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Different Soil Depths (different + soil_depth)
Selected AbstractsDifferent portions of the maize root system host Burkholderia cepacia populations with different degrees of genetic polymorphismENVIRONMENTAL MICROBIOLOGY, Issue 1 2000Luigi Chiarini In order to acquire a better understanding of the spatial and temporal variations of genetic diversity of Burkholderia cepacia populations in the rhizosphere of Zea mays, 161 strains were isolated from three portions of the maize root system at different soil depths and at three distinct plant growth stages. The genetic diversity among B. cepacia isolates was analysed by means of the random amplified polymorphic DNA (RAPD) technique. A number of diversity indices (richness, Shannon diversity, evenness and mean genetic distance) were calculated for each bacterial population isolated from the different root system portions. Moreover, the analysis of molecular variance ( amova) method was applied to estimate the genetic differences among the various bacterial populations. Our results showed that, in young plants, B. cepacia colonized preferentially the upper part of the root system, whereas in mature plants, B. cepacia was mostly recovered from the terminal part of the root system. This uneven distribution of B. cepacia cells among different root system portions partially reflected marked genetic differences among the B. cepacia populations isolated along maize roots on three distinct sampling occasions. In fact, all the diversity indices calculated indicated that genetic diversity increased during plant development and that the highest diversity values were found in mature maize plants, in particular in the middle and terminal portions of the root system. Moreover, the analysis of RAPD patterns by means of the amova method revealed highly significant divergences in the degree of genetic polymorphism among the various B. cepacia populations. [source] Simulating the spatial distribution of clay layer occurrence depth in alluvial soils with a Markov chain geostatistical approachENVIRONMETRICS, Issue 1 2010Weidong Li Abstract The spatial distribution information of clay layer occurrence depth (CLOD), particularly the spatial distribution maps of occurrence of clay layers at depths less than a certain threshold, in alluvial soils is crucial to designing appropriate plans and measures for precision agriculture and environmental management in alluvial plains. Markov chain geostatistics (MCG), which was proposed recently for simulating categorical spatial variables, can objectively decrease spatial uncertainty and consequently increase prediction accuracy in simulated results by using nonlinear estimators and incorporating various interclass relationships. In this paper, a MCG method was suggested to simulate the CLOD in a meso-scale alluvial soil area by encoding the continuous variable with several threshold values into binary variables (for single thresholds) or a multi-class variable (for all thresholds being considered together). Related optimal prediction maps, realization maps, and occurrence probability maps for all of these indicator-coded variables were generated. The simulated results displayed the spatial distribution characteristics of CLOD within different soil depths in the study area, which are not only helpful to understanding the spatial heterogeneity of clay layers in alluvial soils but also providing valuable quantitative information for precision agricultural management and environmental study. The study indicated that MCG could be a powerful method for simulating discretized continuous spatial variables. Copyright © 2009 John Wiley & Sons, Ltd. [source] Variable carbon recovery of Walkley-Black analysis and implications for national soil organic carbon accountingEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2007S. Lettens Summary There is considerable interest in the computation of national and regional soil carbon stocks, largely as the result of the provisions of the Kyoto Protocol. Such stocks are often calculated and compared without proper reference to the uncertainties induced by different analytical methodologies. We illustrate the nature and magnitude of these uncertainties with the present soil organic carbon (SOC) study in Belgium. The SOC recovery of the Walkley-Black method was investigated based on a database of 475 samples of silt loam and sandy soils, which cover different soil depths and vegetation types in northern Belgium. The organic carbon content of the soil samples was measured by the original Walkley-Black method and by a total organic carbon analyser. The recovery was computed as the ratio of these two results per soil sample. Land use, texture and soil sampling depth had a significant influence on the recovery as well as their three-way interaction term (land use × texture × sampling depth). The impact of a land use, texture and sampling depth dependent Walkley-Black correction on the year 2000 SOC inventory of Belgium was determined by regression analysis. Based on new correction factors, the national SOC stocks increased by 22% for the whole country, ranging from 18% for cropland to 31% for mixed forest relative to the standard corrected SOC inventory. The new recovery values influenced therefore not only C stocks in the year 2000, but also the expected SOC change following land use change. Adequate correction of Walkley-Black measurements is therefore crucial for the absolute and comparative SOC assessments that are required for Kyoto reporting and must be computed to take into account the regional status of soil and land use. ,Universal' corrections are probably an unrealistic expectation. [source] Incidence of Phytophthora species in oak forests in Austria and their possible involvement in oak declineFOREST PATHOLOGY, Issue 3 2003Y. Balci Summary A survey on the occurrence of Phytophthora species in oak ecosystems in Austria was conducted from April to May 1999 and in June 2000. The investigations were carried out at 35 study sites distributed throughout the zone of oak forests in eastern Austria. Four oak species, including Quercus robur, Q. petraea, Q. cerris and Q. pubescens were considered in the survey. Rhizosphere soil samples were taken from sample trees, which consisted of healthy and declining trees as indicated by their crown transparency. Young oak leaflets were used as baits to recover Phytophthora species. The assemblage of Phytophthora spp. detected in Austrian oak forests consisted of five species, including Phytophthora quercina, P. citricola, P. gonapodyides, P. europaea and P. syringae. P. quercina and P. citricola were isolated from 11 and seven sites, respectively, and were thus the most common and most widely distributed species. The three other species were recovered only sporadically. P. citricola could be separated into two morphologically and genetically well-characterized types (A and B). Phytophthora species, in particular the common P. quercina and P. citricola occurred on sites showing a wide variety of soil types, soil textures and moisture classes. There was mild evidence for connection between deteriorating crown status and the presence of Phytophthora spp. Furthermore, significant differences in contents of magnesium, as well as calcium, aluminium, nitrogen and carbon at different soil depths (0,10, 10,20 and 20,40 cm) were detected between Phytophthora -infested and Phytophthora -free sites. The results of the present study provide circumstantial evidence that Phytophthora species are involved in oak decline at certain sites in Austria. Résumé Une prospection des espèces de Phytophthora dans les écosystèmes de chênaie a été réalisée en Autriche en avril-mai 1999 et en juin 2000. Les recherches ont été conduites dans 35 sites répartis dans l'ensemble des chênaies de l'est de l'Autriche. Quatre espèces de chênes ont été prises en considération: Quercus robur, Q. petraea, Q. cerris et Q. pubescens. Des échantillons de sol rhizosphérique ont été prélevés au pied d'arbres sains ou dépérissants, jugés d'après la transparence de leur houppier. De jeunes feuilles de chênes ont été utilisées comme piège. Les Phytophthora spp. détectés dans les chênaies autrichiennes appartenaient à cinq espèces : P. quercina, P. citricola, P. gonapodyides, P. europaea et P. syringae. Phytophthora quercina et P. citricola ont été isolés dans 11 et 7 sites respectivement; ils étaient les plus fréquents et les plus largement répandus. Les trois autres espèces n'ont été trouvées que sporadiquement. Chez P. citricola, deux types (A et B) ont pu être distingués, morphologiquement et génétiquement différents. Les espèces de Phytophthora, en particulier P. quercina et P. citricola,étaient présents dans des sites très variés pour les types de sol, leur texture et l'humidité. Phythophthora spp. tendaient àêtre plus fréquemment présents en lien avec la détérioration des houppiers. Par ailleurs, des différences significatives ont été trouvées entre les sites avec ou sans Phytophthora, pour les teneurs en magnésium ainsi qu'en calcium, aluminium, azote et carbone à différentes profondeurs du sol (0,10, 10,20 et 20,40 cm). Les résultats montrent que des espèces de Phytophthora sont impliquées dans le dépérissement des chênes dans certains sites en Autriche. Zusammenfassung Im Rahmen einer breit angelegten Erhebung wurde im April und Mai 1999 sowie im Juni 2000 das Auftreten von Phytophthora -Arten in Eichenwaldökosystemen in Österreich untersucht. Die Erhebungen wurden an 35 Standorten durchgeführt, die über das gesamte natürliche Eichenwaldvorkommen in Ostösterreich verteilt waren. In die Untersuchung wurden die vier Eichenarten Quercus robur, Q. petraea, Q. cerris und Q. pubescens einbezogen. Von jeder , anhand ihres Kronenzustands als gesund bzw. krank eingestuften , Eiche wurden Bodenproben entnommen und aus diesen mittels ,Eichenblatt'-Ködermethode die Phytophthora -Arten isoliert. Das Spektrum der in Österreich isolierten Phytophthora -Arten umfasste die 5 Arten Phytophthora quercina, P. citricola, P. gonapodyides, P. europaea und P. syringae. P. quercina und P. citricola wurden von 11 bzw. 7 der untersuchten Standorte isoliert und waren somit die häufigsten und am weitesten verbreiteten Arten. Die drei anderen Phytophthora -Arten traten hingegen nur sporadisch auf. Innerhalb von P. citricola konnten anhand morphologischer und genetischer Merkmale 2 Typen (Typ A und Typ B) unterschieden werden. Phytophthora -Arten, insbesondere die häufig nachgewiesenen Arten P. quercina und P. citricola wurden an Standorten mit den unterschiedlichsten Bodentypen, -textur und -feuchteklassen nachgewissen. Es wurde ein schwach signifikanter Zusammenhang zwischen dem sich verschlechternden Kronenzustand und dem Vorhandensein von Phytophthora nachgewissen. Darüber hinaus unterschieden sich Phytophthora -infizierte und Phytophthora -freie Standorte in verschiedenen Bodentiefen (0,10, 10,20 und 20,40 cm) signifikant in ihren Magnesium, Kalzium, Aluminium, Stickstoff und Kohlenstoff-Gehalten. Die Ergebnisse der vorliegenden Studie lassen den Schluss zu, dass Phytophthora -Arten an einigen Untersuchungsstandorten in Österreich am Eichensterben beteiligt sind. [source] Development of a stable isotope index to assess decadal-scale vegetation change and application to woodlands of the Burdekin catchment, AustraliaGLOBAL CHANGE BIOLOGY, Issue 7 2007EVELYN KRULL Abstract Forty-four study sites were established in remnant woodland in the Burdekin River catchment in tropical north-east Queensland, Australia, to assess recent (decadal) vegetation change. The aim of this study was further to evaluate whether wide-scale vegetation ,thickening' (proliferation of woody plants in formerly more open woodlands) had occurred during the last century, coinciding with significant changes in land management. Soil samples from several depth intervals were size separated into different soil organic carbon (SOC) fractions, which differed from one another by chemical composition and turnover times. Tropical (C4) grasses dominate in the Burdekin catchment, and thus ,13C analyses of SOC fractions with different turnover times can be used to assess whether the relative proportion of trees (C3) and grasses (C4) had changed over time. However, a method was required to permit standardized assessment of the ,13C data for the individual sites within the 13 Mha catchment, which varied in soil and vegetation characteristics. Thus, an index was developed using data from three detailed study sites and global literature to standardize individual isotopic data from different soil depths and SOC fractions to reflect only the changed proportion of trees (C3) to grasses (C4) over decadal timescales. When applied to the 44 individual sites distributed throughout the Burdekin catchment, 64% of the sites were shown to have experienced decadal vegetation thickening, while 29% had remained stable and the remaining 7% had thinned. Thus, the development of this index enabled regional scale assessment and comparison of decadal vegetation patterns without having to rely on prior knowledge of vegetation changes or aerial photography. [source] Spatial genetic structure links between soil seed banks and above-ground populations of Primula modesta in subalpine grasslandJOURNAL OF ECOLOGY, Issue 1 2006A. SHIMONO Summary 1The spatial genetic structure of soil seed banks establishes the initial template for development of spatial genetic structure in above-ground plants, but is rarely evaluated. 2We used kinship coefficients to analyse the fine-scale spatial genetic autocorrelation of plants and of seed banks from different soil depths for Primula modesta at a subalpine fen site on Mt Asama, central Japan. 3The spatial genetic structure of surface seeds (0,1 cm depth) was significant, while deeper seeds (1,5 cm depth) had no significant genetic structure. We also detected a more pronounced spatial genetic association between the surface seeds and flowering genets than between the deeper seeds and flowering genets. 4These results suggest that the surface seed bank accounts for a large proportion of the previous season's seed dispersal and therefore represents the transient seed bank, whereas the deeper (persistent) seed bank pools the reproductive output of multiple generations. 5Directional analysis indicated that secondary dispersal by running water modifies the spatial genetic structure and extends dispersal distances. Over time, this may impact on the spatial pattern of soil seeds, possibly accounting for the absence of spatial genetic structure in deeper seeds. 6Emerging seedlings and flowering ramets were strongly clustered together at distances up to 20 cm. Surviving seedlings were aggregated at short distances because of the patchy spatial distribution of safe sites for establishment, allowing development and strengthening of the marked fine-scale spatial genetic structure. [source] Fate of the herbicides glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron in two Finnish arable soilsPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 6 2006Pirkko Laitinen Abstract The fate of five herbicides (glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron) was studied in two Finnish sugar beet fields for 26 months. Soil types were sandy loam and clay. Two different herbicide-tolerant sugar beet cultivars and three different herbicide application schedules were used. Meteorological data were collected throughout the study and soil properties were thoroughly analysed. An extensive data set of herbicide residue concentrations in soil was collected. Five different soil depths were sampled. The study was carried out using common Finnish agricultural practices and represents typical sugar beet cultivation conditions in Finland. The overall observed order of persistence was ethofumesate > glyphosate > phenmedipham > metamitron > glufosinate-ammonium. Only ethofumesate and glyphosate persisted until the subsequent spring. Seasonal variation in herbicide dissipation was very high and dissipation ceased almost completely during winter. During the 2 year experiment no indication of potential groundwater pollution risk was obtained, but herbicides may cause surface water pollution. Copyright © 2006 Society of Chemical Industry [source] | ||||||||||