Effects of inoculation of EPS-producing Pantoea agglomerans on wheat rhizosphere aggregation

We investigated plant and soil nitrogen pools and soil processes in monospecific stands of the C₃ sedge Scirpus olneyi and the C₄ grass Spartina patens grown in the field in open top chambers in a brackish marsh on the Chesapeake Bay. Stands of S. olneyi responded to eight years of elevated CO₂, by increased rates of net ecosystem gas exchange and a large stimulation of net ecosystem production. We conducted our study in the summer of 1994 and 1995 when soil cores were collected and aboveground biomass was estimated. Nitrogen concentration in elevated CO₂ treatments was reduced 15% in stems of S. olneyi and 8% in the upper 10 cm of the soil profile. While total plant nitrogen per unit of land area remained the same between treatments, total soil nitrogen showed a non-significant tendency to decrease in the upper 10 cm of the soil profile in elevated CO₂ both years of study. A significant decrease in soil bulk density largely contributed to the observed decrease in soil nitrogen. Exchangeable nitrogen and potential denitrification rates were also reduced in elevated CO₂, but net nitrogen mineralization was unchanged by elevated CO₂ treatment in S. olneyi both years. Plants and soils in a pure stand of the C₄ grass, S. patens, showed none of these effects of elevated CO₂ treatment. Our data provides evidence of changes in nitrogen dynamics of an ecosystem exposed to elevated CO₂ for eight years; however due to the variability in these data, we cannot say if or how these changes are likely to impact the effect of rising CO₂ on primary production or carbon accumulation in this ecosystem in the future.     

Root colonization by symplasmata-forming Enterobacter agglomerans

Abstract Enterobacter agglomerans strains are able to form cell aggregates called symplasmata when grown in a liquid medium. The nitrogen-fixing E. agglomerans strain NO30, isolated from the rhizosphere soil of rice, was inoculated onto roots of axenically grown wheat and rice seedlings and could colonize the roots of both plants. The ability of NO30 cells to colonize the plant roots seemed comparable in the host and non-host plants, as far as colony forming units (cfu) measurements were concerned. Nevertheless, electron microscopy (SEM, TEM) revealed that, in the case of rice, the normal host plant for NO30, the colonization was characterized by the formation of symplasmata, whereas only individual cells were found on wheat roots. Symplasmata formation seems to be specific for colonization of the host plant, rice. This finding also means that colonization of the host plant may be largely underestimated when measured by conventional techniques. Symplasmata formed in liquid medium or on the roots of rice were stained using Thiery's and Swift's technique, and the presence of polysaccharides and proteins was revealed in the extracellular matrix as well as in fibrils anchoring symplasmata to other symplasmata or to plant cells.     

Crop rotation associating a legume and the nickel hyperaccumulator <Emphasis Type="Italic">Alyssum murale</Emphasis> improves the structure and biofunctioning of an ultramafic soil

Nickel (Ni) agromining aims to phytoextract heavy metals using hyperaccumulators whilst at the same time rehabilitating ultramafic soils. After removing the bioavailable metal, ultramafic soils are improved in terms of their agronomic properties with the aim of future agricultural uses. The low fertility of ultramafic soils can be compensated by integrating legumes already used in traditional agro-systems because of their importance in soil nitrogen enrichment. However, few studies have evaluated the potential profits of legumes on Ni agromining and their potential benefits on soil biological fertility. Here, we characterized the effect of a crop rotation with two plants, a legume (Vicia sativa) and a hyperaccumulator (Alyssum murale), on the phytoextraction efficiency and on soil structure and biofunctioning. A pot experiment was set up in controlled conditions to grow A. murale and four treatments were tested: rotation with V. sativa (Ro), fertilized mono-culture (FMo), non-fertilized mono-culture (NFMo) and bare soil without plants (BS). No significant difference was found between the Ro and NFMo treatments for the dry biomass yield. However, the Ro treatment showed the highest Ni concentrations ([Ni]) in A. murale shoots compared to FMo and NFMo treatments. The Ro treatment plants had more than twice as many leaves [Ni] compared to FMo. Soil physico-chemical analyses showed that the Ro treatment was better structured and showed the highest presence of bacterial micro-aggregates, as well as less non-aggregated particles. Legumes integration in Ni-agromining systems could be a pioneering strategy to reduce chemical inputs and to improve soil biofunctioning and thus fertility.     

Adrenomedullin is anti-apoptotic in osteoblasts through CGRP1 receptors and MEK-ERK pathway

Adrenomedullin (ADM) has been shown to mediate multifunctional responses in cell culture and animal system such as regulation of growth and apoptosis. ADM stimulates the proliferation of osteoblasts in vitro and promotes bone growth in vivo. The ability of ADM to influence osteoblastic cell number through inhibition of apoptosis has not yet been studied. To address this question we have investigated its effect on the apoptosis of serum-deprived osteoblastic cells using mouse MC3T3-E1 cells which express both ADM and ADM receptors. Treatment with ADM significantly blunted apoptosis, evaluated by caspase-3 activity, DNA fragmentation quantification and annexin V-FITC labeling. This effect was abolished by the subtype-1 CGRP receptor antagonist, CGRP(8-37). Both ADM and its specific receptor antagonist, the (22-52) ADM fragment exhibited a similar anti-apoptotic effect. Thus, our data suggest that ADM exerts anti-apoptotic effects through CGRP1 receptors. This was substantiated by a similar protective effect of CGRP on MC3T3-E1 cells apoptosis. Accordingly, neutralization of endogenous ADM by a specific antibody enhanced apoptosis. Finally, the selective inhibitor of MAPK kinase (MEK), PD98059, abolished the apoptosis protective effect of ADM and prevented ADM activation of ERK1/2. These data show that ADM acts as a survival factor in osteoblastic cells via a CGRP1 receptor-MEK-ERK pathway, which provides further understanding on the physiological function of ADM in osteoblasts.     

Risk and Outcome after Ablation of Isthmus-Dependent Atrial Flutter in Elderly Patients

MethodsA total of 1187 patients with a mean age 65±12 years consecutively referred for AFL ablation were retrospectively analyzed in the study.Results445 (37.5%) patients were aged ≥70 (range 70 to 93) among which 345 were aged 70 to 79 years (29.1%) and 100 were aged ≥80 (8.4%). In multivariable analysis, AFL-related rhythmic cardiomyopathy and presentation with 1/1 AFL were less frequent (respectively adjusted OR = 0.44, 0.27–0.74, p = 0.002 and adjusted OR = 0.29, 0.16–0.52, p<0.0001). AFL ablation-related major complications were more frequent in patients ≥70 although remained lower than 10% (7.4% in ≥70 vs. 4.2% in <70, adjusted OR = 1.74, 1.04–2.89, p = 0.03). After 2.1±2.7 years, AFL recurrence was less frequent in patients ≥70 (adjusted OR = 0.54, 0.37–0.80, p = 0.002) whereas atrial fibrillation (AF) occurrence was as frequent in the 70–79 and ≥80 age subsets. As expected, cardiac mortality was higher in older patients. Patients aged ≥80 also had a low probability of AFL recurrence (5.0%) and AF onset (19.0%).ConclusionsOlder patients represent 37.5% of patients referred for AFL ablation and displayed a <10% risk of ablation-related complications. Importantly, AFL recurrences were less frequent in patients ≥70 while AF occurrence was as frequent as in patients <70. Similar observations were made in patients ≥80 years. AFL ablation appears to be safe and efficient and should not be ruled out in elderly patients.     

Characterization of organic matter microstructure dynamics during co-composting of sewage sludge, barks and green waste

A microstructure characterization study using transmission electron microscopy (TEM) was conducted to specify organic matter dynamics during the co-composting process of sewage sludge, green waste and barks. TEM results showed that ligneous and polyphenolic compounds brought by barks were not biodegraded during composting. Green waste brought more or less biodegraded ligneous constituents and also an active microbial potential. Chloroplasts and sludge flocs appeared to be relevant indicators of green waste and sewage sludge in composted products, as they were still viewable at the end of the process. TEM characterization of the final product highlighted two main fractions of organic matter, one easily available and a more recalcitrant one, and also a remaining microbial activity. Thus microstructure characterization appeared to be an appropriate way of taking the heterogeneity of the organic constituents' size and composition into account when attempting to specify such compost quality parameters as maturity and stability.     

In situ ageing of fine beech roots (Fagus sylvatica) assessed by transmission electron microscopy and electron energy loss spectroscopy: description of microsites and evolution of polyphenolic substances

Root biomass is quantitatively and qualitatively important in most ecosystems, but its contribution to the pool of organic matter in the soil is not clear. This work was designed to specify root ageing on an ultrastructural scale by transmission electron microscopy combined with microanalysis by electron energy loss spectroscopy. This approach is very suitable for studying the soil/plant interface, and for semi-quantitative analysis of the evolution of polyphenolic substances during root evolution. Three root segments were studied according to a gradient of root senescence: the apical and basal segments of the mycorrhiza and the mycorrhiza-carrier root. Each segment contained a certain proportion of senescent cells, some of which were of fungal origin, and this proportion increased as the root aged. In the three segments, the soil/plant interfaces were differentiated, and the micro-organisms observed in situ were described. Senescent root cells contained many polyphenolic substances and our results showed that these substances were, according to the root segment, differently associated with Ca, N and Si. When all these ultrastructural data are correlated with more global data, they can be usefully applied to root cell physiology, microbiology and pedology. This approach makes it possible to specify the evolution of organic matter in situ in soils whatever its origin.     

Potassium forms in aerated and anoxic soils of different management and potassium fertilizer history

The potassium forms and dominant clay mineralogy were studied in naturally well-drained (Hapludalfs, Eutropept) and poorly-drained soils (Fragiudalfs, Fragiaquept), both composed of the same parent materials (silty-clay or silt loam or clayey-loam). The well-drained soils (i.e. aerated) were cultivated and received larger amounts of K fertilizer; the poorly-drained types (i.e. anoxic) were grasslands and received low amount of K fertilizer. The different aspects investigated-exchangeable and nonexchangeable K, potassium fixation capacity and clay X-ray diffraction diagrams-indicated that the potassium status and the behavior of K-containing clays significantly differed between naturally well-drained aerated soils and anoxic poorly-drained soils. The aerated soils were high in both exchangeable and nonexchangeable K; the K saturation rate was high whereas fixation capacity was moderate. However, the anoxic soils showed a large K depletion and high fixation capacity. The silty-clayey soils studied were more affected by moisture regimes than the silt loam or clayey-loam.The differing K status between aerated and anoxic soils can be explained by several processes and factors, including soil weathering and management and K fertilizer history.