Phytoavailability of lead altered by two Pelargonium cultivars grown on contrasting lead-spiked soils

Purpose

This study assesses the potential of two contrasted fragrant Pelargonium cultivars to induce pH and dissolved organic carbon (DOC) changes in the soil solution, Pb speciation, and their subsequent effects on rhizosphere phytoavailable Pb.

Materials and methods

Rooted plantlets were grown in special devices, floating on aerated nutrient solution in PVC tanks. This setup allows roots to be physically separated, through a mesh, from a 3-mm soil matrix layer that can be considered as rhizosphere soil. Two contrasted soils, each spiked with Pb-rich particles, emitted from a battery recycling industry, were used at total burdens of 500 and 1500 mg Pb kg^?1 in addition to a control unspiked soil. Soil solution pH, phytoavailable Pb, DOC, Pb adsorption, precipitation on roots, and Pb phases in soil and plant were investigated.

Results and discussion

Attar of Roses (Attar) cultivar acidified its rhizosphere by 0.4 pH units in both spiked soils. Concolor Lace (Concolor) was unable to change soil solution pH on soil-1 and increased it by 0.7 units on soil 2. Concentrations of Pb in soil solution from Attar plants were always higher than those of Concolor ones. DOC contents of both unspiked soil-1 and soil-2 without plants were not significantly different. In the case of spiked samples, DOC contents in the rhizosphere soil were increased by three and two times for Attar and Concolor, respectively, compared to the unspiked soil without plant. Both cultivars were able to increase DOC contents, independent of soil type and level of contamination. Accumulation of Pb in shoots and roots was higher in Attar as compared to Concolor due to enhanced available Pb as a result of pH and DOC modifications of the rhizosphere soil. Significant amounts of Pb were adsorbed on roots of both cultivars. X-ray elemental analysis of precipitates on roots revealed the association of Pb with P in cylinder-like structures. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that Pb was present, to a major extent in the inorganic form, mainly as PbSO₄ in the soil, whereas it was complexed with organic species within plant tissues. The conversion of Pb into organic species could decrease toxicity, may enhance plant tolerance, and could increase translocation.

Conclusions

Plant-induced changes were responsible for the modification of lead phases within the soil. Immobile forms present in the source leaded particles as well as in the soils were converted into soluble species, ultimately improving the phytoavailable or soil solubilized Pb.

     

Anaerobic co‐digestion of perennials: Methane potential and digestate nitrogen fertilizer value

Co‐digestion of crop biomass improves the traditional manure‐based biogas yield due to an increased content of easily degradable carbon compounds. In this study, the methane potential of three perennials (grass, legumes, and grass+legume) was determined using various amounts together with animal manure. The nitrogen (N) mineralization dynamics in soil and the N‐fertilizer value of the derived digestates were subsequently tested in both a soil incubation study and a pot experiment with spring barley. Digestion of all tested perennials together with a manure‐based inoculum increased the cumulative methane yield four to five times compared to digestion of the inoculum alone, with the highest increases observed with pure grass. However, the methane potential decreased along with increasing grass biomass concentration. In the plant pot experiment, all tested digestates increased barley shoot biomass by 40–170%, to an extent statistically comparable to mineral N fertilizer. However, the application of the digestate originating from fermentation with pure grass resulted in lower plant growth and a more fluctuating soil mineral N content throughout the incubation study compared to the other digestates. Considering the high dry matter and methane yield ha^?1, the possibility to substitute mineral N fertilizer inputs by leguminous biological N₂ fixation capacity, and the digestate fertilizer value, the integration of grass–legume mixtures or sole legumes into anaerobic digestion systems as co‐substrate for manure seems to be promising. This could furthermore contribute to the diversification of cropping systems for bioenergy production.     

Root trenching: a useful tool to estimate autotrophic soil respiration? A case study in an Austrian mountain forest

We conducted a trenching experiment in a mountain forest in order to assess the contribution of the autotrophic respiration to total soil respiration and evaluate trenching as a technique to achieve it. We hypothesised that the trenching experiment would alter both microbial biomass and microbial community structure and that fine roots (less than 2 mm diameter) would be decomposed within one growing season. Soil CO₂ efflux was measured roughly biweekly over two growing seasons. Root presence and morphology parameters, as well as the soil microbial community were measured prior to trenching, 5 and 15 months after trenching. The trenched plots emitted about 20 and 30% less CO₂ than the control plots in the first and second growing season, respectively. Roots died in trenched plots, but root decay was slow. After 5 and 15 months, fine root biomass was decreased by 9% (not statistically different) and 30%, (statistically different) respectively. When we corrected for the additional trenched-plot CO₂ efflux due to fine root decomposition, the autotrophic soil respiration rose to ~26% of the total soil respiration for the first growing season, and to ~44% for the second growing season. Soil microbial biomass and community structure was not altered by the end of the second growing season. We conclude that trenching can give accurate estimates of the autotrophic and heterotrophic components of soil respiration, if methodological side effects are accounted for, only.     

Post‐anesthetic pulmonary edema in two horses

Case 1 A two‐year old, 462 kg Standard bred horse was anesthetized for arthroscopy and castration. During anesthesia, hyperemia of the mucosal membranes and urticaria were noticed. During 5 hours of anesthesia subcutaneous edema of the eyelids and neck region developed. In the recovery box, the orotracheal (OT) tube was left in situ and secured in place with tape. Following initial attempts to stand, the horse became highly agitated and signs consistent with pulmonary edema developed subsequently. Arterial hypoxemia (PaO₂: 3.7 kPa [28 mmHg]) and hypocapnia (PaCO₂: 3.1 kPa [23 mmHg]) were confirmed. Oxygen and furosemide were administered. The horse was assisted to standing with a sling. Therapy continued with bilateral intra‐nasal oxygen insufflation. Ancillary medical therapy included flunixin meglumine, penicillin, gentamycin and dimethylsulfoxide. Following 7 hours of treatment the arterial oxygen tensions began to increase towards normal values. Case 2 An 11‐year old, 528 kg Paint horse was anesthetized for surgery of a submandibular mass. The 4‐hour anesthetic period was unremarkable. The OT tube was left in situ for the recovery. During recovery, the horse was slightly agitated and stood after three attempts. Clinical signs consistent with pulmonary edema and arterial hypoxemia (PaO₂: 5 kPa [37.5 mmHg]) subsequently developed following extubation. Respiratory signs resolved with medical therapy, including unilateral nasal oxygen insufflation, furosemide, flunixin meglumine and dimethylsulfoxide. The diagnosis of pulmonary edema in these horses was made by clinical signs and arterial blood‐gas analysis. While pulmonary radiographs were not taken to confirm the diagnosis, the clinical signs following anesthesia support the diagnosis in both cases. The etiology of pulmonary edema was most likely multifactorial.     

RhizoTubes as a new tool for high throughput imaging of plant root development and architecture: test,comparison with pot grown plants and validation

Background

In order to maintain high yields while saving water and preserving non-renewable resources and thus limiting the use of chemical fertilizer, it is crucial to select plants with more efficient root systems. This could be achieved through an optimization of both root architecture and root uptake ability and/or through the improvement of positive plant interactions with microorganisms in the rhizosphere. The development of devices suitable for high-throughput phenotyping of root structures remains a major bottleneck.

Results

Rhizotrons suitable for plant growth in controlled conditions and non-invasive image acquisition of plant shoot and root systems (RhizoTubes) are described. These RhizoTubes allow growing one to six plants simultaneously, having a maximum height of 1.1 m, up to 8 weeks, depending on plant species. Both shoot and root compartment can be imaged automatically and non-destructively throughout the experiment thanks to an imaging cabin (RhizoCab). RhizoCab contains robots and imaging equipment for obtaining high-resolution pictures of plant roots. Using this versatile experimental setup, we illustrate how some morphometric root traits can be determined for various species including model (Medicago truncatula), crops (Pisum sativum, Brassica napus, Vitis vinifera, Triticum aestivum) and weed (Vulpia myuros) species grown under non-limiting conditions or submitted to various abiotic and biotic constraints. The measurement of the root phenotypic traits using this system was compared to that obtained using “classic” growth conditions in pots.

Conclusions

This integrated system, to include 1200 Rhizotubes, will allow high-throughput phenotyping of plant shoots and roots under various abiotic and biotic environmental conditions. Our system allows an easy visualization or extraction of roots and measurement of root traits for high-throughput or kinetic analyses. The utility of this system for studying root system architecture will greatly facilitate the identification of genetic and environmental determinants of key root traits involved in crop responses to stresses, including interactions with soil microorganisms.

     

Methacarn preserves mucus integrity and improves visualization of amoebae in gills of Atlantic salmon (Salmo salar L.)

Two aqueous fixation methods (modified Davidson's solution and modified Davidson's solution with 2% (w/v) Alcian blue) were compared against two non‐aqueous fixation methods (methacarn solution and methacarn solution with 2% (w/v) Alcian blue) along with the standard buffered formalin fixation method to (a) improve preservation of the mucous coat on Atlantic salmon, Salmo salar L., gills and (b) to examine the interaction between the amoebae and mucus on the gill during an infection with amoebic gill disease. Aqueous fixatives demonstrated excellent cytological preservation but failed to deliver the preservation of the mucus when compared to the non‐aqueous‐based fixatives; qualitative and semi‐quantitative analysis revealed a greater preservation of the gill mucus using the non‐aqueous methacarn solution. A combination of this fixation method and an Alcian blue/Periodic acid–Schiff staining was tested in gills of Atlantic salmon infected with amoebic gill disease; lectin labelling was also used to confirm the mucus preservation in the methacarn‐fixed tissue. Amoebae were observed closely associated with the mucus demonstrating that the techniques employed for preservation of the mucous coat can indeed avoid the loss of potential mucus‐embedded parasites, thus providing a better understanding of the relationship between the mucus and parasite.     

Use of state‐space modelling to identify ecological covariates associated with trends in pinniped demography

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