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1.
Phillip Sollins Christopher Swanston Timothy Filley Susan Crow Kate Lajtha 《Soil biology & biochemistry》2006,38(11):3313-3324
In mineral soil, organic matter (OM) accumulates mainly on and around surfaces of silt- and clay-size particles. When fractionated according to particle density, C and N concentration (per g fraction) and C/N of these soil organo-mineral particles decrease with increasing particle density across soils of widely divergent texture, mineralogy, location, and management. The variation in particle density is explained potentially by two factors: (1) a decrease in the mass ratio of organic to mineral phase of these particles, and (2) variations in density of the mineral phase. The first explanation implies that the thickness of the organic accumulations decreases with increasing particle density. The decrease in C/N can be explained at least partially by especially stable sorption of nitrogenous N-containing compounds (amine, amide, and pyrrole) directly to mineral surfaces, a phenomenon well documented both empirically and theoretically. These peptidic compounds, along with ligand-exchanged carboxylic compounds, could then form a stable inner organic layer onto which other organics could sorb more readily than onto the unconditioned mineral surfaces (“onion” layering model).To explore mechanisms underlying this trend in C concentration and C/N with particle density, we sequentially density fractionated an Oregon andic soil at 1.65, 1.85, 2.00, 2.28, and 2.55 g cm−3 and analyzed the six fractions for measures of organic matter and mineral phase properties.All measures of OM composition showed either: (1) a monotonic change with density, or (2) a monotonic change across the lightest fractions, then little change over the heaviest fractions. Total C, N, and lignin phenol concentration all decreased monotonically with increasing density, and 14C mean residence time (MRT) increased with particle density from ca. 150 years to >980 years in the four organo-mineral fractions. In contrast, C/N, 13C and 15N concentration all showed the second pattern. All these data are consistent with a general pattern of an increase in extent of microbial processing with increasing organo-mineral particle density, and also with an “onion” layering model.X-ray diffraction before and after separation of magnetic materials showed that the sequential density fractionation (SDF) isolated pools of differing mineralogy, with layer-silicate clays dominating in two of the intermediate fractions and primary minerals in the heaviest two fractions. There was no indication that these differences in mineralogy controlled the differences in density of the organo-mineral particles in this soil. Thus, our data are consistent with the hypothesis that variation in particle density reflects variation in thickness of the organic accumulations and with an “onion” layering model for organic matter accumulation on mineral surfaces. However, the mineralogy differences among fractions made it difficult to test either the layer-thickness or “onion” layering models with this soil. Although SDF isolated pools of distinct mineralogy and organic-matter composition, more work will be needed to understand mechanisms relating the two factors. 相似文献
2.
通过在小麦基础日粮中添加国产酶(EⅠ)和进口酶(EⅡ)两种木聚糖酶制剂,研究木聚糖酶对肉仔鸡各段消化道食糜停留时间和营养物质消化率的影响。试验将7日龄肉仔鸡随机分成5组:小麦基础日粮中分别添加0.05%EⅠ(A1组)、0.02%EⅠ(A2组)、0.02%EⅡ(B1组)、0.05%EⅡ(B2组)、0%(C组),饲喂至21日龄。结果表明:在所有组中,食糜在空肠和回肠的停留时间最长。加酶组使腺胃、结肠、盲肠的停留时间延长,使其它消化道停留时间缩短(P>0.05),A1组、A2组、B1组、B2组使总停留时间分别比对照组减少15.2%、6.4%、13.6%、13.8%。与对照组相比,加酶组可显著提高干物质和粗蛋白的粪消化率。所有组中嗉囊、腺胃、十二指肠和盲肠消化率表现为负值,肌胃、空肠、回肠和结肠各段消化率为正值,且从空肠到结肠消化率有升高的趋势。 相似文献
3.
木聚糖酶对肉仔鸡消化道食糜停留时间和营养消化率的影响 总被引：9，自引：0，他引：9
通过在小麦基础日粮中添加国产酶（EⅠ）和进口酶（EⅡ）两种木聚糖酶制剂,研究木聚糖酶对肉仔鸡各段消化道食糜停留时间和营养物质消化率的影响。试验将7日龄肉仔鸡随机分成5组：小麦基础日粮中分别添加0.05% EⅠ(A1组)、0.02% EⅠ（A2组）、0.02% EⅡ（B1组）、0.05% EⅡ(B2组)、0%（C组）,饲喂至21日龄。结果表明：在所有组中,食糜在空肠和回肠的停留时间最长。加酶组使腺胃、结肠、盲肠的停留时间延长,使其它消化道停留时间缩短(P>0.05),A1组、A2组、B1组、B2组使总停留时间分别比对照组减少15.2%、6.4%、13.6%、13.8%。与对照组相比,加酶组可显著提高干物质和粗蛋白的粪消化率。所有组中嗉囊、腺胃、十二指肠和盲肠消化率表现为负值,肌胃、空肠、回肠和结肠各段消化率为正值,且从空肠到结肠消化率有升高的趋势。 相似文献
4.
为明确广聚萤叶甲Ophraella communa雄虫精液蛋白基因在性别间的表达差异并筛选出在雄虫生殖系统特异性表达的基因,从转录组及蛋白组数据库选取13个精液蛋白基因,采用实时荧光定量PCR技术检测其在广聚萤叶甲不同性别、组织及发育阶段的表达特征。结果显示,在广聚萤叶甲雄虫13个精液蛋白基因中,有9个精液蛋白的mRNA表达水平在雄虫中更高,有5个精液蛋白基因具有专一的雄虫生殖系统特异性,分别为PGK、sucA、ENO、SDH和PLA2b基因,在雄虫生殖系统中的表达量分别较其在头部的表达量高273.01倍、401.48倍、11.21倍、64.27倍和1.86倍。PGK、sucA和ENO基因均在广聚萤叶甲老熟蛹期急剧上调表达,在性成熟成虫中的表达量最高,分别是卵期表达量的43.48倍、31.03倍和11.89倍,三者具有明显的组织和发育阶段时空特异性,推测PGK、sucA和ENO基因参与广聚萤叶甲雄虫生殖的可能性较其余基因更高。 相似文献
5.
Small-scale effects of historical land use and topography on post-cultural tree species composition in an Alpine valley in southern Switzerland 总被引：1，自引：0，他引：1
Investigations of spatial patterns in forest tree species composition are essential in the understanding of landscape dynamics,
especially in areas of land-use change. The specific environmental factors controlling the present patterns, however, vary
with the scale of observation. In this study we estimated abundance of adult trees and tree regeneration in a Southern Alpine
valley in Ticino, Switzerland. We hypothesized that, at the present scale, spatial pattern of post-cultural tree species does
not primarily depend on topographic features but responds instead to small-scale variation in historical land use. We used
multivariate regression trees to relate species abundances to environmental variables. Species matrices were comprised of
single tree species abundance as well as species groups. Groups were formed according to common ecological species requirements
with respect to shade tolerance, soil moisture and soil nutrients. Though species variance could only be partially explained,
a clear ranking in the relative importance of environmental variables emerged. Tree basal area of formerly cultivated Castanea sativa (Mill.) was the most important factor accounting for up to 50% of species’ variation. Influence of topographic attributes
was minor, restricted to profile curvature, and partly contradictory in response. Our results suggest the importance of biotic
factors and soil properties for small-scale variation in tree species composition and need for further investigations in the
study area on the ecological requirements of tree species in the early growing stage. 相似文献
6.
Maxim Dorodnikov Yakov Kuzyakov Guido L.B. Wiesenberg 《Soil biology & biochemistry》2011,43(3):579-589
Turnover of C and N in an arable soil under Free Air Carbon Dioxide (FACE) experiment was studied by the use of 13C natural abundance and 15N-labeled fertilizers. Wheat was kept four growing seasons under ambient and elevated CO2 concentrations and fertilized for three growing seasons. Density fractionation of soil organic matter (SOM) allowed to track 13C and 15N in free particulate organic matter (fPOM; <1.6 g cm−3), particulate organic matter occluded within aggregates with two densities (oPOM 1.6, oPOM 1.6-2.0 g cm−3), and in mineral-associated organic matter (>2.0 g cm−3) fractions. Elevated CO2 and N fertilization did not significantly affect C and N contents in the bulk soil. Calculated mean residence time (MRT) of C and N revealed the qualitative differences of SOM density fractions: (i) the shortest MRTC and MRTN in fPOM confirmed high availability of this fraction to decomposition. Larger C/N ratio of fPOM under elevated vs. ambient CO2 indicated an increasing recalcitrance of FACE-derived plant residues. (ii) There was no difference in MRT of C and N between lighter and heavier oPOMs probably due to short turnover time of soil aggregates which led to oPOM mixing. The increase of MRTC and MRTN in both oPOMs during the experiment confirmed the progressive degradation of organic material within aggregates. (iii) Constant turnover rates of C in the mineral fraction neither confirmed nor rejected the assumed stabilization of SOM to take place in the mineral fraction. Moreover, a trend of decreasing of C and N amounts in the Min fraction throughout the experiment was especially pronounced for C under elevated CO2. Hence, along with the progressive increase of CFACE in the Min fraction the overall losses of C under elevated CO2 may occur at the expense of older “pre-FACE” C. 相似文献
7.
Baumgarten D 《Veterinary microbiology》2002,90(1-4):63-69
A short review of the brucellosis situation, its control and eradication programs are presented. Data from over 1.2 milliom samples collected from more than 50,718 groups of cattle over a period of over 20 years (1979–2000) illustrates that over the last few years the number of individual reactors remain constant at around 3–4%. The percentage of reactive groups of animals decreased over these years, reflecting a better disease management and possibly an improved general education, handling of information on the immune (vaccination) status of animals and testing practices. Reported zoonotic cases are presented, as well as control and eradication programs, including utilization of vaccines. 相似文献
8.
The objective of this study was to determine the effect of dietary fiber on methane (CH4) production in pigs using the Chinese native Lantang gilts as study model. The study consisted of two experiments. In the first, 12 Lantang gilts (58.7±0.37 kg), individually housed in open-circuit respiration chambers were randomly divided into two groups (six replicates per dietary group) and fed either with low fiber diet [LFD; neutral detergent fiber (NDF)=201.5 g/kg] or high fiber diet (HFD; NDF=329.7 g/kg). Wheat bran was the main source of fiber for the LFD while ground rice hull (mixture of rice bran and rice hull) was used in the HFD. Results of the study showed that gilts fed LFD recorded higher (P<0.05) digestibility coefficients for dry matter (DM), total organic carbon (TOC), acid detergent fiber (ADF) and cellulose than those in the HFD. However, digestibility coefficient for NDF did not differ between treatments but that for hemicellulose was higher for HDF than for LDF. Because of the higher NDF and hemicellulose contents in the diet, pigs in the HFD recorded higher (P<0.05) amount of digested NDF (126.1 vs. 83.6 g/d) and hemicellulose (38.7 vs. 11.9 g/d) than those fed LFD. The higher amount of digested NDF and hemicellulose recorded for the HFD treatment was inconsistent with the lower (P<0.01) daily CH4 production from gilts fed the HFD compared to that fed LFD (2.46 vs. 3.90 L/pig). To better explain for the unexpected higher CH4 production from pigs fed LFD, an in vitro fermentation study was conducted using a factorial design comprised of two inocula (collected from low fiber and high fiber diets) and eight substrates (LFD, HFD, wheat bran, ground rice hull and their respective NDF residues). Results of the in vitro trial seems to suggest that the low CH4 production from the HFD animals was primarily the results of low fermentation rates of HFD and the ground rice hull. However, the calculated CH4 productions based on the molar percentage of volatile fatty acids (VFA) in both, in vivo and in vitro experiments reaffirmed the in vivo result, that is, CH4 production from pigs fed HFD was lower than that fed LFD. Although there is a lack of scientific data from this study to fully explain for the unexpected lower CH4 production from pigs fed the HFD, our results seems to suggest that quantity of digested fiber (including NDF) was not the sole factor affecting enteric CH4 production in pigs. 相似文献
9.
Y. Kuzyakov 《Soil biology & biochemistry》2006,38(3):425-448
Five main biogenic sources of CO2 efflux from soils have been distinguished and described according to their turnover rates and the mean residence time of carbon. They are root respiration, rhizomicrobial respiration, decomposition of plant residues, the priming effect induced by root exudation or by addition of plant residues, and basal respiration by microbial decomposition of soil organic matter (SOM). These sources can be grouped in several combinations to summarize CO2 efflux from the soil including: root-derived CO2, plant-derived CO2, SOM-derived CO2, rhizosphere respiration, heterotrophic microbial respiration (respiration by heterotrophs), and respiration by autotrophs. These distinctions are important because without separation of SOM-derived CO2 from plant-derived CO2, measurements of total soil respiration have very limited value for evaluation of the soil as a source or sink of atmospheric CO2 and for interpreting the sources of CO2 and the fate of carbon within soils and ecosystems. Additionally, the processes linked to the five sources of CO2 efflux from soil have various responses to environmental variables and consequently to global warming. This review describes the basic principles and assumptions of the following methods which allow SOM-derived and root-derived CO2 efflux to be separated under laboratory and field conditions: root exclusion techniques, shading and clipping, tree girdling, regression, component integration, excised roots and insitu root respiration; continuous and pulse labeling, 13C natural abundance and FACE, and radiocarbon dating and bomb-14C. A short sections cover the separation of the respiration of autotrophs and that of heterotrophs, i.e. the separation of actual root respiration from microbial respiration, as well as methods allowing the amount of CO2 evolved by decomposition of plant residues and by priming effects to be estimated. All these methods have been evaluated according to their inherent disturbance of the ecosystem and C fluxes, and their versatility under various conditions. The shortfalls of existing approaches and the need for further development and standardization of methods are highlighted. 相似文献
10.
从不同地区采集奶样,将OIE诊断试验中用于牛布病诊断的全乳iELISA与国标中的MRT进行比对。在检测的526份样品中,全乳iELISA检出93份阳性,国内MRT抗原检出31份阳性,英国卫桥的MRT抗原检出44份阳性(检测数为264份);对其中一个地区的31份奶品,除了抗体的检测外,同时进行了奶样的细菌分离、奶样提取DNA的检测,全乳iELISA与乳样DNA提取均检出21份阳性,且一一对应,国内MRT抗原只检出10份阳性。结果表明全乳iELISA敏感性好,操作方便快捷,具有血清学检测所不具备的许多突出优点。 相似文献