Analytical modelling of soil porosity and bulk density across the soil organic matter and land-use continuum.

The thin layer of soil at the earth's surface supports life, storing water and nutrients for plant uptake. These processes occur in the soil pore space, often half the soil volume, but our understanding of how this volume responds to environmental change is poor. Convention, has been to predict soil porosity, or its reciprocal bulk density (BD), from soil texture using pedotransfer functions (PTFs). A texture based approach, invariant to environmental change, prevents feedback from land use or climate change to soil porosity. Moreover, PTFs are often limited to mineral soils with < 20% soil organic matter (SOM) content. Here, we develop an analytical model to predict soil porosity, or BD, as a function of SOM. We test it on two comprehensive, methodologically consistent, temperate national-scale topsoil data sets (0-15 cm) (Wales, n = 1385; Great Britain, n = 2570). The purpose of the approach is to generate an analytical function suitable for predicting soil porosity change with SOM content, while providing insight into the main grain-scale factors determining the porosity emergence. The newly developed function covering the entire SOM gradient allows for impacts of land use, management or climate change to feedback on soil porosity or bulk density through decadal dynamic changes in SOM.

Multiple soil map comparison highlights challenges for predicting topsoil organic carbon concentration at national scale.

Soil organic carbon (SOC) concentration is the fundamental indicator of soil health, underpinning food production and climate change mitigation. SOC storage is highly sensitive to several dynamic environmental drivers, with approximately one third of soils degraded and losing carbon worldwide. Digital soil mapping illuminates where hotspots of SOC storage occur and where losses to the atmosphere are most likely. Yet, attempts to map SOC often disagree. Here we compare national scale SOC concentration map products to reveal agreement of data in mineral soils, with progressively poorer agreement in organo-mineral and organic soils. Divergences in map predictions from each other and survey data widen in the high SOC content land types we stratified. Given the disparities are highest in carbon rich soils, efforts are required to reduce these uncertainties to increase confidence in mapping SOC storage and predicting where change may be important at national to global scales. Our map comparison results could be used to identify SOC risk where concentrations are high and should be conserved, and where uncertainty is high and further monitoring should be targeted. Reducing inter-map uncertainty will rely on addressing statistical limitations and including covariates that capture convergence of physical factors that produce high SOC contents.

Group I and II metabotropic glutamate receptor expression in cultured rat spinal cord astrocytes.

We have examined the development of expression of group I and II metabotropic glutamate receptors (mGluRs) in pure rat spinal cord astrocyte cultures, using immunocytological and calcium imaging techniques. mGluR1alpha and mGluR2/3 antibodies were found to label roughly 10% of the total astrocyte population at all time points examined, whereas mGluR5 was poorly expressed in our culture system. Results from intracellular Ca2+ imaging experiments, measured using fura-2 ratio imaging, suggest that 20% of these cultured astrocytes express functional group I mGluRs (mGluR1 and/or 5). Our results contrast with previously published work in cultured cortical astrocytes where mGluR5 and not mGluR1 is expressed, suggesting that cultured astrocytes from different parts of the CNS exhibit different patterns of mGluR expression.

Motor nerve terminals on abdominal muscles in larval flesh flies, Sarcophaga bullata: comparisons with Drosophila.

Motor nerve terminals on abdominal body-wall muscles 6A and 7A in larval flesh flies were investigated to establish their general structural features with confocal microscopy, transmission electron microscopy, and freeze-fracture procedures. As in Drosophila and other dipterans, two motor axons supply these muscles, and two morphologically different terminals were discerned with confocal microscopy: thin terminals with relatively small varicosities (Type Is), and thicker terminals with larger varicosities (Type Ib). In serial electron micrographs, Type Ib terminals were distinguished from Type Is terminals by their larger cross-sectional area, more extensive subsynaptic reticulum, more mitochondrial profiles, and more clear synaptic vesicles. Type Ib terminals possessed larger synapses and more synaptic contact area per unit terminal length. Although presynaptic dense bars of active zones were similar in mean length for the two terminal types, there were almost twice as many dense bars per synapse for Type Ib terminals. Freeze-fractures through the presynaptic membrane showed particle-free areas indicative of synapses on the P-face, within which were localized aggregations of large intramembranous particles indicative of active zones. These particles were similar in number to those found at active zones of several other arthropod neuromuscular junctions. In general, synaptic structural parameters strongly paralleled those of the anatomically homologous muscles in Drosophila melanogaster. In live preparations, simultaneous focal recording from identified varicosities and intracellular recording indicated that the two terminals produced excitatory junction potentials of similar amplitude in a physiological solution similar to that used for Drosophila.