Dual Inoculation with Rhizophagus irregularis and Bacillus megaterium Improves Maize Tolerance to Combined Drought and High Temperature Stress by Enhancing Root Hydraulics, Photosynthesis and Hormonal Responses.

Climate change is leading to combined drought and high temperature stress in many areas, drastically reducing crop production, especially for high-water-consuming crops such as maize. This study aimed to determine how the co-inoculation of an arbuscular mycorrhizal (AM) fungus (Rhizophagus irregularis) and the PGPR Bacillus megaterium (Bm) alters the radial water movement and physiology in maize plants in order to cope with combined drought and high temperature stress. Thus, maize plants were kept uninoculated or inoculated with R. irregularis (AM), with B. megaterium (Bm) or with both microorganisms (AM + Bm) and subjected or not to combined drought and high temperature stress (D + T). We measured plant physiological responses, root hydraulic parameters, aquaporin gene expression and protein abundances and sap hormonal content. The results showed that dual AM + Bm inoculation was more effective against combined D + T stress than single inoculation. This was related to a synergistic enhancement of efficiency of the phytosystem II, stomatal conductance and photosynthetic activity. Moreover, dually inoculated plants maintained higher root hydraulic conductivity, which was related to regulation of the aquaporins ZmPIP1;3, ZmTIP1.1, ZmPIP2;2 and GintAQPF1 and levels of plant sap hormones. This study demonstrates the usefulness of combining beneficial soil microorganisms to improve crop productivity under the current climate-change scenario.

MgO-mediated activation of active carbon as an affordable strategy to "in situ" degradation of lindane in contaminated soils.

The accumulation in soil landfills of toxic and persistent lindane, widely used as an insecticide, triggers the risk of leaching with the concomitant contamination of surrounding rivers. Thus, viable remediation to eliminate in situ high concentrations of lindane in soil and water becomes an urgent demand. In this line, a simple and cost-effective composite is proposed, including the use of industrial wastes. It includes reductive and non-reductive base-catalyzed strategies to remove lindane in the media. A mixture of magnesium oxide (MgO) and activated carbon (AC) was selected for that purpose. The use of MgO provides a basic pH. In addition, the specific selected MgO forms double-layered hydroxides in water which permits the total adsorption of the main heavy metals in contaminated soils. AC provides adsorption microsites to hold the lindane and a reductive atmosphere that was increased when combined with the MgO. These properties trigger highly efficient remediation of the composite. It permits a complete elimination of lindane in the solution. In soils doped with lindane and heavy metals, it produces a rapid, complete, and stable elimination of lindane and immobilization of the metals. Finally, the composite tested in lindane-highly contaminated soils permits the "in situ" degradation of nearly 70% of the initial lindane. The proposed strategy opens a promising way to face this environmental issue with a simple, cost-effective composite to degrade lindane and fix heavy metals in contaminated soils.

Arabidopsis ALIX Regulates Stomatal Aperture and Turnover of Abscisic Acid Receptors.

The plant endosomal trafficking pathway controls the abundance of membrane-associated soluble proteins, as shown for abscisic acid (ABA) receptors of the PYRABACTIN RESISTANCE1/PYR1-LIKE/REGULATORY COMPONENTS OF ABA RECEPTORS (PYR/PYL/RCAR) family. ABA receptor targeting for vacuolar degradation occurs through the late endosome route and depends on FYVE DOMAIN PROTEIN REQUIRED FOR ENDOSOMAL SORTING1 (FYVE1) and VACUOLAR PROTEIN SORTING23A (VPS23A), components of the ENDOSOMAL SORTING COMPLEX REQUIRED FOR TRANSPORT-I (ESCRT-I) complexes. FYVE1 and VPS23A interact with ALG-2 INTERACTING PROTEIN-X (ALIX), an ESCRT-III-associated protein, although the functional relevance of such interactions and their consequences in cargo sorting are unknown. In this study we show that Arabidopsis (Arabidopsis thaliana) ALIX directly binds to ABA receptors in late endosomes, promoting their degradation. Impaired ALIX function leads to altered endosomal localization and increased accumulation of ABA receptors. In line with this activity, partial loss-of-function alix-1 mutants display ABA hypersensitivity during growth and stomatal closure, unveiling a role for the ESCRT machinery in the control of water loss through stomata. ABA-hypersensitive responses are suppressed in alix-1 plants impaired in PYR/PYL/RCAR activity, in accordance with ALIX affecting ABA responses primarily by controlling ABA receptor stability. ALIX-1 mutant protein displays reduced interaction with VPS23A and ABA receptors, providing a molecular basis for ABA hypersensitivity in alix-1 mutants. Our findings unveil a negative feedback mechanism triggered by ABA that acts via ALIX to control the accumulation of specific PYR/PYL/RCAR receptors.

Using the Maize Nested Association Mapping (NAM) Population to Partition Arbuscular Mycorrhizal Effects on Drought Stress Tolerance into Hormonal and Hydraulic Components.

In this study, a first experiment was conducted with the objective of determining how drought stress alters the radial water flow and physiology in the whole maize nested association mapping (NAM) population and to find out which contrasting maize lines should be tested in a second experiment for their responses to drought in combination with an arbuscular mycorrhizal (AM) fungus. Emphasis was placed on determining the role of plant aquaporins and phytohormones in the responses of these contrasting maize lines to cope with drought stress. Results showed that both plant aquaporins and hormones are altered by the AM symbiosis and are highly involved in the physiological responses of maize plants to drought stress. The regulation by the AM symbiosis of aquaporins involved in water transport across cell membranes alters radial water transport in host plants. Hormones such as IAA, SA, ABA and jasmonates must be involved in this process either by regulating the own plant-AM fungus interaction and the activity of aquaporins, or by inducing posttranscriptional changes in these aquaporins, which in turns alter their water transport capacity. An intricate relationship between root hydraulic conductivity, aquaporins and phytohormones has been observed, revealing a complex network controlling water transport in maize roots.

Maturation in composting process, an incipient humification-like step as multivariate statistical analysis of spectroscopic data shows.

Humification is a process that plant and microbiota residues experiment in natural or agronomic soils under microorganisms action and environmental conditions. Under this process natural biomolecules - such as protein, carbohydrates or lignin - experience secondary biochemical and chemical reactions yielding to the formation of new organic biomolecules normally known as soil humus or humic substances (HS). In parallel, composting of fresh organic residues may be seen as an artificial process that involves many microorganism-induced secondary biochemical reactions that are probably also included in the first steps of natural humification in soils. In this context, we have applied multivariate statistical analysis to diverse and complementary analytical techniques (UV-Visible, synchronous fluorescence, FTIR, 13C- NMR and pyrolysis GS/MS) to follow the structural evolution of three groups of organic material: (i) fresh organic matter materials, (ii) compost of the fresh organic matter materials, and (iii) humic and fulvic acids including standards and references from the International Humic Substances Society. In order to discriminate among the three groups of organic materials, the set of data obtained from each analytical technique was analyzed using complementary statistical techniques: Correlations, Kolmogorov-Smirnov Test and Principal Component Analysis (PCA). The results showed positive correlations between UV-visible and fluorescence indexes and aromatic structures determined by 13C- NMR and pyrolysis GS/MS. However, these indexes were negatively correlated with polysaccharides and amides determined by FTIR, and lipids determined by pyrolysis GS/MS. The Kolmogorov-Smirnov Test showed that E4/E6, ε600, EEt/EBz, ε280 from UV/Visible; A440 from synchronous fluorescence; 1040/1400 and 1515/1715 by FTIR and, LIP from pyrolysis GS/MS were able to discriminate the samples in two different groups. The group formed by the transformed organic substances (humic, fulvic and composted materials) on the one hand, and the raw (fresh) organic materials on the other. These results, considered along with those obtained from the PCA analysis of spectroscopic data, indicated that composting could share secondary reactions and processes with the first steps of natural humification occurring in soil. Likewise, the results show that the organic molecules present in humic and composted materials are chemically different from the biomolecules present in fresh, no-transformed- materials.

Local root ABA/cytokinin status and aquaporins regulate poplar responses to mild drought stress independently of the ectomycorrhizal fungus Laccaria bicolor.

The relatively better performance of mycorrhizal plants subjected to drought stress has commonly been linked to improved root water uptake through the fungal regulation of plant aquaporins and hormones. In this study, we examined the role of ectomycorrhizal fungi in plant water relations and plant hormonal balance under mild drought using split-root seedlings of Populus trichocarpa × deltoides either with or without inoculation with Laccaria bicolor. The root compartments where the drought treatment was applied had higher ABA and lower cytokinin tZR contents, and greater expression of the plant aquaporins PtPIP1;1, PtPIP1;2, PtPIP2;5, and PtPIP2;7. On the other hand, the presence of L. bicolor within the roots down-regulated PtPIP1;4, PtPIP2;3, and PtPIP2;10, and reduced the abundance of PIP2 proteins. In addition, expression of the fungal aquaporins JQ585595 and JQ585596 were positively correlated with root ABA content, while tZR content was positively correlated with PtPIP1;4 and negatively correlated with PtPIP2;7. The results demonstrate a coordinated plant-fungal system that regulates the different mechanisms involved in water uptake in ectomycorrhizal poplar plants.

Involvement of the def-1 Mutation in the Response of Tomato Plants to Arbuscular Mycorrhizal Symbiosis Under Well-Watered and Drought Conditions.

Jasmonic acid (JA) and arbuscular mycorrhizal (AM) symbioses are known to protect plants against abiotic and biotic stresses, but are also involved in the regulation of root hydraulic conductance (L). The objective of this experiment was to elucidate the role of JA in the water relations and hormonal regulation of AM plants under drought by using tomato plants defective in the synthesis of JA (def-1). Our results showed that JA is involved in the uptake and transport of water through its effect on both physiological parameters (stomatal conductance and L) and molecular parameters, mainly by controlling the expression and abundance of aquaporins. We observed that def-1 plants increased the expression of seven plant aquaporin genes under well-watered conditions in the absence of AM fungus, which partly explain the increment of L by this mutation under well-watered conditions. In addition, the effects of the AM symbiosis on plants were modified by the def-1 mutation, with the expression of some aquaporins and plant hormone concentration being disturbed. On the other hand, methyl salicylate (MeSA) content was increased in non-mycorrhizal def-1 plants, suggesting that MeSA and JA can act together in the regulation of L. In a complementary experiment, it was found that exogenous MeSA increased L, confirming our hypothesis. Likewise, we confirmed that JA, ABA and SA are hormones involved in plant mechanisms to cope with stressful situations, their concentrations being controlled by the AM symbiosis. In conclusion, under well-watered conditions, the def-1 mutation mimics the effects of AM symbiosis, but under drought conditions the def-1 mutation changed the effects of the AM symbiosis on plants.

Shoot iron status and auxin are involved in iron deficiency-induced phytosiderophores release in wheat.

BACKGROUND: The release of phytosiderephores (PS) to the rhizosphere is the main root response to iron (Fe) deficiency in graminaceous plants. We have investigated the role of the Fe status in the shoot as well as of the signaling pathways controlled by three relevant phytoregulators - indolacetic acid (IAA), ethylene and nitric oxide (NO) - in the regulation of this root response in Fe-starved wheat plants. To this end, the PS accumulation in the nutrient solution and the root expression of the genes encoding the nicotianamine aminotransferase (TaNAAT) and ferritin (TaFER) have been evaluated in plants subjected to different treatments. RESULTS: The application of Fe to leaves of Fe-deficient plants prevented the increase in both PS root release and TaNAAT gene expression thus showing the relevant role of the shoot to root communication in the regulation of PS root release and some steps of PS biosynthesis. Experiments with specific hormone inhibitors showed that while ethylene and NO did not positively regulate Fe-deficiency induced PS root release, auxin plays an essential role in the regulation of this process. Moreover, the application of IAA to Fe-sufficient plants promoted both PS root release and TaNAAT gene expression thus indicating that auxin might be involved in the shoot to root signaling network regulating Fe-deficiency root responses in wheat. CONCLUSIONS: These results therefore indicate that PS root release in Fe-deficient wheat plants is directly modulated by the shoot Fe status through signaling pathways involving, among other possible effectors, auxin.

Ethylene sensitivity and relative air humidity regulate root hydraulic properties in tomato plants.

MAIN CONCLUSION: The effect of ethylene and its precursor ACC on root hydraulic properties, including aquaporin expression and abundance, is modulated by relative air humidity and plant sensitivity to ethylene. Relative air humidity (RH) is a main factor contributing to water balance in plants. Ethylene (ET) is known to be involved in the regulation of root water uptake and stomatal opening although its role on plant water balance under different RH is not very well understood. We studied, at the physiological, hormonal and molecular levels (aquaporins expression, abundance and phosphorylation state), the plant responses to exogenous 1-aminocyclopropane-1-carboxylic acid (ACC; precursor of ET) and 2-aminoisobutyric acid (AIB; inhibitor of ET biosynthesis), after 24 h of application to the roots of tomato wild type (WT) plants and its ET-insensitive never ripe (nr) mutant, at two RH levels: regular (50%) and close to saturation RH. Highest RH induced an increase of root hydraulic conductivity (Lpo) of non-treated WT plants, and the opposite effect in nr mutants. The treatment with ACC reduced Lpo in WT plants at low RH and in nr plants at high RH. The application of AIB increased Lpo only in nr plants at high RH. In untreated plants, the RH treatment changed the abundance and phosphorylation of aquaporins that affected differently both genotypes according to their ET sensitivity. We show that RH is critical in regulating root hydraulic properties, and that Lpo is affected by the plant sensitivity to ET, and possibly to ACC, by regulating aquaporins expression and their phosphorylation status. These results incorporate the relationship between RH and ET in the response of Lpo to environmental changes.

Tomato ethylene sensitivity determines interaction with plant growth-promoting bacteria.

Background and Aims: Plant growth-promoting bacteria (PGPB) are soil micro-organisms able to interact with plants and stimulate their growth, positively affecting plant physiology and development. Although ethylene plays a key role in plant growth, little is known about the involvement of ethylene sensitivity in bacterial inoculation effects on plant physiology. Thus, the present study was pursued to establish whether ethylene perception is critical for plant-bacteria interaction and growth induction by two different PGPB strains, and to assess the physiological effects of these strains in juvenile and mature tomato ( Solanum lycopersicum ) plants. Methods: An experiment was performed with the ethylene-insensitive tomato never ripe and its isogenic wild-type line in which these two strains were inoculated with either Bacillus megaterium or Enterobacter sp. C7. Plants were grown until juvenile and mature stages, when biomass, stomatal conductance, photosynthesis as well as nutritional, hormonal and metabolic statuses were analysed. Key Results: Bacillus megaterium promoted growth only in mature wild type plants. However, Enterobacter C7 PGPB activity affected both wild-type and never ripe plants. Furthermore, PGPB inoculation affected physiological parameters and root metabolite levels in juvenile plants; meanwhile plant nutrition was highly dependent on ethylene sensitivity and was altered at the mature stage. Bacillus megaterium inoculation improved carbon assimilation in wild-type plants. However, insensitivity to ethylene compromised B. megaterium PGPB activity, affecting photosynthetic efficiency, plant nutrition and the root sugar content. Nevertheless, Enterobacter C7 inoculation modified the root amino acid content in addition to stomatal conductance and plant nutrition. Conclusions: Insensitivity to ethylene severely impaired B. megaterium interaction with tomato plants, resulting in physiological modifications and loss of PGPB activity. In contrast, Enterobacter C7 inoculation stimulated growth independently of ethylene perception and improved nitrogen assimilation in ethylene-insensitive plants. Thus, ethylene sensitivity is a determinant for B. megaterium , but is not involved in Enterobacter C7 PGPB activity.

Arbuscular mycorrhizal symbiosis induces strigolactone biosynthesis under drought and improves drought tolerance in lettuce and tomato.

Arbuscular mycorrhizal (AM) symbiosis alleviates drought stress in plants. However, the intimate mechanisms involved, as well as its effect on the production of signalling molecules associated with the host plant-AM fungus interaction remains largely unknown. In the present work, the effects of drought on lettuce and tomato plant performance and hormone levels were investigated in non-AM and AM plants. Three different water regimes were applied, and their effects were analysed over time. AM plants showed an improved growth rate and efficiency of photosystem II than non-AM plants under drought from very early stages of plant colonization. The levels of the phytohormone abscisic acid, as well as the expression of the corresponding marker genes, were influenced by drought stress in non-AM and AM plants. The levels of strigolactones and the expression of corresponding marker genes were affected by both AM symbiosis and drought. The results suggest that AM symbiosis alleviates drought stress by altering the hormonal profiles and affecting plant physiology in the host plant. In addition, a correlation between AM root colonization, strigolactone levels and drought severity is shown, suggesting that under these unfavourable conditions, plants might increase strigolactone production in order to promote symbiosis establishment to cope with the stress.

Arbuscular mycorrhizal symbiosis and methyl jasmonate avoid the inhibition of root hydraulic conductivity caused by drought.

Hormonal regulation and symbiotic relationships provide benefits for plants to overcome stress conditions. The aim of this study was to elucidate the effects of exogenous methyl jasmonate (MeJA) application on root hydraulic conductivity (L) of Phaseolus vulgaris plants which established arbuscular mycorrhizal (AM) symbiosis under two water regimes (well-watered and drought conditions). The variation in endogenous contents of several hormones (MeJA, JA, abscisic acid (ABA), indol-3-acetic acid (IAA), salicylic acid (SA)) and the changes in aquaporin gene expression, protein abundance and phosphorylation state were analyzed. AM symbiosis decreased L under well-watered conditions, which was partially reverted by the MeJA treatment, apparently by a drop in root IAA contents. Also, AM symbiosis and MeJA prevented inhibition of L under drought conditions, most probably by a reduction in root SA contents. Additionally, the gene expression of two fungal aquaporins was upregulated under drought conditions, independently of the MeJA treatment. Plant aquaporin gene expression could not explain the behaviour of L. Conversely, evidence was found for the control of L by phosphorylation of aquaporins. Hence, MeJA addition modified the response of L to both AM symbiosis and drought, presumably by regulating the root contents of IAA and SA and the phosphorylation state of aquaporins.

Effect of sulphur deprivation on osmotic potential components and nitrogen metabolism in oilseed rape leaves: identification of a new early indicator.

Identification of early sulphur (S) deficiency indicators is important for species such as Brassica napus, an S-demanding crop in which yield and the nutritional quality of seeds are negatively affected by S deficiency. Because S is mostly stored as SO4 (2-) in leaf cell vacuoles and can be mobilized during S deficiency, this study investigated the impact of S deprivation on leaf osmotic potential in order to identify compensation processes. Plants were exposed for 28 days to S or to chlorine deprivation in order to differentiate osmotic and metabolic responses. While chlorine deprivation had no significant effects on growth, osmotic potential and nitrogen metabolism, Brassica napus revealed two response periods to S deprivation. The first one occurred during the first 13 days during which plant growth was maintained as a result of vacuolar SO4 (2-) mobilization. In the meantime, leaf osmotic potential of S-deprived plants remained similar to control plants despite a reduction in the SO4 (2-) osmotic contribution, which was fully compensated by an increase in NO3 (-), PO4 (3-) and Cl(-) accumulation. The second response occurred after 13 days of S deprivation with a significant reduction in growth, leaf osmotic potential, NO3 (-) uptake and NO3 (-) reductase activity, whereas amino acids and NO3 (-) were accumulated. This kinetic analysis of S deprivation suggested that a ([Cl(-)]+[NO3 (-)]+[PO4 (3-)]):[SO4 (2-)] ratio could provide a relevant indicator of S deficiency, modified nearly as early as the over-expression of genes encoding SO4 (2-) tonoplastic or plasmalemmal transporters, with the added advantage that it can be easily quantified under field conditions.

The symbiosis with the arbuscular mycorrhizal fungus Rhizophagus irregularis drives root water transport in flooded tomato plants.

It is known that the presence of arbuscular mycorrhizal fungi within the plant roots enhances the tolerance of the host plant to different environmental stresses, although the positive effect of the fungi in plants under waterlogged conditions has not been well studied. Tolerance of plants to flooding can be achieved through different molecular, physiological and anatomical adaptations, which will affect their water uptake capacity and therefore their root hydraulic properties. Here, we investigated the root hydraulic properties under non-flooded and flooded conditions in non-mycorrhizal tomato plants and plants inoculated with the arbuscular mycorrhizal fungus Rhizophagus irregularis. Only flooded mycorrhizal plants increased their root hydraulic conductivity, and this effect was correlated with a higher expression of the plant aquaporin SlPIP1;7 and the fungal aquaporin GintAQP1. There was also a higher abundance of the PIP2 protein phoshorylated at Ser280 in mycorrhizal flooded plants. The role of plant hormones (ethylene, ABA and IAA) in root hydraulic properties was also taken into consideration, and it was concluded that, in mycorrhizal flooded plants, ethylene has a secondary role regulating root hydraulic conductivity whereas IAA may be the key hormone that allows the enhancement of root hydraulic conductivity in mycorrhizal plants under low oxygen conditions.

Involvement of plant endogenous ABA in Bacillus megaterium PGPR activity in tomato plants.

BACKGROUND: Plant growth-promoting rhizobacteria (PGPR) are naturally occurring soil bacteria which benefit plants by improving plant productivity and immunity. The mechanisms involved in these processes include the regulation of plant hormone levels such as ethylene and abscisic acid (ABA). The aim of the present study was to determine whether the activity of Bacillus megaterium PGPR is affected by the endogenous ABA content of the host plant. The ABA-deficient tomato mutants flacca and sitiens and their near-isogenic wild-type parental lines were used. Growth, stomatal conductance, shoot hormone concentration, competition assay for colonization of tomato root tips, and root expression of plant genes expected to be modulated by ABA and PGPR were examined. RESULTS: Contrary to the wild-type plants in which PGPR stimulated growth rates, PGPR caused growth inhibition in ABA-deficient mutant plants. PGPR also triggered an over accumulation of ethylene in ABA-deficient plants which correlated with a higher expression of the pathogenesis-related gene Sl-PR1b. CONCLUSIONS: Positive correlation between over-accumulation of ethylene and a higher expression of Sl-PR1b in ABA-deficient mutant plants could indicate that maintenance of normal plant endogenous ABA content may be essential for the growth promoting action of B. megaterium by keeping low levels of ethylene production.

Enhancement of root hydraulic conductivity by methyl jasmonate and the role of calcium and abscisic acid in this process.

The role of jasmonic acid in the induction of stomatal closure is well known. However, its role in regulating root hydraulic conductivity (L) has not yet been explored. The objectives of the present research were to evaluate how JA regulates L and how calcium and abscisic acid (ABA) could be involved in such regulation. We found that exogenous methyl jasmonate (MeJA) increased L of Phaseolus vulgaris, Solanum lycopersicum and Arabidopsis thaliana roots. Tomato plants defective in JA biosynthesis had lower values of L than wild-type plants, and that L was restored by addition of MeJA. The increase of L by MeJA was accompanied by an increase of the phosphorylation state of the aquaporin PIP2. We observed that MeJA addition increased the concentration of cytosolic calcium and that calcium channel blockers inhibited the rise of L caused by MeJA. Treatment with fluoridone, an inhibitor of ABA biosynthesis, partially inhibited the increase of L caused by MeJA, and tomato plants defective in ABA biosynthesis increased their L after application of MeJA. It is concluded that JA enhances L and that this enhancement is linked to calcium and ABA dependent and independent signalling pathways.

Iron-dependent modifications of the flower transcriptome, proteome, metabolome, and hormonal content in an Arabidopsis ferritin mutant.

Iron homeostasis is an important process for flower development and plant fertility. The role of plastids in these processes has been shown to be essential. To document the relationships between plastid iron homeostasis and flower biology further, a global study (transcriptome, proteome, metabolome, and hormone analysis) was performed of Arabidopsis flowers from wild-type and triple atfer1-3-4 ferritin mutant plants grown under iron-sufficient or excess conditions. Some major modifications in specific functional categories were consistently observed at these three omic levels, although no significant overlaps of specific transcripts and proteins were detected. These modifications concerned redox reactions and oxidative stress, as well as amino acid and protein catabolism, this latter point being exemplified by an almost 10-fold increase in urea concentration of atfer1-3-4 flowers from plants grown under iron excess conditions. The mutant background caused alterations in Fe-haem redox proteins located in membranes and in hormone-responsive proteins. Specific effects of excess Fe in the mutant included further changes in these categories, supporting the idea that the mutant is facing a more intense Fe/redox stress than the wild type. The mutation and/or excess Fe had a strong impact at the membrane level, as denoted by the changes in the transporter and lipid metabolism categories. In spite of the large number of genes and proteins responsive to hormones found to be regulated in this study, changes in the hormonal balance were restricted to cytokinins, especially in the mutant plants grown under Fe excess conditions.

Thermodynamic and spectroscopic data suggesting hypothetical humic fractions evolution on carbon cycle in soils.

Soil organic matter is considered by soil scientists as the interlayer that connect alive with mineral sides of the soil. In addition, microorganisms have in soil organic matter a source of carbon as well as a source of energy. We can observe a duality that can be analyzed from a biological, physicochemical, or even thermodynamic sense. From this last point of view carbon cycle follows its evolution on burial soil, and under certain temperature and pression conditions, up to fossil fuels or coals through kerogen being humic substances the ending point of biologically linked structures. When biological aspects are minimized, physicochemical aspects are maximized and carbonaceous structures are a source of energy but resilient to microorganism actions. Under these premises, we have isolated, purified, and analyzed different humic fractions. Heat of combustion of these humic fractions here analyzed reflects this situation and fitted the list of evolution stage of carbonaceous materials that step by step accumulates energy. Theoretical value of this parameter calculated from studied humic fractions, and by combination of its biochemical macromolecules yielded an exaggerated value in comparison to the real and measured value indicating a complexity of these humic structures, more than simpler molecules. Heat of combustion and excitation-emission matrices by fluorescence spectroscopy of isolated and purified grey and brown humic materials revealed different values for each fraction. Grey fractions showed a higher heat of combustion values and shorter λexc/λem, whereas brown fractions showed a lower heat of combustion and a larger λexc/λem. These data together with previous chemical analysis indicated a deep structural differentiation that can be observed by the Pyrolysis MS-GC data of the studied samples. Authors hypothesized that this incipient distinction between aliphatic and aromatic cores could evolve independently up to fossil fuel on one hand and coals on the other hand but separately.

Hydroponics versus field lysimeter studies of urea, ammonium and nitrate uptake by oilseed rape (Brassica napus L.).

N-fertilizer use efficiencies are affected by their chemical composition and suffer from potential N-losses by volatilization. In a field lysimeter experiment, (15)N-labelled fertilizers were used to follow N uptake by Brassica napus L. and assess N-losses by volatilization. Use of urea with NBPT (urease inhibitor) showed the best efficiency with the lowest N losses (8% of N applied compared with 25% with urea alone). Plants receiving ammonium sulphate, had similar yield achieved through a better N mobilization from vegetative tissues to the seeds, despite a lower N uptake resulting from a higher volatilization (43% of applied N). Amounts of (15)N in the plant were also higher when plants were fertilized with ammonium nitrate but N-losses reached 23% of applied N. In parallel, hydroponic experiments showed a deleterious effect of ammonium and urea on the growth of oilseed rape. This was alleviated by the nitrate supply, which was preferentially taken up. B. napus was also characterized by a very low potential for urea uptake. BnDUR3 and BnAMT1, encoding urea and ammonium transporters, were up-regulated by urea, suggesting that urea-grown plants suffered from nitrogen deficiency. The results also suggested a role for nitrate as a signal for the expression of BnDUR3, in addition to its role as a major nutrient. Overall, the results of the hydroponic study showed that urea itself does not contribute significantly to the N nutrition of oilseed rape. Moreover, it may contribute indirectly since a better use efficiency for urea fertilizer, which was further increased by the application of a urease inhibitor, was observed in the lysimeter study.