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Rich Sites (rich + site)
Selected AbstractsEffects of experimental acidification and alkalinization on soil and growth and health of Acer saccharum Marsh.JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 6 2008Rock Ouimet Abstract Experimental application of eight acidifying, neutral, or alkalizer compounds (range: ,16 to 16 kmol ha,1 of acid-neutralizing capacity [ANC]) was realized in two northern hardwood stands having significantly different soil base saturation (BS) (a "poor" and a "rich" site) to assess responses of soil physico-chemical properties, and nutrition, growth, and health of sugar maple (Acer saccharum Marsh.) trees in the short (3 y) and longer term (10 y). The treatments influenced the main indicators of acidity in the forest floor (soil exchangeable-Ca saturation [SCa], BS, exchangeable-acidity saturation [SH+Al], and the SCa/SH+Al ratio) at both sites, their values increasing (decreasing for SH+Al) along the ANC treatment gradient in both the short and longer term, except for pH. Base saturation of the upper 15,cm of the mineral B horizons of soils was influenced at the two sites 10 y after treatment application. Although ANC treatments affected nutrient concentrations of tree foliage in the short term, their effect was no longer detectable after 10 y at the two sites. Growth, however, was strongly related to ANC treatments after 10 y, but only at the poor site. From 1990 to 2000, the basal-area growth rate of trees at the poor site was (mean ± SE) ,0.62 ± 0.28,cm2 y,2 tree,1 for the most negative ANC treatment to +0.90 ± 0.20,cm2 y,2 tree,1 for the most positive ANC treatment. A climatic-stress episode occurring in 1995/96 appeared to accentuate the growth decline of trees subjected to the most negative ANC treatment at the poor site. The experimental results support the hypothesis that atmospheric acid deposition load can cause forest soil base-cation depletion, acidification, and predispose sugar maple to health and growth decline in the longer term in base-cation-poor soils, and that the phenomenon may be reversible by adding alkalizers. [source] Mechanisms of DNA breaks induction in vivo by 5-azacytidine: paths of micronucleus induction by azaCJOURNAL OF APPLIED TOXICOLOGY, Issue 3 2008P. Morales-Ramírez Abstract The aim of the present study was to correlate the time-response curves of micronucleated polychromatic erythrocyte (MN-PCE) induction by 5-azacytidine (azaC) with the possible processes involved in DNA break production; this is based on the results previously published by other authors. The MN-PCE induction at two different doses of azaC was determined by sampling blood from the tails of mice before the acute treatment and over nine periods of 8 h each afterwards. Both doses caused two peaks of MN-PCE induction, one at 32 h and another at 48 h, approximately; a shoulder was detected that remained high from 56 h up to the end of the study (72 h). These results suggest that azaC induced DNA breaks and subsequently MN (micronucleus) by three different mechanisms, and in agreement with data in the literature, these could be successively the following: (i) during excision of the large adduct comprising the DNA methyl transferase covalently linked to DNA; (ii) failure of recombination repair or mismatch repair; and (iii) persistent chromosome fragility in G-C rich sites due to DNA demethylation and chromatin decondensation. Copyright © 2007 John Wiley & Sons, Ltd. [source] Thermally stable porous supramolecular frameworks based on the metal and ,,, stacking directed self-assembly of 2,6-pyridyldicarboxylic acid bis-4-pyridylamideJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2003Juan C. Noveron Abstract We report the formation of two thermally stable supramolecular structures based on 2,6-pyridyldicarboxylic acid bis-4-pyridylamide (PyI) and bis(hexafluoroacetylacetonato)manganese(II) that exhibits a microporous structure with cavities bearing hydrogen bonding motifs that can enclathrate acetone and methanol molecules via well-positioned hydrogen bonding interactions. Single-crystal x-ray diffraction in combination with thermogravimetric analysis and X-ray powder diffraction (XRPD) studies were utilized to study the structure and thermal behavior of trans -[Mn(hfacac)2(PyI)2]·2(CH3)2CO (1) and trans -[Mn(hfacac)2(PyI)2]·2CH3OH (2). Our studies indicated that 1 and 2 are isostructural with respect to their supramolecular assembly and trap solvent molecules along the crystallographic b direction via the inwardly directed hydrogen bonding motifs of the PyI component. These solvent molecules can be thermally removed to generate a crystalline material with micropores bearing hydrogen bonding rich sites within an overall supramolecular matrix similar to 1 and 2. The removal of the guest solvent molecules is reversible and can be followed with XRPD. Copyright © 2003 John Wiley & Sons, Ltd. [source] Stress tolerance abilities and competitive responses in a watering and fertilization field experimentJOURNAL OF VEGETATION SCIENCE, Issue 6 2005P. Liancourt Abstract Question: Do water gradients produce patterns of responses to stress and competition similar to those induced by nutrient gradients? Location: French Alps. Methods: We established a split-plot design in a calcareous grassland, with watering and fertilization as main plot treatments and competition as subplot treatment. We followed individual and competitive responses of transplants of the three potential dominant grass species: Bromus erectus, Brachypodium rupestre and Arrhenatherum elatius, in all plots during two growing seasons. Changes in natural relative abundances of the three grass species were also monitored. Results: The growth and the relative abundance of A. elatius were primarily stimulated by nutrient addition and those of B. rupestre by water addition, whereas B. erectus decreased in abundance and had a very low flexibility with enhanced resource supply. Competition intensity increased for all species with both watering and fertilization and the ranking in competitive responses did not change with treatments: A. elatius > B. rupestre > B. erectus. Conclusions: Patterns of dominance were efficiently explained by stress tolerance abilities and competitive responses for dry and poor sites, and wet and rich sites for B. erectus and A. elatius respectively, whereas competitive responses were poor predictors of dominance for B. rupestre in wet and nutrient-poor sites. Further studies are needed to assess the potential role of other processes, such as increasing competitive effect on light with increasing age as well as interference, to explain the dominance of this conservative competitor type of species in wet and nutrient-poor sites. [source] | |||||||||||||