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Other Root (other + root)
Selected AbstractsEffects of metals and pH on in vitro growth of Armillaria ostoyae and other root and butt rot fungi of red spruceFOREST PATHOLOGY, Issue 1 2001P. M. Wargo Armillaria ostoyae, Perenniporia subacida, Resinicium bicolor and Scytinostroma galactinum, root and butt rot fungi found on red spruce, Picea rubens, were tested, in vitro, for their sensitivity to metals typically found in high elevation forest soils where red spruce grows. Rhizomorph production by A. ostoyae from woody inocula in soils from red spruce stands at three elevations at each of five mountainous sites in the eastern United States was inhibited completely in the mineral soil from all elevations at all sites, and was also reduced significantly in the organic horizon from the upper two elevations at three of the sites. Inhibition was correlated with concentrations of metal ions in the soil. Growth of rhizomorphs into an agar medium containing lead and other heavy metals was inhibited for isolates of A. ostoyae from red spruce, but not for an isolate of Armillaria gallica from sugar maple; aluminium inhibited rhizomorph growth of isolates of both species. Mycelial growth of all four root and butt rot fungi was inhibited by lead, aluminium and other heavy metals depending on the solubility and concentration of metal and pH of the medium; growth inhibition was usually greater at an initial pH of 3.5 than at pH 4.5. Metal ions inhibited radial growth of Armillaria species more than that of the other three fungi. Rhizomorph growth of Armillaria was inhibited more than radial growth. Because local spread of A. ostoyae occurs frequently by means of rhizomorph growth between near roots, increases in lead, aluminium and other metals in the forest floor may contribute to this fungus' scarcity in high elevation soils and reduced incidence of infection at these sites in the eastern United States. [source] Data clustering as an optimum-path forest problem with applications in image analysisINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 2 2009Leonardo Marques Rocha Abstract We propose an approach for data clustering based on optimum-path forest. The samples are taken as nodes of a graph, whose arcs are defined by an adjacency relation. The nodes are weighted by their probability density values (pdf) and a connectivity function is maximized, such that each maximum of the pdf becomes root of an optimum-path tree (cluster), composed by samples "more strongly connected" to that maximum than to any other root. We discuss the advantages over other pdf-based approaches and present extensions to large datasets with results for interactive image segmentation and for fast, accurate, and automatic brain tissue classification in magnetic resonance (MR) images. We also include experimental comparisons with other clustering approaches. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 50,68, 2009. [source] Estimation and forecasting in first-order vector autoregressions with near to unit roots and conditional heteroscedasticityJOURNAL OF FORECASTING, Issue 7 2009Theologos Pantelidis Abstract This paper investigates the effects of imposing invalid cointegration restrictions or ignoring valid ones on the estimation, testing and forecasting properties of the bivariate, first-order, vector autoregressive (VAR(1)) model. We first consider nearly cointegrated VARs, that is, stable systems whose largest root, lmax, lies in the neighborhood of unity, while the other root, lmin, is safely smaller than unity. In this context, we define the ,forecast cost of type I' to be the deterioration in the forecasting accuracy of the VAR model due to the imposition of invalid cointegration restrictions. However, there are cases where misspecification arises for the opposite reasons, namely from ignoring cointegration when the true process is, in fact, cointegrated. Such cases can arise when lmax equals unity and lmin is less than but near to unity. The effects of this type of misspecification on forecasting will be referred to as ,forecast cost of type II'. By means of Monte Carlo simulations, we measure both types of forecast cost in actual situations, where the researcher is led (or misled) by the usual unit root tests in choosing the unit root structure of the system. We consider VAR(1) processes driven by i.i.d. Gaussian or GARCH innovations. To distinguish between the effects of nonlinear dependence and those of leptokurtosis, we also consider processes driven by i.i.d. t(2) innovations. The simulation results reveal that the forecast cost of imposing invalid cointegration restrictions is substantial, especially for small samples. On the other hand, the forecast cost of ignoring valid cointegration restrictions is small but not negligible. In all the cases considered, both types of forecast cost increase with the intensity of GARCH effects. Copyright © 2009 John Wiley & Sons, Ltd. [source] Root and canal morphology of maxillary first and second permanent molar teeth in a Ugandan populationINTERNATIONAL ENDODONTIC JOURNAL, Issue 9 2007C. M. Rwenyonyi Abstract Aim, To investigate the root and canal morphology of permanent maxillary molar teeth from a Ugandan population. Methodology, Maxillary first (n = 221) and second molar (n = 221) teeth were collected from patients attending dental clinics in Kampala. Teeth were prepared using a clearing technique: the pulp chambers were accessed and the teeth placed consecutively into 5% sodium hypochlorite, 10% nitric acid, then methyl salicylate. Indian ink was injected into the pulp chambers to demonstrate the canal system. Results, In the first molars, 95.9% of the teeth had separate roots. The mesiobuccal root was fused with the palatal root in 3% of specimens and with the distobuccal root in 0.5% of teeth. In the second molars, 86% of the teeth had separate roots. The mesiobuccal root was fused with the palatal root in 6.3% of specimens and with the distobuccal root in 6.8% of teeth. Apical deltas were more frequent in the mesiobuccal root when compared with distobuccal and palatal roots of both the first and second molars. A type I canal configuration (>75%) was the most frequent in all the roots of both the first and second molars. Canal intercommunications and lateral canals were more frequent in the mesiobuccal root when compared with other roots. Conclusions, The mesiobuccal root tended to have more variations in the canal system followed by the distobuccal root, whereas the palatal root had the least. The findings in root and canal morphology of this Ugandan population were different from previous studies, which may partly be attributed to racial differences. [source] Root competition: beyond resource depletionJOURNAL OF ECOLOGY, Issue 4 2006H. JOCHEN SCHENK Summary 1Root competition is defined as a reduction in the availability of a soil resource to roots that is caused by other roots. Resource availability to competitors can be affected through resource depletion (scramble competition) and by mechanisms that inhibit access of other roots to resources (contest competition, such as allelopathy). 2It has been proposed that soil heterogeneity can cause size-asymmetric root competition. Support for this hypothesis is limited and contradictory, possibly because resource uptake is affected more by the amount and spatial distribution of resource-acquiring organs, relative to the spatial distribution of resources, than by root system size per se. 3Root competition intensity between individual plants generally decreases as resource availability (but not necessarily habitat productivity) increases, but the importance of root competition relative to other factors that structure communities may increase with resource availability. 4Soil organisms play important, and often species-specific, roles in root interactions. 5The findings that some roots can detect other roots, or inert objects, before they are contacted and can distinguish between self and non-self roots create experimental challenges for those attempting to untangle the effects of self/non-self root recognition, self-inhibition and root segregation or proliferation in response to competition. Recent studies suggesting that root competition may represent a ,tragedy-of-the-commons' may have failed to account for this complexity. 6Theories about potential effects of root competition on plant diversity (and vice versa) appear to be ahead of the experimental evidence, with only one study documenting different effects of root competition on plant diversity under different levels of resource availability. 7Roots can interact with their biotic and abiotic environments using a large variety of often species-specific mechanisms, far beyond the traditional view that plants interact mainly through resource depletion. Research on root interactions between exotic invasives and native species holds great promise for a better understanding of the way in which root competition may affect community structure and plant diversity, and may create new insights into coevolution of plants, their competitors and the soil community. [source] Ethylene insensitivity impedes a subset of responses to phosphorus deficiency in tomato and petuniaPLANT CELL & ENVIRONMENT, Issue 12 2008HYE-JI KIM ABSTRACT The role of ethylene in growth and developmental responses to low phosphorus stress was evaluated using ethylene-insensitive ,Never-ripe' (Nr) tomato and etr1 petunia plants. Low phosphorus increased adventitious root formation in ,Pearson' (wild-type) tomato plants, but not in Nr, supporting a role for ethylene in adventitious root development and showing that ethylene is important for this aspect of phosphorus response. Low phosphorus reduced ethylene production by adventitious roots of both genotypes, suggesting that ethylene perception , not production , regulates carbon allocation to adventitious roots at the expense of other roots under low phosphorus stress. With the exception of its effect on adventitious rooting, Nr had positive effects on growth and biomass accumulation in tomato whereas etr1 tended to have negative effects on petunia. This was particularly evident during the recovery from transplanting, when the effective quantum yield of photosystem II of etr1 petunia grown with low phosphorus was significantly lower than ,Mitchell Diploid', suggesting that etr1 petunia plants may undergo more severe post-transplant stress at low phosphorus availability. Our results demonstrate that ethylene mediates adventitious root formation in response to phosphorus stress and plays an important role for quick recovery of plants exposed to multiple environmental stresses, i.e. transplanting and low phosphorus. [source] | |||||||||||||