1,721,005 research outputs found
Influence of tree internal N status on uptake and translocation of C and N in beech: a dual C-13 and N-15 labeling approach
No full textInfluence of plant internal nitrogen (N) stocks on carbon (C) and N uptake and allocation in 3-year-old beech (Fagus sylvatica L.) was studied in two N-15- and C-13-labeling experiments. In the first experiment, trees were grown in sand and received either no N nutrition (-N treatment) or 4 mM unlabeled N (+N treatment) for 1 year. The -N- and +N-pretreated trees were then supplied with 4 mM N-15 and grown in a (CO2)-C-13 atmosphere for 24 weeks. In the second experiment, trees were pretreated with 4 mM 15N for 1 year and then supplied with unlabeled N for 24 weeks and the remobilization of stored N-15 was monitored. On the whole-plant level, uptake of new C was significantly reduced in -N-pretreated trees; however, partitioning of new C was not altered, although there was a trend toward increased belowground respiration. The amount of N taken up was not influenced by N nutrition in the previous year. In +N-pretreated trees, partitioning of new N was dominated by the fine roots (59.7% at Week 12), whereas in -N-pretreated trees, partitioning of new N favored stem, coarse roots and fine roots (24, 21 and 31.9%, respectively, at Week 12), indicating the formation of N stores. The contribution of previous-year N to leaf N was about 15%. The N remobilized for leaf formation had been stored in stem and coarse roots. We conclude that, within a growing season, the growth of beech is strongly determined by the availability of tree internal N stores, whereas the current N supply is of less importance
Influence of tree internal N status on uptake and translocation of C and N in beech: a dual C-13 and N-15 labeling approach
No full textInfluence of plant internal nitrogen (N) stocks on carbon (C) and N uptake and allocation in 3-year-old beech (Fagus sylvatica L.) was studied in two N-15- and C-13-labeling experiments. In the first experiment, trees were grown in sand and received either no N nutrition (-N treatment) or 4 mM unlabeled N (+N treatment) for 1 year. The -N- and +N-pretreated trees were then supplied with 4 mM N-15 and grown in a (CO2)-C-13 atmosphere for 24 weeks. In the second experiment, trees were pretreated with 4 mM 15N for 1 year and then supplied with unlabeled N for 24 weeks and the remobilization of stored N-15 was monitored. On the whole-plant level, uptake of new C was significantly reduced in -N-pretreated trees; however, partitioning of new C was not altered, although there was a trend toward increased belowground respiration. The amount of N taken up was not influenced by N nutrition in the previous year. In +N-pretreated trees, partitioning of new N was dominated by the fine roots (59.7% at Week 12), whereas in -N-pretreated trees, partitioning of new N favored stem, coarse roots and fine roots (24, 21 and 31.9%, respectively, at Week 12), indicating the formation of N stores. The contribution of previous-year N to leaf N was about 15%. The N remobilized for leaf formation had been stored in stem and coarse roots. We conclude that, within a growing season, the growth of beech is strongly determined by the availability of tree internal N stores, whereas the current N supply is of less importance
Partitioning of remobilised N in young beech (Fagus sylvatica L.) is not affected by elevated [CO2]
No full textEffects of elevated CO2 concentration ([CO2]) on the remobilisation of tree internal nitrogen (N) of 3-year-old beech (Fagus sylvatica L.) was determined in a labeling experiment. Trees were pre-treated with 15N for 1 year and the remobilization of stored N was monitored in ambient (350 ppm) or elevated [CO2] (700 ppm) in the subsequent year. N taken up during the pre-treatment made up 24.7% of total N at the start of the experiment. This value was almost halved after 24 weeks of growth for both CO2-treatments. Significant differences in the partitioning of the remobilized N were only observed transiently after 6 weeks of growth but no CO2-effect was observed at the end of the growing season.La partition de N remobilisé chez de jeunes hêtres (Fagus sylvatica L.) n’est pas affectée par une concentration élevée en CO2. Les effets de concentrations élevées en CO2 sur la remobilisation de l’azote interne de plants de hêtre (Fagus silvatica L.) âgés de 3 ans ont été étudiés dans une expérimentation avec marquage. Les arbres ont été prétraités avec du 15N pendant un an et la remobilisation de l’azote stocké a été suivie a des concentrations de 350 ppm et de 700 ppm l’année suivante. L’azote fixé pendant le prétraitement correspond à 24,7 % de l’azote total au début de l’expéri-mentation. Cette valeur était presque diminuée de moitié après 24 semaines de croissance pour les deux traitements étudiés. Des différences significatives dans la partition de l’azote remobilisé ont été observées seulement de façon passagère après 6 semaines de croissance mais il n’a pas été observé d’effet du CO2 à la fin de la période de croissance
Effects of elevated carbon dioxide concentration on growth and N-2 fixation of young Robinia pseudoacacia
No full textEffects of elevated CO2 concentration ([CO2]) on carbon (C) and nitrogen (N) uptake and N source partitioning (N-2 fixation versus mineral soil N uptake) of 1-year-old Robinia pseudoacacia were determined in a dual C-13 and N-15 continuous labeling experiment. Seedlings were grown for M weeks in ambient (350 ppm) or elevated [CO2] (700 ppm) with (NH4)-N-15 (NO3)-N-15 as the only mineral nitrogen source. Elevated [CO2] increased the fraction of new C in total C, but it did not alter C partitioning among plant compartments. Elevated [CO,] also increased the fraction of new N in total N and this was coupled with a shift in N source partitioning toward N-2 fixation. Soil N uptake was unaffected by elevated [CO2], whereas N-2 fixation was markedly increased by the elevated [CO2] treatment, mainly because of increased specific fixation (mg N mg(-1) nodule). As a result of increased N-2 fixation, the C/N ratio of tree biomass tended to decrease in the elevated [CO2] treatment. Partitioning of N uptake among plant compartments was unaffected by elevated [CO2]. Total dry mass of root nodules doubled in response to elevated [CO2], but this effect was not significant because of the great variability of root nodule formation. Our results show that, in the N-2-fixing R. pseudoacacia, increased C uptake in response to increased [CO2] is matched by increased N-2 fixation, indicating that enhanced growth in elevated [CO2] might not be restricted by N limitations
Modelling the long-term stabilization of carbon from maize in a silty soil
No full textSoil organic carbon (SOC) models have been widely used to predict SOC change with changing environmental and management conditions, but the accuracy of the prediction is often open to question. Objectives were (i) to quantify the amounts of C derived from maize in soil particle size fractions and at various depths in a long-term field experiment using C-13/C-12 analysis, (ii) to model changes in the organic C, and (iii) to compare measured and modelled pools of C. Maize was cultivated for 24 years on a silty Luvisol which resulted in a stock of 1.9 kg maize-derived C m(-2) (36% of the total organic C) in the Ap horizon. The storage of maize-derived C in particle size fractions of the Ap horizon decreased in the order clay (0.65 kg C m(-2)) > fine and medium silt (0.43) > coarse silt (0.33) > fine sand (0.13) > medium sand (0.12) > coarse sand (0.06) and the turnover times of C-3-derived C ranged from 26 (fine sand) to 77 years (clay). The turnover times increased with increasing soil depth. We used the Rothamsted Carbon Model to model the C dynamics and tested two model approaches: model A did not have any adjustable parameters, but included the Falloon equation for the estimation of the amount of inert organic matter (IOM) and independent estimations of C inputs into the soil. The model predicted well the changes in C-3-derived C with time but overestimated the changes in maize-derived C 1.6-fold. In model B, the amounts of IOM and C inputs were optimized to match the measured C-3- and C-4-derived SOC stocks after 24 years of continuous maize. This model described the experimental data well, but the modelled annual maize C inputs (0.41 kg C m(-2) a(-1)) were less than the independently estimated total input of maize litter C (0.63 kg C m(-2) a(-1)) and even less than the annual straw C incorporated into the soil (0.46 kg C m(-2) a(-1)). These results indicated that the prediction of the Rothamsted Carbon Model with independent parameterization served only as an approximation for this site. The total amount of organic C associated with the fraction 0-63 mu m agreed well with the sum of the pools 'microbial biomass', 'humified-organic matter' and IOM of the model B. However, the amount of maize-derived C in this fraction (3.4 g kg(-1)) agreed only satisfactorily with the sum of maize-derived C in the pools 'microbial biomass' and 'humified organic matter' (2.6 g kg(-1))
Effects of elevated carbon dioxide concentration on growth and N-2 fixation of young Robinia pseudoacacia
No full textEffects of elevated CO2 concentration ([CO2]) on carbon (C) and nitrogen (N) uptake and N source partitioning (N-2 fixation versus mineral soil N uptake) of 1-year-old Robinia pseudoacacia were determined in a dual C-13 and N-15 continuous labeling experiment. Seedlings were grown for M weeks in ambient (350 ppm) or elevated [CO2] (700 ppm) with (NH4)-N-15 (NO3)-N-15 as the only mineral nitrogen source. Elevated [CO2] increased the fraction of new C in total C, but it did not alter C partitioning among plant compartments. Elevated [CO,] also increased the fraction of new N in total N and this was coupled with a shift in N source partitioning toward N-2 fixation. Soil N uptake was unaffected by elevated [CO2], whereas N-2 fixation was markedly increased by the elevated [CO2] treatment, mainly because of increased specific fixation (mg N mg(-1) nodule). As a result of increased N-2 fixation, the C/N ratio of tree biomass tended to decrease in the elevated [CO2] treatment. Partitioning of N uptake among plant compartments was unaffected by elevated [CO2]. Total dry mass of root nodules doubled in response to elevated [CO2], but this effect was not significant because of the great variability of root nodule formation. Our results show that, in the N-2-fixing R. pseudoacacia, increased C uptake in response to increased [CO2] is matched by increased N-2 fixation, indicating that enhanced growth in elevated [CO2] might not be restricted by N limitations
Shifts in amino sugar and ergosterol contents after addition of sucrose and cellulose to soil
No full textAn incubation experiment with organic soil amendments was carried out with the aim to determine whether formation and use of microbial tissue (biomass and residues) could be monitored by measuring glucosamine and muramic acid. Living fungal tissue was additionally determined by the cell-membrane component ergosterol. The organic amendments were fibrous maize cellulose and sugarcane sucrose adjusted to the same C/N ratio of 15. In a subsequent step, spherical cellulose was added without N to determine whether the microbial residues formed initially were preferentially decomposed. In the non-amended control treatment, ergosterol remained constant at 0.44 mu g g(-1) soil throughout the 67-day incubation. It increased to a highest value of 1.9 mu g g(-1) soil at day 5 in the sucrose treatment and to 5.0 mu g g(-1) soil at day 33 in the fibrous cellulose treatment. Then, the ergosterol content declined again. The addition of spherical cellulose had no further significant effects on the ergosterol content in these two treatments. The non-amended control treatment contained 48 mu g muramic acid and 650 mu g glucosamine g(-1) soil at day 5. During incubation, these contents decreased by 17% and 19%, respectively. A 33% increase in muramic acid and an 8% increase in glucosamine were observed after adding sucrose. Consequently, the ratio of fungal C to bacterial C based on bacterial muramic acid and fungal glucosamine was lowered in comparison with the other two treatments. No effect on the two amino sugars was observed after adding cellulose initially or subsequently during the second incubation period. This indicates that the differences in quality between sucrose and cellulose had a strong impact on the formation of microbial residues. However, the amino sugars did not indicate a preferential decomposition of microbial residues as N sources. (C) 2007 Elsevier Ltd. All rights reserved
Formation and use of microbial residues after adding sugarcane sucrose to a heated soil devoid of soil organic matter
No full textA 67-day incubation experiment was carried out with a soil initially devoid of any organic matter due to heating, which was amended with sugarcane sucrose (C-4-sucrose with a delta C-13 value of -10.5 parts per thousand), inorganic N and an inoculum for recolonisation and subsequently at day 33 with C-3-cellulose (delta C-13 value of -23.4 parts per thousand). In this soil, all organic matter is in the microbial biomass or in freshly formed residues, which makes it possible to analyse more clearly the role of microbial residues for decomposition of N-poor substrates. The average delta C-13 value over the whole incubation period was -10.7 parts per thousand in soil total C in the treatments without C-3-cellulose addition. In the CO2 evolved, the delta C-13 values decreased from -13.4 parts per thousand to -15.4 parts per thousand during incubation. In the microbial biomass, the delta C-13 values increased from -11. 5 parts per thousand to -10. 1 parts per thousand at days 33 and 38. At day 67, 36% of the C-4-sucrose was left in the treatment without a second amendment. The addition of C-3-cellulose resulted in a further 7% decrease, but 4% of the C-3-cellulose was lost during the second incubation period. Total microbial biomass C declined from 200 mu g g(-1) soil at day 5 to 70 mu g g(-1) soil at day 67. Fungal ergosterol increased to 1.5 mu g g(-1) soil at day 12 and declined more or less linearly to 0.4 mu g g(-1) soil at day 67. Bacterial muramic acid declined from a maximum of 35 mu g g(-1) soil at day 5 to a constant level of around 16 mu g g(-1) soil. Glucosamine showed a peak value at day 12. Galactosamine remained constant throughout the incubation. The fungal C/bacterial C ratio increased more or less linearly from 0.38 at day 5 to 1.1 at day 67 indicating a shift in the microbial community from bacteria to fungi during the incubation. The addition Of C-3-cellulose led to a small increase in C-3-derived microbial biomass C, but to a strong increase in C-4-derived microbial biomass C. At days 45 and 67, the addition of N-free C-3-cellulose significantly decreased the C/N ratio of the microbial residues, suggesting that this fraction did not serve as an N-source, but as an energy source. (c) 2007 Elsevier Ltd. All rights reserved
Microbial use of maize cellulose and sugarcane sucrose monitored by changes in the C-13/C-12 ratio
No full textAn arable soil with organic matter formed from C3-vegetation was amended initially with maize cellulose (C-4-cellulose) and sugarcane sucrose (C-4-Sucrose) in a 67-day laboratory incubation experiment with microcosms at 25 degrees C. The amount and isotopic composition (C-13/C-12) Of Soil organic C, CO2 evolved, microbial biomass C, and microbial residue C were determined to prove whether the formation of microbial residues depends on the quality of the added C source adjusted with NH4NO3 to the same C/N ratio of 15. In a subsequent step, C-3-cellulosc (3 mg C g(-1) soil) was added without N to soil to determine whether the microbial residues formed initially from C-4-substrate are preferentially decomposed to maintain the N-demand of the soil microbial community. At the end of the experiment, 23% Of the two C-4-substrates added was left in the soil, while 3% and 4% of the added C-4-cellulose and C-4-sucrose, respectively, were found in the microbial biomass. The addition of the two C-4-substrates caused a significant 100% increase in C-3-derived CO, evolution during the 5-33 day incubation period. The addition of C-3-cellulose caused a significant 50% increase in C-4-derived CO2 evolution during the 38-67 day incubation period. The decrease in microbial biomass C-4-C accounted for roughly 60% of this increase. Cellulose addition promoted microorganisms strongly able to recycle N immediately from their own tissue by "cryptic growth" instead of incorporating NO3- from the soil solution. The differences in quality of the microbial residues produced by C-4-cellulose and C-4-Sucrose decomposing microorganisms are also reflected by the difference in the rates of CO2 evolution, but not in the rates of net N mineralization. (c) 2007 Elsevier Ltd. All rights reserved
Use of microcalorimetry to study microbial activity during the transition from oxic to anoxic conditions
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