| 1. |
- Bengtson, Per, et al.
(författare)
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Relieving substrate limitation-soil moisture and temperature determine gross N transformation rates
- 2005
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 111:1, s. 81-90
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Tidskriftsartikel (refereegranskat)abstract
- A field experiment was designed with the objective to reveal the interactions between soil moisture, temperature, total, dissolved, and phosphate buffer extractable C and N, and microbial activity in the control of in situ gross N mineralization and immobilization rates in a deciduous forest. We had three alternative hypotheses to explain variations of the gross N transformations: 1) microorganisms are C limited, 2) microorganisms are N limited, or 3) neither C nor N limit the microorganisms but moisture and temperature conditions. Each hypothesis had specific criteria to be fulfilled for its acceptance. The results demonstrated that gross N transformation rates were more dependent on and variable with soil moisture and temperature than the size of the different C and N pools. The immobilization of N was dependent on the gross mineralization rate, suggesting that the production of enzymes for mineralization of organic N and the immobilization of N from the surrounding soil is disconfirmed when the intracellular N content of the microorganisms is sufficiently high. If the microorganisms are starved for N, enzyme systems involved in both the assimilation and mineralization of N are activated. The mean in situ gross N mineralization rate was two orders of magnitude higher than the natural N deposition in the area and the N addition in the NITREX experiments, meaning that a reduction in the gross N mineralization rate of about 1% would be enough to compensate for the addition of inorganic N. This decrease would hardly be detectable given the great spatial and temporal variability of N transformation rates.
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| 2. |
- Bengtson, Per, et al.
(författare)
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Spatial distributions of plants and gross N transformation rates in a forest soil
- 2006
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 94:4, s. 754-764
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 1 This work demonstrates that spatial distribution of understorey vegetation and gross N transformation rates in a mixed beach-oak forest is closely correlated within a distance of a few metres. The findings imply that plant diversity and productivity have a major influence on gross rates of N transformation and vice versa. 2 A geostatistical analysis was used to evaluate the spatial relationships between abundance and species composition of the understorey vegetation and in situ gross N mineralization, NH4+ immobolization and nitrification rates. 3 The gross N transformation rates and the plants spatial variation were correlated within the forest, but plant distribution was more dependent on the fraction of mineralized N that was nitrified than on individual N transformation rates. 4 The total cover of the understorey vegetation varied more in space than the species composition, and was higher in areas with high N transformation rates. 5 Plant species benefiting from high net nitrification rates were more common in areas with a low activity of mineralizing and nitrifying microorganisms, possibly because the net and gross rates were independent of each other. In fact, those species occurred most often in areas in which a large fraction of mineralized N was nitrified. 6 Beech and oak trees also had an effect on the spatial variation of the understorey vegetation. Beech trees provided conditions more suitable for plants benefiting from NO3-, whereas the vascular plant cover was greater under oak trees, probably in response to a higher light interception than under beech trees. 7 Oak generally had a positive impact on gross N transformation rates compared with beech, perhaps reflecting differences in litter quality and climate caused by the two species. 8 The influence of trees alone could not explain the full magnitude of the variation of N transformation rates or the presence of overlapping areas with high mineralization and immobilization rates. These were probably caused by other factors, such as soil moisture content. 9 This work sheds new light on the small-scale spatial links between above-ground plant diversity and abundance, and below-ground microbial N transformations.
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| 3. |
- Falkengren-Grerup, Ursula, et al.
(författare)
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Land use effects on soil N, P, C and pH persist over 40-80 years of forest growth on agricultural soils
- 2006
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 1872-7042 .- 0378-1127. ; 225:1-3, s. 74-81
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Tidskriftsartikel (refereegranskat)abstract
- Previous cultivation may have long-lasting effects on oak forests, e.g., nitrogen (N) and carbon (C) depletion, phosphorus (P) enrichment and lowered soil acidity, which may influence soil processes, wood production and plant diversity. We used a large database on land use to sample 18 sites where oak had been planted 40-80 years ago on continuously forested land and formerly cultivated fields that had similar soil properties before the different land uses. We estimated the 'total' pools of N, P and C and 'available' fractions of N and P at three soil depths. The soil data were compared with element concentrations in leaves of four plant species. Soil solution concentration of nitrate at 50-60 cm was used as an estimate of nitrate leaching. Total N and mineralisable N in the soil were higher in the continuously forested land than in the formerly cultivated fields and this was reflected in the N concentration in Dryopteris filix-mas. Total P and available P tended to be lower in the continuously forested land than in the formerly cultivated fields which were reflected in the P concentrations in Dryopteris and Quercus robur Soil C was higher and pH was lower in the continuously forested land than in the formerly cultivated fields. Leaching of NO3--N started to appear in higher concentrations below pH 4.5 and the leaching is interpreted more as a pH than a land use effect. Aluminium (At) concentrations were higher in Dryopteris and Quercus and the iron (Fe) concentration in Milium effusum. while calcium (Ca) was lower in all plant species. Potassium (K) was lower in Stellaria holostea and no difference was found for the magnesium (Mg) concentration in plants. As previous land use seems to affect soil nutrients and potentially toxic elements it is important to identify the limiting factors for the different ecosystem components to be able to manage the forests correctly. It is probable that areas with significant N deposition are not N-limited even in the N-depleted formerly cultivated fields and that a higher P content and soil pH there may result in higher biomass production and changes in plant diversity. The risk of nitrate leaching in the most acidic, continuously forested land must also be taken into consideration in the management of forests.
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| 4. |
- Göransson, Pernilla, et al.
(författare)
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Colonisation by arbuscular mycorrhizal and fine endophytic fungi in four woodland grasses - variation in relation to pH and aluminium
- 2008
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 40:9, s. 2260-2265
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Tidskriftsartikel (refereegranskat)abstract
- Acidic soils are harsh environments for plants. One of the major problems is the potential toxicity of aluminium (Al) and hydrogen ions at a pH below 5: another is the shortage of nutrients usually accompanying soil acidity. The aim of this study was to elucidate the relationship between arbuscular mycorrhizal (AM) colonisation and soil acidity (measured by pH and Al concentration) in order to evaluate the possibility that AM fungi facilitate the existence of plants on acidic soils. We sampled tussocks of four grass species, Elymus caninus, Poa nemoralis, Deschampsia cespitosa and Deschampsia flexuosa, together with samples of the surrounding soil, in oak forests of varying soil pH in southern Sweden. We determined pH, easily reacting Al (Air), extractable Al (Al-BaCl2) and phosphate in the soil samples, analysed the shoots for Al and phosphorous and quantified the degree of AM and fine endophyte (FE) colonisation in the roots. E. caninus was found on the least acidic soils and had the highest AM colonisation of all the species studied, while D. flexuosa, which was found on the most acidic soils, had the lowest AM colonisation. P nemoralis and D. cespitosa were intermediate with respect to pH and AM colonisation. The colonisation of AM fungi exceeded FE colonisation for E caninus and P. nemoralis, while the opposite was true for the two Deschampsia species. Our results indicated a negative relationship between Air and the degree of AM colonisation at the within-species level. The low colonisation of AM fungi on acidic soils may to some extent be explained by a sensitivity of AM fungi to Air: this parameter showed a stronger negative association with AM colonisation than did pH and Al-BaCl2. We hypothesize that Al toxicity is a critical factor for plant nutrition in forest soils through the impact on symbiotic fungi. (C) 2008 Elsevier Ltd. All rights reserved.
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| 5. |
- Göransson, Pernilla, et al.
(författare)
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Genetic adaptation to soil acidification: experimental evidence from four grass species
- 2009
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Ingår i: Evolutionary Ecology. - : Springer Science and Business Media LLC. - 1573-8477 .- 0269-7653. ; 23:6, s. 963-978
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic acidification has reduced soil pH and released potentially toxic aluminium (Al) ions in many regions. This investigation examines whether increased acidity has caused genetic adaptation to acidic conditions within the grass species Elymus caninus, Poa nemoralis, Deschampsia cespitosa and D. flexuosa. We sampled tussocks (genets) of each species in two regions of southern Sweden, differing in their exposure to acidifying deposition. The tolerance of the genets was tested in a solution experiment with different pH and Al concentrations. Our data suggest that species found at lower pH field locations have a greater tolerance to low pH and high Al levels than species found on less acidic soils. Analysis of variance showed a significant average effect of population and (or) genet in most species; however, we found little evidence of genetic adaptation to acidic conditions at the regional, population and micro-site level. In fact, there was no consistent change in the ranking of populations or genets with varying pH or Al concentration. Based on these results, we hypothesize that phenotypic plasticity rather than genetic adaptation has been favoured as the predominant mechanism to cope with soil acidity in the four grass species.
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| 6. |
- Månsson, Katarina, et al.
(författare)
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Plant-microbial competition for nitrogen uncoupled from soil C:N ratios
- 2009
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 118:12, s. 1908-1916
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Tidskriftsartikel (refereegranskat)abstract
- A green house experiment was designed to test the idea that competition for inorganic nitrogen (N) between plants and heterotrophic microorganisms occurs in soils with high C:N ratios, qualifying for N limited microbial activity, but not at low C:N ratios. The short- term (24 h) N-15 uptake by the grass Festuca gigantea and microorganisms in planted and unplanted soils was determined, and the bacterial activity was measured by the H-3-thymidine incorporation technique. Two deciduous forest soils, with C:N-ratios of 20 and 31, and the 20 soil amended with litter to a C:N ratio of 34, were used. A novel and important part of the experimental design was the preparation of the unplanted reference soil with plants present until the competition assay started by the addition of N-15 labelled ammonium (NH4+) or nitrate (NO3-). The results suggested that plants and soil microorganisms competed for mineral N but under influence of other factors than the soil C:N ratio. The plants reduced the microbial uptake of NH4+ and NO3- in the soil with low C:N ratio, which also had the lowest bacterial activity. The plants had a larger N uptake than microorganisms in the two natural soils but smaller in the litter-amended, and their presence enhanced the bacterial activity, especially in the latter soil. The litter-amended soil with its high C:N ratio and easily decomposable C was the soil that best fulfilled the criteria for competition, including a net consumption of mineral N during the assay, the lowest plant uptake of mineral N due to the high N immobilization by microorganisms, and a reduced microbial N-15 uptake-to-bacterial activity in the presence of plants. Thus, other factors, such as the decomposability of the soil C and the bacterial activity, were more important than the soil C:N ratio to the outcome of plant-microbial competition for N.
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| 7. |
- Nilsson, Lars Ola, et al.
(författare)
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Growth of ectomycorrhizal mycelia and composition of soil microbial communities in oak forest soils along a nitrogen deposition gradient
- 2007
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 1432-1939 .- 0029-8549. ; 153:2, s. 375-384
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Tidskriftsartikel (refereegranskat)abstract
- Deciduous forests may respond differently from coniferous forests to the anthropogenic deposition of nitrogen (N). Since fungi, especially ectomycorrhizal (EM) fungi, are known to be negatively affected by N deposition, the effects of N deposition on the soil microbial community, total fungal biomass and mycelial growth of EM fungi were studied in oak-dominated deciduous forests along a nitrogen deposition gradient in southern Sweden. In-growth mesh bags were used to estimate the production of mycelia by EM fungi in 19 oak stands in the N deposition gradient, and the results were compared with nitrate leaching data obtained previously. Soil samples from 154 oak forest sites were analysed regarding the content of phospholipid fatty acids (PLFAs). Thirty PLFAs associated with microbes were analysed and the PLFA 18:2 omega 6,9 was used as an indicator to estimate the total fungal biomass. Higher N deposition (20 kg N ha(-1) y(-1) compared with 10 kg N ha(-1) y(-1)) tended to reduce EM mycelial growth. The total soil fungal biomass was not affected by N deposition or soil pH, while the PLFA 16:1 omega 5, a biomarker for arbuscular mycorrhizal (AM) fungi, was negatively affected by N deposition, but also positively correlated to soil pH. Other PLFAs positively affected by soil pH were, e.g., i14:0, a15:0, 16:1 omega 9, a17:0 and 18:1 omega 7, while some were negatively affected by pH, such as i15:0, 16:1 omega 7t, 10Me17:0 and cy 19:0. In addition, N deposition had an effect on the PLFAs 16: 1 omega 7c and 16:1 omega 9 (negatively) and cy 19:0 (positively). The production of EM mycelia is probably more sensitive to N deposition than total fungal biomass according to the fungal biomarker PLFA 18:2 omega 6,9. Low amounts of EM mycelia covaried with increased nitrate leaching, suggesting that EM mycelia possibly play an important role in forest soil N retention at increased N input.
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| 8. |
- Nilsson, Lars Ola, et al.
(författare)
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Soil N chemistry in oak forests along a nitrogen deposition gradient
- 2006
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 1573-515X .- 0168-2563. ; 80:1, s. 43-55
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic N deposition may change soil conditions in forest ecosystems as demonstrated in many studies of coniferous forests, whereas results from deciduous forests are relatively scarce. Therefore the influence of N deposition on several variables was studied in situ in 45 oak-dominated deciduous forests along a N deposition gradient in southern Sweden, where the deposition ranged from 10 to 20 kg N ha(-1) year(-1). Locally estimated NO3- deposition, as measured with ion-exchange resins (IER) on the soil surface, and grass N concentration (%) were positively correlated with earlier modelled regional N deposition. Furthermore, the delta N-15 values of grass and uppermost soil layers were negatively correlated with earlier modelled N deposition. The data on soil NO3-, measured with IER in the soil, and grass N concentration suggest increased soil N availability as a result of N deposition. The delta N-15 values of grass and uppermost soil layers indicate increased nitrification rates in high N deposition sites, but no large downward movements of NO3- in these soils. Only a few sites had NO3- concentrations exceeding 1 mg N 1(-1) in soil solution at 50 cm depth, which showed that N deposition to these acid oak-dominated forests has not yet resulted in extensive leaching of N. The d15N enrichment factor was the variable best correlated with NO3- concentrations at 50 cm and is thus a variable that potentially may be used to predict leaching of NO3- from forest soils.
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| 9. |
- Postma, Jacqueline, et al.
(författare)
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Root colonisation by arbuscular mycorrhizal, fine endophytic and dark septate fungi across a pH gradient in acid beech forests
- 2007
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 39:2, s. 400-408
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Tidskriftsartikel (refereegranskat)abstract
- Colonisation by root endophytes can be beneficial to plants growing on acid, nutrient-poor soils. Arbuscular mycorrhizal (AM) fungi can supply herbs with nutrients and may give protection against aluminium toxicity. Two other root colonising fungi, fine endophytes (FE) and dark septate fungi (DSE), are less well known but are potentially of benefit to their host plant. AM fungi are the most prevalent symbionts in herbs at neutral to acidic soil pH. At extremely low pH, fungal growth can be limited and AM colonisation is usually rare. Fine. and dark septate endophytes, on the other hand, have been observed more often under these conditions. In order to relate endophyte colonisation to a gradient in soil pH, we investigated root colonisation by AM, FE and DSE in Maianthemum bifolium, Galium odoratum, Mercurialis perennis and Stellaria nemorum, from a range of acidic beech forests. With decreasing pH, colonisation by AM decreased, whereas the other two endophytes increased. AM and FE colonisation were inversely correlated in Maianthemum bifolium. We compared changes in root colonisation with those in chemical composition of soil and leaf samples and found a positive correlation between leaf magnesium concentrations and the presence of DSE in Galium odoratum. Aluminium concentration in Maianthemum bifolium tended to be lower when FE colonisation was high, suggesting a possible role for the fungi in plant protection against Al. We suggest that FE and DSE may replace AM fungi in herbaceous vegetation at extremely low pH, counteracting some of the negative effects of high soil acidity on plants.
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