Effects of irrigation sources on ammonia-oxidizing bacterial communities in a managed turf-covered aridisol

Ammonia-oxidizing bacteria (AOB) perform the rate-limiting step of nitrification, a key process in the global nitrogen cycle. In this study, chemical factors controlling AOB activity, diversity, and composition in a turfgrass-covered aridisol irrigated with groundwater, Colorado River water, or reclaimed wastewater were examined. Activity of AOB contributed an average of 96% of potential nitrification activity in four soils examined, and this activity correlated positively with ammonium concentration and negatively with salinity of the irrigation water. AOB abundance, as determined by quantitative polymerase chain reaction, also correlated positively with ammonium concentration in the irrigation water but negatively with soil salinity. Characterization of AOB communities by denaturing gradient gel electrophoresis showed the presence in every soil of AOB taxa, most commonly found in high-ammonia environments. The soil with the fewest years of management had the least diverse AOB population, compared to the other three soils, and much lower specific nitrification activity. This soil was irrigated with highly saline Colorado River water, which likely exerted acute negative effects on the activity of AOB. In summary, this study revealed that, although AOB activity and growth responded positively to ammonium availability in irrigation water, the salinity of the water and soil had strong negative effects on these aspects of the AOB community.     

Evaluation of Two Textiles with or without Polymer Addition for Dewatering Effluent from an Intensive Biofloc Production System

Intensive, recirculating aquaculture systems create concentrated wastes high in solid content. Geotextile has successfully dewatered aquaculture effluent; however, burlap, made from natural plant fiber, may provide similar filtering capabilities at a lower cost. The trial was designed as a 2 × 2 factorial to evaluate burlap bags and geotextile bags with or without polymer addition for dewatering Nile tilapia, Oreochromis niloticus, effluent from an intensive biofloc production system. There were no significant interactions (P > 0.05) between the main effects on the removal efficiency of total suspended solids (TSS) concentration. There were no significant differences (P > 0.05) in the main effect of textile; however, there were significant differences (P≤ 0.001) in the main effect of polymer on the removal efficiency of TSS concentration from effluent. Overall, TSS removal efficiency in textile‐only treatments was 81%, whereas textile treatments in combination with polymer removed 98%. Partial budget analysis indicated that the cost per kilogram of solids (dry weight) removed from untreated effluent was US$1.52, 1.51, 0.16, and 0.14 for the geotextile with polymer (GP), geotextile without polymer (GNP), burlap with polymer (BP), and burlap without polymer (BNP) treatments, respectively. The BP could provide an effective treatment process for removing TSS in discharged effluent.     

不容忽视的球拍平衡

问题一:我是一个女生,从初中开始打羽毛球,最近又接触上了网球运动。我感觉从羽毛球到网球有些转不过来,主要是手腕的问题,这可能也是一个很多人会遇到的问题。我想问一下王指导怎么在有一定羽毛球基础的情况下,找打网球的感觉?王良佐:如果换一个角度来想的话,你有打羽毛球的基础,在人和球之间距离的判断上,你相比一般女孩子就有了一些优势。如果你什么     

Rapid development of enhanced atrazine degradation in a Dundee silt loam soil under continuous corn and in rotation with cotton

Mississippi Delta cotton (Gossypium hirsutum L.) production in rotation with corn (Zea mays L.) was evaluated in field experiments from 2000 to 2005 at Stoneville, Mississippi. Plots maintained under minimum tillage were established in 2000 on a Dundee silt loam with treatments including continuous cotton or corn and alternate cotton-corn rotations. Mineralization and dissipation of 14C [ring]-labeled atrazine were evaluated in the laboratory on soils collected prior to herbicide application in the first, second, third, and sixth years of the study. In soils collected in 2000, a maximum of 10% of the atrazine was mineralized after 30 days. After 1 year of herbicide application, atrazine-treated soils mineralized 52-57% of the radiolabeled atrazine in 30 days. By the sixth year of the study, greater than 59% of the atrazine was mineralized after 7 days in soils treated with atrazine, while soils from plots with no atrazine treatment mineralized less than 36%. The data also indicated rapid development of enhanced atrazine degradation in soils following 1 year of corn production with atrazine use. Atrazine mineralization was as rapid in soils under a rotation receiving biannual atrazine applications as in soils under continuous corn receiving annual applications of atrazine. Cumulative mineralization kinetics parameters derived from the Gompertz model (k and ti) were highly correlated with a history of atrazine application and total soil carbon content. Changes in the soil microbial community assessed by total fatty acid methyl ester (FAME) analysis indicated significant interactions of cropping system and sampling date, with FAME indicators for soil bacteria responsible for differences in community structure. Autoclaved soil lost all ability to mineralize atrazine, and atrazine-mineralizing bacteria were isolated from these plots, confirming the biological basis for atrazine mineralization. These results indicate that changes in degradative potential of a soil can occur rapidly and some changes in soil properties may be associated with cropping systems, which can contribute to enhanced atrazine degradation potential.     

Variability in the yield of benzophenanthridine alkaloids in wildcrafted vs cultivated bloodroot (Sanguinaria canadensis L.)

Populations of bloodroot [Sanguinaria canadensis L. (Papaveraceae)] are found throughout the eastern forests of North America, with particular abundance in the southern Appalachian Mountains. Increasingly, it is finding use in Europe as a nonantibiotic animal feed supplement to promote weight gain. As efforts to cultivate this herb are underway, there is a need to understand the effect of agronomic permutations on both the dry mass rhizome yield and the yield of benzophenanthridine alkaloids. Month-to-month variability of the concentration of the alkaloids sanguinarine and chelerythrine in both cultivated and wildcrafted bloodroot was examined. The alkaloid yield was consistently higher, but more variable, in wildcrafted plants. On average, cultivated rhizomes were both larger and more consistently sized than those that were wildcrafted. The concentration of a suite of trace elements was measured in soil that was collected concomitantly with each plant accession. Differences in element profiles were compared against alkaloid yields.     

Effects of glyphosate on soil microbial communities and its mineralization in a Mississippi soil

Transgenic glyphosate-resistant (GR) soybean [Glycine max (L.) Merr.] has enabled highly effective and economical weed control. The concomitant increased application of glyphosate could lead to shifts in the soil microbial community. The objective of these experiments was to evaluate the effects of glyphosate on soil microbial community structure, function and activity. Field assessments on soil microbial communities were conducted on a silt loam soil near Stoneville, MS, USA. Surface soil was collected at time of planting, before initial glyphosate application and 14 days after two post-emergence glyphosate applications. Microbial community fatty acid methyl esters (FAMEs) were analyzed from these soil samples and soybean rhizospheres. Principal component analysis of the total FAME profile revealed no differentiation between field treatments, although the relative abundance of several individual fatty acids differed significantly. There was no significant herbicide effect in bulk soil or rhizosphere soils. Collectively, these findings indicate that glyphosate caused no meaningful whole microbial community shifts in this time period, even when applied at greater than label rates. Laboratory experiments, including up to threefold label rates of glyphosate, resulted in up to a 19% reduction in soil hydrolytic activity and small, brief (<7 days) changes in the soil microbial community. After incubation for 42 days, 32-37% of the applied glyphosate was mineralized when applied at threefold field rates, with about 9% forming bound residues. These results indicate that glyphosate has only small and transient effects on the soil microbial community, even when applied at greater than field rates.     

Effects of short- and long-term fasting on plasma and stomach ghrelin,and the growth hormone/insulin-like growth factor I axis in the tilapia, Oreochromis mossambicus

Ghrelin is a highly conserved peptide hormone secreted by the stomach, which is involved in the regulation of food intake and energy expenditure. Ghrelin stimulates growth hormone (GH) release, and increases appetite in a variety of mammalian and non-mammalian vertebrates, including several fish species. Studies were conducted to investigate the effect of feeding and fasting on plasma and stomach ghrelin, and the growth hormone/insulin-like growth factor I (IGF-I) axis in the Mozambique tilapia, a euryhaline teleost. No postprandial changes in plasma and stomach ghrelin levels or stomach ghrelin mRNA levels were observed. Plasma levels of GH, IGF-I and glucose all increased postprandially which agrees with the anabolic roles of these factors. Fasting for 4 and 8 d did not affect ghrelin levels in plasma or stomach. Plasma GH was elevated significantly after 4 and 8 d of fasting, while plasma IGF-I levels were reduced. Plasma ghrelin levels were elevated significantly after 2 and 4 wk of fasting, but no change was detected in stomach ghrelin mRNA levels. Four weeks of fasting did not affect plasma GH levels, although plasma IGF-I and glucose were reduced significantly, indicating that GH resistance exists during a prolonged nutrient deficit (catabolic state). These results indicate that ghrelin may not be acting as a meal-initiated signal in tilapia, although it may be acting as a long-term indicator of negative energy balance.     

MAGNETIC RESONANCE IMAGING OF THE INITIAL ACTIVE STAGE OF EQUINE LAMINITIS AT 4.7 T

Equine laminitis is a severely debilitating disease. There is a poor understanding of the underlying pathophysiology, and traditional imaging modalities have limited diagnostic capacity. High field strength magnetic resonance (MR) imaging allows direct visualization of the laminae, which other modalities do not. This would prove useful both in assessment of clinical patients and in further investigation into the pathophysiology of the disease. The objective of this study was to characterize the anatomic changes within the equine foot associated with the initial active stage of laminitis. Images obtained using a 4.7 T magnet were compared with digital radiographs using histologic diagnosis as the reference standard. Objective measurements and subjective evaluation for both modalities were evaluated for the ability to predict the histologic diagnosis in horses with clinical signs of laminitis as well as in clinically normal horses and horses that were in a population at risk for developing laminitis. Signal intensity and architectural changes within the corium and laminae were readily seen at 4.7 T, and there was a strong association with the histologic diagnosis of active laminitis. Measurements obtained with MR imaging were more sensitive and specific predictors of laminitis than those obtained radiographically. Subjective evaluation with MR imaging was more sensitive than with radiography and should become more specific with greater understanding of normal anatomy.     

Computation-guided backbone grafting of a discontinuous motif onto a protein scaffold

The manipulation of protein backbone structure to control interaction and function is a challenge for protein engineering. We integrated computational design with experimental selection for grafting the backbone and side chains of a two-segment HIV gp120 epitope, targeted by the cross-neutralizing antibody b12, onto an unrelated scaffold protein. The final scaffolds bound b12 with high specificity and with affinity similar to that of gp120, and crystallographic analysis of a scaffold bound to b12 revealed high structural mimicry of the gp120-b12 complex structure. The method can be generalized to design other functional proteins through backbone grafting.     

Imaging of germinal center selection events during affinity maturation

The germinal center (GC) is an important site for the generation and selection of B cells bearing high-affinity antibodies, yet GC cell migration and interaction dynamics have not been directly observed. Using two-photon microscopy of mouse lymph nodes, we revealed that GC B cells are highly motile and extend long cell processes. They transited between GC dark and light zones and divided in both regions, although these B cells resided for only several hours in the light zone where antigen is displayed. GC B cells formed few stable contacts with GC T cells despite frequent encounters, and T cells were seen to carry dead B cell blebs. On the basis of these observations, we propose a model in which competition for T cell help plays a more dominant role in the selection of GC B cells than previously appreciated.