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- Mattsson, Marie, et al.
(författare)
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Temporal variability in bioassays of the stomatal ammonia compensation point in relation to plant and soil nitrogen parameters in intensively managed grassland
- 2009
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Ingår i: Biogeosciences. - Kaltenburg-Lindau : Copernicus Publications (on behalf of the European Geosciences Union). - 1726-4170 .- 1726-4189. ; 6:2, s. 171-179
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Tidskriftsartikel (refereegranskat)abstract
- The exchange of ammonia between crop canopies and the atmosphere depends on a range of plant parameters and climatic conditions. However, little is known about effects of management factors. We have here investigated the stomatal ammonia compensation point in response to cutting and fertilization of a grass sward dominated by Lolium perenne. Tall grass had a very low NH3 compensation point (around 1 nmol mol−1), reflecting the fact that leaf nitrogen (N) concentration was very low. During re-growth after cutting, leaf tissue concentrations of NO3−, NH4+, soluble N and total N increased along with apoplastic NH4+ concentrations. In contrast, apoplastic pH decreased resulting in largely unaltered NH3 compensation points. Nitrogen fertilization one week after cutting caused the apoplastic NH4+ concentration of the newly emerging leaves to increase dramatically. The NH3 compensation point peaked between 15 and 25 nmol mol−1 the day after the fertiliser was applied and thereafter decreased over the following 10 days until reaching the same level as before fertilisation. Ammonium concentrations in leaf apoplast, bulk tissue and litter were positively correlated (P=0.001) throughout the experimental period. Bulk tissue NH4+ concentrations, total plant N and soil NH4+ concentrations also showed a positive correlation. A very high potential for NH3 emission was shown by the plant litter.
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| 5. |
- David, M., et al.
(författare)
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Ammonia sources and sinks in an intensively managed grassland canopy
- 2009
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Ingår i: Biogeosciences. - Goettingen, Germany : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 6:9, s. 1903-1915
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Tidskriftsartikel (refereegranskat)abstract
- Grasslands represent canopies with a complex structure where sources and sinks of ammonia (NH3) may coexist at the plant level. Moreover, management practices such as mowing, hay production and grazing may change the composition of the sward and hence the source-sink relationship at the canopy level as well as the interaction with the atmosphere. There is therefore a need to understand the exchange of ammonia between grasslands and the atmosphere better, especially regarding the location and magnitude of sources and sinks. Fluxes of atmospheric NH3 within a grassland canopy were assessed in the field and under controlled conditions using a dynamic chamber technique (cuvette). These cuvette measurements were combined with extraction techniques to estimate the ammonium (NH+4 ) concentration and the pH of a given part of the plant or soil, leading to an estimated ammo- nia compensation point (Cp ). The combination of the cuvette and the extraction techniques was used to identify the poten- tial sources and sinks of NH3 within the different compart- ments of the grassland: the soil, the litter or senescent “litter leaves”, and the functioning “green leaves”. A set of six field experiments and six laboratory experiments were performed in which the different compartments were either added or removed from the cuvettes.The results show that the cuvette measurements agree with the extraction technique in ranking the strength of compartment sources. It suggests that in the studied grassland the green leaves were mostly a sink for NH3 with a compensation point around 0.1–0.4 μg m−3 and an NH3 flux of 6 to 7 ng m−2 s−1. Cutting of the grass did not increase the NH3 fluxes of the green leaves. The litter was found to be the largest source of NH3 in the canopy, with a Cp of up to 1000μgm−3 NH3 andanNH3 fluxupto90ngm−2 s−1. The litter was found to be a much smaller NH3 source when dried (Cp =160 μg m−3 and FNH3 =35 ng m−2 s−1 NH3 ). Moreover emissions from the litter were found to vary with the relative humidity of the air. The soil was a strong source of NH3 in the period immediately after cutting (Cp =320 μg m−3 and FNH3 =60 ng m−2 s−1 ), which was nevertheless always smaller than the litter source. The soil NH3 emissions lasted, however, for less than one day, and were not observed with sieved soil. They could not be solely explained by xylem sap flow extruding NH+4 . These results indicate that future research on grassland-ammonia relationships should focus on the post-mowing period and the role of litter in interaction with meteorological conditions.
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| 7. |
- Mattsson, Lars-Åke, 1945, et al.
(författare)
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Efficacy and tolerability of continuous combined hormone replacement therapy in early postmenopausal women
- 2007
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Ingår i: Menopause Int. ; 13:3, s. 124-131
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Continuous combined hormone replacement therapy (ccHRT) based on estradiol valerate (E(2)V) and medroxyprogesterone acetate (MPA) is effective for relief of menopausal symptoms three years or more after the menopause. This study was undertaken to examine the efficacy and tolerability of ccHRT in early postmenopausal women (last menstrual period 1.3 years before study entry). STUDY DESIGN: This was a 52-week, randomized, double-blind, multinational study of ccHRT comprising three different dose combinations of E(2)V/MPA in 459 early postmenopausal non-hysterectomized women experiencing 30 or more moderate to severe hot flushes a week and/or vasomotor symptoms requiring treatment. MAIN OUTCOMES MEASURES: The primary endpoint was change in frequency and severity of moderate to severe hot flushes at 12 weeks. Secondary outcome measures included number of bleeding days and evaluation of tolerability. RESULTS: The frequency of hot flushes was reduced by >/=70% after one month (P<0.001 for all doses at week 2 onwards), with little evidence of statistically different dose effects. Severity of flushing was also attenuated by ccHRT. Mean number of bleeding days fell to <1 per 28-day cycle at 52 weeks. Rates of amenorrhoea approached 80-90% at the end of the study, but were significantly lower at several time points with the highest-dose regimen (2 mg E(2)V + 5 mg MPA) than with the lower-dose options (1 mg E(2)V + 2.5 mg MPA and 1 mg E(2)V + 5 mg MPA; P<0.05). Adverse events declined in frequency over time with all regimens but throughout the study were more numerous with the highest-dose regimen than with lower doses (P= 0.0002). CONCLUSIONS: Continuous combined HRT was effective for the relief of climacteric symptoms in early postmenopausal women and was well tolerated.
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| 9. |
- Sutton, M. A., et al.
(författare)
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Dynamics of ammonia exchange with cut grassland : Strategy and implementation of the GRAMINAE Integrated Experiment
- 2009
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Ingår i: Biogeosciences. - : Copernicus Publications (on behalf of the European Geosciences Union). - 1726-4170 .- 1726-4189. ; 6:3, s. 309-331
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Tidskriftsartikel (refereegranskat)abstract
- A major international experiment on ammonia (NH3) biosphere-atmosphere exchange was conducted over intensively managed grassland at Braunschweig, Germany. The experimental strategy was developed to allow an integrated analysis of different features of NH3 exchange including: a) quantification of nearby emissions and advection effects, b) estimation of net NH3 fluxes with the canopy by a range of micrometeorological measurements, c) analysis of the sources and sinks of NH3 within the plant canopy, including soils and bioassay measurements, d) comparison of the effects of grassland management options on NH3 fluxes and e) assessment of the interactions of NH3 fluxes with aerosol exchange processes. Additional technical objectives included the inter-comparison of different estimates of sensible and latent heat fluxes, as well as continuous-gradient and Relaxed Eddy Accumulation (REA) systems for NH3 fluxes. The prior analysis established the spatial and temporal design of the experiment, allowing significant synergy between these objectives. The measurements were made at 7 measurement locations, thereby quantifying horizontal and vertical profiles, and covered three phases: a) tall grass canopy prior to cutting (7 days), b) short grass after cutting (7 days) and c) re-growing sward following fertilization with ammonium nitrate (10 days). The sequential management treatments allowed comparison of sources-sinks, advection and aerosol interactions under a wide range of NH3 fluxes. This paper describes the experimental strategy and reports the grassland management history, soils, environmental conditions and air chemistry during the experiment, finally summarizing how the results are coordinated in the accompanying series of papers.
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