| 1. |
- 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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| 2. |
- Herrmann, B., et al.
(författare)
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Vertical structure and diurnal variability of ammonia exchange potential within an intensively managed grass canopy
- 2009
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Ingår i: Biogeosciences. - Kaltenburg-Lindau : Copernicus on behalf of the European Geosciences Union. - 1726-4170 .- 1726-4189. ; 6:1, s. 15-23
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Tidskriftsartikel (refereegranskat)abstract
- Stomatal ammonia compensation points (χs) of grass species on a mixed fertilized grassland were determined by measurements of apoplastic [NH4+] and [H>+] in the field. Calculated χs values were compared with in-canopy atmospheric NH3 concentration (χa) measurements.Leaf apoplastic [NH4+] increased by a factor of two from the lowest level in the canopy to the top level. Bulk leaf [NH4+] and especially [NO3−] slightly increased at the bottom of the canopy and these concentrations were very high in senescent plant litter. Calculated χs values were below atmospheric χs at all canopy levels measured, indicating that the grassland was characterized by NH3 deposition before cutting. This was confirmed by the χa profile, showing the lowest χa close to the ground (15 cm above soil surface) and an increase in χa with canopy height. Neither χs nor χa could be measured close to the soil surface, however, the [NH4+] in the litter material indicated a high potential for NH3 emission.A diurnal course in apoplastic [NH4+] was seen in the regrowing grass growing after cutting, with highest concentration around noon. Both apoplastic and tissue [NH4+] increased in young grass compared to tall grass. Following cutting, in-canopy gradients of atmospheric χa showed NH3 emission but since calculated χs values of the cut grass were still lower than atmospheric NH3 concentrations, the emissions could not entirely be explained by stomatal NH3 loss. High tissue [NH4+] in the senescent plant material indicated that this fraction constituted an NH3 source. After fertilization, [NH4+] increased both in apoplast and leaf tissue with the most pronounced increase in the former compared to the latter. The diurnal pattern in apoplastic [NH4+] was even more pronounced after fertilization and calculated χs values were generally higher, but remained below atmospheric [NH3].
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| 3. |
- Mattsson, Marie, et al.
(författare)
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Contribution of different grass species to plant-atmosphere ammonia exchange in intensively managed grassland
- 2009
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Ingår i: Biogeosciences. - Kaltenburg-Lindau : European Geosciences Union. - 1726-4170 .- 1726-4189. ; 6:1, s. 59-66
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Tidskriftsartikel (refereegranskat)abstract
- Species diversity in grasslands usually declines with increasing input of nitrogen from fertilizers or atmospheric deposition. Conversely, species diversity may also impact the build-up of soil and plant nitrogen pools. One important pool is NH3/NH4+ which also can be exchanged between plant leaves and the atmosphere. Limited information is available on how plant-atmosphere ammonia exchange is related to species diversity in grasslands. We have here investigated grass species abundance and different foliar nitrogen pools in 4-year-old intensively managed grassland. Apoplastic pH and NH4+ concentrations of the 8 most abundant species (Lolium perenne, Phleum pratense, Festuca pratensis, Lolium multiflorum, Poa pratensis, Dactylis glomerata, Holcus lanatus, Bromus mollis) were used to calculate stomatal NH3 compensation points. Apoplastic NH4+ concentrations differed considerably among the species, ranging from 13 to 117 μM, with highest values in Festuca pratensis. Also apoplastic pH values varied, from pH 6.0 in Phleum pratense to 6.9 in Dactylis glomerata. The observed differences in apoplastic NH4+ and pH resulted in a large span of predicted values for the stomatal NH3 compensation point which ranged between 0.20 and 6.57 nmol mol−1. Three species (Lolium perenne, Festuca pratensis and Dactylis glomerata) had sufficiently high NH3 compensation point and abundance to contribute to the bi-directional NH3 fluxes recorded over the whole field. The other 5 grass species had NH3 compensation points considerably below the atmospheric NH3 concentration and were thus not likely to contribute to NH3 emission but only to NH3 uptake from the atmosphere. Evaluated across species, leaf bulk-tissue NH4+ concentrations correlated well (r2=0.902) with stomatal NH3 compensation points calculated on the basis of the apoplastic bioassay. This suggests that leaf tissue NH4+ concentrations combined with data for the frequency distribution of the corresponding species can be used for predicting the NH3 exchange potential of a mixed grass sward.
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| 4. |
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| 5. |
- Sutton, Mark A., et al.
(författare)
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Dynamics of ammonia exchange with cut grassland : Synthesis of results and conclusions of the GRAMINAE Integrated Experiment
- 2009
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Ingår i: Biogeosciences. - Goettingen : Nicolaus Copernicus University Press. - 1726-4170 .- 1726-4189. ; 6:12, s. 2907-2934
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Tidskriftsartikel (refereegranskat)abstract
- Improved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3) in the atmosphere. The GRAMINAE Integrated Experiment combined novel measurement and modelling approaches to provide the most comprehensive analysis of the interactions to date. Major intercomparisons of micrometeorological parameters and NH3 flux measurements using the aerodynamic gradient method and relaxed eddy accumulation (REA) were conducted. These showed close agreement, though the REA systems proved insufficiently precise to investigate vertical flux divergence. Grassland management had a large effect on fluxes: emissions increased after grass cutting (−50 to 700 ng m-2 s-1 NH3) and after N-fertilization (0 to 3800 ng m-2 s -1) compared with before the cut (−60 to 40 ng m-2 s -1). © Author(s) 2009.
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| 6. |
- Tonderski, Karin S., et al.
(författare)
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Våtmarker : Närsaltsfällor och/eller myllrande mångfald?
- 2003
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Ingår i: Vatten: tidskrift för vattenvård. - Nykvarn : Föreningen Vatten. - 0042-2886. ; 59:4, s. 259-270
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Tidskriftsartikel (refereegranskat)abstract
- This paper summarizes the state-of-the-art with respect to wetlands for nutrient removal and biodiversity enhancement, as expressed at a research workshop in December 2002. In the end of 2002, 260 and 884 wetlands had been constructed in Sweden with subsidies from LIP and the European Union, respectively. Most frequently, the aims were to remove nutrients from water and enhance biodiversity. The question raised is if we know how to design multifunctional wetlands. Should a wetland be deep or shallow, with or without macrophytes to be an efficient nutrient sink? Diverging opinions are presented, but generally it appears that fairly shallow wetlands at least partly covered by emergent macrophytes are favourable. The importance of extreme high flows and hydraulic short-circuiting is highlighted, and Danish and Norwegian approaches to wetlands construction are presented. Also, there is a risk that nutrient retaining wetlands develop a fairly trivial flora and fauna unless special care is taken. Intentional establishment of desirable and less common species, as well as creation of a variation of depth gradients to favour such species are such measures. Others are allowing for water level variations, as well as vegetation management such as grazing and harvesting.
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