A method for controlling the within-root CO2 concentration

Abstract A method is presented for the control of carbon dioxide concentrations within the roots of Fraxinus pennsylvanica Marsh. The results indicated a linear fit of the root CO₂ concentrations to the CO₂ levels of the treatment gases: y= l.l. x+105 (r= 0.98, 18 d.f.). The method presented for controlling CO₂ can be easily modified for other gas mixtures and plant species.     

Linkage of MIKE SHE to Wetland-DNDC for carbon budgeting and anaerobic biogeochemistry simulation

This study reports the linkage between MIKE SHE and Wetland-DNDC for carbon dynamics and greenhouse gases (GHGs) emissions simulation in forested wetland.Wetland-DNDC was modified by parameterizing management measures, refining anaerobic biogeochemical processes, and was linked to the hydrological model – MIKE SHE. As a preliminary application, we simulated the effect of water table position and forest management practices on GHGs emissions and carbon dynamics to test the capabilities of the models for simulating seasonal and long-term carbon budget. Simulation results show that water table changes had a remarkable effect on GHGs fluxes. Anaerobic conditions in forested wetland soils reduce organic matter decomposition and stimulate CH₄ production. Decrease in the water table from the wetland surface decreases methane flux, while CO₂ emission was lower with a rise in the water table. When there is a drop in water availability, wetlands can become a net source of atmospheric CO₂ as photosynthesis is decreased and respiration loss enhanced. Forest management activities i.e. harvest, fertilization and reforestation practices were parameterized in the model. We predicted carbon fluxes and stores on a pine forest under different forest management scenarios during 160 years. Results show that average long-term carbon storage in ecosystem pools increased with increasing rotation length; Soil carbon showed only minor, long-term responses to harvesting events. In contrast, carbon sequestered in tree biomass and litter fluctuated widely, in concert with the harvest cycle. Application of nitrogen fertilizer increased average carbon storage in all ecosystem pools and wood products. We presented the linkage of MIKE SHE and Wetland-DNDC as a way to use of simulation modeling tools for assessing GHGs mitigation strategies, carbon budgeting and forest management.     

A method to reduce the invasiveness of fetal catheterization in the cow

Surgical intervention in general anesthesia (GA) of the cow in late gestation is a stressful condition for both mother and fetus, potentially leading to premature delivery or fetal death. The present study hypothesized that fetal catheterization at days 246–253 (90% of gestation) is done with less physical and metabolic stress for the mother and fetus, when the surgery is performed on a standing cow and local anesthesia (LA) rather than on a recumbent cow in general anesthesia. Fetal and uterine maternal intra-vascular catheters were implanted during general anesthesia (GA, n=24) or local analgesia (LA, n=7). Blood gases and metabolite levels in the fetal calves and their mothers were measured during surgery and for 5 days post-operatively. During surgery, venous blood pH was higher (7.44±0.01 versus 7.39±0.01, P<0.05) and hemoglobin and oxygen contents lower in LA cows compared with GA cows (9.3±0.3 mg/dl versus 11.8±0.2 mg/dl, P<0.001 and 10.1±0.3 ml/dl versus 12.6±0.6 ml/dl, P<0.05). The differences between the two groups of fetuses reflected those of their dams in that LA fetuses showed lower arterial oxygen pressure (18.3±1.4 mmHg versus 24.8±1.4 mmHg, P<0.05) and hemoglobin (7.81±0.30 mg/dl versus 9.22±0.21 mg/dl P<0.01) and furthermore, they also showed higher blood glucose (2.4±0.2 mM versus 1.4±0.1 mM, P<0.01). During the 5 days post-surgery, 10 GA fetuses (42%) and 1 LA fetus (14%) died in utero. Bacterial contamination was implicated in six of the GA deaths and in the one LA death. In the dams with surviving calves, differences in hemoglobin (9.49±0.21 mg/dl versus 11.17±0.23 mg/dl P<0.001) and O₂ct (10.9±0.3 ml/dl versus 12.5±0.5 ml/dl, P<0.05) were still present, and in addition, blood glucose was higher in LA versus GA cows (4.3±0.2 mM versus 3.8±0.1 mM, P<0.05). The choice of surgical method did not affect post-surgery blood chemistry in the surviving fetuses, except that the higher blood glucose in the LA fetuses at surgery tended to be maintained also post-operatively (2.0±0.2 mM versus 1.5±0.1 mM, P=0.07). The observed differences in blood chemistry parameters between the two methods of surgery and possibly in the fetal death may be explained by differences in catheterization method and the associated differences in physical and metabolic stress during and after surgery. Thus, surgery upon a standing cow in local anesthesia should be considered as an alternative to surgery in universal anesthesia for fetal catheterization in the cow in late gestation.     

Effect of ethylene and culture environment on development of papaya nodal cultures

Papaya (Carica papaya L.) nodal cultures modified the atmosphere of the headspace of the vessel used for culture maintenance by producing ethylene. Under culture maintenance nodal cultures grew poorly and leaves senesced. Incubating nodal cultures under a range of ethylene concentrations suggested that this poor performance was caused in part, by the production of ethylene and its accumulation in the headspace of the vessel. To further evaluate the role of ethylene accumulation in growth suppression, aminoethoxyvinylglycine (AVG), 1-aminocyclopropane-1-carboxylic acid (ACC) and silver thiosulphate (STS), were added to the nutrient medium and ethylene measurements performed during culture growth. The ethylene-suppressant, AVG, (1.2 μM) and the ethylene-antagonist, STS, (0.3 mM) significantly improved nodal culture growth (283 and 289% respectively), leaf area production (350 and 211% respectively) and reduced leaf senescence, while the ethylene-precursor, ACC, (1.5 mM) significantly decreased culture growth (71%), leaf area production (88%) and promoted leaf senescence. Furthermore, nodal culture growth was significantly better at 20 °C than 30 °C since ethylene production and accumulation were less in these conditions. Better control or management of ethylene accumulation produces healthier nodal cultures for micro-propagation and may be a way of improving productivity of other papaya shoot culture systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Elevated CO2 and nutrient addition after soil N cycling and N trace gas fluxes with early season wet-up in a California annual grassland

We examined the effects of growth carbon dioxide (CO₂)concentration and soil nutrient availability on nitrogen (N)transformations and N trace gas fluxes in California grasslandmicrocosms during early-season wet-up, a time when rates of Ntransformation and N trace gas flux are high. After plant senescenceand summer drought, we simulated the first fall rains and examined Ncycling. Growth at elevated CO₂ increased root productionand root carbon:nitrogen ratio. Under nutrient enrichment, elevatedCO₂ increased microbial N immobilization during wet-up,leading to a 43% reduction in gross nitrification anda 55% reduction in NO emission from soil. ElevatedCO₂ increased microbial N immobilization at ambientnutrients, but did not alter nitrification or NO emission. ElevatedCO₂ did not alter soil emission of N₂O ateither nutrient level. Addition of NPK fertilizer (1:1:1) stimulatedN mineralization and nitrification, leading to increased N₂Oand NO emission from soil. The results of our study support a mechanisticmodel in which elevated CO₂ alters soil N cycling and NOemission: increased root production and increased C:N ratio in elevatedCO₂ stimulate N immobilization, thereby decreasingnitrification and associated NO emission when nutrients are abundant.This model is consistent with our basic understanding of how C availabilityinfluences soil N cycling and thus may apply to many terrestrial ecosystems.     

Copper exposure impairs intra- and extracellular acid-base regulation during hypercapnia in the fresh water rainbow trout (Oncorhynchus mykiss)

In order to evaluate the impact of water-borne copper on acid-base regulation in fresh water rainbow trout, chronically cannulated fish were exposed to copper (0.6 mg 1⁻¹), hypercapnia (water PCO₂ of 6 mmHg) or a combination of copper and hypercapnia, while a fourth untreated group served as the control. Blood samples obtained at 0 h, 4 h and 24 h were analysed for acid-base status, ion concentrations and respiratory parameters. Tissue samples from caudal skeletal muscle, liver and gill filaments were examined for intracellular acid-base status, ion- and water contents, and copper concentration. Exposure to copper alone elicited a small extracellular metabolic alkalosis, no changes in arterial PO₂, and a minor decrease in plasma ion concentrations. Hypercapnia alone increased arterial PCO₂ from approximately 2 mmHg to 7.2 mmHg, but the extracellular respiratory acidosis present at 4 h was almost completely compensated at 24 h due to an increase in plasma bicarbonate concentration [HCO₃ ⁻] from 8.1 mM to 24.4 mM. Combined exposure to hypercapnia and copper resulted in a slightly larger acidosis at 4 h, and the fish failed to restore extracellular pH at 24 h, because plasma [HCO₃ ⁻] only increased to 16.3 mM. Fish exposed to hypercapnia and copper also showed a delayed recovery of intracellular pH in skeletal muscle, compared to fish exposure to hypercapnia only. Thus, copper exposure impaired both extracellular and intracellular acid-base regulation during hypercapnia. When seen in connection with only minor effects of copper on osmoregulatory and respiratory parameters, the reduced ability to regulate acid-base suggests that acid-base regulation may be one of the most copper-sensitive branchial functions. Accepted: 18 August 1998     

Release and uptake of volatile inorganic and organic gases through the snowpack at Niwot Ridge,Colorado

Whole air drawn from four heights within the high elevation (3,340 m asl), deep, winter snowpack at Niwot Ridge, Colorado, were sampled into stainless steel canisters, and subsequently analyzed by gas chromatography for 51 volatile inorganic and organic gases. Two adjacent plots with similar snow cover were sampled, one over bare soil and a second one from within a snow-filled chamber where Tedlar/Teflon-film covered the ground and isolated it from the soil. This comparison allowed for studying effects from processes in the snowpack itself versus soil influences on the gas concentrations and fluxes within and through the snowpack. Samples were also collected from ambient air above the snow surface for comparison with the snowpack air. Analyzed gas species were found to exhibit three different kinds of behavior: (1) One group of gases, i.e., carbon dioxide (CO₂), chloroform (CHCl₃), dimethylsulfide (CH₃)₂S, carbondisulfide (CS₂), and dichlorobromomethane (CHBrCl₂), displayed higher concentrations inside the snow, indicating a formation of these species and release into the atmosphere. (2) A second group of compounds, including carbon monoxide (CO), carbonyl sulfide (COS), the hydrocarbons methane, ethane, ethyne, benzene, and the halogenated compounds methylchloride (CH₃Cl), methylbromide (CH₃Br), dibromomethane (CH₂Br₂), bromoform (CHBr₃), tetrachloromethane (CCl₄), CFC-11, CFC-12, HCFC-22, CFC-113, 1,2-dichloroethane, methylchloroform, HCFC-141b, and HCFC-142b, were found at lower concentrations in the snow, indicating that the snow and/or soil constitute a sink for these gases. (3) For 21 other gases absolute concentrations, respectively concentration gradients, were too low to unequivocally identify their uptake or release behavior. For gases listed in the first two groups, concentration gradients were incorporated into a snowpack gas diffusion model to derive preliminary estimates of fluxes at the snow-atmosphere interface. The snowpack gradient flux technique was found to offer a highly sensitive method for the study of these surface gas exchanges. Microbial activities below this deep, winter snowpack appear to be the driving mechanism behind these gas sources and sinks. Flux results were applied to a simple box model to assess the potential contribution of the snowpack uptake rates to atmospheric lifetimes of these species.     

Soil–atmosphere exchange of greenhouse gases in a Eucalyptus marginata woodland, a clover-grass pasture, and Pinus radiata and Eucalyptus globulus plantations

Soils provide the largest terrestrial carbon store, the largest atmospheric CO₂ source, the largest terrestrial N₂O source and the largest terrestrial CH₄ sink, as mediated through root and soil microbial processes. A change in land use or management can alter these soil processes such that net greenhouse gas exchange may increase or decrease. We measured soil–atmosphere exchange of CO₂, N₂O and CH₄ in four adjacent land‐use systems (native eucalypt woodland, clover‐grass pasture, Pinus radiata and Eucalyptus globulus plantation) for short, but continuous, periods between October 2005 and June 2006 using an automated trace gas measurement system near Albany in southwest Western Australia. Mean N₂O emission in the pasture was 26.6 μg N m⁻² h⁻¹, significantly greater than in the natural and managed forests (< 2.0 μg N m⁻² h⁻¹). N₂O emission from pasture soil increased after rainfall events (up to 100 μg N m⁻² h⁻¹) and as soil water content increased into winter, whereas no soil water response was detected in the forest systems. Gross nitrification through ¹⁵N isotope dilution in all land‐use systems was small at water holding capacity < 30%, and under optimum soil water conditions gross nitrification ranged between < 0.1 and 1.0 mg N kg⁻¹ h⁻¹, being least in the native woodland/eucalypt plantation < pine plantation < pasture. Forest soils were a constant CH₄ sink, up to −20 μg C m⁻² h⁻¹ in the native woodland. Pasture soil was an occasional CH₄ source, but weak CH₄ sink overall (−3 μg C m⁻² h⁻¹). There were no strong correlations (R < 0.4) between CH₄ flux and soil moisture or temperature. Soil CO₂ emissions (35–55 mg C m⁻² h⁻¹) correlated with soil water content (R < 0.5) in all but the E. globulus plantation. Soil N₂O emissions from improved pastures can be considerable and comparable with intensively managed, irrigated and fertilised dairy pastures. In all land uses, soil N₂O emissions exceeded soil CH₄ uptake on a carbon dioxide equivalent basis. Overall, afforestation of improved pastures (i) decreases soil N₂O emissions and (ii) increases soil CH₄ uptake.     

Benefits and trade‐offs of replacing synthetic fertilizers by animal manures in crop production in China: A meta‐analysis

Recycling of livestock manure to agricultural land may reduce the use of synthetic fertilizer and thereby enhance the sustainability of food production. However, the effects of substitution of fertilizer by manure on crop yield, nitrogen use efficiency (NUE), and emissions of ammonia (NH₃), nitrous oxide (N₂O) and methane (CH₄) as function of soil and manure properties, experimental duration and application strategies have not been quantified systematically and convincingly yet. Here, we present a meta‐analysis of these effects using results of 143 published studies in China. Results indicate that the partial substitution of synthetic fertilizers by manure significantly increased the yield by 6.6% and 3.3% for upland crop and paddy rice, respectively, but full substitution significantly decreased yields (by 9.6% and 4.1%). The response of crop yields to manure substitution varied with soil pH and experimental durations, with relatively large positive responses in acidic soils and long‐term experiments. NUE increased significantly at a moderate ratio (<40%) of substitution. NH₃ emissions were significantly lower with full substitution (62%–77%), but not with partial substitution. Emissions of CH₄ from paddy rice significantly increased with substitution ratio (SR), and varied by application rates and manure types, but N₂O emissions decreased. The SR did not significantly influence N₂O emissions from upland soils, and a relative scarcity of data on certain manure characteristic was found to hamper identification of the mechanisms. We derived overall mean N₂O emission factors (EF) of 0.56% and 0.17%, as well as NH₃ EFs of 11.1% and 6.5% for the manure N applied to upland and paddy soils, respectively. Our study shows that partial substitution of fertilizer by manure can increase crop yields, and decrease emissions of NH₃ and N₂O, but depending on site‐specific conditions. Manure addition to paddy rice soils is recommended only if abatement strategies for CH₄ emissions are also implemented.     

Simulated dynamics of Ne@C60 aggregates beyond dissociation

Molecular dynamics (MD) computer simulations are utilized to better understand the dynamics of small (N = 5) endohedral Ne@C₆₀ aggregates. Multiple runs at various temperatures are used to increase the reliability of our statistics. The aggregate holds together until somewhere between T = 1150 and 1200 K, where it dissociates, showing no intermediate sign of melting or fullerene disintegration. When the temperature is increased to around T = 4000 K, the encapsulated neon atoms begin to leave the aggregate, with the fullerene molecules still remaining intact. At temperatures near T = 4400 K, thermal disintegration of the fullerenes preempts the aggregate dissociation. Above this temperature neon atoms are more quickly released and the fullerenes form a larger connected structure, with bonding taking place in atom pairs from different original fullerene molecules. Escape constants and half lives are calculated for the temperature range 4000 K ≤ T ≤ 5000 K. The agreements and disagreements of results of this work with experiments suggest that classical MD simulations are useful in describing fullerene systems at low temperatures and near disintegration, but require development of new techniques before it is possible to accurately model windowing at temperatures below T = 3000 K.