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Mg Concentrations (mg + concentration)
Selected AbstractsSeasonal records of climatic change in annually laminated tufas: short review and future prospects,JOURNAL OF QUATERNARY SCIENCE, Issue 5 2005J. E. Andrews Abstract Many Recent and fossil freshwater tufa stromatolites contain millimetre-scale, alternating laminae of dense micrite and more porous or sparry crystalline calcites. These alternating laminae have been interpreted to represent seasonally controlled differences in the biotic activity of microbes, and/or seasonally controlled changes in the rate of calcification. Either way, couplets of these microbially mediated alternating calcified laminae are generally agreed to represent annual seasonality. Combined stable isotope (,18O and ,13C) and trace element (Mg, Sr, Ba) geochemistry from Recent tufa stromatolites show that seasonal climatic information is available from these calcites. Variability in ,18O (and in one case Mg concentration) has been shown to be controlled primarily by stream temperature change, usually driven by solar insolation. In arid climates, seasonal evaporation can also cause ,18O enrichment by at least 1,. Variability in ,13C results potentially from: (1) seasonal change in plant uptake of 12C-enriched CO2; (2) seasonal change in degassing of 12C-enriched CO2 in the aquifer system; and (3) precipitation of calcite along the aquifer or river flow path, a process that increases ,13C of dissolved inorganic carbon (DIC) in the remaining water. Mechanisms 2 and 3 are linked because calcite precipitates in aquifers where degassing occurs, e.g. air pockets. The latter mechanism for ,13C enrichment has also been shown to cause sympathetic variation between trace element/Ca ratios and ,13C because trace elements with partition coefficients much greater than 1 (e.g. Sr, Ba) remain preferentially in solution. Since degassing in air pockets will be enhanced during decreased recharge when water saturation of the aquifer is lowest, sympathetic variation in trace element/Ca ratios and ,13C is a possible index of recharge and therefore precipitation intensity. High-resolution geochemical data from well-dated tufa stromatolites have great potential for Quaternary palaeoclimate reconstructions, possibly allowing recovery of annual seasonal climatic information including water temperature variation and change in rainfall intensity. However, careful consideration of diagenetic effects, particularly aggrading neomorphism, needs to be the next step. Copyright © 2005 John Wiley & Sons, Ltd. [source] Growth and Hematological Changes of Rockfish, Sebastes schlegeli (Hilgendorf) Exposed to Dietary Cu and CdJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 2 2005Ju-Chan Kang Cd and Cu toxicological effect on growth and hematological parameters was investigated in juvenile rockfish Sebasres schlegeli after sub-chronic dietary Cd (0, 0.5, 5, 25, and 125 mg/kg) and Cu exposure (0, 50, 125, 250, and 500 mg/kg) for 60 d. In the experiment of dietary Cd exposure, weight and length SGR of the rockfish were significantly different from control, and a significant inverse relationship was observed between weight gain and the exposure concentration of dietary Cd at 25, 125 mg/kg (P > 0.05). Hematwrit and hemoglobin decreased significantly and were dose dependently in all Cd exposure. Glucose in serum was also increased significantly (P < 0.05). The concentration of total protein in serum was significantly lower than control at 5, 25, and 125 mgkg. No differences were observed in serum calcium concentration. Magnesium concentration in serum was increased signillcantly with dietary Cd concentration. In the experiment of dietary Cu exposure, Cu was inhibited weight gain and growth rate. No differences were observed in hematocrit, hemoglobin and RBCs compared to control. Contents of total protein, glucose, and Ca in serum remained stable. Mg concentration in serum was increased significantly at 500 mg/kg. [source] Nitride-based quantum structures and devices on modified GaN substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Piotr Perlin Abstract We have studied the properties of InGaN layers and quantum wells grown on gallium nitride substrates with intentional surface misorientation with respect to its crystalline c -axis. Misorientation varied in the range from 0 up to 2 degree. The indium content was changed by using the different growth temperature (between 750 °C and 820 °C) during metalorganic vapor phase epitaxy. With increasing misorientation angle the average indium content decreased significantly. This effect was accompanied by the strong increase of the emission line bandwidth suggesting more pronounced indium segregation. The results of cathodoluminescence measurements show that these effects correspond to different number of atomic steps/terraces existing on the surface of gallium nitride substrate. Very interesting result is also demonstrated concerning p-type GaN layers. With increasing misorientation, the free hole density drastically increases above 1018 cm,3. This improvement in p-type doping is not related to the increased Mg concentration but to the reduction in the compensating donor density. Using this advantage we demonstrate nitride light emitters with improved electrical properties. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mg-doped AlGaN grown on an AlN/sapphire template by metalorganic chemical vapour depositionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2006Hongbo Yu Abstract The growth of high-performance Mg-doped p-type AlxGa1,xN (x = 0.35) layers using low-pressure metalorganic chemical vapour deposition on an AlN/sapphire template is reported. The influence of growth conditions on the p-type conductivity of the AlxGa1,xN (x = 0.35) alloy was investigated. It was found that the p-type resistivity of the AlGaN alloy demonstrates a marked dependence on the Mg concentration, V/III ratio and group III element flow rate. A minimum p-type resistivity of 3.5 , cm for AlxGa1,xN (x = 0.35) epilayers was achieved. A Ni/Au (10 nm/100 nm) ohmic contact was also fabricated and a specific contact resistivity of 8.1 × 10,2 , cm2 was measured. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of Mg fluctuation on the electrical and optical properties in p-GaN/undoped GaN layers dependent on the growth temperaturePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003C. S. Kim Abstract The effects of heavly Mg doping dependent on the growth temperature of p-GaN layers grown on undoped GaN layers by metalorganic chemical vapor deposition (MOCVD) on electrical and optical properties were studied by capacitance,voltage (C,V) and temperature-dependent photoluminescence (TDPL), respectively. At high growth temperature of p-GaN above 1110 °C, optical microscopy images as well as atomic force microscopy (AFM) images show polygonal hillocks on heavily Mg-doped GaN surface. It was also found that fluctuation of Mg concentration ([Mg]) measured by secondary ion mass spectroscopy (SIMS) was increased with increasing growth temperature. These phenomena were appeared to decrease NA,ND and change PL emission from 3.1,3.2 eV of conduction band-to-shallow Mg acceptor (e, A) transition to 2.8,2.9 eV of Mg-related deep donor-to-acceptor pair (DAP) transition. [source] Effects of salt stress on purslane (Portulaca oleracea) nutritionANNALS OF APPLIED BIOLOGY, Issue 1 2009M. Teixeira Abstract The objective of this study was to determine the influence of saline stress on the chemical composition of purslane (Portulaca oleracea), in particular the mineral composition. Four salinity levels were investigated using irrigation solutions with electrical conductivity values of 0.8, 6.8, 12.8 and 24.2 dS m,1 and two planting dates (May and July) were tested. Samples of full-grown leaf and stems of purslane were harvested after 7 and 15 days of the saline treatment exposure. Chemical analysis (dry matter basis) of leaves showed significant differences among the different saline treatments for all the characteristics measured. Salinity levels, planting date and harvest time significantly influenced (P < 0.05) the levels of crude protein, total lipids, ash and carbohydrate content. Salinity treatments did not significantly (P > 0.05) affect the water content of purslane leaves. The crude protein content of purslane leaves decreased with increasing salinity levels and time of exposure to treatment. However, carbohydrates and mineral residue content increased. An unusual phenomenon was noted for intermediate salinity levels, whereby an increase in total lipid content was measured in leaves of plants exposed to salinity treatments of 6.8 and 12.8 dS m,1. The highest mineral residue content was seen in leaves of purslane exposed to the highest salinity treatment. The mineral composition was also affected by salinity levels, Na and Cl uptake, and accumulation increased with increasing salinity in irrigation solution; Mg concentration was not significantly (P > 0.05) affected by salinity levels, although a slight increase was seen, and Ca, K and Zn levels significantly (P < 0.05) decreased. Ca and Zn preferentially accumulated in the leaves, while K and Na values were higher in the stems. A significant increase (P < 0.05) in relative ratio of Na/K, Mg/K, Na/Ca and Mg/Ca was observed with increasing salinity levels. A decrease in the yield of purslane was only observed for the most severe saline treatment, where the highest ratio of Mg/Ca was seen. This study reveals that purslane is relatively tolerant to conditions of moderate salinity, thus improving its potential to become a key vegetable crop for animal and human consumption. [source] Dietary magnesium did not affect calcium and phosphorus content in juvenile grouper, Epinephelus coioidesAQUACULTURE NUTRITION, Issue 4 2010C.-X. YE Abstract Most of magnesium (Mg) in fish is located in the bone. Dietary calcium (Ca) and phosphorous (P) has been reported to affect scales and vertebrae Mg dramatically in juvenile grouper, but the effect of dietary Mg on tissue Ca and P is unknown. This study was conducted to investigate the effect of dietary Mg supplement on growth, feed efficiency, morphometry, and the ash and Ca, P, sodium (Na) content in scales and vertebrae of juvenile grouper. Seven experimental diets were formulated to contain graded levels of Mg by supplementing the basal diet with 0, 200, 400, 600, 800, 1000 and 2000 mg kg,1 Mg in the form of Mg sulphate (MgSO4·7H2O). Juvenile grouper with an initial body weight of 11.8 ± 0.1 g were fed to apparent satiation twice per day for 10 weeks. Dietary Mg supplement had no significant effect on growth, feed efficiency, and Mg concentration in scales and vertebrae of grouper, which indicates the Mg requirement of grouper was met in fish fed the basal diet. Mg supplements had significant effect on morphometry index such as body length, condition factor, viscera somatic index and mesenteric fat index. Extra dietary Mg supplement to the basal diet had no negative effect on ash, Ca and P concentrations in scales and vertebrae. [source] Growth and photorefractive properties of Mg:Ce:Cu:LiNbO3 crystals grown by Czochralski methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2006Y. X. Fan Abstract In this paper, photorefractive properties of Mg:Ce:Cu:LiNbO3 crystals were studied. The crystals doped with different concentration of Mg ions have been grown by the Czochralski method. Mg concentrations in grown crystals were analyzed by an inductively coupled plasma optical emission spectrometry (ICP-OE/MS). The crystal structures were analyzed by the X-ray powder diffraction (XRD), ultraviolet-visible (UV-Vis) absorption spectra and infrared (IR) transmitatance spectra. The photorefractive properties of crystals were experimentally studied by using two-beam coupling. In this experiment we determined the writing time, maximum diffraction efficiency and the erasure time of crystals samples with He-Ne laser. The results showed that the dynamic range (M/#), sensitivity (S) and diffraction efficiency (,) were dependent on the Mg doping concentration, and the Mg(4.58mol%):Ce:Cu:LiNbO3 crystal was the most proper holographic recording media material among the six crystals studied in the paper. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nitrogen, Phosphorus, Potassium, Magnesium and Calcium Removal by Brown Midrib Sorghum Sudangrass in the Northeastern USAJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 6 2006Q. M. Ketterings Abstract For the long-term sustainability of the dairy industry in the Northeastern USA, manure nutrient application rates should not exceed crop nutrient removal once above-optimum soil fertility levels are reached. Dairy producers have shown a growing interest in brown midrib (BMR) forage sorghum (Sorghum bicolor (L.) Moench.) × sudangrass (Sorghum sudanense Piper) hybrids (S × S) as a more environmentally sound alternative to maize (Zea mays L.) but data on S × S nutrient removal rates are scant. Our objectives were to determine N, P, K, Ca and Mg removal with harvest as impacted by N application rate, using six N rate studies in New York. One of the six sites had a recent manure history. Although site-to-site differences existed, N application tended to decrease P and K and increase N, Ca and Mg concentrations in BMR S × S forage. Nutrient removal and yield were highly correlated for all sites except one location that showed a K deficiency. The crop removed large amounts of P and K in the manured site, suggesting that BMR S × S is an excellent scavenger of these nutrients. If manure is applied mid-season, forage K levels are likely too high for feeding to non-lactating cows. [source] Effects of chromium stress on the subcellular distribution and chemical form of Ca, Mg, Fe, and Zn in two rice genotypesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2010Fanrong Zeng Abstract A hydroponic experiment was carried out to study effects of chromium (Cr) stress on the subcellular distribution and chemical form of Ca, Mg, Fe, and Zn in two rice genotypes differing in Cr accumulation. The results showed that Ca, Mg, Fe, and Zn ions were mainly located in cell walls and vacuoles in roots. However, large amounts of metal ions were transferred from the vacuole to the nucleus and to other functional organelles in shoots. Chromium concentrations in the nutrient solution of 50 ,M and above significantly decreased Ca concentrations in the chloroplast/trophoplast, the nucleus, and in mitochondria. It further increased Mg concentrations in the nucleus and in mitochondria, as well as Zn and Fe concentrations in the chloroplast/trophoplast. These Cr-induced changes in ion concentrations were associated with a significant reduction in plant biomass. It is suggested that Cr stress interferes with the functions of mineral nutrients in rice plants, thus causing a serious inhibition of plant growth. The chemical forms of the four nutrients were determined by successive extraction. Except for Ca, which was mainly chelated with insoluble phosphate and oxalic acid, Mg, Zn, and Fe were extractable by 80% ethanol, d-H2O, and 1,M NaCl. The results indicated that these low,molecular weight compounds, such as organic acids and amino acids, may play an important role in deposition and translocation of Mg, Zn, and Fe in the xylem system of rice plants. [source] Raman spectroscopy of synthetic, geological and biological vaterite: a Raman spectroscopic studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2010U. Wehrmeister Abstract Raman spectroscopy was used to study vaterite samples of biological, geological and synthetic origin. The Raman band positions and the full width at half-maximum (FWHM) of the lattice modes and the internal modes of the carbonate ion of all specimens show no significant differences between vaterites of different origin. With increasing Mg concentrations, synthetic vaterite samples show increasing FWHM in the region of the lattice modes and the three ,1 bands, whereas no change in luminescence was detected. In contrast, in situ measurements of vaterite areas in freshwater cultured pearls (FWCPs) by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) together with the Raman spectra obtained at the same points show that the luminescence intensity in biological samples is affected by the magnesium content. The Raman spectroscopic features of vaterite and parisite-(Ce) are compared, and their similarities suggest that the structure of vaterite contains at least three crystallographically independent carbonate groups and similar carbonate group layers. A band at 263 cm,1 is observed for the first time in this study, whereas it could be demonstrated that bands previously reported at 130 and 190 cm,1 do not belong to vaterite. Copyright © 2009 John Wiley & Sons, Ltd. [source] Low oxygen treatment prior to cold storage decreases the incidence of bitter pit in ,Golden Reinders' applesJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2010Jesús Val Abstract BACKGROUND: The effect of subjecting ,Golden Reinders' apples to a low O2 pre-treatment (LOT; 1,2% O2) was evaluated as a strategy to decrease the rate of bitter pit (BP) incidence after standard cold storage (ST). Immediately after harvest, apples were stored for 10 days at 20 °C under low O2. Thereafter, apples were cold-stored (0,4 °C) for 4 months and changes were monitored in terms of BP incidence, fruit quality traits and mineral element concentrations. RESULTS: After 4 months cold storage, LOT apples presented a 2.6-fold decrease in the rate of BP incidence (14%) versus the values obtained for standard cold-stored fruits (37% BP incidence). LOT increased flesh firmness, total soluble solids and titratable acidity as compared to the quality traits determined for cold-stored fruits. Lower cortex Ca and Mg concentrations as compared to ST apples were determined in association with LOT, 2 months after cold storage. CONCLUSION: Application of a LOT prior to cold storage may be a promising strategy to reduce the incidence of BP and preserve fruit quality, which should be further investigated. Copyright © 2009 Society of Chemical Industry [source] Essential elements and contaminants in tissues of commercial pelagic fish from the Eastern Mediterranean SeaJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 9 2009Beyza Ersoy Abstract BACKGROUND: It is important to determine the concentrations of essential and non-essential metals in fish for human health. The essential elements and contaminants (Pb and Cd) were determined seasonally in the muscle and liver of some pelagic fish species round herring (Etrumeus teres), chub mackerel (Scomber japonicus), golden grey mullet (Liza aurata) and Mediterranean horse mackerel (Trachurus mediterraneus) from the Iskenderun Bay, Eastern Mediterranean Sea. RESULTS: The Na, K, Ca and Mg were the most abundant elements in muscle and liver tissues. The Na, K, Ca and Mg concentrations in fish tissues were between 51.7 and 3426 mg kg,1. Muscle accumulated the lowest levels of elements. Trace element and contaminant levels in muscle were highest in spring and summer. The Cu, Zn and Cr concentrations were highest in summer. The Ni, Mn and Fe concentrations were highest in spring. The maximum Pb concentrations in the muscle and liver of fish species was 0.39 and 0.80 mg kg,1 in autumn. The maximum Cd concentration in the muscle of fish was 0.27 mg kg,1 in spring and the maximum Cd concentration in the liver was 0.78 mg kg,1 in summer. CONCLUSION: The Cr, Pb, Cd, Cu and Zn levels in muscle were found to be lower than permissible limits reported by various authorities. Estimated weekly and daily intake for Pb and Cd by consumption of fish muscle were far below the PTWI and PTDI values established by FAO/WHO. Copyright © 2009 Society of Chemical Industry [source] Fruit quality of mini-watermelon as affected by grafting and irrigation regimesJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 6 2008Simona Proietti Abstract BACKGROUND: The Mediterranean region suffers water deficit that affects fruit yield and quality. Grafting improves crop tolerance to disease and drought, but the taste and quality of fruit may be negatively affected. The aim of the present work was to determine the quality parameters of mini-watermelon, ungrafted or grafted onto a squash hybrid rootstock, and grown under different irrigation regimes: 1.0, 0.75, and 0.5 of evapotranspiration (ET) rates. RESULTS: The interaction between grafting and irrigation rate was not significant for the variables tested. The highest fruit yields were recorded at 1.0 ET and at 0.75 ET with respect to 0.5 ET, and they were obtained in grafted plants. Fruit quality was slightly affected by drought, with an increase in K, Mg and spermine concentrations, especially with 0.5 ET. Nitrate concentration in the watermelon pulp was very low (average 10 mg kg,1 fresh weight). Fruit quality parameters were similar in grafted and ungrafted plants, whereas the titratable acidity (TA), juice electrical conductivity, TSS/TA ratio, K and Mg concentrations were improved in the grafted one. Lycopene, dehydroascorbate (DAscA) and total vitamin C contents for grafted plants were higher by 40.5%, 13% and 7.3%, respectively, than those from ungrafted plants. Spermidine and putrescine concentrations were reduced by grafting (by 24% and 59%, respectively). CONCLUSION: Grafting of mini-watermelon under irrigation deficit did not modify crop response to water availability, but increased productivity and induced small positive changes in plant quality and nutritional value. Copyright © 2008 Society of Chemical Industry [source] Mg in GaN: the structure of the acceptor and the electrical activityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2003H. Alves Abstract We investigated GaN and AlGaN grown by metal organic chemical vapour deposition (MOCVD) and molecular beam epitaxy (MBE) doped with different Mg concentrations by photoluminescence Hall-effect and SIMS measurements. Optically detected magnetic resonance (ODMR) experiments were used to study the structure of the Mg-acceptors. The ODMR experiments reveal that the spin-density of the hole is equally distributed on the four nearst Nitrogen neighbors. Structural variations observed for Mg in MOCVD material are explained in terms of crystalfield variations caused by potential fluctuations due to the presence of compensating donors. Especially for highly doped MOCVD samples saturation of the free hole concentration and a strong 2.9 eV recombination are observed. Considering that compensating donors like nitrogen vacancies hydrogen and complexes of both form during growth we are able to calculate the experimental determined free hole concentrations. In MOCVD samples codoped with Mg and Si a decrease of the acceptor binding energy with increasing donor concentration was observed. The effect is caused by Coulomb interaction between the ionized acceptors and the free holes. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Local vibrational modes and compensation effects in Mg-doped GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2003A. Hoffmann Abstract The compensation and self-compensation effects in Mg-doped GaN is studied by low-temperature photoluminescence and Raman spectroscopy using a series of samples with different Mg concentrations. Strongly doped samples are found to be highly compensated in electrical measurement. The compensation mechanism is directly related to the incorporation of Mg leading to the additional formation of three different deep donor levels. Furthermore, hydrogen forms defect complexes with Mg and compensates the acceptor states. These complexes were observed as local vibrational modes in Raman spectra in the range of 2200 cm,1. The direct incorporation of Mg can be controlled by local vibrational modes in the region of GaN host phonons. Investigating the intensity dependence of the different Mg,H complexes and the LVM of activated Mg the Raman spectra give a clear direct evidence of the degree of compensation and p-conductivity. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Atomic layer deposition of Zn1,xMgxO buffer layers for Cu(In,Ga)Se2 solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2007T. Törndahl Abstract Fabrication of Zn1,xMgxO films by atomic layer deposition (ALD) has been studied for use as buffer layers in Cu(In,Ga)Se2 (CIGS)-based solar cell devices. The Zn1,xMgxO films were grown using diethyl zinc, bis-cyclopentadienyl magnesium and water as precursors in the temperature range from 105 to 180°C. Single-phase ZnO-like films were obtained for x,<,0·2, followed by a two phase region of ZnO- and MgO-like structures for higher Mg concentrations. Increasing optical band gaps of up to above 3·8,eV were obtained for Zn1,xMgxO with increasing x. It was found that the composition of the Zn1,xMgxO films varied as an effect of deposition temperature as well as by increasing the relative amount of magnesium precursor pulses during film growth. Completely Cd-free CIGS-based solar cells devices with ALD-Zn1,xMgxO buffer layers were fabricated and showed efficiencies of up to 14·1%, which was higher than that of the CdS references. Copyright © 2006 John Wiley & Sons, Ltd. [source] Leaf Litter Decomposition and Monodominance in the Peltogyne Forest of Marací Island, Brazil1BIOTROPICA, Issue 3 2002Dora M. Villela ABSTRACT The forest type dominated by Peltogyne gracilipes (Caesalpiniaceae) on the riverine Marací Island is the least speciesrich of any recorded for Brazilian Amazonia. Because the forest has high soil and foliar Mg concentrations, and Mg is known to be toxic to plant growth at high concentrations, this study tested the hypothesis that dominance by Peltogyne is related to Mg leaf litter amounts and decomposition. We predicted that decomposition of Peltogyne leaves would differ from that of other species, and that their decomposition would result in a pulse of Mg release. Three plots (50 × 50 m) were established in each of three forest types: Peltogyne -rich forest (PRF; dominated by P. gracilipes),Peltogyne-poor forest (PPF), and forest without Peltogyne (FWP). Three leaf litter decomposition experiments tested if decomposition of mixed leaf litter in coarse- mesh (CM) litterbags differed among forests (experiment 1); whether or not decomposition and nutrient release of Ecclinusa guianensis, Lueheopsis duckeana, and Peltogyne in CM litterbags differed among forests and species (experiment 2); and using fine-mesh (FM) litterbags, investigated the differences in the influence of fauna! activity on Ecclinusa and Peltogyne decomposition (experiment 3). Decomposition was independent of the presence and dominance of Peltogyne, since decomposition rates in both PRF and FWP were in general lower than in PPF. These differences appeared to be related to fauna] activity. The decomposition of Peltogyne leaves was lower than that of the other species tested and was more affected by microbial and physical action. It is possible that the monodominance of Peltogyne is related to its deciduousness and faster decomposition in the dry season, which coincides with a large leaf fall. Magnesium was lost quickly from the Peltogyne leaves and the resultant pulses of Mg into the soil during the heavy rains at the beginning of the wet season may be deleterious for other species that are not adapted to high solution Mg concentrations. Results obtained were consistent with the hypothesis that Peltogyne dominance is related to the pattern of its leaf decomposition and the seasonal pulses of toxic Mg. RESUMO A floresta dominada por Peltogyne gracilipes (Caesalpiniaceae) na Ilha fluvial de Maracáé a mais pobre em espécies reportada para a Amazõnia brasileira. Devido a esta floresta possuir altas concentra¸ões de Mg no solo e nas folhas, e pelo fato de Mg ser conhecidamente tóxico para o crescimento das plantas quando em altas concentra¸ões, este estudo testou a hipótese de que a dominãncia de Peltogyne está relacionada com as quantidades de Mg e com a decomposi¸ão das folhas da serrapilheira. Esperou-se encontrar um padrão de decomposi¸ão diferente para folhas de Peltogyne, e que as folhas de Peltogyne apresentassem um pulso de libera¸ão de Mg. Três parcelas (50 × 50 m) foram estabelecidas em cada um dos três tipos florestais: floresta rica em Peltogyne (PRF; dominada por P. gracilipes), floresta pobre em Peltogyne (PPF) e floresta sem Peltogyne (FWP). Três experimentos de decomposi¸ão de folhas da serrapilheira testaram se a decomposi¸ão de folhas mistas da serrapilheira em sacos de serrapilheira de malha grossa (CM) difere entre florestas (experimento 1), se a decomposi¸ão e a libera¸ão de nutrientes de Ecclinusa guianensis, Lueheopsis duckeana, e Peltogyne em sacos de serrapilheira CM difere entre florestas e entre espécies (experimento 2), e usou sacos de serrapilheira de malha fina (FM) para investigar as diferen¸as na influência da atividade da fauna na decomposi¸ão de Ecclinusa e Peltogyne (experimento 3). A decomposi¸ão foi independente da presen¸a e dominãncia de Peltogyne, já que as taxas de decomposi¸ão em PRF e FWP foram em geral menores que em PPF. Estas diferencas parecem estar relacionadas à atividade da fauna. A decomposi¸ão de folhas de Peltogyne foi menor que a das demais espécies testadas e foi mais afetada pela a¸ão microbiológica e flsica. é possível que a dominãncia de Peltogyne esteja relacionada com a sua deciduidade e com a rápida decomposi¸ão na esta¸ão seca, a qual coincide com uma grande queda de folhas. Magnésio foi perdido rapidamente das folhas de Peltogyne e os pulsos resultantes de Mg no solo durante as fortes chuvas no início da esta¸ão chuvosa podem ser deletérios para outras espécies que não estão adaptadas as altas concentra¸ões deste íon. Os resultados obtidos foram consistentes com a hipótese de que a dominãncia de Peltogyne está relacionada com o padrão de decomposi¸ão de suas folhas e com os pulsos sazonais de Mg tóxico. [source] | |||||||||||||||||||