on the basis of their intended effects on crop plants, referred to as ‘claims’. In the EU, standardized protocols will be required to validate the claims of biostimulant products to access the EU market, but which protocols will prove be efficient, robust and applicable to a range of crops still needs to be determined. Although many data are available, from the laboratory to the field, it seems important to generate parallel data sets by using the same biostimulants in the laboratory, in the greenhouse and in the field. By combining the data sets, the value of the different tests and the efficacy of the field and contained use approaches can be best evaluated. In order to set up an evaluation platform for biostimulants in Belgium, a project, named BioStimTest, has been initiated with the support of the Walloon Region of Belgium and coordinated by the company Redebel. Organic, inorganic and microbial biostimulant products, as available on the market, are being tested on winter wheat, maize and potato with field trials. Laboratory bioassays on model plants, seed germination tests, measurements of biomass and root development in hydroponic cultures, biomass and physiological measurements of greenhouse-grown plants are all used to compare these data with plant performance in the field. Improvement of nitrogen use efficiency and of drought tolerance are the two biostimulant claims considered by the project. Accordingly, different fertilization regimes and the limitation of the rain supplies by controlled rainout shelters are used in the field experiments, under the temperate climate of Belgium. [less ▲]

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See detailDevelopmental plasticity of Brachypodium distachyon in response to P deficiency: modulation by inoculation with phosphate-solubilizing bacteria
Baudson, Caroline ULiege; Delory, Benjamin; Spaepen, Stijn et al

in Plant Direct (2021), 5(1), 00296

Mineral phosphorus (P) fertilisers must be used wisely in order to preserve rock phosphate, a limited and non-renewable resource. The use of bio-inoculants to improve soil nutrient availability and ... [more ▼]

Mineral phosphorus (P) fertilisers must be used wisely in order to preserve rock phosphate, a limited and non-renewable resource. The use of bio-inoculants to improve soil nutrient availability and trigger an efficient plant response to nutrient deficiency is one potential strategy in the attempt to decrease P inputs in agriculture. An in vitro co-cultivation system was used to study the response of Brachypodium distachyon to contrasted P supplies (soluble and poorly soluble forms of P) and inoculation with P solubilizing bacteria. Brachypodium's responses to P conditions and inoculation with bacteria were studied in terms of developmental plasticity and P use efficiency. Brachypodium showed plasticity in its biomass allocation pattern in response to variable P conditions, specifically by prioritizing root development over shoot productivity under poorly soluble P conditions. Despite the ability of the bacteria to solubilize P, shoot productivity was depressed in plants inoculated with bacteria, although the root system development was maintained. The negative impact of bacteria on biomass production in Brachypodium might be attributed to inadequate C supply to bacteria, an increased competition for P between both organisms under P-limiting conditions, or an accumulation of toxic bacterial metabolites in our cultivation system. Both P and inoculation treatments impacted root system morphology. The modulation of Brachypodium’s developmental response to P supplies by P solubilizing bacteria did not lead to improved P use efficiency. Our results support the hypothesis that plastic responses of Brachypodium cultivated under P-limited conditions are modulated by P solubilizing bacteria. The considered experimental context impacts plant–bacteria interactions. Choosing experimental conditions as close as possible to real ones is important in the selection of P solubilizing bacteria. Both persistent homology and allometric analyses proved to be useful tools that should be considered when studying the impact of bio-inoculants on plant development in response to varying nutritional context. [less ▲]

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See detailQuantitative Structure-Activity Relationship of Humic-Like Biostimulants Derived From Agro-Industrial Byproducts and Energy Crops
Savy, Davide ULiege; Brostaux, Yves ULiege; Cozzolino, V. et al

in Frontiers in Plant Science (2020), 11

Humic-like substances (HLSs) isolated by alkaline oxidative hydrolysis from lignin-rich agro-industrial residues have been shown to exert biostimulant activity toward maize (Zea mays L.) germination and ... [more ▼]

Humic-like substances (HLSs) isolated by alkaline oxidative hydrolysis from lignin-rich agro-industrial residues have been shown to exert biostimulant activity toward maize (Zea mays L.) germination and early growth. The definition of a quantitative structure-activity relationship (QSAR) between HLS and their bioactivity could be useful to predict their biological properties and tailor plant biostimulants for specific agronomic and industrial uses. Here, we created several projection on latent structure (PLS) regression by using published analytical data on the molecular composition of lignin-derived HLS obtained by both 13C-CPMAS-NMR spectra directly on samples and 31P-NMR spectra after derivatization of hydroxyl functions with a P-containing reagent (2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane). These spectral data were used to model the effect of HLS on the elongation of primary root, lateral seminal roots, total root apparatus, and coleoptile of maize. The 13C-CPMAS-NMR data suggested that methoxyl and aromatic moieties positively affected plant growth, while the carboxyl/esterified functions showed a negative impact on the overall seedling development. Alkyl C seems to promote Col elongation while concomitantly reducing that of the root system. Additionally, 31P-NMR-derived spectra revealed that the elongation of roots and Col were enhanced by the occurrence of aliphatic hydroxyl groups, and guaiacyl and p-Hydroxyphenyl lignin monomers. The PLS models based on raw dataset from 13C-CPMAS-NMR spectra explained more than 74% of the variance for the length of lateral seminal roots, total root system and coleoptile, while other parameters derived from 13C-CPMAS-NMR spectra, namely the Hydrophobicity and Hydrophilicity of materials were necessary to explain 83% of the variance of the primary root length. The results from 31P-NMR spectra explained the observed biological variance by 90, 96, 96, and 93% for the length of primary root, lateral seminal roots, total root system and coleoptile, respectively. This work shows that different NMR spectroscopy techniques can be used to build up PLS models which can predict the bioactivity of lignin-derived HLS toward early growth of maize plants. The established QSAR may also be exploited to enhance by chemical techniques the bioactive properties of HLS and enhance their plant stimulation capacity. © Copyright © 2020 Savy, Brostaux, Cozzolino, Delaplace, du Jardin and Piccolo. [less ▲]

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See detailEffects of physico-chemical and biological properties of soil on the allelopathic activity of barley (Hordeum vulgare L. subsp. vulgare) root exudates against Bromus diandrus Roth. and Stelleria media L. weeds
Bouhaouel, Imen; Gfeller, Aurélie; Boudabous, Khaled et al

in Allelopathy Journal (2020), 49(1), 17-34

In greenhouse experiment, the allelopathic effects of 6-barley genotypes were assessed on the morphological features of weeds, Bromus diandrus Roth. and Stelleria media L. The inhibitory effects of root ... [more ▼]

In greenhouse experiment, the allelopathic effects of 6-barley genotypes were assessed on the morphological features of weeds, Bromus diandrus Roth. and Stelleria media L. The inhibitory effects of root exudates depended on the barley genotype and the physico-chemical properties of the soil, and their interactions. The sandy soils with low organic matter and nutrients content showed more the allelopathic potential. A predictive model of the allelopathic activity of barley was proposed based on soil properties and tested weeds. Overall, the stepwise model showed that the content of phenolic acids was the major determinant of allelopathic activity, besides the soil chemical characteristics (electrical conductivity and carbon and sodium content). Soil microbial communities decreased the allelopathic activity of barley. Drainage and aeration might explain the slightly higher inhibitory activity in a non-autoclaved sandy substrate than a clay-loam substrate. When recommending allelopathic barley genotypes for cultivation, the environmental factors, physico-chemical properties of soil and rhizosphere microbiome might reduce or enhance their allelopathic potential. [less ▲]

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See detailDynamics and mechanisms of volatile organic compound exchanges in a winter wheat field
Bachy, Aurélie ULiege; Aubinet, Marc ULiege; Amelynck, C. et al

in Atmospheric Environment (2020), 221

The understanding of biogenic volatile organic compound (BVOC) exchanges has become a key scientific issue because of their high reactivity and their impact in the atmosphere. However, so far, few studies ... [more ▼]

The understanding of biogenic volatile organic compound (BVOC) exchanges has become a key scientific issue because of their high reactivity and their impact in the atmosphere. However, so far, few studies have focused on BVOCs exchanged by agricultural species, and in particular by winter wheat, despite this species being the leading worldwide crop in terms of harvested area. This study for the first time investigated BVOC exchanges from winter wheat during most developmental stages of the plant. Fluxes were measured in Belgium at the ecosystem-scale using the disjunct eddy covariance by mass scanning technique, and a proton-transfer-reaction mass spectrometer for BVOC ambient mixing ratio measurements. As is usually observed for crops and grasses, the winter wheat field emitted mainly methanol, although bi-directional exchanges were observed. The second most exchanged compound was acetic acid which was captured during the entire growing season. Bi-directional exchanges of acetaldehyde and acetone were also reported. Terpene exchanges were 22 times smaller than oxygenated VOC (OVOC) exchanges. For all compounds, the exchanges were the most pronounced at the end of the growing season, i.e., under warm, dry and sunny conditions. Senescence-induced emissions were furthermore observed for methanol and acetaldehyde. For all investigated OVOCs, the exchanges very likely originated from both the soil and the plants. Despite their mixed origin, the MEGAN (Model of Emissions of Gases and Aerosols from Nature) v2.1 up-scaling model could adequately reproduce the methanol, acetaldehyde and acetone exchanges measured at this site during the mature and senescence phases of the plant, when the standard emission factor and the leaf age factor were adapted based on the measurements. In contrast, the model failed to reproduce the measured acetic acid exchanges. When the standard emission factor values currently assigned in MEGAN were applied, however, the exchanges were largely over-estimated for all compounds. © 2019 Elsevier Ltd [less ▲]

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See detailIdentification of barley (hordeum vulgare L. SubSp. Vulgare) root exudates allelochemicals, their autoallelopathic activity and against bromus diandrus Roth. Germination
Bouhaouel, Imen ULiege; Richard, Gaetan ULiege; Fauconnier, Marie-Laure ULiege et al

in Agronomy (2019), 9(7), 345-363

Crops with weed suppressive root exudates or the direct use of bioherbicidal allelochemicals is a new approach in integrated weed management systems. In this context, the allelopathic activity and ... [more ▼]

Crops with weed suppressive root exudates or the direct use of bioherbicidal allelochemicals is a new approach in integrated weed management systems. In this context, the allelopathic activity and chemical composition of root exudates from six genotypes (modern varieties and landraces) of barley were characterized. The phenolic acids appeared to be particularly implicated in the inhibitory action of barley root exudates against Bromus diandrus. The amount of these compounds was higher in sandy substrate than in sandy-clay-loam substrate. Ten phenolic acids and one phenylpropanoid derivative were present, in addition to saponarin, a newly identified flavonoid in barley root exudates. Seven compounds explaining variability in the inhibitory activity of barley roots (stepwise analysis) and one compound detected only in highly allelopathic genotypes were toxic against receiver plants. Most compounds had a greater inhibitory effect on the growth of great brome than the barley genotypes. The synergistic and/or additive effect of the eight compounds appeared to be the source of the toxicity. Benzoic acid, the mixture of compounds, saponarin and salicylic acid were the most effcient compounds against the great brome and the less aggressive against barley. Overall, the results revealed the allelopathic potential of the water-soluble compounds exuded by the roots of living barley plants. These compounds included saponarin, a flavonoid not yet recognized as a barley root allelochemical. [less ▲]

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See detailBiostimulant effects of rhizobacteria on wheat growth and nutrient uptake depend on nitrogen application and plant development
Nguyen, Minh Luan ULiege; Spaepen, Stijn; du Jardin, Patrick ULiege et al

in Archives of Agronomy and Soil Science (2019)

The capacity of plant growth-promoting rhizobacteria (PGPR) - Bacillus amyloliquefaciens GB03 (BamGB03), B. megaterium SNji (BmeSNji), and Azospirillum brasilense 65B (Abr65B) – to enhance growth and ... [more ▼]

The capacity of plant growth-promoting rhizobacteria (PGPR) - Bacillus amyloliquefaciens GB03 (BamGB03), B. megaterium SNji (BmeSNji), and Azospirillum brasilense 65B (Abr65B) – to enhance growth and nutrient uptake in wheat was evaluated under different mineral N fertilizer rates, in sterile vs. non-sterile soils, and at different developmental stages. In gnotobiotic conditions, the three strains significantly increased plant biomass irrespective of the N rates. Under greenhouse conditions using non-sterile soil, growth promotion was generally highest at moderate N rate, followed by full N dose, while no significant effect of the inoculants was observed in the absence of N fertilizer. At 50N, plant biomass was most significantly increased in roots (up to +45% with Abr65B) at stem-elongation stage and in the ears (+19–23% according to the strains) at flowering stages. For some nutrients (N, P, Mn, and Cu), the biomass increases in roots and ears was paralleled with lowered nutrient concentrations in the same organs. Nevertheless, growth stimulation resulted in higher total nutrient uptake and nutrient uptake efficiency. Furthermore, Abr65B and BmeSNji counteracted the repression of root development caused by high N supply. Therefore, combining PGPR with a proper cultivated system, N rate, and plant stage could enhance their biostimulant effects. [less ▲]

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See detailBiostimulant Effects of Bacillus strains on wheat from in vitro towards field conditions are modulated by nitrogen supply
Nguyen, Minh Luan; Glaes, Johann; Spaepen, Stijn et al

in Journal of Plant Nutrition and Soil Science (2019), 182

Bacillus velezensisstrains, belonging to plant growth-promoting rhizobacteria (PGPR), areincreasingly used as microbial biostimulant. However, their field application to winter wheatunder temperate ... [more ▼]

Bacillus velezensisstrains, belonging to plant growth-promoting rhizobacteria (PGPR), areincreasingly used as microbial biostimulant. However, their field application to winter wheatunder temperate climate remains poorly documented. Therefore, threeB. velezensisstrainsIT45, FZB24 and FZB42 were tested for their efficacy under these conditions. Two biological in-teraction systems were firstly developed under gnotobiotic and greenhouse conditions combinedwith sterile or non-sterile soil, respectively, and finally assayed in the field during two yearscoupled with different N fertilization rates. Under gnotobiotic conditions, all three strains signifi-cantly increased root growth of 14 d-old spring and winter wheat seedlings. In the greenhouseusing non-sterile soil, only FZB24 significantly increased root biomass of spring wheat (+31%).The three strains were able to improve nutrient uptake of the spring wheat grown in the green-house, particularly for the micronutrients Fe, Mn, Zn, and Cu, but the observed increases innutrient uptake were dependent on the organs and the elements. The root biomass increases ininoculated plants coincided with lowered nutrient concentrations of P and K. In 2014, under fieldconditions and absence of any N fertilizer supply, FZB24 significantly increased grain yields by983 kg ha–1, or 14.9%, in relation to non-inoculated controls. The three strains in the 2015 fieldtrial failed to confirm the previous positive results, likely due to the low temperatures occurringduring and after inoculations. The Zeleny sedimentation value, indicative of flour quality, wasunaffected by the inoculants. The results are discussed in the perspective of bacterial applicationto wheat under temperate agricultural practices [less ▲]

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See detailInteractions of allelochemicals with plant plasma membrane: a case study with alkaloids from barley
Lebecque, Simon ULiege; Crowet, Jean-Marc ULiege; du Jardin, Patrick ULiege et al

Poster (2018, April)

Allelopathy is defined as “any direct or indirect harmful effect by one plant on another through production of chemical compounds that escape into the environment” (Rice, 1974).This phenomenon is seen as ... [more ▼]

Allelopathy is defined as “any direct or indirect harmful effect by one plant on another through production of chemical compounds that escape into the environment” (Rice, 1974).This phenomenon is seen as a potential tool for weeds management within the framework of sustainable agriculture. While many studies investigated the mode of action of various allelochemicals (molecules emitted by allelopathic plants), little attention was given to their initial contact with the plant plasma membrane. In our work, this key step is explored for two alkaloids, gramine and hordenine, that are allelochemicals produced by barley. [less ▲]

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See detailUse of molecular dynamics simulations to study the interactions between barley allelochemicals and plant plasma membrane
Lebecque, Simon ULiege; Crowet, Jean-Marc ULiege; du Jardin, Patrick ULiege et al

Poster (2018, March)

Gramine and hordenine, two alkaloids produced by barley, were shown to inhibit the growth of a common weed (Matricaria recutita L.). This feature could be useful in order to reach a more sustainable weeds ... [more ▼]

Gramine and hordenine, two alkaloids produced by barley, were shown to inhibit the growth of a common weed (Matricaria recutita L.). This feature could be useful in order to reach a more sustainable weeds management. In vitro experiments have proven that both molecules do interact with lipid bilayers (made of a phosphatidylglycerol (PG) lipid) mimicking plant plasma membranes and are able to modify some of their properties. Moreover, gramine was shown to be more effective than hordenine in both inhibiting weeds growth and altering lipid bilayers properties, suggesting that interactions with membranes could be linked to their mode of action. Molecular dynamics (MD) simulations are carried out in order to get an insight into the molecular mechanisms that underlie these interactions with model membranes and to discriminate between gramine behavior and hordenine behavior. [less ▲]

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See detailInteraction between the barley allelochemical compounds gramine and hordenine and artificial lipid bilayers mimicking the plant plasma membrane
Lebecque, Simon ULiege; Crowet, Jean-Marc ULiege; Lins, Laurence ULiege et al

in Scientific Reports (2018), 8

Some plants affect the development of neighbouring plants by releasing secondary metabolites into their environment. This phenomenon is known as allelopathy and is a potential tool for weed management ... [more ▼]

Some plants affect the development of neighbouring plants by releasing secondary metabolites into their environment. This phenomenon is known as allelopathy and is a potential tool for weed management within the framework of sustainable agriculture. While many studies have investigated the mode of action of various allelochemicals (molecules emitted by allelopathic plants), little attention has been paid to their initial contact with the plant plasma membrane (PPM). In this paper, this key step is explored for two alkaloids, gramine and hordenine, that are allelochemicals from barley. Using in vitro bioassays, we first showed that gramine has a greater toxicity than hordenine towards a weed commonly found in northern countries (Matricaria recutita L.). Then, isothermal titration calorimetry was used to show that these alkaloids spontaneously interact with lipid bilayers that mimic the PPM. The greater impact of gramine on the thermotropic behaviour of lipids compared to hordenine was established by means of infrared spectroscopy. Finally, the molecular mechanisms of these interactions were explored with molecular dynamics simulations. The good correlation between phytotoxicity and the ability to disturb lipid bilayers is discussed. In this study, biophysical tools were used for the first time to investigate the interactions of allelochemicals with artificial PPM. [less ▲]

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See detailDecrease in the photosynthetic performance of temperate grassland species does not lead to a decline in the gross primary production of the ecosystem
Digrado, Anthony ULiege; Gourlez de la Motte, Louis ULiege; Bachy, Aurélie ULiege et al

in Frontiers in Plant Science (2018), 9

Plants, under stressful conditions, can proceed to photosynthetic adjustments in order to acclimatize and alleviate the detrimental impacts on the photosynthetic apparatus. However, it is currently ... [more ▼]

Plants, under stressful conditions, can proceed to photosynthetic adjustments in order to acclimatize and alleviate the detrimental impacts on the photosynthetic apparatus. However, it is currently unclear how adjustment of photosynthetic processes under environmental constraints by plants influences CO2 gas exchange at the ecosystem-scale. Over a two-year period, photosynthetic performance of a temperate grassland ecosystem was characterized by conducting frequent chlorophyll fluorescence (ChlF) measurements on three primary grassland species (Lolium perenne L., Taraxacum sp., and Trifolium repens L.). Ecosystem photosynthetic performance was estimated from measurements performed on the three dominant grassland species weighed based on their relative abundance. In addition, monitoring CO2 fluxes was performed by eddy covariance. The highest decrease in photosynthetic performance was detected in summer, when environmental constraints were combined. Dicot species (Taraxacum sp. and T. repens) presented the strongest capacity to up-regulate PSI and exhibited the highest electron transport efficiency under stressful environmental conditions compared with L. perenne. The decline in ecosystem photosynthetic performance did not lead to a reduction in gross primary productivity, likely because increased light energy was available under these conditions. The carbon amounts fixed at light saturation were not influenced by alterations in photosynthetic processes, suggesting photosynthesis was not impaired. Decreased photosynthetic performance was associated with high respiration flux, but both were influenced by temperature. Our study revealed variation in photosynthetic performance of a grassland ecosystem responded to environmental constraints, but alterations in photosynthetic processes appeared to exhibit a negligible influence on ecosystem CO2 fluxes. [less ▲]

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See detailBiogenic volatile organic compound emissions from senescent maize leaves and a comparison with other leaf developmental stages
Mozaffar, Md Ahsan ULiege; Schoon, N.; Bachy, Aurélie ULiege et al

in Atmospheric Environment (2018), 176

Plants are the major source of Biogenic Volatile Organic Compounds (BVOCs) which have a large influence on atmospheric chemistry and the climate system. Therefore, understanding of BVOC emissions from all ... [more ▼]

Plants are the major source of Biogenic Volatile Organic Compounds (BVOCs) which have a large influence on atmospheric chemistry and the climate system. Therefore, understanding of BVOC emissions from all abundant plant species at all developmental stages is very important. Nevertheless, investigations on BVOC emissions from even the most widespread agricultural crop species are rare and mainly confined to the healthy green leaves. Senescent leaves of grain crop species could be an important source of BVOCs as almost all the leaves senesce on the field before being harvested. For these reasons, BVOC emission measurements have been performed on maize (Zea mays L.), one of the most cultivated crop species in the world, at all the leaf developmental stages. The measurements were performed in controlled environmental conditions using dynamic enclosures and proton transfer reaction mass spectrometry (PTR-MS). The main compounds emitted by senescent maize leaves were methanol (31% of the total cumulative BVOC emission on a mass of compound basis) and acetic acid (30%), followed by acetaldehyde (11%), hexenals (9%) and m/z 59 compounds (acetone/propanal) (7%). Important differences were observed in the temporal emission profiles of the compounds, and both yellow leaves during chlorosis and dry brown leaves after chlorosis were identified as important senescence-related BVOC sources. Total cumulative BVOC emissions from senescent maize leaves were found to be among the highest for senescent Poaceae plant species. BVOC emission rates varied strongly among the different leaf developmental stages, and senescent leaves showed a larger diversity of emitted compounds than leaves at earlier stages. Methanol was the compound with the highest emissions for all the leaf developmental stages and the contribution from the younggrowing, mature, and senescent stages to the total methanol emission by a typical maize leaf was 61, 13, and 26%, respectively. This study shows that BVOC emissions from senescent maize leaves cannot be neglected and further investigations in field conditions are recommended to further constrain the BVOC emissions from this important C4 crop species. [less ▲]

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See detailPhysiological and biochemical parameters: new tools to screen barley root exudates allelopathic potential (*Hordeum vulgare* L. subsp. *vulgare*
Bouhaouel, Imen; Gfeller, Aurélie; Boudabous, Khaoula et al

in Acta Physiologiae Plantarum (2018), 40(2), 1-14

Morphological markers/traits are often used in the detection of allelopathic stress, but optical signals including chlorophyll a fluorescence emission could be useful in developing new screening ... [more ▼]

Morphological markers/traits are often used in the detection of allelopathic stress, but optical signals including chlorophyll a fluorescence emission could be useful in developing new screening techniques. In this context, the allelopathic effect of barley (Hordeum vulgare subsp. vulgare) root exudates (three modern varieties and three landraces) were assessed on the morphological (root and shoot length, biomass accumulation), physiological (Fv/Fm and F0), and biochemical (chlorophyll and protein contents) variables of great brome (Bromus diandrus Roth., syn. Bromus rigidus Roth. subsp. gussonii Parl.). All the measured traits were affected when great brome was grown in a soil substrate in which barley plants had previously developed for 30 days before being removed. The response of receiver plants was affected by treatment with activated charcoal, dependent on barley genotype and on the nature of the growing substrate. The inhibitory effect was lower with the addition of the activated charcoal suggesting the release of putative allelochemicals from barley roots into the soil. The barley landraces were more toxic than modern varieties and their effect was more pronounced in sandy substrate than in silty clay sand substrate. In our investigation, the chlorophyll content and Fv/Fm were the most correlated variables with barley allelopathic potential. These two parameters might be considered as effective tools to quantify susceptibility to allelochemical inhibitors in higher plants. [less ▲]

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See detailEnvironmental controls of methanol emissions from a grazed grassland in Dorinne, Belgium
Michel, Colin ULiege; Heinesch, Bernard ULiege; Bachy, Aurélie ULiege et al

Poster (2017, October 20)

Despite the growing interest for oxygenated volatile organic compounds (OVOC) over the last 15 years due to their role in the atmospheric chemistry, current knowledge about OVOC exchanges by grassland and ... [more ▼]

Despite the growing interest for oxygenated volatile organic compounds (OVOC) over the last 15 years due to their role in the atmospheric chemistry, current knowledge about OVOC exchanges by grassland and the environmental factors driving them remains lacunar. However, those ecosystems represent an important part of the total earth surface (13.37%). This study conducted on a grazed grassland therefore aims to quantify OVOC exchanges over full grazing seasons in order to understand the mechanisms behind these exchanges. It took place within the activities of the CROSTVOC project (CROp Stress VOC) and therefore gives an important attention to the stress induced fluxes. BVOC flux measurements were performed with a PTR-MS for the measurements of OVOC mixing ratios on two different scales: the eddy Covariance method was used during two whole grazing seasons (2014 and 2015) and in the 2016 summer, measurements were also performed on a smaller scale by using all-teflon automated dynamic chambers. The chambers allowed measuring accurately the impact of grazing by following simultaneously undisturbed and grazed grassland patches. This study pointed out that several OVOC were exchanged in variable quantities, with methanol being by far the most important. Methanol fluxes exhibited a clear diurnal cycle with close-to-zero fluxes at night and maximum fluxes at midday. The flux was also much larger in the summer than during autumn or spring. For the eddy Covariance data, the average methanol flux in the summer (0.033 μg.m-2s-1) was in the same range of other studies, being lower than the average found by Bamberger et al. in 2010 (0.080 μg.m-2s-1) and by Ammann (0.077 μg.m-2s-1). Fluxes from the chambers were slightly lower with an average value of 0.27 μg.m-2s-1 but they were measured in the late summer. Driver analysis is still ongoing but first results showed that the flux was strongly correlated at short time scale (half hourly for the EC method and one and a half hourly for the chambers) to the photosynthetic photon flux density and the latent heat flux. We believe that their influence comes mainly from the control practiced by stomatal conductance in non-steady state conditions and expansion of cell walls in steady state conditions. The cuvette data showed that grazing resulted in significantly enhanced emissions of methanol that lasted for several days. On the contrary, the eddy Covariance method cannot distinguish between grazed and non-grazed grass and only a small fraction of the method footprint had been grazed the previous days on average. Our eddy-covariance data suggested that an increase in the stocking density did not contribute to a significant rise of methanol emission. The limited variability in stocking density during the two growing seasons and the more powerful effect of other drivers likely induced that the flux variability due to the SD was too low to be measured by the eddy Covariance method. In depth comparisons between the eddy-covariance data and the dynamic chambers data will be carried out. [less ▲]

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See detailEnvironmental controls of biogenic volatile organic compound emissions from a grazed grassland in Dorinne, Belgium
Michel, Colin ULiege; Heinesch, Bernard ULiege; Bachy, Aurélie ULiege et al

Poster (2017, June 15)

Despite the growing interest for oxygenated volatile organic compounds (OVOC) over the last 15 years due to their role in the atmospheric chemistry, current knowledge about OVOC exchanges by grassland and ... [more ▼]

Despite the growing interest for oxygenated volatile organic compounds (OVOC) over the last 15 years due to their role in the atmospheric chemistry, current knowledge about OVOC exchanges by grassland and the environmental factors driving them still entails gaps. However, those ecosystems represent an important part of the total earth surface (13.37%). This study conducted on a grazed grassland therefore aims to quantify OVOC exchanges over full grazing seasons in order to understand the mechanisms behind these OVOC exchanges. The Eddy Covariance method was used for flux quantification, with a PTR-MS for the measurements of OVOCs mixing ratios. It took place within the activities of the CROSTVOC project (CROp Stress VOC) and therefore gives an important attention to the stress induced fluxes. BVOC flux measurements were also performed on a smaller scale by using all-teflon automated dynamic chambers covering a surface of 0.1 m² each. [less ▲]

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See detailGrazing-induced BVOC fluxes from a managed grassland
Mozaffar, Ahsan ULiege; Schoon, N.; Bachy, Aurélie ULiege et al

Poster (2017, April 28)

Detailed reference viewed: 39 (5 ULiège)