Soil organic matter (SOM) forms the largest terrestrial pool of carbon outside of sedimentary rocks. Radiocarbon is a powerful tool for assessing soil organic matter dynamics. However, due to the ...nature of the measurement, extensive 14C studies of soil systems remain relatively rare. In particular, information on the extent of spatial and temporal variability in 14C contents of soils is limited, yet this information is crucial for establishing the range of baseline properties and for detecting potential modifications to the SOM pool. This study describes a comprehensive approach to explore heterogeneity in bulk SOM 14C in Swiss forest soils that encompass diverse landscapes and climates. We examine spatial variability in soil organic carbon (SOC) 14C, SOC content and C : N ratios over both regional climatic and geologic gradients, on the watershed- and plot-scale and within soil profiles. Results reveal (1) a relatively uniform radiocarbon signal across climatic and geologic gradients in Swiss forest topsoils (0-5 cm, Δ14C = 130 ± 28.6, n = 12 sites), (2) similar radiocarbon trends with soil depth despite dissimilar environmental conditions, and (3) micro-topography dependent, plot-scale variability that is similar in magnitude to regional-scale variability (e.g., Gleysol, 0-5 cm, Δ14C 126 ± 35.2, n = 8 adjacent plots of 10 × 10 m). Statistical analyses have additionally shown that Δ14C signature in the topsoil is not significantly correlated to climatic parameters (precipitation, elevation, primary production) except mean annual temperature at 0-5 cm. These observations have important consequences for SOM carbon stability modelling assumptions, as well as for the understanding of controls on past and current soil carbon dynamics.
Soil organic matter (SOM) forms the largest terrestrial pool of carbon outside of sedimentary rocks. Radiocarbon is a powerful tool for assessing soil organic matter dynamics. However, due to the ...nature of the measurement, extensive .sup.14 C studies of soils systems remain relatively rare. In particular, information on the extent of spatial and temporal variability in .sup.14 C contents of soils is limited, yet this information is crucial for establishing the range of baseline properties and for detecting potential modifications to the SOM pool. This study describes a comprehensive approach to explore heterogeneity in bulk SOM .sup.14 C in Swiss forest soils that encompass diverse landscapes and climates. We examine spatial variability in soil organic carbon (SOC) .sup.14 C, SOC content and C:N ratios over both regional climatic and geologic gradients, on the watershed- and plot-scale and within soil profiles. Results reveal (1) a relatively uniform radiocarbon signal across climatic and geologic gradients in Swiss forest topsoils (0-5 cm, Î.sup.14 C=159±36.4, n=12 sites), (2) similar radiocarbon trends with soil depth despite dissimilar environmental conditions, and (3) micro-topography dependent, plot-scale variability that is similar in magnitude to regional-scale variability (e.g., Gleysol, 0-5 cm, Î.sup.14 C 126±35.2, n=8 adjacent plots of 10x10m). Statistical analyses have additionally shown that Î.sup.14 C signature in the topsoil is not significantly correlated to climatic parameters (precipitation, elevation, primary production) except mean annual temperature at 0-5 cm. These observations have important consequences for SOM carbon stability modelling assumptions, as well as for the understanding of controls on past and current soil carbon dynamics.
The effects of green manures, sorghum residues and farmyard manure on N dynamics and crop yields were studied during three dry and wet seasons on a Typic Sombriudox in South Rwanda. In addition, a ...resin core study was conducted within a 4-year green manure field experiment to follow the seasonal pattern of N mineralization and leaching after application of residues from Tephrosia vogelii, Sorghum bicolor, a mixture of both materials, and farmyard manure. During the dry season, topsoil (0-20 cm) mineral N remained constant. At the beginning of the wet season, the rainfall pattern determined N availability. With low rainfall intensities a mineralization flush occurred, doubling topsoil mineral N concentrations within 5 days after wetting. In contrast, under heavy rains at the onset of the rainy season, topsoil mineral N decreased by 50-70% within the first two weeks. The application of organic fertilizers has a strong influence on N availability, but the effects can be negated by heavy rainfall. Incorporation of leaves from Tephrosia vogelii (2.71 dm ha⁻¹) and farmyard manure (7 t dm ha⁻¹) doubled the mineralization flush after the first rains. During the rest of the wet season, N release by the green manure was small, whereas the farmyard manure was found to mobilize N after a period of N immobilization. Incorporation of sorghum residues had only a small effect, while mixing the straw with green and farmyard manure immobilized N temporarily. Nitrogen leaching, measured by exchange resins at a depth of 20 cm, was increased up to 50% by the incorporation of green and farmyard manure. This points to rapid N translocation of easily mineralizable N. The additional incorporation of sorghum residues reduced N leaching of both materials significantly. Since rainfall is often unpredictable, the synchronization of N released from crop residues with crop Í demand may require additional management practices.
The aim of this study was to estimate (i) the influence of different soil types on the net input of new C into soils under CO2 enrichment and (ii) the stability and fate of these new C inputs in ...soils. We exposed young beech–spruce model ecosystems on an acidic loam and calcareous sand for 4 years to elevated CO2. The added CO2 was depleted in 13C, allowing to trace new C inputs in the plant–soil system. We measured CO2‐derived new C in soil C pools fractionated into particle sizes and monitored respiration as well as leaching of this new C during incubation for 1 year. Soil type played a crucial role in the partitioning of C. The net input of new C into soils under elevated CO2 was about 75% greater in the acidic loam than in the calcareous sand, despite a 100% and a 45% greater above‐ and below‐ground biomass on the calcareous sand. This was most likely caused by a higher turnover of C in the calcareous sand as indicated by 30% higher losses of new C from the calcareous sand than from the acidic loam during incubation. Therefore, soil properties determining stabilization of soil C were apparently more important for the accumulation of C in soils than tree productivity. Soil fractionation revealed that about 60% of the CO2‐derived new soil C was incorporated into sand fractions. Low natural 13C abundance and wide C/N ratios show that sand fractions comprise little decomposed organic matter. Consistently, incubation indicated that new soil C was preferentially respired as CO2. During the first month, evolved CO2 consisted to 40–55% of new C, whereas the fraction of new C in bulk soil C was 15–23% only. Leaching of DOC accounted for 8–23% of the total losses of new soil C. The overall effects of CO2 enrichment on soil C were small in both soils, although tree growth increased significantly on the calcareous sand. Our results suggest that the potential of soils for C sequestration is limited, because only a small fraction of new C inputs into soils will become long‐term soil C.
Summary
Soil contains the major part of carbon in terrestrial ecosystems, but the response of this carbon to enriching the atmosphere in CO
2
and to increased N deposition is not completely ...understood. We studied the effects of CO
2
concentrations at 370 and 570 μmol CO
2
mol
−1
air and increased N deposition (7 against 0.7 g N m
−2
year
−1
) on the dynamics of soil organic C in two types of forest soil in model ecosystems with spruce and beech established in large open‐top chambers containing an acidic loam and a calcareous sand. The added CO
2
was depleted in
13
C and thus the net input of new C into soil organic carbon and the mineralization of native C could be quantified.
Soil type was the greatest determining factor in carbon dynamics. After 4 years, the net input of new C in the acidic loam (670 ± 30 g C m
−2
) exceeded that in the calcareous sand (340 ± 40 g C m
−2
) although the soil produced less biomass. The mineralization of native organic C accounted for 700 ± 90 g C m
−2
in the acidic loam and for 2800 ± 170 g C m
−2
in the calcareous sand. Unfavourable conditions for mineralization and a greater physico‐chemical protection of C by clay and oxides in the acidic loam are probably the main reasons for these differences. The organic C content of the acidic loam was 230 g C m
−2
more under the large than under the small N treatment. As suggested by a negligible impact of N inputs on the fraction of new C in the acidic loam, this increase resulted mainly from a suppressed mineralization of native C. In the calcareous sand, N deposition did not influence C concentrations. The impacts of CO
2
enrichment on C concentrations were small. In the uppermost 10 cm of the acidic loam, larger CO
2
concentrations increased C contents by 50–170 g C m
−2
. Below 10 cm depth in the acidic loam and at all soil depths in the calcareous sand, CO
2
concentrations had no significant impact on soil C concentrations. Up to 40% of the ‘new’ carbon of the acidic loam was found in the coarse sand fraction, which accounted for only 7% of the total soil volume. This suggests that a large part of the CO
2
‐derived ‘new’ C was incorporated into the labile and easily mineralizable pool in the soil.
The short-term dynamics of carbon and water fluxes across the soil–plant–atmosphere continuum are still not fully understood. One important constraint is the lack of methodologies that enable ...simultaneous measurements of soil CO2 concentration and respective isotopic composition at a high temporal resolution for longer periods of time. δ13C of soil CO2 can be used to derive information on the origin and physiological history of carbon, andδ18O in soil CO2 aids in inferring the interaction between CO2 and soil water. We established a real-time method for measuring soil CO2 concentration, δ13C andδ18O values across a soil profile at higher temporal resolutions (0.05–0.1 Hz) using an off-axis integrated cavity output spectroscopy (OA-ICOS). We also developed a calibration method correcting for the sensitivity of the device against concentration-dependent shifts in δ13C and δ18O values under highly varying CO2 concentration. The deviations of measured data were modelled, and a mathematical correction model was developed and applied for correcting the shift. By coupling an OA-ICOS with hydrophobic but gas-permeable membranes placed at different depths in acidic and calcareous soils, we investigated the contribution of abiotic and biotic components to total soil CO2 release. We found that in the calcareous Gleysol, CO2 originating from carbonate dissolution contributed to the total soil CO2 concentration at detectable degrees, potentially due to CO2 evasion from groundwater. The13C-CO2 of topsoil at the calcareous soil site was found reflect δ13C values of atmospheric CO2, and theδ13C of topsoil CO2 at the acidic soil site was representative of the biological respiratory processes. δ18O values of CO2 in both sites reflected the δ18O of soil water across most of the depth profile, except for the 80 cm depth at the calcareous site where a relative enrichment in 18O was observed.
Background. It has been suggested that fluid resuscitation before surgical control of hemorrhage may lead to increased bleeding because of the elevated blood pressures and clotting factor dilution. ...This study was designed to assess the effects of isotonic saline solution resuscitation on blood coagulation during uncontrolled hemorrhage.
Methods. Twenty-four female Sprague-Dawley rats were randomized into four groups with different resuscitation regimens: group A, no resuscitation; group B, 40 ml/kg in 4 minutes; group C, 80 ml/kg in 4 minutes; and group D, 80 ml/kg in 1 minute. Baseline blood samples were collected just before a sharp resection of 75% of the tail to initiate the hemorrhage; 15 minutes later the resuscitation began. Additional blood samples were obtained at 60 minutes after resection. The blood was analyzed for platelets, fibrinogen, prothrombin time, and activated partial thromboplastin time.
Results. The largest differences between time 0 and 60 minutes were observed in group D with platelets decreasing 43.36%±7.86%, fibrinogen decreasing 57.10%±16.88%, and prothrombin time increasing from an average 16.5 to 19.2 seconds. These differences were statistically significant (
p<0.05) with the Student's t test.
Conclusions. The results suggested that even though the volume of resuscitation fluid did not appear to affect clotting time when compared with that of nonresuscitated animals, the rate of extremely large volume infusions may play an important role in the cessation of bleeding and consequently in the management of uncontrolled hemorrhagic shock.
Background: Attempts to modify traditional fluid resuscitation have been based on animal models that evaluate several variables including anesthesia. This study presents the effects of early saline ...resuscitation from severe uncontrolled hemorrhage in unanesthetized rats.
Methods: Sixty-three female Sprague-Dawley rats were equally divided into three groups: group A, nonresuscitated; and groups B and C, resuscitated with isotonic saline (40 and 80 mL/kg, respectively). Hemodynamics, blood loss, survival time, and mortality were recorded for 360 minutes after the hemorrhage, which was initiated by 75% resection of the tail.
Results: In group C, 80 mL/kg of saline significantly lowered mortality (24% vs 76% and 71% for groups A and B, respectively) with concomitant increases in mean survival time (241 ± 103 min vs 146 ± 108 and 175 ± 92 min for groups A and B, respectively). There were no statistically significant differences in blood loss, hematocrit, or hemodynamic parameters among the groups.
Conclusions: Early and adequate isotonic saline resuscitation of unanesthetized rats improved outcome despite continuing hemorrhage. The significantly lower mortality rate and increased survival time were not a result of transiently improved arterial pressure and did not correlate with blood loss. No significant bleeding increases were noted in the resuscitated groups. (Surgery 1998;124:568-74.)
Current climate change models predict significant changes in rainfall patterns across Europe. To explore the effect of drought on soil CO sub(2) efflux (F sub(Soil)) and on the contribution of litter ...to F sub(Soil) we used rain shelters to simulate a summer drought (May to July 2007) in an intensively managed grassland in Switzerland by reducing annual precipitation by around 30% similar to the hot and dry year 2003 in Central Europe. We added super(13)C-depleted as well as unlabelled grass/clover litter to quantify the litter-derived CO sub(2) efflux (F sub(Litter)). Soil CO sub(2) efflux and the super(13)C/ super(12)C isotope ratio (d super(13)C) of the respired CO sub(2) after litter addition were measured during the growing season 2007. Drought significantly decreased F sub(Soil) in our litter addition experiment by 59% and F sub(Litter) by 81% during the drought period itself (May to July), indicating that drought had a stronger effect on the CO sub(2) release from litter than on the belowground-derived CO sub(2) efflux (F sub(BG), i.e. soil organic matter (SOM) and root respiration). Despite large bursts in respired CO sub(2) induced by the rewetting after prolonged drought, drought also reduced F sub(Soil) and F sub(Litter) during the entire super(13)C measurement period (April to October) by 26% and 37%, respectively. Overall, our findings show that drought decreased F sub(Soil) and altered its seasonality and its sources. Thus, the C balance of temperate grassland soils respond sensitively to changes in precipitation, a factor that needs to be considered in regional models predicting the impact of climate change on ecosystems C balance.
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