Structure-disrupting ions: detection of qualitative change in an enzyme

Preparations of erythrocyte glucose-6-phosphate dehydrogenase from normal individuals show similar degrees of inhibition by neutral salts. Preparations from Caucasian subjects with different hereditary deficiency syndromes differ from each other and from normal subjects, indicating a qualitative difference in these specific "deficient" enzymes. Sensitivity to neutral salts may be a means of detecting an amino acid substitution.     

Long-term plant growth legacies overwhelm short-term plant growth effects on soil microbial community structure

Plant-soil feedbacks are gaining attention for their ability to determine plant community development. Plant-soil feedback models and research assume that plant-soil interactions occur within days to weeks, yet, little is known about how quickly and to what extent plants change soil community composition. We grew a dominant native plant (Pseudoroegneria spicata) and a dominant non-native plant (Centaurea diffusa) separately in both native- and non-native-cultivated field soils to test if these species could overcome soil legacies and create new soil communities in the short-term. Soil community composition before and after plant growth was assessed in bulk and rhizosphere soils using phospholipid fatty acid analyses. Nematode abundance and mycorrhizal colonization were also measured following plant growth. Field-collected, native-cultivated soils showed greater bacterial, Gram (−), fungal, and arbuscular mycorrhizal PLFA abundance and greater PLFA diversity than field-collected, non-native-cultivated soils. Both plant species grew larger in native- than non-native-cultivated soils, but neither plant affected microbial composition in the bulk or rhizosphere soils after two months. Plants also failed to change nematode abundance or mycorrhizal colonization. Plants, therefore, appear able to create microbial legacies that affect subsequent plant growth, but contrary to common assumptions, the species in this study are likely to require years to create these legacies. Our results are consistent with other studies that demonstrate long-term legacies in soil microbial communities and suggest that the development of plant-soil feedbacks should be viewed in this longer-term context.     

Postoperative complications in a lamb after major surgery

INTODUCTION: Anaesthesia in lambs undergoing experimental surgery may develop problems associated with age-related immune incompetency: a postoperative complication in a 3 week old Scottish blackface lamb after spinal surgery is presented. CASE HISTORY AND MANAGEMENT: Both lamb and ewe were in good condition. The ewe was vaccinated against Clostridium perfringens and Clostridium tetani 5 weeks pre-partum. There were no apparent problems with the lamb's intake of colostrum. Pre-anaesthetic medication was intramuscular medetomidine (10 μg kg(-1)). Anaesthesia was induced and maintained with sevoflurane in oxygen. Morphine (0.5 mg kg(-1)), meloxicam (0.6 mg kg(-1)) and ketamine (1 mg kg(-1) followed by 10 μg kg(-1) minute(-1)) were administered intravenously (IV) for perioperative analgesia. Atracurium (0.5 mg kg(-1) IV, followed by 0.17 mg kg(-1) injected when the first twitch of the four, train-of four count was palpated) was used to improve muscle relaxation. The lamb's trachea was intubated and the lungs mechanically ventilated to maintain normocapnia. Intrathecal morphine (0.2 mg kg(-1)), IV meloxicam (0.3 mg kg(-1)) and edrophonium (0.5 mg kg(-1)) were administered before recovery. Operative and initial recovery periods were unremarkable. Three hours after surgery the lamb became depressed. Tachycardia (180-250 beats minute(-1)), tachypnoea (30 breaths minute(-1)), poor peripheral perfusion and cold pelvic limb extremities were present mimicking severe pain, and/or hypovolaemic shock. Analgesics - morphine (total dose 1.3 mg kg(-1)) - and IV fluid therapy boluses - crystalloids (300 mL), colloids (120 mL) and fresh whole blood (60 mL) - failed to ameliorate clinical signs and so the lamb was euthanized 10 hours after surgery. Post-mortem findings supported a possible diagnosis of peracute Clostridium perfringens enterotoxaemia. CONCLUSION: Clostridium perfringens enterotoxaemia should be considered when clinical signs of severe pain and/or hypovolaemic shock fail to respond to analgesics and fluid resuscitation in lambs after major surgery.     

Recovery of fertilizer nitrogen from continuous corn soils under contrasting tillage management

Tillage systems influence soil properties and may influence the availability of applied and mineralized soil N. This laboratory study (20°C) compared N cycling in two soils, a Wooster (fine, loamy Typic Fragiudalf) and a Hoytville (fine, illitic Mollic Epiaqualf) under continuous corn (Zea mays) production since at least 1963 with no-tillage (NT), minimum (CT) and plow tillage (PT) management. Fertilizer was added at the rate of 100 mg ¹⁵N kg^–1–1 soil as 99.9% ¹⁵N as NH₄Cl or Ca(NO₃)₂ and the soils were incubated in leaching columns for 1 week at 34 kPa before being leached periodically with 0.05 M CaCl₂ for 26 weeks. As expected, the majority of the ¹⁵NO₃^– additions were removed from both soils with the first leaching. The majority of applied ¹⁵NH₄⁺ additions were recovered as ¹⁵NO₃^– by week 5, with the NT soils demonstrating faster nitrification rates compared with soils under other tillage practices. For the remaining 22 weeks, only low levels of ¹⁵NO₃^– were leached from the soils regardless of tillage management. In the coarser textured Wooster soils (150 g clay kg^–1), mineralization of native soil N in the fertilized soils was related to the total N content (r² 0.99) and amino acid N (r² 0.99), but N mineralization in the finer textured Hoytville (400 g clay kg^–1) was constant across tillage treatments and not significantly related to soil total N or amino acid N content. The release of native soil N was enhanced by NH₄⁺ or NO₃^– addition compared to the values released by the unfertilized control and exceeded possible pool substitution. The results question the use of incubation N mineralization tests conducted with unfertilized soils as a means for predicting soil N availability for crop N needs.     

Ionic concentrations in a blanket peat bog in northern England and correlations with deposition and climate variables

Soil solution was collected to identify seasonal trends in its chemistry and to examine relationships between the concentrations of ions and variables that may control them. Samples were collected fortnightly at 10 cm and 50 cm depth in a blanket peat soil at Moor House–Upper Teesdale National Nature Reserve in the northern Pennine uplands of England. Dissolved organic carbon at 10 cm peaked each summer and correlated most strongly with temperature. At both depths Na⁺ and Cl^– were the dominant ions, reflecting the oceanic climate. Over the 3‐year sampling period, concentrations of the principal anions and cations at 10 cm varied little except during the autumns of 1994 and 1995 following unusually dry summers. At these times concentrations of SO₄^2–‐S increased from < 3 μmol to a maximum of 430 μmol and were balanced by smaller increases in Na⁺, Mg²⁺, Ca²⁺ and H⁺. The SO₄^2– concentration at 10 cm was most strongly correlated with depth to the water Table 3 weeks prior to sampling. At 50 cm depth in the peat a small increase in SO₄^2– occurred only during the autumn of 1995, and the concentration of SO₄^2– at this depth correlated most strongly with that at 10 cm. At neither depth were there any strong correlations with deposition. The increase in H⁺ concentration associated with the peak in SO₄^2– at 10 cm depth represents a fall in pH from usual values around 4.2 to 3.5.

Table 3. Deposition flux of ions in bulk precipitation at Moor House from weekly samplings 1994 to 1996 in kg ha^?1 year^?1. The UK flux is derived from 32 sites of the United Kingdom Precipitation Composition Monitoring Network 1992 to 1994 and the standard deviation (SD) relates to the variation between these sites ( Review Group on Acid Rain, 1997 )

Human-mediated vegetation switches as processes in landscape ecology

Switches are processes in which there is positive feedback between vegetation and environment. Landscape features can be created and modified by switches. The concept has previously been used with physical factors and non-human animals as the switch mediator, i.e. the factor which the vegetation modifies and which in turn affects the vegetation. Here, the switch concept is extended to include some types of human behaviour as possible switch mediators. With this extension, the switch concept can explain the impact on the landscape of some types of human behaviour. Examples are given of the behaviour of mower drivers, mowing up to a boundary which they create and/or maintain, and of walkers trampling tracks which they create and/or maintain. Other possibilities are discussed briefly. It is concluded that the concept of a human-mediated switch can unify the study of human behaviour, vegetation processes and landscape ecology.     

Biodegradation of nitrilotriacetic acid and related imino aand amino acids in river water

With a gas chromatography procedure capable of quantitatively de tecting nitrilotriacetic acid, N-methyliminodiacetic acid, iminodiacetic acid, sarcosine, and glycine at concentrations of 0.025 milligram per liter, it was shown that these compounds were biodegraded by river water. In particular, nitrilotriacetic acid was degraded without the accumulation of any of the amino acids mentioned above or the appearance of any new peaks in the gas chromatography analysis.