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1.
Stevens  D.P.  McLaughlin  M.J.  Alston  A.M. 《Plant and Soil》1997,192(1):81-93
Avena sativa (oats) and Lycopersiconesculentum (tomatoes) were grown in dilute nutrientsolutions supplemented with Al only, F only or acombination of both. In solutions containing Al andF, shoot growth was limited when predicted Alr(Al3+, AlOH2+ and Al(OH) )activities were < 0.1 M, activities three orders ofmagnitude lower than the critical value determinedwith Al only. The data suggest that at the activitiesused in these experiments, Alr is most toxic,AlF2+ and AlF are toxic to a lesserextent, and AlF3, AlF and F-are least toxic. Fluoride concentrations in shootsgrown in solutions correlated best with positivelycharged AlF species (i.e.AlF2+, AlF ) and the molar ratio ofF:Al in most plants shoots was about 3:2. However,when activities of positively chargedAlF species were low (< 50 M)and theactivity of AlF3 species high (500 M) the molarratio of F:Al in plant shoots suggested AlF3 wastaken up. These findings are discussed in relation toplant uptake and toxicity. Measured concentrations of Alr and F- insolutions containing Al and F were compared withconcentrations predicted by a computer model(GEOCHEM-PC). The method for measuring F-concentrations, using a non-complexing buffer and Fion-selective electrode, gave good agreement withpredicted F- concentrations. The8-hydroxyquinoline method for measuring Alrconcentrations did not agree with predictedconcentrations, highlighting the limitations of thismethod when measuring Alr in the presence of F ina multi-ligand system with high concentrations of Fand Al.  相似文献   

2.
Models of the effects of atmosphericN deposition in forested watersheds have notadequately accounted for the effects of aquatic andnear-stream processes on the concentrations and loadsof NO in surface waters. This studycompared the relative effects of aquatic andnear-stream processes with those from the terrestrialecosystem on the retention and transport ofNO in two contrasting stream reaches ofthe Neversink River, a forested watershed in theCatskill Mountains of New York that receives among thehighest load of atmospheric N deposition in thenortheastern United States. Stream water samples werecollected every two hours and ground-water andtributary samples were collected daily at base flowconditions during four 48-hour periods from April toOctober 1992, and NO mass balances werecalculated for each site. Results indicated diurnalvariations in stream NO concentrations inboth reaches during all four sampling periods; this isconsistent with uptake of NO byphotoautotrophs during daylight hours. Mass-balanceresults revealed significant stream reach losses ofNO at both sites during all samplingperiods. The diurnal variations in NO concentrations and the retention of NO relative to terrestrial contributions to the streamreaches were greater downstream than upstream becausephysical factors such as the head gradients ofinflowing ground water and the organic matter contentof sediment are more favorable to uptake anddenitrification downstream. The mass retention ofNO increased as the mean 48-hr streamdischarge increased at each site, indicating that theresponsible processes are dependent onNO supply. Low stream temperatures duringthe April sampling period, however, probably reducedthe rate of retention processes, resulting in smallerlosses of NO than predicted from streamdischarge alone. Water samples collected from thestream, the hyporheic zone, and the alluvial groundwater at sites in both reaches indicated that the neteffect of hyporheic processes on downstreamNO transport ranged from conservativemixing to complete removal by denitrification. Therelative effects of biological uptake anddenitrification as retention mechanisms could not bequantified, but the results indicate that bothprocesses are significant. These results generallyconfirm that aquatic and near-stream processes causesignificant losses of NO in the NeversinkRiver, and that the losses by these processes atdownstream locations can exceed the NO contributions to the stream from the terrestrialenvironment during summer and fall base-flowconditions. Failure to consider these aquatic andnear-stream processes in models of watershed responseto atmospheric N deposition could result inunderestimates of the amount of NO leaching from forested ecosystems and to an inabilityto unequivocally relate geographic differences inNO concentrations of stream waters tocorresponding differences in terrestrial processes.  相似文献   

3.
Carvalho  M.C.S.  van Raij  B. 《Plant and Soil》1997,192(1):37-48
The chemical barrier to root development existing in the subsoils of acid soils is a subject of increasing interest. In order to better understand the factors involved in the amelioration of subsoil acidity, the effects of calcium sulphate, phosphogypsum and calcium carbonate on the properties of the solid and liquid phases of subsoil samples and on the growth and nutrient uptake by maize (Zea mays L.) were evaluated. The soils used were two alic red-yellow latosols, two acric dusky red latosols and one alic dark-red latosol from the State of São Paulo, Brazil. A vertical split-root technique was used in a greenhouse experiment, with the plants initially grown in a small pot with 130 g fertile soil, which was introduced in a larger pot containing 2 dm3 of the subsoil samples. The treatments consisted of a control (C) and applications of calcium carbonate (CC), calcium sulphate (CS) and phosphogypsum (PG) at the rate of 10 mmolc Ca2+ dm-3. CS and PG reduced soil acidity, but in a much smaller proportion than CC. Calcium carbonate reduced the activity of Al3+ because of the increase in pH. Total aluminum and calcium contents in the soil solution were much higher for the red-yellow latosols than for the other soils, indicating lower sorption of Ca2+ and in these soils. The activity of Al in the soil solution was decreased in different ways for the five soils, depending on the ionic strength and the formation of the ionic pair and, in the case of PG, the formation of complexes of Al with F (AlF2+, and ). The subsoil samples presented severe restrictions for maize root growth and all three treatments were equally effective in increasing root development, which could be attributed to the supply of calcium in one of the acric dusky red latosols and a combined effect of the amendment in reducing the activity of Al and increasing the activity of Ca in the soil solution in the other soils. As a consequence the three treatments increased in the same manner water, N and K uptake from the subsoil and the dry matter production of maize. It can be concluded that, for the soils considered in this research, phosphogypsum is an effective amendment for acid subsoils containing low calcium or toxic aluminum contents.  相似文献   

4.
Regulation of mineral nitrogen uptake in plants   总被引:15,自引:0,他引:15  
In the biosphere plants are exposed to different forms of N, which comprise mineral and organic N forms in soils as well as gaseous NH3, NOx, and molecular N2 in the atmosphere. The form of N uptake is mainly determined by its abundance and accessibility, which make and the most important N forms for plant nutrition under agricultural conditions. With minor importance, the form of N uptake is also subject to plant preferences, by which plants maintain their cation/anion balance during uptake. However, some species seem to have an obligatory preference which even prevents their growth on certain other N sources. In general, uptake of a certain N form closely matches the growth-related demand of the plant, at least when N transport to the root surface is not limiting. In addition, many plants accumulate large pools of N during vegetative growth which are remobilized in the generative stage. As a consequence, systems responsible for N transport need to be tightly regulated in their expression and activity upon sensing N availability and plant demand. Employing the tools of molecular genetics, the first plant genes encoding transporters for inorganic N have recently been isolated and characterized. These data can now complete the wealth of physiological and nutritional studies on N uptake. The present article will focus on the uptake of and into root cells and tries to link data derived from physiological, genetic and molecular studies.  相似文献   

5.
Priha  O.  Lehto  T.  Smolander  A. 《Plant and Soil》1999,206(2):191-204
Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) seedlings were grown in a greenhouse for four months in three different soils. The soils were from a field afforestation site on former agricultural land: soil from a pine site, soil from a spruce site and soil from a birch site. Pots without seedlings were included. The aim was to discover, independent of the effects of the different quality of aboveground litter and microclimate under the tree species, whether the roots change the microbial activities and chemical characteristics of the soil, whether the changes are dependent on the tree species, and whether the changes vary in different soils. Pine, spruce and birch had, on average, five, one and six meters of roots, respectively. Birch had by far the highest number of short root tips, on average 11 450 per seedling, compared to 1900 and 450 in pine and spruce seedlings, respectively. The majority of the short roots of pine and spruce were brown sheathed mycorrhizas, and those of birch were mycorrhizas in an early stage of development. The seedlings caused no major changes in either the soil pH or the concentrations of nutrients in the soils, but did affect the microbial characteristics of the soils. The effect of the tree species did not differ in different soils. Microbial biomass C and N, C mineralization rate and the concentration of ergosterol were all higher under birch and pine than under spruce and in plantless soils. Nitrate concentrations were lowest under pine and birch, but rates of net N mineralization, nitrification and denitrification did not differ under different seedlings. The stimulative effect of pine and especially birch on soil microbes was possibly due to them having more roots and releasing more root exudates to soil. There were, however, indications that not only the length/mass of roots determined the changes in microbial activities, but also differences in root activities per unit of root or in the quality of root exudates.  相似文献   

6.
Voigt  P.W.  Godwin  H.W.  Morris  D.R. 《Plant and Soil》1998,205(1):51-56
White clover (Trifolium repens L.) is widely distributed in the Appalachian region, except on highly acid soils. We used a procedure where a thin layer of soil is placed on top of solidified water agar to characterize effects of acid soil on seedling root growth. Our objectives were to evaluate the soil-on-agar technique by using four soils (non-limed and limed) with diverse chemical characteristics and to relate root emergence to the chemical properties of the soils. We used three white clover cultivars, Grasslands Huia, Grasslands Tahora and Sacramento. Daily counts of root emergence from soil into agar were made for 12 d. Liming hastened white clover root emergence in three of the four soils. Days to 40% emergence were closely related (P < 0.01) to soil pH and to species of soil solution Al that are associated with Al toxicity in dicotyledonous plants. The r2 values for the regression of days to 40% root emergence on were 0.95, 0.96, 0.94 and 0.96, respectively. Apparently, the primary factor responsible for delayed root emergence in the soil-on-agar procedure was Al toxicity. Because of the close relationship between root emergence and activity of toxic species of soil solution Al, we propose that the soil-on-agar technique should be useful for characterizing the response of many small-seeded species to Al.  相似文献   

7.
The role of litter tannins in controlling soil nitrogen (N) cycling may explain the competitive ability of Kalmia relative to black spruce (Picea mariana), although this has not been demonstrated experimentally. Here, the protein-precipitation capacities of purified tannins and leaf extracts from Kalmia and black spruce were compared. The resistance to degradation of tannin-protein precipitates from both species were compared by monitoring carbon (C) and N dynamics in humus amended with protein, purified tannins or protein-tannin precipitates. The purity of the precipitates was verified using solid-state (13)C nuclear magnetic resonance (NMR) spectra. The ability of mycorrhizal fungi associated with both species to grow on media amended with tannin-protein complexes as the principal N source was also compared. The protein precipitation capacity of Kalmia tannins was superior to those of black spruce. Humus amended with protein increased both mineral and microbial N, whereas humus amended with tannin-protein precipitates increased dissolved organic N. Mycorrhizal fungi associated with Kalmia showed better growth than those associated with black spruce when N was provided as tannin-protein precipitates. These data suggest that Kalmia litter increases the amount of soil N sequestered as tannin-protein complexes, which may improve the competitive ability of Kalmia relative to black spruce by favouring N uptake by mycorrhizas associated with the former.  相似文献   

8.
Functional diversities of microorganisms in arctic soil samples at three incubation temperatures were assessed using sole-carbon-source-utilization (SCSU). Soil samples from four sites were collected from the rhizosphere and non-rhizosphere soils. Microorganisms were extracted from samples and inoculated into ECO-Biolog plates and incubated at 4, 10 and 28 °C. Calculations of Shannon–Weaver diversity and Shannon–Weaver evenness were based on the substrate utilization in the Biolog plates. Shannon–Weaver diversities (H) in rhizosphere samples were significantly greater ( H = 3.023 ± 0.197; P < 0.005) than in non-rhizosphere samples ( H = 2.770 ± 0.154). Similarly, the evenness (E) of the inoculated microbial cells exhibited significant differences (P < 0.005) between the rhizosphere and non-rhizosphere soil samples ( E = 0.880 ± 0.057 for soils with rhizosphere; E = 0.807 ± 0.044 for non-rhizosphere samples). Higher microbial diversity and evenness were observed in samples incubated at 4 °C than at 28 °C [least significant difference (lsd) = 0.29], and evenness indices were higher in rhizosphere samples than in non-rhizosphere soils incubated at all three temperatures (lsd = 0.02). Principal component analysis (PCA) of the multivariate data set differentiated the soil samples on the relatively gross scale of microbial communities isolated from rhizosphere and non-rhizosphere soils at all three temperatures.  相似文献   

9.
Gross and net nitrogen (N) ammonification and nitrification were measured in soils from an uncut and recently cut upland and peatland conifer stand in northwestern Ontario, Canada. Rates of gross total inorganic N immobilization were similar to gross mineralization, resulting in low net mineralization rates in soils from all four upland and peatland conifer stands. Gross ammonification rates were variable but similar in soils from uncut and cut peatland hollows (18–19mgNkg–1day–1) and upland forest floor soils (14–19mgNkg–1day–1). Gross ammonium ( ) immobilization rates were also variable but similar to ammonification rates. Median gross nitrification rates were within 0–2mgNkg–1day–1 in soils from all four upland and peatland cut and uncut stands, although rates were consistently higher for the soils from the cut stands. Large variability in gross nitrification rates were observed in peatland soils, however the highest gross nitrification rates were measured in saturated peatland soils. Net rates remained low in the soils from all four stands due to high nitrate ( ) immobilization and very fast turnover (<0.2 day). Our results suggest that potential losses may be negated by high immobilization in uncut and cut boreal forest stands. This study reveals the potential for the interaction of N production and consumption processes in regulating N retention in upland and peatland conifer forests, and the resilience of the boreal forest to disturbance.  相似文献   

10.
Summary Barley plants (Hordeum vulgare L.) grown from seed for 28 days in flowing solution culture were subjected to different root temperatures (3, 5, 7, 9, 11, 13, 17, 25°C) for 14 days with a common air temperature of 25/15°C (day/night). Uptake of NH4 and NO3 ions was monitored separately and continuously from solutions maintained at 10 M NH4NO3 and pH 6.0. Effects of root temperature on unit absorption rate , flux and inflow were compared. After 5 days , and increased with temperature over the range 3–11°C for NH4 ions and over the range 3–13°C for NO3 ions, with little change for either ion above these temperatures. Q10 temperature coefficients for NH4 ions (3–13°C) were 1.9, 1.7 and 1.6 for , and respectively, the corresponding values for NO3 ions being 5.0, 4.5 and 4.6. For both ions, , and changed with time as did their temperature dependence over the range 3–25°C, suggesting that rates of ontogenetic development and the extent of adaptation to temperature may have varied among treatments.  相似文献   

11.
A simple linear relationship between the J coupling constant and the linewidth (1/2) of in-phase NMR peaks has been identified. This relationship permits the rapid and accurate determination of polypeptide J coupling constants from a simple inspection of amide cross peaks in homonuclear 1H TOCSY or 1H NOESY spectra. By using the appropriate set of processing parameters we show that J = 0.5(1/2) – MW/5000 + 1.8 for TOCSY spectra and J = 0.6(1/2) – MW/5000 – 0.9 for NOESY spectra, where 1/2 is the half-height linewidth in Hz and MW is the molecular weight of the protein in Da. The simplicity of this relationship, combined with the ease with which 1/2 measurements can be made, means that J coupling constants can now be rapidly determined (up to 100 measurements in less than 30 min) without the need for any complex curve-fitting algorithms. Tests on 11 different polypeptides involving more than 650 separate J measurements have shown that this method yields coupling constants with an rmsd error (relative to X-ray data) of less than 0.9 Hz. Furthermore, the correlation coefficient between the predicted NMR coupling constants and those derived from high-resolution X-ray crystal structures is typically better than 0.89. These simple linear relationships have been found to be valid for peptides as small as 1 kDa to proteins as large as 20 kDa. Despite the method's simplicity, these results are comparable to the accuracy and precision of the best techniques published to date.  相似文献   

12.
A long-term field experiment was initiated to simulate chronic atmospheric N deposition, a widespread phenomenon in industrial regions of the world. Eight years of experimental nitrate ( ) additions (3 g -N m–2 per year) to four different northern hardwood forests located along a 500 km geographic gradient dramatically increased leaching losses of -N, dissolved organic carbon (DOC), and dissolved organic nitrogen (DON). During the last two water years, the average increase in solution -N and DON leaching from the -amended plots was 2.2 g N m–2, equivalent to 72% of the annual experimental N addition. Results indicate that atmospheric N deposition may rapidly saturate some northern hardwood ecosystems across an entire biome in the upper Great Lakes Region of the USA. Changes in soil C and N cycling induced by chronic N deposition have the potential in this landscape to significantly alter the flux of DOC and DON from upland to aquatic ecosystems. Michigan Gradient study site characteristics are similar to those of European forests most susceptible to N saturation.  相似文献   

13.
Sitka spruce planted on nutrient-poor soils in mixture with pine or larch, unlike pure spruce, does not become N deficient and does not require N fertilizer. To test the hypothesis that N availability in the soil is enhanced beneath mixed species, the seasonal changes in different N forms were compared in humus (L+F+H) and soil beneath 15-year-old Sitka spruce (SS) and mixed Sitka spruce-Scots pine (SS and SP) planted on a gleyed heathland soil. Amounts of mineral and organic N extracted from humus in spring were significantly (p < 0.05) higher in SS and SP than in SS. Larger amounts were measured in the underlying soil, which favoured the deeper-rooting spruce and pine in SS and SP plots. Annual net N mineralization, measured by in-situ incubation, was 32 and 47 kg N ha-1 in the surface 10 cm beneath SS and (SS and SP), respectively. In spring, readily mineralized organic N (waterlogged incubation at 30°C) was higher in humus and soil from (SS and SP) than from SS by 15 kg N ha-1. The larger N pools beneath (SS and SP) were consistent with the higher total N content of the humus beneath (SS and SP), 446 compared with 255 kg N ha-1 beneath SS. This indicated that beneath (SS and SP) N had been transferred from the underlying soil.  相似文献   

14.
In aqueous medium etiolated wheat seedlings release superoxide anion ( ). Interaction of a synthetic antioxidant, butylated hydroxytoluene (BHT, ionol), with oxygen in the aqueous medium is accompanied by formation. This suggests that under certain conditions BHT behaves as a prooxidant. A natural antioxidant, superoxide dismutase (SOD), and also a wound healing preparation, emulsified denatured placenta (EDP), do not exhibit the prooxidant properties. In contrast to BHT, they reduce production by the etiolated wheat seedling system.  相似文献   

15.
Effects of light on the short term competition for organic and inorganic nitrogen between maize and rhizosphere microorganisms were investigated using a mixture of amino acid, ammonium and nitrate under controlled conditions. The amount and forms of N added in the three treatments was identical, but only one of the three N forms was labeled with 15N. Glycine was additionally labeled with 14C to prove its uptake by maize and incorporation into microbial biomass in an intact form. Maize out-competed microorganisms for during the whole experiment under low and high light intensity. Microbial uptake of 15N and 14C was not directly influenced by the light intensity, but was indirectly related to the impact the light intensity had on the plant. More was recovered in microbial biomass than in plants in the initial 4 h under the two light intensities, although more 15N-glycine was incorporated into microbial biomass than in plants in the initial 4 h under low light intensity. Light had a significant effect on uptake by maize, but no significant effects on the uptake of or 15N-glycine. High light intensity significantly increased plant uptake of and glycine 14C. Based on 14C to 15N recovery ratios of plants, intact glycine contributed at least 13% to glycine-derived nitrogen 4 h after tracer additions, but it contributed only 0.5% to total nitrogen uptake. These findings suggest that light intensity alters the competitive relationship between maize roots and rhizosphere microorganisms and that C4 cereals such as maize are able to access small amounts of intact glycine. We conclude that roots were stronger competitor than microorganisms for inorganic N, but microorganisms out competed plants during a short period for organic N, which was mineralized into inorganic N within a few hours of application to the soil and was thereafter available for root uptake.  相似文献   

16.
Root/microbe competition was investigated as a mechanism controlling fertilizer N uptake by coniferous forest trees. Combinations of biocides both with and without 15N labelled urea, were applied to microcosms containing Sitka spruce seedlings, to selectively inhibit target microbial groups which may be competing with roots for N. After 1 growing season, concentrations of fertilizer N and total N in the trees, as well as populations of microbes and animals, were determined. Biocidal inhibition of microbial populations, particularly of fungi, was associated with significant increases in concentraions of fertilizer N and total N in Sitka spruce seedlings. Application of the fungicide benlate, for example, increased the concentration of fertilizer-derived N in spruce needles by one order of magnitude, and was associated with significant reductions in FDA-active hyphal lengths of fungi. This approach to investigating N-flow offers considerable potential for short term experiments involving competition for fertilizer/available N, where the microbial biomass represents the major sink for N in competition with roots.  相似文献   

17.
U. Schleiff 《Plant and Soil》1986,94(1):143-146
Summary The water uptake rates of roots in saline soils are depressed by the simultaneously decreasing matric and osmotic water potentials in the soil surrounding the roots (rhizospheric soil). Unfortunately there are no reliable tools available for direct measurements of the effect of decreasing water potentials in the rhizospheric soil on the uptake rate of soil water by roots. This paper presents some results of a vegetation technique for studying the effect of different combinations of osmotic and matric water potentials in the rhizospheric soil on the water uptake rates of barley roots. Water uptake rates were reduced to a greater extent by decreasing soil matric water potentials than by decreasing soil osmotic water potentials. According to the results of this experiment, there was no relationship between the total soil water potential of a sandy soil and the water uptake rates when the roots were exposed to different combinations of and .  相似文献   

18.
We have added glucose and nutrients to manipulate soil microbial activity and nutrient availability in a boreal spruce forest to study the performance of birch and spruce seedlings in relation to the soil microbial community. The proportion of aboveground biomass in the seedlings was largest in plots amended with extra nutrients, while ectomycorrhizal (ECM) colonisation was low in these plots. ECM appeared beneficial for growth of both species, but only at low levels of colonisation (<25% ECM colonised root-tips). The soil microbial biomass, as determined by total PLFA, was largest in plots treated with glucose and there was a significant negative relationship between birch seedling size and levels of total PLFA in soil. This could be taken to suggest that poor seedling growth was due to nutrient limitation caused by microbial assimilation. However, the treatment response of the birch seedlings was generally weak, and spruce often showed no response at all to the addition of nutrients and glucose. The most consistent parameter for the variation in plant performance, as well as for the microbial soil community, was the block-effect. This suggests a strong spatial structure in the soil microbial community, and that this structure was robust with respect to our treatments even though they continued over a 3-year period.  相似文献   

19.
Summary In pot experiments with barley, mustard, leek, lettuce and spinach, and in a field experiment with 30 cultivars of barley uptakes of K, Mg, Ca, Na and N were studied at varying concentrations and activities of these cations in the soil solution.The sum of macro cations (K, Mg, Ca, Na) in meq per 100 g aerial plant parts were independent of the chemical composition of the soil solution, but dependent on plant species and on the N concentration in the plant.The ratios of mean net inflows of Mg, Ca and K into plants and corresponding cation activity ratios (aMg/aCa and ) in the soil solution were linearly related and highly correlated under conditions in which growth rate and/or rate of incorporation into new tissues constituted the rate determining step of cation uptake. Consequently, mean net inflows of K, Mg and Ca were independent of ion concentration and ion activity of K, Mg or Ca in the soil solution under the conditions of constant activity ratio.The results agree with the concept that plants have a finite cation uptake capacity, and that plants are in a equilibrium-like state with the activities of K, Mg, and Ca ions in the soil solution. The results indicate that both ratios and content of exchangeable cations should be considered in our evaluation of soil test data.  相似文献   

20.
Summary The influence of NPK-fertilizer on decomposition of litter layers and deposited logging residues (brash) on a clearfelled Sitka spruce stand was followed during two years by zero-tension lysimetry and litterbags. Root development of second rotation planted trees on this peaty gley soil are restricted to the litter layers (LFH) and without fertilizer are dependent on its decomposition for release of nutrients. A comparison of fertilized and control plots showed few site differences and similar hydrological properties. Fertilizer addition (urea-N, rock-P and KCl) immediately raised leachate concentrations of NH4−N, K and PO4−P, the last remaining high over the period. NO3−N increased dramatically in the second year leachates from the fertilized area. Within two years 45, 60 and 75% of added NPK respectively were recovered in leachates. Two-year-old litter in litterbags lost weight significantly more slowly after fertilization. The calculated values were 0.28 (control plot) and 0.15 (fertilized plot). Mean values were derived from individual regressions and allowed microsite variation to be assessed. The difference in is attributed to available C limitation although N concentration of needles increased on both plots, P concentration increased slowly on the control plot while K and Mg decreased on both. Ca concentrations doubled with fertilization and remained constant over two years. The rapid loss of fertilizer and slight response from planted trees indicate delayed application of fertilizers may be desirable.  相似文献   

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