1,721,095 research outputs found
Influence of tree internal nitrogen reserves on the response of beech (Fagus sylvatica) trees to elevated atmospheric carbon dioxide concentration
No full textWe examined the influence of plant internal nitrogen (N) reserves on the response of 3-year-old beech (Fagus sylvatica L.) trees to elevated atmospheric CO2 concentration ([CO2]) in a dual N-15 and C-13 long-term labeling experiment. Trees were grown on sand and received either no N nutrition (-N treatment) or 4 mM N (+N treatment) for I year. The -N and +N pretreated trees were then placed in growth chambers and grown in 350 (ambient) or 700 ppm (elevated) of a (CO2)-C-13 atmosphere for 24 weeks. In all treatments, trees were supplied with 4 mM N-15 during the experiment. Irrespective of tree N reserves, elevated [CO2] increased cumulative carbon (C) uptake by about 30% at Week 24 compared with that for trees in the ambient treatment. Elevated [CO2] also caused a shift in C allocation to belowground compartments, which was more pronounced in -N trees than in +N trees. In +N trees, belowground allocation of new C at Week 24 was 67% in ambient [CO2] compared with 70% in elevated [CO2]. The corresponding values for -N trees were 70 and 79%. The increase in C allocation in response to elevated [CO2] was most evident as an increase in belowground respiration; however, specific root respiration was unaffected by the CO2 or N treatments. Although elevated [CO2] increased root growth and belowground respiration, it had no effect on N uptake at Week 24. As a result of increased C uptake, N concentrations were decreased in trees in the elevated [CO2] treatment compared with trees in the ambient treatment in both N treatments. Partitioning of new N uptake was unaffected by elevated [CO2] in +N trees. In -N trees, however, N allocation to the stem decreased in response to elevated [CO2]] and N allocation to fine roots increased, suggesting a reduction in the formation of N reserves in response to elevated [CO2] We conclude that the response of beech trees to elevated [CO2] is affected by internal N status and that elevated [CO2] may influence the ability of the trees to form N reserves
Influence of tree internal nitrogen reserves on the response of beech (Fagus sylvatica) trees to elevated atmospheric carbon dioxide concentration
No full textWe examined the influence of plant internal nitrogen (N) reserves on the response of 3-year-old beech (Fagus sylvatica L.) trees to elevated atmospheric CO2 concentration ([CO2]) in a dual N-15 and C-13 long-term labeling experiment. Trees were grown on sand and received either no N nutrition (-N treatment) or 4 mM N (+N treatment) for I year. The -N and +N pretreated trees were then placed in growth chambers and grown in 350 (ambient) or 700 ppm (elevated) of a (CO2)-C-13 atmosphere for 24 weeks. In all treatments, trees were supplied with 4 mM N-15 during the experiment. Irrespective of tree N reserves, elevated [CO2] increased cumulative carbon (C) uptake by about 30% at Week 24 compared with that for trees in the ambient treatment. Elevated [CO2] also caused a shift in C allocation to belowground compartments, which was more pronounced in -N trees than in +N trees. In +N trees, belowground allocation of new C at Week 24 was 67% in ambient [CO2] compared with 70% in elevated [CO2]. The corresponding values for -N trees were 70 and 79%. The increase in C allocation in response to elevated [CO2] was most evident as an increase in belowground respiration; however, specific root respiration was unaffected by the CO2 or N treatments. Although elevated [CO2] increased root growth and belowground respiration, it had no effect on N uptake at Week 24. As a result of increased C uptake, N concentrations were decreased in trees in the elevated [CO2] treatment compared with trees in the ambient treatment in both N treatments. Partitioning of new N uptake was unaffected by elevated [CO2] in +N trees. In -N trees, however, N allocation to the stem decreased in response to elevated [CO2]] and N allocation to fine roots increased, suggesting a reduction in the formation of N reserves in response to elevated [CO2] We conclude that the response of beech trees to elevated [CO2] is affected by internal N status and that elevated [CO2] may influence the ability of the trees to form N reserves
Laboratory estimates of trace gas emissions following surface application and injection of cattle slurry
No full textApplying cattle slurry to soil may induce emissions of the greenhouse gases N2O and CH4. Our objective was to determine the effects of different application techniques (surface application and slit injection) of cattle (Bostaurus) slurry on the decomposition of slurry organic matter and the emissions of N2O and CH4. The effects of slurry application (43.6 m(3) ha(-1)) were studied for 9 wk under controlled laboratory conditions using a soil microcosm system with automated monitoring of the CO2, N2O, and CH4 fluxes, The soil used was a silty loam (Ap horizon of a cambisol) with a constant water-filled pore space of 67% during the experiment. About 38% of the organic matter applied with the slurry was decomposed within 9 wk. Production of CO2 was not affected by the application technique. Emissions of N2O and CN4 from the injected slurry were significantly higher than from the surface-applied slurry, probably because of restricted aeration at the injected-slurry treatment. Total N2O-N emissions were 0.2% (surface application) and 3.3% (slit injection) of the slurry N added, Methane emission occurred only during the first Few days followimg application. The total net nux of CH4-C for 2 wk was -12 g ha(-1) for the control (CH4 uptake), 2 g ha(-1) far the surface-applied slurry, and 39 g ha(-1) for the injected slurry. Slurry injection, which is recommended to reduce NH3 volatilization, appears to increase emissions of the greenhouse gases N2O and CH4 from the fertilized fields
O produced by denitrification in soils
No full textWe investigated oxygen and site-specific nitrogen isotope effects of N2O produced in the NO3--to-N2O step of denitrification. Arable sand and silt loam soils with varying NO3- availability were incubated under N-2/C2H2 atmosphere in order to establish anaerobic conditions and to block N2O reduction. Dual isotope and isotopomer ratios of emitted N2O were determined by analysis of delta O-18, average delta N-15 (delta N-15(bulk)) and N-15 site preference (SP is equal to difference in delta N-15 between the central and peripheral N positions of the asymmetric N2O molecule). The average N enrichment factor of the NO3--to-N2O step ranged from -47.9 to -53.6 parts per thousand, which is between the reported ranges of enrichment factors of nitrification and denitrification. SP varied with time, and mean values were between 3.1 and 8.9 parts per thousand, which is higher compared to SP reported from pure cultures of denitrifiers but lower compared to nitrifiers and fungal denitrifiers. This shows that SP of N2O produced in soils might be seen as a semiquantitative indicator for the different pathways of N2O production but not specific enough to quantify the relative contribution of denitrification to the total N2O flux in systems where several source processes are important. delta O-18 of N2O from all treatments was less variable compared to delta O-18 of soil NO3-, indicating that there was a relatively large O exchange with water during N2O formation.Deutsche Forschungsgemeinschaft (DFG
Use of C-13 and N-15 mass spectrometry to study the decomposition of Calamagrostis epigeios in soil column experiments with and without ash additions
No full textThe dynamics of C and N in terrestrial ecosystems are not completely understood and the use of stable isotopes may be useful to gain further insight in the pathways of CO2 emissions and leaching of dissolved organic carbon (DOC) and nitrogen (DON) during decomposition of litter. Objectives were (i) to study the decomposition dynamics of Calamagrostis epigeios, a common grass species in forests, using C-13-depleted and N-15-enriched plants and (ii) to quantify the effect wood ash addition on the decomposition and leaching of DOC and DON. Decomposition was studied for 128 days under aerobic conditions at 8 degrees C and moisture close to field capacity in a spodic dystric Cambisol with mor-moder layer. Variants included control plots and additions of (i) Calamagrostis litter and (ii) Calamagrostis litter plus 4 kg ash m(-2). Decomposition of Calamagrostis resulted in a CO2 production of 76.2 g CO2-C (10% of added C) after 128 days and cumulative DOC production was 14.0 g C m(-2) out of which 0.9 g C m(-2) was Calamagrostis-derived (0.1% of added C). The specific CO2 formation and specific DOC production from Calamagrostis were 6 times higher (CO2) and 4 times smaller (DOC) than those from the organic layer. The amount of Calamagrostis-derived total N (NH4+, NO3-, DON) leached was 0.7 g N m(-2) (4.8% of added N). Cumulative DON production was 0.8 g N m(-2) which was slightly higher than for the control. During soil passage, much of the DOC and DON was removed due to sorption or decomposition. DOC and DON releases from the mineral soil (17 cm depth) were 6.3 g C m(-2) and 0.5 g N m(-2). (ii) Addition of ash resulted in a complete fixing of CO2 for 40 days due to carbonatisation. Afterwards, the CO2 production rates were similar to the variant without ash addition. Production of DOC (98.6 g C m(-2)) and DON (2.5 g N m(-2)) was marked, mainly owing to humus decay. However, Calamagrostis-derived DOC and Calamagrostis-derived total N were only 3.9 g C m(-2) (0.5 % of added C) and 0.5 g m(-2) (3.4% of added N). The specific DOC production rate from the organic layer was 6 rimes higher than that from Calamagrostis. The results suggest that with increasing humification from fresh plant residues to more decomposed material (O-F and O-H layers) the production ratio of DOC/CO2-C increases. Addition of alkaline substances to the forest floor can lead to a manifold increase in DOC production
Carbon dynamics determined by natural C-13 abundance in microcosm experiments with soils from long-term maize and rye monocultures
No full textUnderstanding carbon dynamics in soil is the key to managing soil organic matter. Our objective was to quantify the carbon dynamics in microcosm experiments with soils from long-term rye and maize monocultures using natural C-13 abundance. Microcosms with undisturbed soil columns from the surface soil (0-25 cm) and subsoil (25-50 cm) of plots cultivated with rye (C-3-plant) since 1878 and maize (C-4-plant) since 1961 with and without NPK fertilization from the long-term experiment 'Ewiger Roggen' in Halle, Germany, were incubated for 230 days at 8 degreesC and irrigated with 2 mm 10(-2) M CaCl2 per day. Younger, C-4-derived and older, C-3-derived percentages of soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass (C-mic) and CO2 from heterothropic respiration were determined by natural C-13 abundance. The percentage of maize-derived carbon was highest in CO2 (42-79%), followed by C-mic (23-46%), DOC (5-30%) and SOC (5-14%) in the surface soils and subsoils of the maize plots. The percentage of maize-derived C was higher for the NPK plot than for the unfertilized plot and higher for the surface soils than for the subsoils. Specific production rates of DOC, CO2-C and C-mic from the maize-derived SOC were 0.06-0.08% for DOC, 1.6-2.6% for CO2-C and 1.9-2.7% for Cmic, respectively, and specific production rates from rye-derived SOC of the continuous maize plot were 0.03-0.05% for DOC, 0.1-0.2% for CO2-C and 0.3-0.5% for C-mic. NPK fertilization did not affect the specific production rates. Strong correlations were found between C-4-derived C-mic and C-4-derived SOC, DOC and CO2-C (r greater than or equal to 0.90), whereas the relationship between C-3-derived C-mic and C-3-derived SOC, DOC and CO2-C was not as pronounced (r less than or equal to 0.67). The results stress the different importance of former (older than 40 years) and recent (younger than 40 years) litter C inputs for the formation of different C pools in the soil. (C) 2003 Elsevier Ltd. All rights reserved
Controls of temporal and spatial variability of methane uptake in soils of a temperate deciduous forest with different abundance of European beech (Fagus sylvatica L.)
No full textAerated forest soils are a significant sink for atmospheric methane (CH(4)). Soil properties, local climate and tree species can affect the soil CH(4) sink. A two-year field study was conducted in a deciduous mixed forest in the Hainich National Park in Germany to quantify the sink strength of this forest for atmospheric CH(4) and to determine the key factors that control the seasonal, annual and spatial variability of CH(4) uptake by soils in this forest. Net exchange of CH(4) was measured using closed chambers on 18 plots in three stands exhibiting different beech (Fagus sylvatica L) abundance and which differed in soil acidity, soil texture, and organic layer thickness. The annual CH(4) uptake ranged from 2.0 to 3.4 kg CH(4)-C ha(-1). The variation of CH(4) uptake over time could be explained to a large extent (R(2) = 0.71, P < 0.001) by changes in soil moisture in the upper 5 cm of the mineral soil. Differences of the annual CH(4) uptake between sites were primarily caused by the spatial variability of the soil clay content at a depth of 0-5 cm (R(2) = 0.5, P < 0.01). The CH(4) uptake during the main growing period (May-September) increased considerably with decreasing precipitation rate. Low CH(4) uptake activity during winter was further reduced by periods with soil frost and snow cover. There was no evidence of a significant effect of soil acidity, soil nutrient availability, thickness of the humus layer or abundance of beech on net-CH(4) uptake in soils in this deciduous forest. The results show that detailed information on the spatial distribution of the clay content in the upper mineral soil is necessary for a reliable larger scale estimate of the CH(4) sink strength in this mixed deciduous forest. The results suggest that climate change will result in increasing CH(4) uptake rates in this region because of the trend to drier summers and warmer winters. (C) 2009 Elsevier Ltd. All rights reserved.Deutsche Forschungsgemeinschaft (DFG) [1086
Soil organic carbon in density fractions of tropical soils under forest – pasture – secondary forest land use changes
No full textOur knowledge of effects of land use changes and soil types on the storage and stability of different soil organic carbon (SOC) fractions in the tropics is limited. We analysed the effect of land use (natural forest, pasture, secondary forest) on SOC storage (depth 0–0.1 m) in density fractions of soils developed on marine Tertiary sediments and on volcanic ashes in the humid tropics of northwest Ecuador. The origin of organic carbon stored in free light (< 1.6 g cm−3) fractions, and in two light fractions (LF) occluded within aggregates of different stability, was determined by means of δ13C natural abundance. Light occluded organic matter was isolated in a first step after aggregate disruption by shaking aggregates with glass pearls (occluded I LF) and in a subsequent step by manual destruction of the most stable microaggregates that survived the first step (occluded II LF). SOC storage in LFs was greater in volcanic ash soils (7.6 ± 0.6 Mg C ha−1) than in sedimentary soils (4.3 ± 0.3 Mg C ha−1). The contribution of the LFs to SOC storage was greater in natural forest (19.2 ± 1.2%) and secondary forest (16.6 ± 1.0%) than in pasture soils (12.8 ± 1.0%), independent of soil parent material. The amount of SOC stored in the occluded I LF material increased with increasing silt + clay content (sedimentary soils, r = 0.73; volcanic ash soils, r = 0.58) and aggregation (sedimentary soils, r = 0.52; volcanic ash soils, r = 0.45). SOC associated with occluded I LF, had the smallest proportion of new, pasture-derived carbon, indicating the stabilizing effect of aggregation. Fast turnover of the occluded II LF material, which was separated from highly stable microaggregates, strongly suggested that this fraction is important in the initial process of aggregate formation. No pasture-derived carbon could be detected in any density fractions of volcanic ash soils under secondary forest, indicating fast turnover of these fractions in tropical volcanic ash soils
Differential response of mineral-associated organic matter in tropical soils formed in volcanic ashes and marine Tertiary sediment to treatment with HCl, NaOCl, and Na4P2O7
No full textThe Effect of Elevated [CO2] on Uptake and Allocation of13C and15N in Beech (Fagus sylvatica L.) during Leafing
No full textA continuous dual 13CO2 and 15NH415NO3 labelling experiment was undertaken to determine the effects of ambient (350μmol mol‐1) or elevated (700μmol mol‐1) atmospheric CO2 concentrations on C and N uptake and allocation within 3‐year‐old beech (Fagus sylvatica L.) during leafing. After six weeks of growth, total carbon uptake was increased by 63 % (calculated on total C content) under elevated CO2 but the carbon partitioning was not altered. 56 % of the new carbon was found in the leaves. On a dry weight basis was the content of structural biomass in leaves 10 % lower and the lignin content remained unaffected under elevated as compared to ambient [CO2]. Under ambient [CO2] 37 %, and under elevated [CO2] 51 %, of the lignin C of the leaves derived from new assimilates. For both treatments, internal N pools provided more than 90 % of the nitrogen used for leaf‐growth and the partitioning of nitrogen was not altered under elevated [CO2]. The C/N ratio was unaffected by elevated [CO2] at the whole plant level, but the C/N ratio of the new C and N uptake was increased by 32 % under elevated [CO2]
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