| 1. |
- Granberg, G, et al.
(författare)
-
Effects of temperature, and nitrogen and sulfur deposition, on methane emission from a boreal mire
- 2001
-
Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 82:7, s. 1982-1998
-
Tidskriftsartikel (refereegranskat)abstract
- To evaluate the effects of increased air temperature in combination with increased deposition of N and/or S on methane emission. we have raised in situ the temperature and rates of deposition of N and S in a poor fen lawn area of a boreal mixed mire. The experiment was laid out in a factorial design, where the mean daily air temperature 0.3 In above the vegetation surface was increased (by 3.6 degreesC) using greenhouse enclosures. A significant increase in the cover of sedges was observed in the N-supplemented plots after the third year of treatment. All three experimental factors had significant effects on the methane emission. The effects of temperature and N deposition strongly interacted with the sedge cover, which was the single variable explaining most variation in methane emission. Raised temperature affected the emission positively when the sedge cover was high but showed no effect when the sedge cover was low. Nitrogen addition affected methane emission negatively when the sedge cover was high and had a zero or slightly positive effect at low sedge cover. These positive temperature and negative N interaction effects with sedge cover were likely due to changed biomass allocation patterns in the plants. The S additions had negative effects on methane emissions at ambient temperature but no effect at raised temperature. This interaction effect was possibly a result of different retention of S, since the total S concentration was higher in the S addition treatments at normal but not at raised temperature. The results stress the fact that a given variable may affect biogeochemical processes in different directions or to differing degrees depending on other variables. both experimental and natural. Most importantly, the effects of added nitrogen, but also of increased temperature. were critically dependent on the density of sedges.
|
|
| 2. |
- Sjöberg, G, et al.
(författare)
-
Long-term N addition effects on the C mineralization and DOC production in mor humus under spruce
- 2003
-
Ingår i: Soil Biology & Biochemistry. - 0038-0717. ; 35:10, s. 1305-1315
-
Tidskriftsartikel (refereegranskat)abstract
- This study was based on laboratory incubations of mor humus from two N fertilized stands of Norway spruce in Sweden (Skogaby and Strasan), which had received repeated N additions (100 kg N ha(-1) yr(-1) as (NH4)(2)SO4 at Skogaby and 35, 73 and 108 kg ha(-1) yr(-1), as NH4NO3 at Strasan) during 8 and 24-29 years, respectively. The aim was to investigate long-term N effects on the mineralization of C and production of DOC. Mor humus (Oe and Oa) was incubated in columns at 20 degreesC for 49 days. Columns were leached once a week with artificial throughfall solution, which was analyzed for DOC, total N, NH4+-N and NO3--N. Prior to each leaching event, CO2 evolution from the columns was determined. C-to-N ratios in the N-treated Oe layers at Strasan (21-24) and Skogaby (24) were significantly lower than those of the controls (Strasan, 32; Skogaby, 28). The cumulative amount Of CO2-C showed a significant treatment effect in the Oe layer at Skogaby, i.e. 18 and 29 mg C g(-1) C in the N treatment and control, respectively. At Strasan, the cumulative CO2-C was significantly lower in the N3 treatment compared to the control in both layers (33 compared to 74 mg C g(-1) C in the Oe layer and 16 compared to 35 mg C g(-1) C in the Oa layer). Neither the DOC nor the DON production showed any significant treatment effects at the two sites. However, DOC was lower in the fertilized Oe layer at Skogaby throughout the incubation. The leaching of DON was highest in the Oe layers at both sites, and DON increased with time at Skogaby while there was a decreasing trend at Strasan. The DOC-to-DON ratio tended to be lower in the fertilized Oe layers at both sites. The NH4+ leaching at Skogaby decreased in the N-treated Oe and Oa layers. At Strasan, NH4+ from the Oe layer increased in N2 and control. The NO3- leaching was low and constant in both Skogaby layers. At Strasan, NO3- increased in the Oe layer of N1. Cumulative CO2 was positively correlated to C-to-N ratio (r(2) = 0.71, p < 0.01) and to cumulative DOC (r(2) = 0.63, p < 0.05) in the Oe layer at Strasan. Our conclusion was that long-term N additions caused decreased C-to-N ratios and decreased CO2 evolution rates. The correlation between CO2 and C-to-N ratio in the Oe layers at Strasan may be due to a changed quality of the fertilized forest floor material and presence of more N efficient microorganisms.
|
|
| 3. |
- Sundh, I, et al.
(författare)
-
Fluxes of methane and carbon dioxide on peat-mining areas in Sweden
- 2000
-
Ingår i: Ambio. - 0044-7447 .- 1654-7209. ; 29:8, s. 499-503
-
Tidskriftsartikel (refereegranskat)abstract
- Drainage and peat harvesting may induce considerable changes in the fluxes to the atmosphere of the greenhouse gases CH4 and CO2 in peatlands. In this study, fluxes of CH4 and CO2 were measured with the closed chamber method in 6 Swedish peatlands that are being mined. Fluxes of CH4 were much higher from ditches than from mining "strips", i.e. emissions from ditches dominated in most peatlands. The total CH4 emission during the growing season (0.41 to 4.5 g CH4 m(-2) yr(-1)) was similar to emissions from virgin peatlands. Emissions from ditches can probably be kept low by keeping the ditches clear from vegetation. Like CH4, CO2 was released to the atmosphere from both ditches and strips in most peatlands. The total emission during the growing season (0.23 to 1.0 kg CO2 m(-2) yr(-1)) was strongly dominated by the strips. Compared to the total peat yield during mining these CO2 emission rates imply that on average ca 6% of the peat carbon is lost by microbial decomposition in the mire.
|
|
| 4. |
|
|
