The influx and efflux of organic acids across the root-soil interface were investigated in intact, sterile maize (Zea mays L.) roots under a variety of exp
Freeze-thaw and dry-wet cycles are common phenomena in temperate regions. Such events may have a significant influence on the functioning of the soil microbial community. Using non-targeted metabolomics, we compared the effects of a single freeze-thaw or dry-wet event on microbial metabolism in an agricultural soil with and without plants. We showed that a dry-wet cycle had a greater impact on solute and metabolite concentrations in the unplanted soil than a freeze-thaw cycle. Drying or freezing caused increases in dissolved organic C, sugars and polyols, suggesting enhanced microbial production to alleviate temperature or moisture stress. Increased nucleobase concentration in the unplanted soil after a dry-wet cycle, and increased amino acids following both stresses, suggested a breakdown of microbial DNA and proteins released from damaged cells. The impacts of stress on metabolites in the planted soil were less than in the unplanted soil. In conclusion, our findings indicate that the soil microbial community responds quickly to stress events by accumulating osmotic solutes (e.g. sugars and polyols) and that a freeze-thaw event causes less disruption than dry-rewetting, and that plants have a key role in the mitigation of the freezing or drying effects on soil microbial communities.
The role of organic acids in the mobilization of plant nutrients from the rhizosphere was assessed in seven contrasting soil types. The results indicated t
A large number of sheep graze extensively managed grasslands, including upland and hill areas. Excretal deposition of nitrogen (N) to upland soil is a potentially large source of the powerful greenhouse gas (GHG), nitrous oxide (N2O), however, few studies have assessed urine-patch N2O emissions from upland areas. Current default excretal N2O emission factors (EFs) are based on intensively managed lowland systems, with cattle excreta as the N source. We hypothesised that N2O emissions could differ substantially from those of lowland systems, due to differences in soil type, climate, topography, pasture composition and management factors along altitudinal and productivity gradients. We investigated N2O emission factors across two seasons (spring and autumn), for an extensive semi-improved, temperate grassland using IPCC-compliant and representative sheep urine patches (in terms of urine chemical composition, urine patch size and N loading rates). An automated GHG monitoring system provided high-frequency GHG data from sheep urine patches (756 and 1112 kg N ha−1 applied in spring and autumn, respectively), reference artificial sheep urine patches (1066 and 1004 kg N ha−1 applied in spring and autumn, respectively) and control treatments. In spring, urine patch N2O emission factors were −0.02 ± 0.04 (artificial sheep urine) and 0.03 ± 0.09% (real sheep urine) of the applied N; in autumn emission factors were 0.02 ± 0.03 (artificial sheep urine) and 0.08 ± 0.04% (real sheep urine) of the applied N. These values are much lower than default inventory values (1% of applied N) for excreta deposited by grazing livestock. There was a greater pasture foliar N content following urine application in spring as opposed to autumn, and a significantly longer residence time of extractable mineral N in autumn. Our findings demonstrate the importance of generating country-specific N2O EFs based on altitude/productivity gradients of livestock production, with implications for national inventories and the accuracy of sustainability metrics of lamb produced in the UK uplands.
A SEM ultrastructural study of two isolates of a soil fungus, Penicillium thomii, is presented, which compares the morphology of critical point-dried tissues with cryofixed material. The paper also reports features of the isolates which sometimes are different from the usual diagnostic morphological data for this fungus. Thus, branched penicilli have been seen in one of the isolates on MEA, yet monoverticillate penicilli are regarded as a major feature of P. thomii. In the same isolate the stipes appear non-vesiculate on both agars unlike the vesiculate stipes normally associated with this species from light microscope observations. Some wrinkling is seen in the stipes and phialides from critical point-dried specimens and this phenomenon is generally absent in cryofixed samples, although in one isolate, collapse of some of the phialides occurred. Critical point-drying results in shrinkage of conidia. Penicillium thomii is an important species in soil ecosystems and thus an accurate description of its morphological features is desirable for proper classification although it is a widely held belief that no character in Penicillium taxonomy is totally invariant.
A study of the weathering phenomena brought about by the growth of Lecanora alra on a substrate of magnesium silicate minerals (serpentinite) has been carried out mainly by X-ray diffraction and scanning electron microscopy. The lichen thallus contains appreciable amounts of crystalline magnesium oxalate dihydrate, which occurs as an insoluble extra-cellular precipitate and derives from the decomposition of magnesium silicates (particularly chrysotile) by oxalic acid secreted by the mycobiont. In theory magnesium oxalate dihydrate should be capable of incorporating large amounts of heavy metal ions into its structure, as indeed the electron probe evidence indicates has happened, thus suggesting a mechanism for enabling some lichens to cope with environments that are high in these generally harmful ions. The only weathering product detected in the lichen weathering crust is an X-ray amorphous silica gel which often retains the fibrous morphology of the chrysotile from which it forms.
