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| 2. |
- Choma, Michal, et al.
(författare)
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Recovery of the ectomycorrhizal community after termination of long-term nitrogen fertilisation of a boreal Norway spruce forest
- 2017
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Ingår i: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 29, s. 116-122
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Elsevier Ltd and British Mycological Society.Ectomycorrhizal fungi (ECM) are a fundamental component of boreal forests promoting tree growth and participating in soil nutrient cycling. Increased nitrogen (N) input is known to largely influence ECM communities but their potential recovery is not well understood. Therefore, we studied the effects of long-term N-fertilisation on ECM communities, and their recovery after termination of N treatment. Fungal ITS sequencing data indicated that N-fertilisation (34 kg N ha-1 y-1) for 46 y decreased the relative abundance of ECM species in the fungal community and suppressed originally dominating medium-distance fringe exploration types adapted to N-limited conditions, while the ECM diversity remained unaffected. In other plots, 23 y after termination of fertilisation at 73 kg N ha-1 y-1 for 23 y, the relative abundance of ECM species shifted closer to, but did not reach, control levels. These observations indicate only slow recovery of ECM community, likely due to a high soil N retention capacity.
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| 3. |
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| 4. |
- Rappe George, Martin, et al.
(författare)
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Indications that long-term nitrogen loading limits carbon resources for soil microbes
- 2017
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 115, s. 310-321
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Tidskriftsartikel (refereegranskat)abstract
- Microbial communities in the organic horizon (O-horizon) of forest soils play key roles in terrestrial nitrogen (N) cycling, but effects on them of long-term high N loading, by N deposition or experimental addition, are not fully understood. Thus, we investigated N-loading effects on soil microbial biomass N, carbon (C) and phosphorus stoichiometry, hydrolytic and oxidative enzymes, community composition (via phospholipid fatty acids, PLFA) and soil chemistry of the O-horizon in study plots of three well-studied experimental Norway spruce (Picea abies) forests in Sweden and the Czech Republic. These forests span substantial gradients in current N deposition, experimental N addition and nitrate (NO3 −) leaching. Current N deposition ranges from ∼3 kg ha−1 year−1 of N in central Sweden (Stråsan) to ∼15 kg ha−1 year−1 of N in SW Sweden (Skogaby) and Czech Republic (Čertovo). Furthermore, accumulated historical N loading during 1950–2000 (which include experimental N addition performed at Stråsan and Skogaby) ranged ∼200–∼2000 kg ha−1 of N. Across all sites and treatments, current NO3 − leaching ranged from low (∼0.1 kg ha−1 year−1 of N) at Stråsan, to high (∼15 kg ha−1 year−1 of N) at Skogaby and Čertovo. We found significantly lower C/N ratios and greater amounts of extractable inorganic N species in the forest soils’ O-horizons at the high N loading plots. Microbial biomass and basal respiration decreased under experimental N addition treatments and tended to decrease with increased N deposition. Similarly, activities of hydrolytic enzyme activity associated with N acquisition were lower, although differences in activities at specific sites with the highest and intermediate historical N deposition levels failed statistical significance. Conversely, activities of soil hydrolytic enzymes associated with C acquisition were greater in study plots exposed high N loading. PLFA profiles indicated shifts in microbial community composition induced by long-term N load, towards higher and lower relative abundance of Gram-positive and Gram-negative bacteria, respectively (but no changes in fungal relative abundance). Taken together, our results suggest that long-term N loading of N-limited Norway spruce forests aggravates limitation of other resources, likely of C, for soil microbial communities. Although microbial variables in the soil O-horizon differed between plots exposed to low and high current N loading, microbial variables in plots that leached small amounts and large amounts of NO3 − exposed to high N load were similar. © 2017
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| 5. |
- Rappe George, Martin
(författare)
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Nitrogen in soil water of coniferous forests : effects of anthropogenic disturbances
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In boreal and temperate forests, long-term elevated nitrogen (N) load may eventually saturate forest ecosystems with N, i.e. total N ecosystem input exceed ecosystem sinks for N, and N losses via soil water transport may then increase and negatively impact environmental quality. This thesis is based upon four studies (reported in papers I-IV), and the overall aims were to assess and analyse effects on soil water N in coniferous forests of two types of anthropogenic disturbance: “chemical disturbance” (long-term experimental N addition and N deposition), and “physical disturbance” (clear-cutting and subsequent soil scarification). Effects of these disturbances were addressed in both field experiments and process-based ecosystem modelling. In the field experiments, soil water N was collected from both organic (O) horizons and mineral soil, at 0.5 m depth, during several growing seasons to assess temporal variation in the N concentration (Paper I). In addition, microbial variables in soil samples of the O-horizon were analysed in the laboratory to assess responses of the soil microbial community to long-term N addition in forest experiments and along a N deposition gradient (Papers II and IV). In the modelling, a process-based ecosystem carbon and N model (CoupModel) was calibrated to measurements obtained during the regeneration phase of a Scots pine (Pinus sylvestris L.) forest in an N fertilization experiment where soil scarification was applied (Paper III). The results showed that long-term N addition to a boreal Norway spruce (Picea abies (L.) Karst) forest can alter the quantity and seasonal dynamics of dissolved organic nitrogen (DON) concentrations in soil water collected from the O-horizon. However, DON concentrations were low in soil water collected from mineral soil under all N treatments and probably only contributed to small net N losses in this forest. Although microbial variables of the O-horizon were affected by N loading they were similar under N loading that resulted in the leaching of small amounts of nitrate (<2 kg ha⁻¹ year⁻¹ of NO₃-N) and those that resulted in the leaching of large amounts (>15 kg ha⁻¹ year⁻¹ of NO₃-N). Further, soil scarification increased soil water N leaching from a Scots pine forest, as calculated with the CoupModel, during the regeneration phase, particularly in previously N-fertilized pine stands.
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| 6. |
- Rappe George, Martin, et al.
(författare)
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Nitrogen leaching following clear-cutting and soil scarification at a Scots pine site – A modelling study of a fertilization experiment
- 2017
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Ingår i: Forest Ecology and Management. - : Elsevier. - 0378-1127 .- 1872-7042. ; 385, s. 281-294
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Tidskriftsartikel (refereegranskat)abstract
- Boreal forest stands fertilized with nitrogen (N) might be susceptible to elevated N leaching following clear-cutting, with consequences for water quality and soil acidification. Here, we studied a forest fertilization experiment with N, 165 Hagfors, in Sweden during the first six years (2006–2011) following clear-cutting. The N fertilization treatments were 0 kg ha−1 (0 N) and 450 kg ha−1 of N (450 N), supplied during 1981–1992 to a Scots pine (Pinus sylvestris L.) stand: the stand was harvested in March 2006. Following clear-cutting, disc trenching was performed and furrows (F), ridges (R) and areas in-between two furrows (IB) were created. We calculated the N leaching fluxes and ecosystem N budget during 2006–2011 as affected by previous N fertilization, disc trenching and interactions thereof, at Hagfors by the use of a process-based biogeophysical ecosystem model (CoupModel). The model was calibrated against measurements of soil water and temperature dynamics and previously reported measurements of N in soil solution, soil organic matter and vegetation biomass. Criteria for acceptance of model estimates were based on the range enclosed by the 95% confidence intervals of the mean of the field data used in calibration sampled at low frequency (1–2 occasions) and a combination of the mean error and the coefficient of the determination for variables sampled at a higher frequency (28–1921 occasions). The accepted model estimates of the mean annual leaching rates of N were 3.1 (range 1.4–22.7) and 2.4 (range 0.8–7.0) kg ha−1 of N year−1 in the treatments 0 N and 450 N, respectively, without disc trenching. Disc trenching increased N leaching during the regeneration phase, more so in the 450 N treatment (mean 6.1, range 1.9–16.7 kg ha−1 of N year−1) than in the 0 N treatment (mean 4.6, range 1.9–12.9 kg ha−1 of N year−1). Overall, differences in the posterior model parameter estimates between N treatments and disc trenched treatments F, R and IB were related to the soil physical component: the differences resulted in enhanced drainage in the disc trenched treatments. We conclude that vegetation biomass N accumulation controlled soil water N leaching, and disc trenching increased N leaching from the previously N fertilized plots at Hagfors by its effects on water drainage flow and vegetation N uptake. This finding warrants more research since N fertilization followed by soil scarification in boreal forests is a practice which may increase in the future.
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| 7. |
- Rappe George, Martin, et al.
(författare)
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The impact of four decades of annual nitrogen addition on dissolved organic matter in a boreal forest soil
- 2013
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 10, s. 1365-1377
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Tidskriftsartikel (refereegranskat)abstract
- Addition of mineral nitrogen (N) can alter the concentration and quality of dissolved organic matter (DOM) in forest soils. The aim of this study was to assess the effect of long-term mineral N addition on soil solution concentration of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in Strasan experimental forest (Norway spruce) in central Sweden. N was added yearly at two levels of intensity and duration: the N1 treatment represented a lower intensity but a longer duration (43 yr) of N addition than the shorter N2 treatment (24 yr). N additions were terminated in the N2 treatment in 1991. The N treatments began in 1967 when the spruce stands were 9 yr old. Soil solution in the forest floor O, and soil mineral B, horizons were sampled during the growing seasons of 1995 and 2009. Tension and non-tension lysimeters were installed in the O horizon (n = 6), and tension lysimeters were installed in the underlying B horizon (n = 4): soil solution was sampled at two-week intervals. Although tree growth and O horizon carbon (C) and N stock increased in treatments N1 and N2, the concentration of DOC in O horizon leachates was similar in both N treatments and control. This suggests an inhibitory direct effect of N addition on O horizon DOC. Elevated DON and nitrate in O horizon leachates in the ongoing N1 treatment indicated a move towards N saturation. In B horizon leachates, the N1 treatment approximately doubled leachate concentrations of DOC and DON. DON returned to control levels, but DOC remained elevated in B horizon leachates in N2 plots nineteen years after termination of N addition. We propose three possible explanations for the increased DOC in mineral soil: (i) the result of decomposition of a larger amount of root litter, either directly producing DOC or (ii) indirectly via priming of old SOM, and/or (iii) a suppression of extracellular oxidative enzymes.
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| 8. |
- Shibabaw, Tebkew, et al.
(författare)
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The combined impacts of land use change and climate change on soil organic carbon stocks in the Ethiopian highlands
- 2023
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Ingår i: Geoderma Regional. - : Elsevier BV. - 2352-0094. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Land Use Change (LUC), especially deforestation in tropical regions, significantly contributes to global anthropogenic greenhouse gas (GHG) emissions. Here, we address potential combined impacts of LUC and Climate Change (CC) on Soil Organic Carbon (SOC) stocks in the Ethiopian highlands. The soil model Q was employed to predict SOC stocks for various combinations of LUC and CC scenarios until the year 2100. Four reference scenarios (cropland, bushland, natural forest, and Eucalyptus plantations under contemporary climatic conditions) were evaluated against reported measurements of SOC stocks. We studied impacts of six common LUC scenarios, including deforestation and planting Eucalyptus, on SOC stocks under contemporary and future climates. To assess the impact of CC, effects of elevated temperature (mean annual temperature + 2.6 °C) together with three litterfall scenarios (no change in litterfall, a 5% reduction and 22% increase, designated CC0, CCd, and CCi, respectively) were considered to test potential vegetation responses to increases in temperature and atmospheric CO2 concentrations. Most of the tested combinations of LUC and CC led to losses of SOC stocks. Losses were most severe, both relatively and absolutely, in the deforestation scenarios: up to 30% was lost if natural forest was converted to cropland and temperature increased (under the CC0 scenario). Gains in SOC stocks of 4–19% were modelled when sparse vegetation was converted to more dense vegetation like Eucalyptus plantation with substantially increased litterfall (the CCi scenario). Elevated temperature accelerated decomposition rates, leading to circa 8% losses of SOC stocks. We conclude that effects of LUC and CC on SOC stocks are additive and changes in litterfall caused by LUC determine which has the largest impact. Hence, deforestation is the biggest threat to SOC stocks in the Ethiopian highlands, and stocks in sparse vegetation systems like cropland and bushland are more sensitive to CC0 than LUC. We recommend conservation of natural forests and longer rotation periods for Eucalyptus plantations to preserve SOC stocks. Finally, we suggest that use of the Q model is a viable option for national reporting changes in SOC stocks at Tier 3 within the LULUCF sector to the United Nations Framework Convention on Climate Change (UNFCCC) as it is widely applicable and robust, although it only requires input data on a few generally available variables.
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