土壤有机质模型的比较分析

土壤有机质作为土壤C库,其含量和动态变化对全球C循环、土壤肥力、土壤质量和健康起着重要作用。SOM模型利用经验性的假设和已有数据对土壤有机质含量和动态变化进行模拟,尤其是可以对无法取得足够必要数据的试验进行模拟,所以SOM模型成为定量研究土壤有机质积累分解的重要手段,利用SOM模型有助于对土壤有机质分解机理的研究,并且可通过SOM模型对土壤CO2排放量、植物生产量进行预测。同时也可对农业管理措施做出评估,文中对几种SOM模型进行了概述,尤其对有影响的RothC模型和CENTURY模型进行了比较分析。     

Comparison of near infra-red spectroscopy, neutral detergent fibre assay and in-vitro organic matter digestibility assay for rapid determination of the biochemical methane potential of meadow grasses

This paper investigates near infra-red spectroscopy (NIRS) as an indirect and rapid method to assess the biochemical methane potential (BMP) of meadow grasses. Additionally analytical methods usually associated with forage analysis, namely, the neutral detergent fibre assay (NDF), and the in-vitro organic matter digestibility assay (IVOMD), were also tested on the meadow grass samples and the applicability of the models in predicting the BMP was studied. Based on these, regression models were obtained using the partial least squares (PLS) method. Various data pre-treatments were also applied to improve the models. Compared to the models based on the NDF and IVOMD predictions of BMP, the model based on the NIRS prediction of BMP gave the best results. This model, with data pre-processed by the mean normalisation method, had an R² value of 0.69, a root mean square error of prediction (RMSEP) of 37.4 and a residual prediction deviation (RPD) of 1.75.     

Predicting the energetic value of forage from digestibility of organic matter in vitro or solubility in potassium hydroxide

The digestibility of dry matter, organic matter and energy, and the content of digested energy, were determined on 56 diets, including hay, haylage, silage and pellets, in balance trials with wethers. All diets were analysed for solubility of organic matter in KOH, total protein, crude fibre, N-free extract and digestible organic matter content determined in vitro (D value).The D value proved to be the most accurate in vitro method for predicting digestible energy value in vivo. Solubility of organic matter in KOH and crude-fibre content predicted the energy value of the diet with less accuracy.Regression equations are presented for predicting the organic matter digestibility and energy value of the diets from the results of laboratory analyses.     

Comparison of the accuracy of semiempirical and some DFT methods for predicting heats of formation

A comparison is made of the relative accuracy of some NDDO semiempirical methods and the DFT functionals LYP and PW91 using both double and triple zeta basis sets. The comparison is between the calculated heat of formation and that reported in the NIST database.Electronic Supplementary Material Parameters for the tailored method are available in the supplementary material; these are suitable for use with MOPAC2002. All raw data (experimental heats of formation, geometries, total energies and heats of formation for the various methods, etc.) are also provided in CAChe format. Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

Suitability of cell-wall constituents as predictors of organic matter digestibility in some tropical and subtropical by-products

The van Soest detergent method for determination of cell wall constituents is suggested as a good routine analysis for plant material of high fibre content. The chemical composition of the fibre fraction of 24 tropical and subtropical by-products has been investigated, and simple and multiple correlation coefficients have been calculated between organic matter digestibility in vivo and in vitro, and the contents of different cell wall fractions.The acid detergent fibre (ADF) gave the highest negative correlation with the digestibility of organic material independent from the botanical origin of the sample. The ADF fraction proved superior to the Weende crude fibre as well as to single fractions of the cell walls such as lignin, cutin and silica.The determination of ADF is more convenient, and needs only half the time and half the expenditure required for the Weende crude fibre analysis. There is the additional aspect of health: determination of ADF in the detergent analysis requires no use of asbestos.     

百日咳疑似病例实验室检测法的比较研究

目的 对2019年河南省监测医院的百日咳疑似病例进行实时荧光聚合酶链式反应(real-time polymerase chain reaction,real-time PCR)和定量ELISA实验室检测比较.方法 4家监测医院采集百日咳疑似病例的鼻咽拭子和血清,通过real-time PCR检测百日 咳鲍特菌(Bord...     

Bias when predicting crude protein,dry matter digestibility and voluntary intake of tropical grasses by near-infrared reflectance

A study was made of the bias (non-random error) of regressions for predicting crude protein (CP) content, dry matter digestibility (DMD) in vivo and voluntary intake (VI) of forage from its near-infrared reflectance (NIRR) properties measured at 19 wavelengths. The regression was derived from 97 samples including six tropical grasses, leaf and stem fractions, pelleted and chopped forms and regrowths varying from 28 to 150 days.Bias associated with differences in feed type was proved to exist in regression equations for predicting nutritive value when it was shown that the residual errors of these regressions were significantly reduced by including the combined effects of grass species, fraction, form and age. Measures of the bias which might be expected were calculated for two contrasting situations. The internal measure of bias (IMB) was ‘estimated’ as a possible average bias of a feed type when predicting nutritive value for samples of similar types to those used when deriving the calibration equation, while the extrapolation measure of bias (EMB) was ‘estimated’ as that associated with prediction of the nutritive value for feed types not included in the calibration equation.Crude protein was estimated with a residual standard deviation (RSD) of ± 0.77% when regressed against the 19 reflectance values, but when information on grass species, parts and regrowth was also included in the regression the RSD was reduced to ± 0.46%. The maximum difference in the IMB between grass species was 0.80% crude protein, while for EMB it was 3.35% crude protein. When separated leaf and stem were considered the differences were larger.Dry matter digestibility was estimated with an RSD of ± 2.7% which decreased to ± 1.8% when grass species, age, form and study were taken into account. Grass species had only a small effect on IMB but the maximum difference for EMB between species reached 5.6%. The EMB indicated that the largest differences between deviations were associated with age of regrowth but this effect was absent with the IMB.Voluntary intake was estimated with an RSD of ± 7.2 g/kg W^0.75/day, which decreased to ± 2.5 g/kg W^0.75/day when grass species, form, part and age were taken into account. The largest bias was for pelleted and chopped forage with mean differences of 14.5 for IMB and 28.8 g/kg W^0.75/day for EMB, respectively.It was concluded that when nutritive value is predicted by NIRR the estimates may often be biased according to the grass species, plant part or physical form of the sample tested and that the pattern of bias may be complicated. In order to obtain accurate predictions from NIRR full account must be taken of this bias. This might be achieved by correcting the nutritive value estimates made from an NIRR regression, based on a large number of feed types, by addition of the bias associated with the feed type being estimated.     

Comparison of classifier fusion methods for predicting response to anti HIV-1 therapy

Background

Analysis of the viral genome for drug resistance mutations is state-of-the-art for guiding treatment selection for human immunodeficiency virus type 1 (HIV-1)-infected patients. These mutations alter the structure of viral target proteins and reduce or in the worst case completely inhibit the effect of antiretroviral compounds while maintaining the ability for effective replication. Modern anti-HIV-1 regimens comprise multiple drugs in order to prevent or at least delay the development of resistance mutations. However, commonly used HIV-1 genotype interpretation systems provide only classifications for single drugs. The EuResist initiative has collected data from about 18,500 patients to train three classifiers for predicting response to combination antiretroviral therapy, given the viral genotype and further information. In this work we compare different classifier fusion methods for combining the individual classifiers.

Principal Findings

The individual classifiers yielded similar performance, and all the combination approaches considered performed equally well. The gain in performance due to combining methods did not reach statistical significance compared to the single best individual classifier on the complete training set. However, on smaller training set sizes (200 to 1,600 instances compared to 2,700) the combination significantly outperformed the individual classifiers (p<0.01; paired one-sided Wilcoxon test). Together with a consistent reduction of the standard deviation compared to the individual prediction engines this shows a more robust behavior of the combined system. Moreover, using the combined system we were able to identify a class of therapy courses that led to a consistent underestimation (about 0.05 AUC) of the system performance. Discovery of these therapy courses is a further hint for the robustness of the combined system.

Conclusion

The combined EuResist prediction engine is freely available at http://engine.euresist.org.     

Degradability characteristics of dry matter and crude protein of forages in ruminants

Twelve corn silages, 22 grass silages and 14 grass hays, obtained from various farms located in the lower Fraser Valley region of British Columbia, and 16 alfalfa hays, grown primarily in the Columbia basin of central Washington State, were evaluated using both the rumen and the mobile nylon bag in situ techniques. Nylon bags containing each forage were incubated in duplicate for 0, 2, 4, 8, 12, 24, 48, 72, or 96 h in two of six non-lactating Holstein cows fitted with rumen and duodenal cannulae. All forage types were evaluated in terms of the following dry matter (DM) and crude protein (CP) digestion characteristics: soluble fraction A, degradable fraction B, degradation rate, lag phase, and effective degradability. The mobile nylon bag technique was used to determine intestinal disappearance of DM and CP from the forages following pre-incubation in the rumen for 12 h. Significant (P < 0.05) differences in degradation characteristics occurred within all forages with regard to the soluble and potentially degradable DM and CP fractions. Soluble CP content in the rumen varied from 44.08 to 75.37% and from 18.74 to 65.38% in the corn and grass silages, respectively, and from 48.27 to 75.43% and from 30.13 to 65.95% in the alfalfa and grass hays, respectively. Significant differences within each forage type were also observed for the degradable CP in fraction B: 10.89 to 45.28% for corn silage, 20.72 to 82.77% for grass silage, 16.67 to 44.88% for grass hay and 25.44 to 62.93% for alfalfa hays. Significant differences (P > 0.05) were observed in fractional rates of ruminal DM degradation of the grass hays and corn silages. Significant differences did exist in the fractional rates of ruminal CP degradation within all forage types with the exception of alfalfa hays. Effective degradabilities of DM and CP were also significantly different between samples of a particular forage type. The mobile nylon bag data indicated that approximately 20% of the original CP in the grass silage, grass hay and alfalfa hay samples disappeared in the intestine and that there was significant variation between individual samples. On average, in the corn silage samples more than 10% of the original nitrogenous material disappeared in the intestine. The results presented in this study clearly demonstrate that the use of tabulated values for describing individual batches of forages in terms of their degradability characteristics is inaccurate since they may not reflect the particular forage being used in the ration and thus may lead to errors in diet formulation.     

Comparison of survey methods for monitoring Clark's Nutcrackers and predicting dispersal of whitebark pine seeds

ABSTRACT Clark's Nutcrackers (Nucifraga columbiana) disperse seeds of whitebark pines (Pinus albicaulis) in western North America by their scatter‐hoarding behavior. Because of declines in whitebark pine, resource managers are seeking an effective means of monitoring nutcracker population trends and the probability of seed dispersal by nutcrackers. We tested the reliability of four survey techniques (standard point counts, playback point counts, line transects, and Breeding Bird Survey routes) for estimating population size by conducting surveys at sites where a portion of the nutcracker population was marked with radio transmitters. The efficacy of distance sampling, based on detection rates from our unadjusted surveys, was also assessed. We conducted counts of whitebark pine cones within stands and related the probability of seed dispersal within stands to cone production and nutcracker abundance. We conducted 70 h of surveys for Clark's Nutcrackers at eight sites from July through November in 2007 and 2009 and estimated cone densities at six of these sites. Detection rates for all survey techniques were low and variable and we detected an average of 5.6 nutcrackers per 30 min of survey time. We also found no difference in detection rates among survey types, although significantly more nutcrackers were detected during surveys conducted during the peak of whitebark pine cone harvest (P < 0.0001). Nutcracker abundance was not correlated with cone density (P= 0.29) and we observed nutcrackers pouching seeds at all sites. Thus, cone density did not provide reliable information on whether seed dispersal was likely to occur. We suggest that alternate methods be considered for monitoring populations and assessing seed dispersal probability because we did not reliably detect nutcrackers using conventional survey techniques and because nutcracker abundance was not correlated with cone density.     

In vitro digestibility of seasonal forages used by wapiti and roe deer in northeastern China

Seasonal changes in in vitro dry matter digestibility (IVDMD) of five forage classes (browses, sedges, forbs. ferns and the bark of Ulmus spp.) used by wapiti and roe deer were determined in relation to chemical composition, using the two-stage technique of in vitro trial with rumen inocula from one wapiti and one roe deer captured in winter. Wapiti and roe deer showed remarkable fluctuation in IVDMD among seasons and forage classes. IVDMD decreased from 43.8-64.3% in spring to 29.4-40.5% in winter for wapiti, and from 52.4-77.4% in spring to 25.9-36.5% in winter for roe deer. There was significant variation in IVDMD among species of browses for wapiti and roe deer. IVDMD ranged from 28.5% to 58.7% in twigs and from 39.8% to 58.2% in leaves for wapiti, and from 24.1% to 67.7% in twigs and from 40.0% to 71.7% in leaves for roe deer. Roe deer had higher IVDMD (40.0-71.7%) in both leaves and twigs of browses than wapiti (35.9-58.7%) during snow-free seasons, but IVDMD of twigs was lower for roc deer (25.9-36.5%) than wapiti (29.4-38.4%) in winter. Significant multiple correlation was found between NDF and ADF, and IVDMD in sedges, forbs and ferns for both wapiti and roe deer, whereas only roe deer showed the significant multiple correlation for leaves of browses.     

Investigation of some methods for increasing the digestibility in vitro of microalgae

In order to increase the availability of the cell bound protein in Scenedesmus algae, mechanical, enzymatic, and chemical methods of degrading the cell wall structure were investigated. Mechanical treatment involved the use of a ball-mill. The algae suspension together with glass beads was milled in a water-cooled chamber equipped with rotating disks. The enzyme tested was a cellulolytic enzyme (Meicelase) and the chemical employed was hydrogen peroxide. In the ball-mill experiments a complete disintegration was achieved ina disintegrator, working with batches. Trails wwere also performed with a continuous disintegrator and the depedence of disintegration on bead size and flow rate was studied. The disintegration determined by microscropic cell count was compared to the increase of the pepsin digestibility. The meicelase treatment caused a slight increase of the pepsin digestibility, as measured after 3 hr pepsin incubation. No increase of the pepsin disgestibility could be detected with hydrogen peroxide treatment. After the ball-mill disintegration 95% of contaminating bacteria were killed and yields of extractable proteins were higher. The capacity of availble continuous ball-mills is such that they could be used on a pilot-plant scale and the energy cost of disintegration would be of the same magnitude as that of separation.     

Principles governing the use of chemical methods for assessing the nutritive value of forages: A review

The potentially digestible organic matter of forages is the sum of the apparently digested cell contents and the truly digested cell walls. These two fractions can accurately be predicted from a knowledge of the ash and cell wall content and an estimate of cell wall digestibility. A determination of cell wall content is valuable as an indicator of both the voluntary consumption of forages and the efficiency of utilization of metabolizable energy (ME) for growth and fattening. A separate estimate of the digested cell walls is essential as the basis for estimating the digestion of organic matter achieved in practice. The major outstanding problem in practice is still to find a rapid, universal and accurate method of assessing cell wall potential digestibility. The energy value of the digested organic matter can be calculated from a knowledge of the protein content of forages and ME from this estimate of digested energy. Attempts to predict ME from lignin or lignocellulose alone, while rapid and less costly, invariably have errors of at least ± 7% and recent research on the effect of environment on chemical composition suggests that if the existing relations are applied outside their local climatic zones, or in abnormal seasons, the errors may well be greater.     

The search for indigenous lunar organic matter

Early lunar conditions are not inconsistent with the production of large quantities of prebiological organic matter now sequestered in the lunar subsurface. The absence of substantial water and organic compounds from the superficial layers of the lunar surface may not be indicative of the composition of deeper regions.     

Effect of a leaf-shredding invertebrate on organic matter dynamics and phosphorus spiralling in heterotrophic laboratory streams

Summary The effect of invertebrate shredders on organic matter dynamics and phosphorus spiralling was studied over a 30-week period in laboratory streams. The streams were fed by groundwater, layered with cobble and gravel from a natural stream, covered with opaque material to eliminate algal growth, and initially contained 195 g/m² of autumn-shed leaves. Four weeks after leaf addition, leaf-shredding snails (Goniobasis clavaeformis) were added to each of three streams in densities of 75, 220, and 800/m². A fourth stream contained no snails and served as a control.Presence of snails increased the loss rates of coarse particulate organic matter (CPOM) and total organic matter (TOM), primarily by increasing leaf fragmentation and seston export. Although snail feeding increased specific metabolism of microbes associated with CPOM and cobble surfaces, it was not enough to compensate for reduction in bacterial cell numbers per unit surface area and in stream TOM. Consequently mineralization of detritus and whole stream phosphorus utilization rate were maximum in the stream with no snails and decreased with increasing snail density. From previous simulations of a stream model based on the nutrient spiralling concept, we predicted that there should be an intermediate shredder density which would minimize phosphorus spiralling length (maximize phosphorus utilization) in a natural stream nearby. Our current results conflict with the model-based predictions primarily because the increase in microbial metabolism was less important than reduction in bacterial cell numbers and total benthic organic matter resulting from snail feeding. Although our results indicate macroinvertebrate shredders reduce phosphorus utilization in headwater streams, shreders may increase nutrient utilization downstream where riparian inputs are lower, thus linking low- and high-order streams.Research supported by the National Science Foundation's Ecosystem Studies Program under Interagency Agreement No. BSR-8103181, A02 with the U.S. Department of Energy, under Contract No. DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.Publication No. 2394, Environmental Sciences Division, ORNL     

Comparison of measured and modelled copper binding by natural organic matter in freshwaters

Fifteen freshwater samples containing significant concentrations of dissolved organic carbon-[DOC]-were titrated with copper under standardised conditions (pH 6 and 7), and concentrations of Cu(2+)-[Cu(2+)]-were measured with an ion-selective electrode. Measured values of [Cu(2+)], which were in the range 10(-11)-10(-5) moll(-1), were compared with those simulated using Humic Ion-Binding Models V and VI. It was assumed that copper speciation was controlled by the organic matter, represented by fulvic acid (FA), together with inorganic solution complexation (calculated with an inorganic speciation model). The models were calibrated by adjusting a single quantity, the concentration of FA. The optimised value-[FA](opt)-was that giving the best agreement, according to least squares, between measured and simulated [Cu(2+)]. The calculations took into account competition by other dissolved (filterable) metals (Mg, Al, Ca, Fe(II), Fe(III), Zn); in the case of Fe(III) it was assumed either that all the dissolved metal was truly in solution, or that the activity of Fe(3+) was controlled by equilibrium with Fe(OH)(3). The assumption about Fe(III) had relatively small effects on the fitting of Model V, but was significant for Model VI, because Model VI represents low-abundance, high-affinity binding sites in humic matter, which are sensitive to Fe(III) competition. Because of its inclusion of the high-affinity sites, Model VI provided better fits of the data than did Model V. Furthermore, Model VI with Fe(3+) activity controlled by Fe(OH)(3) gave smaller variation in the ratio of [FA](opt) to [DOC] than Model VI with all Fe(III) assumed to be in solution. The average [FA](opt)/[DOC] found from the Cu titrations was 1.30, which implies that 65% of the organic matter is 'active' with respect to metal binding. The average ratio of 1.30 is in reasonable agreement with ratios obtained by applying the model to field data sets for charge balance (1.22), Al speciation (1.56) and base titrations of Cu-amended waters (1.45). It is concluded that Model VI/Fe(OH)(3) provides the most reliable predictions of dissolved metal speciation in natural waters; at a total Cu concentration of 1 microM, the predicted concentration of Cu(2+) is expected to be correct to within a factor of 3.6 in 95% of cases.     

The prediction of intake potential and organic matter digestibility of grass silages by near infrared spectroscopy analysis of undried samples

A study was undertaken to examine a range of sample preparation and near infrared reflectance spectroscopy (NIRS) methodologies, using undried samples, for predicting organic matter digestibility (OMD g kg⁻¹) and ad libitum intake (g kg⁻¹ W^0.75) of grass silages. A total of eight sample preparation/NIRS scanning methods were examined involving three extents of silage comminution, two liquid extracts and scanning via either external probe (1100-2200 nm) or internal cell (1100-2500 nm). The spectral data (log 1/R) for each of eight methods were examined by three regression techniques each with a range of data transformations. The 136 silages used in the study were obtained from farms across Northern Ireland, over a two year period, and had in vivo OMD (sheep) and ad libitum intake (cattle) determined under uniform conditions. In the comparisons of the eight sample preparation/scanning methods, and the differing mathematical treatments of the spectral data, the sample population was divided into calibration (n = 91) and validation (n = 45) sets. The standard error of performance (SEP) on the validation set was used in comparisons of prediction accuracy. Across all 8 sample preparation/scanning methods, the modified partial least squares (MPLS) technique, generally minimized SEP's for both OMD and intake. The accuracy of prediction also increased with degree of comminution of the forage and with scanning by internal cell rather than external probe. The system providing the lowest SEP used the MPLS regression technique on spectra from the finely milled material scanned through the internal cell. This resulted in SEP and R² (variance accounted for in validation set) values of 24 (g/kg OM) and 0.88 (OMD) and 5.37 (g/kg W^0.75) and 0.77 (intake) respectively. These data indicate that with appropriate techniques NIRS scanning of undried samples of grass silage can produce predictions of intake and digestibility with accuracies similar to those achieved previously using NIRS with dried samples.