Linearity and temperature control of the Fleisch pneumotachograph

We have investigated the optimal thermal conditions of a Fleisch no. 4 pneumotachograph (PT) necessary for recording maximal forced expiratory maneuvers (MFEM). Our PT assembly was tested with a computer-driven pump and found to be linear up to 14 l/s. Thermocouples (TC) were placed in a peripheral, mid, and a central capillary of the PT. Stable temperature control and consistent PT calibration were best obtained by proportional thermostatic control via the peripheral TC. When the PT was heated to 35 degrees C or above, expirations from either the pump (air at 33 degrees C saturated) or a subject cooled the PT, thus affecting its response. With the PT heated to 30 degrees C, repeated blows caused little change in PT temperature, with no evidence of condensation, thus indicating optimal thermal conditions for recording MFEM.     

Effects of tree species composition on the CO2 and N2O efflux of a Mediterranean mountain forest soil

Background and Aims

Tree species composition shifts can alter soil CO₂ and N₂O effluxes. We quantified the soil CO₂ and N₂O efflux rates and temperature sensitivity from Pyrenean oak, Scots pine and mixed stands in Central Spain to assess the effects of a potential expansion of oak forests.

Methods

Soil CO₂ and N₂O effluxes were measured from topsoil samples by lab incubation from 5 to 25 °C. Soil microbial biomass and community composition were assessed.

Results

Pine stands showed highest soil CO₂ efflux, followed by mixed and oak forests (up to 277, 245 and 145 mg CO₂-C m^?2 h^?1, respectively). Despite contrasting soil microbial community composition (more fungi and less actinomycetes in pine plots), carbon decomposability and temperature sensitivity of the soil CO₂ efflux remain constant among tree species. Soil N₂O efflux rates and its temperature sensitivity was markedly higher in oak stands than in pine stands (70 vs. 27 μg N₂O-N m^?2 h^?1, Q₁₀, 4.5 vs. 2.5).

Conclusions

Conversion of pine to oak forests in the region will likely decrease soil CO₂ effluxes due to decreasing SOC contents on the long run and will likely enhance soil N₂O effluxes. Our results present only a seasonal snapshot and need to be confirmed in the field.     

Effect of O2 and CO2 in N2, He, and SF6 on chick embryo blood pressure and heart rate

Arterial pressure of chick embryos was measured electromanometrically to investigate the effect of altered gaseous environments on blood pressure (BP) and heart rate (HR). The experiments were made in eggs incubated for 14-16 days at 38 degrees C without impeding the diffusive respiratory gas exchange through the shell and chorioallantois. In air, the HR was counted 260-270 beats/min and the BP increased from 14/7 Torr at day 14 to 21/12 Torr at day 16. Both the BP and HR decreased with hypoxia, whereas hyperoxia affected a slight increase in BP and little change in HR. Hypercapnia decreased the HR and tended to enhance a systolic maximum pressure. The effect of hypoxia was augmented markedly in the presence of hypercapnia and vice versa. When N2 was replaced with helium (He), the effect of hypoxia was mitigated significantly. On the contrary, replacement of N2 with sulfur hexafluoride (SF6) augmented the effect of hypoxia. Because the respiratory gas exchange of the egg takes place by diffusion through the shell and chorioallantoic capillaries, the effect of He and SF6 atmospheres on BP and HR is attributed to an altered diffusivity of O2 and CO2 in these inert gases.     

Fluxes of N2O,CH4 and CO2 on afforested boreal agricultural soils

After drainage of natural boreal peatlands, the decomposition of organic matter increases and peat soil may turn into a net source of CO₂ and N₂O, whereas CH₄ emission is known to decrease. Afforestation is a potential mitigation strategy to reduce greenhouse gas emission from organic agricultural soils. A static chamber technique was used to evaluate the fluxes of CH₄, N₂O and CO₂ from three boreal organic agricultural soils in western Finland, afforested 1, 6 or 23 years before this study. The mean emissions of CH₄ and N₂O during the growing seasons did not correlate with the age of the tree stand. All sites were sources of N₂O. The highest daily N₂O emission during the growing season, measured in the oldest site, was as high as 29 mg N₂O m^–2d^–1. In general, organic agricultural soils are sinks for methane. Here, the oldest site acted as a small sink for methane, whereas the two youngest afforested organic soils were sources for methane with maximum emission rates (up to 154 mg m^–2d^–1) similar to those reported for minerogenous natural peatlands. Soil respiration rates decreased with the age of the forest. The high soil respiration in the younger sites, probably resulted from the high biomass production of herbs, could create soil anaerobiosis and increase methane production. Our results show that afforestation of agricultural peat soils does not abruptly terminate the N₂O emissions during the first two decades, and afforestation can even enhance methane emission for a few years. The carbon accumulation in the developing tree stand can partly compensate the carbon loss from soil.     

Synthesis of biomolecules from N2, CO,and H2O by electric discharge

A model primitive gas containing a mixture of N₂, CO and water vapor over a water pool (300 mL, 37 °C) was subjected to electric discharges. The discharge vessel (7 L in volume) was equipped with a CO₂ absorber (The CO₂ being formed during the discharge), thus simulating possible absorption of CO₂ in the primitive ocean. The vessel also has a cold trap ( –15 °C), which protects the primary products against the further decomposition in the discharge phase by enabling these products to adhere to the trap. Since the partial pressures of CO and N₂ decreased at rates of 1.5–1.7 cmHg day^–1 and 0.1–0.2 cmHg day^–1, respectively, the gases were added at regular intervals. The solution was analyzed at regular intervals for HCN, HCHO and urea, and maximum concentrations of about 50, 2, and 140 mM were observed. The discharge phase was continued for 6 months. In the solution, glycine (5.6% yield based on the carbon), glycylglycine (0.64%), orotic acid (0.004%) and small amounts of the other amino acids were found.     

Influence of carbon availability on the production of NO, N2O, N2 and CO2 by soil cores during anaerobic incubation

Net productions of permanent soil atmosphere gases (N₂, CO₂, O₂) and temporary gases (N₂O, NO) were monitored in soil cores using a non-interfering, fully automated measuring technique allowing highly time resolved measurements over prolonged periods. The influence of changes in available organic carbon on CO₂, N₂O, NO and N₂ production was studied by changing the soil carbon content through aerobic preincubations of different length, up to 21 days.The aerobic preincubation caused an increase in NO₃ ^- concentration and a decrease in available carbon content. Available carbon content dominated both CO₂ and total N gas (N₂+N₂O+NO) production during anaerobiosis. Both CO₂ and total N gas production rates decreased with increasing length of the previous aerobic preincubation, this in spite of the higher initial NO₃ ^- concentration.Total denitrification rates were closely related to the anaerobic CO₂ production rates. No relation was found between water soluble carbon content and total denitrification. The N₂O/N₂ ratio could be explained by an interaction of carbon availability, NO₃ ^- concentration and enzyme status. Net N₂O consumption was monitored. The balance between cumulative total N gas production and NO₃ ^- consumption varied according to the different treatments. Cumulative N₂O production exceeded cumulative N₂ production for 0 up to 5 days.     

Soil-atmosphere exchange of CH4, CO2, NOx,and N2O in the Colorado shortgrass steppe under elevated CO2

In late March 1997, an open-top-chamber (OTC) CO₂ enrichment study was begun in the Colorado shortgrass steppe. The main objectives of the study were to determine the effect of elevated CO₂ (720 mol mol^–1) on plant production, photosynthesis, and water use of this mixed C₃/C₄ plant community, soil nitrogen (N) and carbon (C) cycling and the impact of changes induced by CO₂ on trace gas exchange. From this study, we report here our weekly measurements of CO₂, CH₄, NO_x and N₂O fluxes within control (unchambered), ambient CO₂ and elevated CO₂ OTCs. Soil water and temperature were measured at each flux measurement time from early April 1997, year round, through October 2000. Even though both C₃ and C₄ plant biomass increased under elevated CO₂ and soil moisture content was typically higher than under ambient CO₂ conditions, none of the trace gas fluxes were significantly altered by CO₂ enrichment. Over the 43 month period of observation NO_x and N₂O flux averaged 4.3 and 1.7 in ambient and 4.1 and 1.7 g N m^–2 hr ^–1 in elevated CO₂ OTCs, respectively. NO_x flux was negatively correlated to plant biomass production. Methane oxidation rates averaged –31 and –34 g C m^–2 hr^–1 and ecosystem respiration averaged 43 and 44 mg C m^–2 hr^–1 under ambient and elevated CO₂, respectively, over the same time period.     

Dynamics of dissolved O2, CO2, CH4, and N2O in a tropical coastal swamp in southern Thailand

We studied the distribution of dissolved O₂, CO₂, CH₄, and N₂O in a coastal swamp system in Thailand with the goal to characterize the dynamics of these gases within the system. The gas concentrations varied spatially and seasonally in both surface and ground waters. The entire system was a strong sourcefor CO₂ and CH₄, and a possible sink for atmospheric N₂O. Seasonal variation in precipitation primarily regulated the redox conditions in the system. However, distributions of CO₂, CH₄, and N₂O in the river that received swamp waters were not always in agreement with redox conditions indicated by dissolvedO₂ concentrations. Sulfate production through pyriteoxidation occurred in the swamp with thin peat layerunder aerobic conditions and was reflected by elevatedSO ₄ ^2– /Cl^– in the river water. When SO ₄ ^2– /Cl^– was high, CO₂ and CH₄ concentrations decreased, whereas the N₂O concentration increased. The excess SO ₄ ^2– in the river water was thus identified as a potential indicator for gas dynamics in this coastal swamp system.     

Microbially mediated CH4 consumption and N2O emission is affected by elevated CO2, soil water content, and composition of semi-arid grassland species

Elevated CO₂ affects plant productivity, but also water availability and plant species composition in semi-arid grasslands, thereby potentially causing complex effects on CH₄ consumption and N₂O emission. We studied the effects of atmospheric CO₂ concentration (400 vs 780 μL L^?1), water content (15 vs 20% gravimetric soil moisture), and composition of semi-arid grassland species (perennial grasses Bouteloua gracilis, Hesperostipa comata, and Pascopyrum smithii; sub-shrub Artemisia frigida; invasive forb Linaria dalmatica grown in monoculture and all five species together) on CH₄ consumption and N₂O emission in a full factorial greenhouse experiment. We used a unique method where we measured microbial effects on CH₄ consumption and N₂O emission in isolation from effects of gas diffusivity. Microbially mediated CH₄ consumption was significantly higher under elevated CO₂ (by 20%), but was not affected by soil water content or plant species composition. Microbially mediated N₂O emission was not significantly affected by elevated CO₂, but was significantly higher with high water content (by 67%) and differed significantly among species. Treatment effects on CH₄ consumption and N₂O emission often could not be explained simply by differences in soil moisture, suggesting that treatment-induced changes in other soil and microbial properties played a role in causing these effects.     

CO2和O3浓度倍增及其复合作用对大豆叶绿素含量的影响

利用开顶箱(OTC)法研究了在CO2和O3浓度倍增及其复合作用下,大豆叶片叶绿素含量及叶绿素a／b值的变化规律。结果表明,不同生育时期大豆叶片中叶绿素含量不同,Chla、Chlb和ChlT都表现出低．高一低的趋势,而且不同处理间变化不同步。不同处理间比较,O3处理的植株叶绿素含量下降最为明显,其次是复合处理的影响,而CO2浓度倍增对提高叶片叶绿素含量有一定的作用。Chla/b呈下降趋势,受CO2倍增影响最明显,有利于提高作物的光合性能。     

Fungal community composition and metabolism under elevated CO2 and O3

Atmospheric CO₂ and O₃ concentrations are increasing due to human activity and both trace gases have the potential to alter C cycling in forest ecosystems. Because soil microorganisms depend on plant litter as a source of energy for metabolism, changes in the amount or the biochemistry of plant litter produced under elevated CO₂ and O₃ could alter microbial community function and composition. Previously, we have observed that elevated CO₂ increased the microbial metabolism of cellulose and chitin, whereas elevated O₃ dampened this response. We hypothesized that this change in metabolism under CO₂ and O₃ enrichment would be accompanied by a concomitant change in fungal community composition. We tested our hypothesis at the free-air CO₂ and O₃ enrichment (FACE) experiment at Rhinelander, Wisconsin, in which Populus tremuloides, Betula papyrifera, and Acer saccharum were grown under factorial CO₂ and O₃ treatments. We employed extracellular enzyme analysis to assay microbial metabolism, phospholipid fatty acid (PLFA) analysis to determine changes in microbial community composition, and polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE) to analyze the fungal community composition. The activities of 1,4-β-glucosidase (+37%) and 1,4,-β-N-acetylglucosaminidase (+84%) were significantly increased under elevated CO₂, whereas 1,4-β-glucosidase activity (−25%) was significantly suppressed by elevated O₃. There was no significant main effect of elevated CO₂ or O₃ on fungal relative abundance, as measured by PLFA. We identified 39 fungal taxonomic units from soil using DGGE, and found that O₃ enrichment significantly altered fungal community composition. We conclude that fungal metabolism is altered under elevated CO₂ and O₃, and that there was a concomitant change in fungal community composition under elevated O₃. Thus, changes in plant inputs to soil under elevated CO₂ and O₃ can propagate through the microbial food web to alter the cycling of C in soil.     

Biomass allocation, needle structural characteristics and nutrient composition in Scots pine seedlings exposed to elevated CO2 and O3 concentrations

Three-year-old Scots pine (Pinus sylvestris L.) seedlings were exposed to ambient or elevated ozone (O₃) (1.52ambient) and carbon dioxide (CO₂) (590 µmol mol^-1) concentrations during two growing seasons in open-top field chambers (OTCs). Five different treatments were applied in the chambers: filtered air, ambient air, elevated O₃, elevated CO₂, and elevated O₃ and CO₂ combined. Ambient plots outside the OTCs were also included, but the chamber ambient was used as a control in O₃ and CO₂ treatments due to a significant chamber effect. Increases in yellowing and chlorotic mottling of previous-year (C+1) needles and in the amount of cytoplasmic ribosomes and electron density of the chloroplast stroma in current-year (C) and C+1 needle mesophyll cells were observed in elevated O₃ at both CO₂ concentrations. Elevated O₃ alone caused a non-significant 10.9% decrease in plant total dry mass and a significant decrease in manganese (Mn) content of C needles. CO₂ enrichment caused a significant increase in needle cross-sectional width after the first year of exposure, and an accumulation of starch and slight curling and swelling of the chloroplast thylakoids in the mesophyll tissue of C needles after the second year of exposure. Calcium and Mn contents were increased and copper and nitrogen contents were decreased, significantly, in CO₂-exposed needles. A non-significant 19.1% increase in plant total dry mass was measured in elevated CO₂ alone, whereas a 14.8% reduction in total dry mass, together with a significant reduction in current-year main shoot length, was found in the combined treatment. Overall, in spite of decreases in O₃-induced visible injuries by CO₂, elevated CO₂ levels were not able to counteract the impact of O₃ in this experiment.     

Effects of elevated CO2 and O3 on N-cycling and N2O emissions: a short-term laboratory assessment

Background and aims

Elevated atmospheric CO₂ (eCO₂) and tropospheric O₃ (eO₃) can alter soil microbial processes, including those underlying N₂O emissions, as an indirect result of changes in plant inputs. In this study, effects of eCO₂ and eO₃ on sources of N₂O in a soybean (Glycine max (L.) Merr.) agroecosystem in Illinois (SoyFACE) were investigated. We hypothesized that increases in available C and anaerobic microhabitat under eCO₂ would stimulate N₂O emissions, with a proportionally larger increase in denitrification derived N₂O (N₂O_D) compared to nitrification plus nitrifier denitrification derived N₂O (N₂O_N+ND). We expected opposite effects under eO₃.

Methods

Isotopically labeled ¹⁵NH ₄ ¹⁴ NO₃ and ¹⁴NH ₄ ¹⁵ NO₃ were used to evaluate mineral N transformations, N₂O_D, and N₂O_N+ND in a 12-day incubation experiment.

Results

We observed minimal effects of eCO₂ and eO₃ on N₂O emissions, movement of ¹⁵?N through mineral N pools, soil moisture content and C availability. Possibly, altered C and N inputs by eCO₂ and eO₃ were small relative to the high soil organic C content and N-inputs via biological N₂-fixation, minimizing potential effects of eCO₂ and eO₃ on N-cycling.

Conclusion

We conclude that eCO₂ and eO₃ did not affect N₂O emissions in the short term. However, it remains to be tested whether N₂O emissions in SoyFACE will be unaltered by eCO₂ and eO₃ on a larger temporal scale under field conditions.     

Effects of bovine urine, plants and temperature on N2O and CO2 emissions from a sub-tropical soil

Grazing ruminants urinate and deposit N onto pastoral soils at rates up to 1,000 kg ha^?1, with most of this deposited N present as urea. In urine patches, nitrous oxide (N₂O) emissions can increase markedly. Soil derived CO₂ fluxes can also increase due to priming effects.While N₂O fluxes are affected by temperature, no studies have examined the interaction of pasture plants, urine and temperature on N₂O fluxes and the associated CO₂ fluxes. We postulated the response of N₂O emissions to bovine urine application would be affected by plants and temperature. Dairy cattle urine was collected, labelled with ¹⁵N, and applied at 590 kg N ha^?1 to a sub-tropical soil,with and without pasture plants at 11°, 19°, and 23°C. Over the experimental period (28 days), 0.2% (11°C with plants) to 2.2% (23°C with plants) of the applied N was emitted as N₂O. At 11°C, plants had no effect on cumulative N₂O-N fluxes, whereas at 23°C, the presence of plants significantly increased the flux, suggesting plant-derived C supply affected the N₂O producing microbes. In contrast, a significant urine application effect on the cumulative CO₂ flux was not affected by varying temperature from 11?C23°C or by growing plants in the soil. This study has shown that plants and their responses to temperature affect N₂O emissions from ruminant urine deposition. The results have significant implications for forecasting and understanding the effect of elevated soil temperatures on N₂O emissions and CO₂ fluxes from grazed pasture systems.     

Drainage increases CO2 and N2O emissions from tropical peat soils

Tropical peatlands are vital ecosystems that play an important role in global carbon storage and cycles. Current estimates of greenhouse gases from these peatlands are uncertain as emissions vary with environmental conditions. This study provides the first comprehensive analysis of managed and natural tropical peatland GHG fluxes: heterotrophic (i.e. soil respiration without roots), total CO₂ respiration rates, CH₄ and N₂O fluxes. The study documents studies that measure GHG fluxes from the soil (n = 372) from various land uses, groundwater levels and environmental conditions. We found that total soil respiration was larger in managed peat ecosystems (median = 52.3 Mg CO₂ ha^?1 year^?1) than in natural forest (median = 35.9 Mg CO₂ ha^?1 year^?1). Groundwater level had a stronger effect on soil CO₂ emission than land use. Every 100 mm drop of groundwater level caused an increase of 5.1 and 3.7 Mg CO₂ ha^?1 year^?1 for plantation and cropping land use, respectively. Where groundwater is deep (≥0.5 m), heterotrophic respiration constituted 84% of the total emissions. N₂O emissions were significantly larger at deeper groundwater levels, where every drop in 100 mm of groundwater level resulted in an exponential emission increase (exp(0.7) kg N ha^?1 year^?1). Deeper groundwater levels induced high N₂O emissions, which constitute about 15% of total GHG emissions. CH₄ emissions were large where groundwater is shallow; however, they were substantially smaller than other GHG emissions. When compared to temperate and boreal peatland soils, tropical peatlands had, on average, double the CO₂ emissions. Surprisingly, the CO₂ emission rates in tropical peatlands were in the same magnitude as tropical mineral soils. This comprehensive analysis provides a great understanding of the GHG dynamics within tropical peat soils that can be used as a guide for policymakers to create suitable programmes to manage the sustainability of peatlands effectively.     

渗滤液负荷和灌溉深度对土壤氧化亚氮与二氧化碳释放的影响

采用预设取样器和静态箱气相色谱法,对渗滤液灌溉条件下,土柱土壤不同深度剖面 N2O的浓度以及N2O和CO2的表面释放通量进行了监测.结果表明: 渗滤液灌溉可促进N2O的生成和释放,灌溉后24 h内土柱N2O的释放通量与表土下10 cm(r=0.944,P< 0.01)、20 cm(r=0.799,P<0.01)、30 cm(r=0.666,P<0.01)和40 cm(r=0.482,P<0.05)处所生成的N2O浓度呈显著相关,且相关程度依次递减.渗滤液灌溉还促进了CO2的释放,但N2O与CO2释放通量之间无显著相关性(P>0.05).渗滤液的灌溉负荷主要决定温室气体释放总量的强弱(N2O和CO2,以CO2当量计),灌溉负荷为6 mm·d-1条件下温室气体释放总量为灌溉负荷2 mm·d-1的3倍多.采用表土下20 cm处灌溉方式可比表土下10 cm处灌溉方式削减47%的温室气体释放总量.渗滤液灌溉土壤14 d内,N2O释放量约占温室气体释放总量的57.0%～91.0%.