Linking sequestration of 13C and 15N in aggregates in a pasture soil following 8 years of elevated atmospheric CO2

The influence of N availability on C sequestration under prolonged elevated CO₂ in terrestrial ecosystems remains unclear. We studied the relationships between C and N dynamics in a pasture seeded to Lolium perenne after 8 years of elevated atmospheric CO₂ concentration (FACE) conditions. Fertilizer‐¹⁵N was applied at a rate of 140 and 560 kg N ha^2?1 y^2?1 and depleted ¹³C‐CO₂ was used to increase the CO₂ concentration to 60 Pa pCO₂. The ¹³C–¹⁵N dual isotopic tracer enabled us to study the dynamics of newly sequestered C and N in the soil by aggregate size and fractions of particulate organic matter (POM), made up by intra‐aggregate POM (iPOM) and free light fraction (LF). Eight years of elevated CO₂ did not increase total C content in any of the aggregate classes or POM fractions at both rates of N application. The fraction of new C in the POM fractions also remained largely unaffected by N fertilization. Changes in the fractions of new C and new N (fertilizer‐N) under elevated CO₂ were more pronounced between POM classes than between aggregate size classes. Hence, changes in the dynamics of soil C and N cycling are easier to detect in the POM fractions than in the whole aggregates. Within N treatments, fractions of new C and N in POM classes were highly correlated with more new C and N in large POM fractions and less in the smaller POM fractions. Isotopic data show that the microaggregates were derived from the macro‐aggregates and that the C and N associated with the microaggregates turned over slower than the C and N associated with the macroaggregates. There was also isotopic evidence that N immobilized by soil microorganisms was an important source of N in the iPOM fractions. Under low N availability, 3.04 units of new C per unit of fertilizer N were sequestered in the POM fractions. Under high N availability, the ratio of new C sequestered per unit of fertilizer N was reduced to 1.47. Elevated and ambient CO₂ concentrations lead to similar ¹⁵N enrichments in the iPOM fractions under both low and high N additions, clearly showing that the SOM‐N dynamics were unaffected by prolonged elevated CO₂ concentrations.     

Toxicity of arsenate in Silene vulgaris, accumulation and degradation of arsenate-induced phytochelatins

The results presented in this paper describe the short- and long-term toxicity of arsenate in Silene vulgaris . Short-term toxicity, measured as inhibition of root elongation, depended on phosphate nutrition, arsenate being much less toxic at high phosphate supply. At low phosphate levels more arsenic was taken up by the plants. Under chronic exposure, toxicity (measured as inhibition of biomass production) did not increase with time. In addition, the accumulation of phytochelatins (PCs) as a function of toxicity and duration of exposure was studied. Short-term PC accumulation (over a 3 d period) was positively correlated with exposure. Isolation of peptide complexes from prolongedly exposed plants showed that PC₂, PC₃ and PC₄ were present, although the latter not until at least 3 d exposure. Arsenic co-eluted mainly with PC₂ and PC₃. Fractions containing PC₄ were devoid of As, probably due to dissociation of the complexes during extraction or elution. The breakdown of PCs after arresting As exposure was very slow. This could explain the continuous accumulation of PCs throughout longer periods of As exposure.     

Benthic macrofauna and sediments in the Severn Estuary

In the Severn Estuary and Bristol Channel, a multivariate analysis indicated eight groupings of macrobenthic fauna, each associated with a different physical habitat. Samples were faunistically impoverished, especially in sublittoral areas, but greater species richness was associated with reefs of Sabellaria alveolata , which extended well into the estuary.     

Intra-Operative Analysis of Scoliosis Surgery in 3-D

Scoliosis is a three-dimensional deformity characterized by coronal, sagittal and axial rotation of the spine. Surgical fusion of the spine is required in severe cases. Assessment of the surgical procedure requires enough accuracy and flexibility to allow planning of individual interventions or implant designs. Conventional 2-D radiography and even 3-D CT scanning have limitations for in-depth analysis of scoliosis that limit the ability to see the three-dimensional deformity and expose the patient to considerable doses of radiation, respectively. Our stereophotogrammetric analysis is able to provide accurate, intraoperative measurement of vertebral movement during surgical manuevres. Stereophoto pairs taken at each stage of the operation and robust statistical techniques can be used to determine rotation, translation, goodness of fit, and overall spinal contour before, during, and after the surgical instrumentation. A demonstration of data available from this system is included.