Effects of grazing intensity and grazing exclusion on litter decomposition in the temperate steppe of Nei Mongol,China

Aims Grazing intensity and grazing exclusion affect ecosystem carbon cycling by changing the plant community and soil micro-environment in grassland ecosystems. The aims of this study were: 1) to determine the effects of grazing intensity and grazing exclusion on litter decomposition in the temperate grasslands of Nei Mongol; 2) to compare the difference between above-ground and below-ground litter decomposition; 3) to identify the effects of precipitation on litter production and decomposition. Methods We measured litter production, quality, decomposition rates and soil nutrient contents during the growing season in 2011 and 2012 in four plots, i.e. light grazing, heavy grazing, light grazing exclusion and heavy grazing exclusion. Quadrate surveys and litter bags were used to measure litter production and decomposition rates. All data were analyzed with ANOVA and Pearson’s correlation procedures in SPSS. Important findings Litter production and decomposition rates differed greatly among four plots. During the two years of our study, above-ground litter production and decomposition in heavy-grazing plots were faster than those in light-grazing plots. In the dry year, below-ground litter production and decomposition in light-grazing plots were faster than those in heavy-grazing plots, which is opposite to the findings in the wet year. Short-term grazing exclusion could promote litter production, and the exclusion of light-grazing could increase litter decomposition and nutrient cycling. In contrast, heavy-grazing exclusion decreased litter decomposition. Thus, grazing exclusion is beneficial to the restoration of the light-grazing grasslands, and more human management measures are needed during the restoration of heavy-grazing grasslands. Precipitation increased litter production and decomposition, and below-ground litter was more vulnerable to the inter-annual change of precipitation than above-ground litter. Compared to the light-grazing grasslands, heavy-grazing grasslands had higher sensitivity to precipitation. The above-ground litter decomposition was strongly positively correlated with the litter N content (R² = 0.489, p < 0.01) and strongly negatively correlated with the soil total N content (R² = 0.450, p < 0.01), but it was not significantly correlated with C:N and lignin:N. Below-ground litter decomposition was negatively correlated with the litter C (R² = 0.263, p < 0.01), C:N (R² = 0.349, p < 0.01) and cellulose content (R² = 0.460, p < 0.01). Our results will provide a theoretical basis for ecosystem restoration and the research of carbon cycling.     

Rainfall and parasitic wasp (Hymenoptera: Ichneumonoidea) activity in successional forest stages at Barro Colorado Nature Monument, Panama, and La Selva Biological Station, Costa Rica

1 In 1997, we ran two Malaise insect traps in each of four stands of wet forest in Costa Rica (two old‐growth and two 20‐year‐old stands) and four stands of moist forest in Panama (old‐growth, 20, 40 and 120‐year‐old stands). 2 Wet forest traps caught 2.32 times as many ichneumonoids as moist forest traps. The average catch per old‐growth trap was 1.89 times greater than the average catch per second‐growth trap. 3 Parasitoids of lepidopteran larvae were caught in higher proportions in the wet forest, while pupal parasitoids were relatively more active in the moist forest. 4 We hypothesize that moisture availability is of key importance in determining parasitoid activity, community composition and trophic interactions.     

Nature of Novel 2D van der Waals Heterostructures for Superior Potassium Ion Batteries

Novel 2D van der Waals heterostructures with innovative bimetallic oxychloride (Bi‐ and Sb‐based oxychloride) nanosheets that are well dispersed on reduced graphene oxide nanosheets, are established through element engineering for superior potassium ion battery (PIBs) anodes. This material displays an exceptional electrochemical performance, obtaining a discharge capacity as high as 360 mAh g^?1 at 100 mA g^?1 after running 1000 cycles for over 9 months with a capacity preservation percentage of 88.5% and achieving a discharge capacity as high as 319 mAh g^?1 at 1000 mA g^?1, in addition to the low charge/discharge plateaus for anodes and promising full cell performance. More significantly, the nature of such 2D van der Waals heterostructures, including the element engineering for morphology control, the function of each component of heterostructures, the mechanism of potassium ion storage, and the process of K⁺ intercalation accompanied with the lattice distortion and chemical bond breakages, is explored in depth. This study is critical for not only paving the way for the practical application of PIBs but also shedding light on fundamentals of potassium ion storage in 2D van der Waals heterostructures.     

Dynamics and modulation studies of human voltage gated Kv1.5 channel

The voltage gated Kv1.5 channels conduct the ultrarapid delayed rectifier current (IK_ur) and play critical role in repolarization of action potential duration. It is the most rapidly activated channel and has very little or no inactivated states. In human cardiac cells, these channels are expressed more extensively in atrial myocytes than ventricle. From the evidences of its localization and functions, Kv1.5 has been declared a selective drug target for the treatment of atrial fibrillation (AF). In this present study, we have tried to identify the rapidly activating property of Kv1.5 and studied its mode of inhibition using molecular modeling, docking, and simulation techniques. Channel in open conformation is found to be stabilized quickly within the dipalmitoylphosphatidylcholine membrane, whereas most of the secondary structure elements were lost in closed state conformation. The obvious reason behind its ultra-rapid property is possibly due to the amino acid alteration in S4–S5 linker; the replacement of Lysine by Glutamine and vice versa. The popular published drugs as well as newly identified lead molecules were able to inhibit the Kv1.5 in a very similar pattern, mainly through the nonpolar interactions, and formed sable complexes. V512 is found as the main contributor for the interaction along with the other important residues such as V505, I508, A509, V512, P513, and V516. Furthermore, two screened novel compounds show surprisingly better inhibitory potency and can be considered for the future perspective of antiarrhythmic survey.     

Downstream protein separation by surfactant precipitation: a review

In a conventional protein downstream processing (DSP) scheme, chromatography is the single most expensive step. Despite being highly effective, it often has a low process throughput due to its semibatch nature, sometimes with nonreproducible results and relatively complex process development. Hence, more work is required to develop alternative purification methods that are more cost-effective, but exhibiting nearly comparable performance. In recent years, surfactant precipitation has been heralded as a promising new method for primary protein recovery that meets these criteria and is a simple and cost-effective method that purifies and concentrates. The method requires the direct addition of a surfactant to a complex solution (e.g. a fermentation broth) containing the protein of interest, where the final surfactant concentration is maintained below its critical micelle concentration (CMC) in order to allow for electrostatic and hydrophobic interactions between the surfactant and the target protein. An insoluble (hydrophobic) protein–surfactant complex is formed and backextraction of the target protein from the precipitate into a new aqueous phase is then carried out using either solvent extraction, or addition of a counter-ionic surfactant. Importantly, as highlighted by past researchers, the recovered proteins maintain their activity and structural integrity, as determined by circular dichroism (CD). In this review, various aspects of surfactant precipitation with respect to its general methodology and process mechanism, system parameters influencing performance, protein recovery, process selectivity and process advantages will be highlighted. Moreover, comparisons will be made to reverse micellar extraction, and the current drawbacks/challenges of surfactant precipitation will also be discussed. Finally, promising directions of future work with this separation technique will be highlighted.     

Application of PIXE analysis to the study of the regional distribution of trace elements in normal human brain

A particle-induced X-ray emission (PIXE) analysis method is presented, which allows measurement of eight elements (i.e., K, Ca, Mn, Fe, Cu, Zn, Se, and Rb) in human brain samples of only a few mg dry weight. The precision and accuracy of the method were investigated by analyzing animal brain matter with both PIXE and instrumental neutron activation analysis (INAA). The method was applied to measure the 8 elements in 46 different regions of 3 human brains. The sections analyzed originated from either the left or the right cerebral hemisphere, brain stem, and cerebellum. For one of the brains, sections were also analyzed from 26 corresponding regions of both hemispheres. For all elements, similar concentrations were found in the corresponding areas of the left and right sides of the brain. The concentrations (in μg/g dry weight) of the elements K, Fe, Cu, Zn, Se, and Rb were consistently higher in cortical structures than in white matter. Deep nuclei and brain stem, which have a mixed composition, showed intermediate values for K, Zn, Se, and Rb. A hierarchical cluster analysis indicated that the various brain regions clustered into two large groups, one comprising gray and mixed matter regions and the other, white and mixed matter brain areas.     

Paleolimnological evidence for recent acidification of Big Moose Lake,Adirondack Mountains,N.Y. (USA)

Big Moose L. has become significantly more acidic since the 1950s, based on paleolimnological analyses of sediment cores. Reconstruction of past lakewater pH using diatom assemblage data indicates that from prior to 1800 to ca. 1950, lakewater pH was about 5.8. After the mid-1950s, the inferred pH decreased steadily and relatively quickly to about 4.6. Alkalinity reconstructions indicate a decrease of about 30 eq · l^-1 during the same period. There was a major shift in diatom assemblage composition, including a nearly total loss of euplanktonic taxa. Chrysophyte scale assemblages and chironomid (midge larvae remains also changed in a pattern indicating decreasing lakewater pH starting in the 1950s. Accumulation rates of total Ca, exchangeable and oxide Al, and other metals suggest recent lake-watershed acidification. Cores were dated using²¹⁰Pb, pollen, and charcoal. Indicators of watershed change (deposition rates of Ti, Si, Al) do not suggest any major erosional events resulting from fires or logging. Accumulation rates of materials associated with combustion of fossil fuels (polycyclic aromatic hydrocarbons, coal and oil soot particles, some trace metals, and sulfur) are low until the late 1800s-early 1900s and increase relatively rapidly until the 1920s–1930s. Peak rates occurred between the late 1940s and about 1970, when rates declined.The recent decrease in pH of Big Moose L. cannot be accounted for by natural acidification or processes associated with watershed disturbance. The magnitude, rate and timing of the recent pH and alkalinity decreases, and their relationship to indicators of coal and oil combustion, indicate that the most reasonable explanation for the recent acidification is increased atmospheric deposition of strong acids derived from combustion of fossil fuels.     

A comparative study of ammonium toxicity at different constatn pH of the nutrient solution

Seedlings of 14 species were grown for 14–28 days on nutrient solution with 6 mmol.l⁻¹ NH₄ as the sole nitrogen source. Solutions acidity was were kept constant at pH 4.0, 5.0, 6.0 and 7.0 by continuous titration with diluted KOH. The following species were used: barley, maize, oats sorghum, yellow and white lupin, pea, soybean, carrot, flax, castor-oil, spinach, sugarbeet and sunflower. Most plant species grew optimally at pH 6.0 with slight reductions at pH 5.0. Growth of many species was severely inhibited at pH 4.0, but this inhibition was not observed with the legume and cereal species. Yield depressions at pH 4.0 relative to pH 6.0 were well correlated with the respective relative decreases of the K concentration in their roots (P<0.002). In the roots of two species (sunflower and flax) total N concentrations were also strongly reduced at pH 4.0. apparently, the interactions between uptake of K, NH₄ and H ions become the prevalent problem at suboptimal pH. At pH 7.0, yields were also considerably decreased, with the exception of the lupines. At this pH, the roots of the growth inhibited plants were characterized by increased levels of total N and free NH₄. It is thought that the binding capacity of the roots for NH₄ is an important factor in preventing NH₄/NH₃ toxicity at supraoptimal pH.     

Modification of Ca2+-activated K+ channels in cultured medullary thick ascending limb cells by N-bromoacetamide

Summary Ca²⁺-activated K⁺ channels were studied in cultured medullary thick ascending limb (MTAL) cells using the patch-clamp technique in the inside-out configuration. The Ca²⁺ activation site was modified using N-bromoacetamide (NBA). 1mm NBA in the bath solution, at 2.5 m Ca²⁺ reduces the open probability,P _o , of the channel to <0.01, without an effect on single-channel conductance. NBA-modified channels are still Ca²⁺-sensitive, requiring 25mm Ca²⁺ to raiseP _o to 0.2. Both before and after NBA modification channel openings display at least two distributions, indicative of more than one open state. High Ca²⁺ (1mm) protects the channels from modification. Also presented is a second class of Ca²⁺-activated K⁺ channels which are normally present in MTAL cells which open infrequently at 10 m Ca²⁺ (P _o =0.01) but have aP _o of 0.08 at 1mm Ca²⁺. We can conclude (i) that NBA modifies the channel by shifting Ca²⁺-sensitivity to very high Ca²⁺, (ii) that NBA acts on a site involved in Ca²⁺ gating, and (iii) that a low affinity channel is present in the apical cell membrane with characteristics similar to those of normal channels modified with NBA.     

Volume regulation in the early proximal tubule of theNecturus kidney

Summary The ability of early proximal tubule cells of theNecturus kidney to regulate volume was evaluated using light microscopy, video analysis and conventional microelectrodes.Necturus proximal tubule cells regulate volume in both hyperand hyposmotic solutions. Volume regulation in hyperosmotic fluids is HCO ₃ ^– dependent and is associated with a decrease in the relative K⁺ conductance of the basolateral cell membrane and a decrease in the resistance ratio,R _a /R _bl . Volume regulation in hyposmotic solutions is also dependent upon the presence of HCO ₃ ^– but is also inhibited by 2mm Ba²⁺ in the basolateral solution. Hyposmotic regulation is accompanied by an increase in the relative K⁺ conductance of the basolateral cell membrane and an increase inR _a /R _bl . Neither hypo- nor hyposmotic regulation have any affect on the depolarization of the basolateral cell membrane potential induced by HCO ₃ ^– removal. We conclude that volume regulation in the early proximal tubule of the kidney involves both HCO ₃ ^– -dependent transport systems and the basolateral K⁺ conductance.