| 1. |
- Andresen, Louise C., et al.
(author)
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Uptake of pulse injected nitrogen by soil microbes and mycorrhizal and non-mycorrhizal plants in a species-diverse subarctic heath ecosystem
- 2008
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In: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 313:1-2, s. 283-295
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Journal article (peer-reviewed)abstract
- N-15 labeled ammonium, glycine or glutamic acid was injected into subarctic heath soil in situ, with the purpose of investigating how the nitrogen added in these pulses was subsequently utilized and cycled in the ecosystem. We analyzed the acquisition of N-15 label in mycorrhizal and non-mycorrhizal plants and in soil microorganisms, in order to reveal probable differences in acquisition patterns between the two functional plant types and between plants and soil microorganisms. Three weeks after the label addition, with the N-15-forms added with same amount of nitrogen per square meter, we analyzed the N-15-enrichment in total soil, in soil K2SO4 (0.5 M) extracts and in the microbial biomass after vacuum-incubation of soil in chloroform and subsequent K2SO4 extraction. Furthermore the N-15-enrichment was analyzed in current years leaves of the dominant plant species sampled three, five and 21 days after label addition. The soil microorganisms had very high N-15 recovery from all the N sources compared to plants. Microorganisms incorporated most N-15 from the glutamic acid source, intermediate amounts of N-15 from the glycine source and least N-15 from the NH4+ source. In contrast to microorganisms, all ten investigated plant species generally acquired more N-15 label from the NH4+ source than from the amino acid sources. Non-mycorrhizal plant species showed higher concentration of N-15 label than mycorrhizal plant species 3 days after labeling, while 21 days after labeling their acquisition of N-15 label from amino acid injection was lower than, and the acquisition of N-15 label from NH4 injection was similar to that of the mycorrhizal species. We conclude that the soil microorganisms were more efficient than plants in acquiring pulses of nutrients which, under natural conditions, occur after e. g. freeze-thaw and dry rewet events, although of smaller size. It also appears that the mycorrhizal plants in the short term may be less efficient than non-mycorrhizal plants in nitrogen acquisition, but in a longer term show larger nitrogen acquisition than non-mycorrhizal plants. However, the differences in N-15 uptake patterns may also be due to differences in leaf longevity and woodiness between plant functional groups.
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| 2. |
- Björk, Robert G., 1974, et al.
(author)
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Linkages between N turnover and plant community structure in a tundra landscape
- 2007
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In: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 294:1-2, s. 247-261
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Journal article (peer-reviewed)abstract
- The spatial distribution of organic soil nitrogen (N) in alpine tundra was studied along a natural environmental gradient, covering five plant communities, at the Latnjajaure Field Station, northern Swedish Lapland. The five communities (mesic meadow, meadow snowbed, dry heath, mesic heath, and heath snowbed) are the dominant types in this region and are differentiated by soil pH. Net N mineralization, net ammonification, and net nitrification were measured using 40-day laboratory incubations based on extractable NH4+ and NO3-. Nitrification enzyme activity (NEA), denitrification enzyme activity (DEA), amino acid concentrations, and microbial respiration were measured for soils from each plant community. The results show that net N mineralization rates were more than three times higher in the meadow ecosystems (mesic meadow 0.7 mu g N g(-1) OM day(-1) and meadow snowbed 0.6 mu g N g(-1) OM day(-1)) than the heath ecosystems (dry heath 0.2 mu g N g(-1) OM day(-1), mesic heath 0.1 mu g N g(-1) OM day(-1) and heath snowbed 0.2 mu g N g(-1) OM day(-1)). The net N mineralization rates were negatively correlated to organic soil C/N ratio (r = -0.652, P < 0.001) and positively correlated to soil pH (r = 0.701, P < 0.001). Net nitrification, inorganic N concentrations, and NEA rates also differed between plant communities; the values for the mesic meadow were at least four times higher than the other plant communities, and the snowbeds formed an intermediate group. Moreover, the results show a different pattern of distribution for individual amino acids across the plant communities, with snowbeds tending to have the highest amino acid N concentrations. The differences between plant communities along this natural gradient also illustrate variations between the dominant mycorrhizal associations in facilitating N capture by the characteristic functional groups of plants.
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| 3. |
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| 4. |
- Finlay, Roger
(author)
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Carbon flow in the rhizosphere: carbon trading at the soil-root interface
- 2009
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In: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 321, s. 5-33
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Research review (peer-reviewed)abstract
- The loss of organic and inorganic carbon from roots into soil underpins nearly all the major changes that occur in the rhizosphere. In this review we explore the mechanistic basis of organic carbon and nitrogen flow in the rhizosphere. It is clear that C and N flow in the rhizosphere is extremely complex, being highly plant and environment dependent and varying both spatially and temporally along the root. Consequently, the amount and type of rhizodeposits (e.g. exudates, border cells, mucilage) remains highly context specific. This has severely limited our capacity to quantify and model the amount of rhizodeposition in ecosystem processes such as C sequestration and nutrient acquisition. It is now evident that C and N flow at the soil-root interface is bidirectional with C and N being lost from roots and taken up from the soil simultaneously. Here we present four alternative hypotheses to explain why high and low molecular weight organic compounds are actively cycled in the rhizosphere. These include: (1) indirect, fortuitous root exudate recapture as part of the root's C and N distribution network, (2) direct re-uptake to enhance the plant's C efficiency and to reduce rhizosphere microbial growth and pathogen attack, (3) direct uptake to recapture organic nutrients released from soil organic matter, and (4) for inter-root and root-microbial signal exchange. Due to severe flaws in the interpretation of commonly used isotopic labelling techniques, there is still great uncertainty surrounding the importance of these individual fluxes in the rhizosphere. Due to the importance of rhizodeposition in regulating ecosystem functioning, it is critical that future research focuses on resolving the quantitative importance of the different C and N fluxes operating in the rhizosphere and the ways in which these vary spatially and temporally.
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| 5. |
- Goransson, Hans, et al.
(author)
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The vertical distribution of N and K uptake in relation to root distribution and root uptake capacity in mature Quercus robur, Fagus sylvatica and Picea abies stands
- 2008
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In: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 306:1-2, s. 129-137
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Journal article (peer-reviewed)abstract
- We have measured the uptake capacity of nitrogen (N) and potassium (K) from different soil depths by injecting N-15 and caesium (Cs; as an analogue to K) at 5 and 50 cm soil depth and analysing the recovery of these markers in foliage and buds. The study was performed in monocultures of 40-year-old pedunculate oak (Quercus robur), European beech (Fagus sylvatica) and Norway spruce (Picea abies (L.) Karst.) located at an experimental site in Palsgard, Denmark. The markers were injected as a solution through plastic tubes around 20 trees of each species at either 5 or 50 cm soil depth in June 2003. After 65 days foliage and buds were harvested and the concentrations of N-15 and Cs analysed. The recovery of N-15 in the foliage and buds tended to be higher from 5 than 50 cm soil depth in oak whereas they where similar in spruce and beech after compensation for differences in immobilization of N-15 in the soil. In oak more Cs was recovered from 5 than from 50 cm soil depth whereas in beech and spruce no difference could be detected. Out of the three investigated tree species, oak was found to have the lowest capacity to take up Cs at 50 cm soil depth compared to 5 cm soil depth also after compensating for differences in discrimination against Cs by the roots. The uptake capacity from 50 cm soil depth compared with 5 cm was higher than expected from the root distribution except for K in oak, which can probably be explained by a considerable overlap of the uptake zones around the roots and mycorrhizal hyphae in the topsoil. The study also shows that fine roots at different soil depths with different physiological properties can influence the nutrient uptake of trees. Estimates of fine root distribution alone may thus not reflect the nutrient uptake capacity of trees with sufficient accuracy. Our study shows that deep-rooted trees such as oak may have lower nutrient uptake capacity at deeper soil layers than more shallow-rooted trees such as spruce, as we found no evidence that deep-rooted trees obtained proportionally more nutrients from deeper soil layers. This has implications for models of nutrient cycling in forest ecosystems that use the distribution of roots as the sole criterion for predicting uptake of nutrients from different soil depths.
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| 6. |
- Göransson, Hans, et al.
(author)
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Do oaks have different strategies for uptake of N, K and P depending on soil depth?
- 2007
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In: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 297:1-2, s. 119-125
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Journal article (peer-reviewed)abstract
- The uptake of nutrients from deep soil layers has been shown to be important for the long-term nutrient sustainability of forest soils. When modelling nutrient uptake in forest ecosystems, the nutrient uptake capacity of trees is usually defined by the root distribution. However, this leads to the assumption that roots at different soil depths have the same capacity to take up nutrients. To investigate if roots located at different soil depths differ in their nutrient uptake capacity, here defined as the nutrient uptake rate under standardized conditions, a bioassay was performed on excised roots (< 1 mm) of eight oak trees (Quercus robur L.). The results showed that the root uptake rate of Rb-86(+) (used as an analogue for K+ stop) declined with increasing soil depth, and the same trend was found for NH4+. The root uptake rate of H2PO4-, on the other hand, did not decrease with soil depth. These different physiological responses in relation to soil depth indicate differences in the oak roots, and suggest that fine roots in shallow soil layers may be specialized in taking up nutrients such as K+ and NH4+ which have a high availability in these layers, while oak roots in deep soil layers are specialized in taking up other resources, such as P, which may have a high availability in deep soil layers. Regardless of the cause of the difference in uptake trends for the various nutrients, these differences have consequences for the modelling of the soil nutrient pool beneath oak trees and raise the question of whether roots can be treated uniformly, as has previously been done in forest ecosystem models.
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| 7. |
- Göransson, Hans, et al.
(author)
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Estimating the relative nutrient uptake from different soil depths in Quercus robur, Fagus sylvatica and Picea abies
- 2006
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In: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 286:1-2, s. 87-97
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Journal article (peer-reviewed)abstract
- The distribution of fine roots and external ectomycorrhizal mycelium of three species of trees was determined down to a soil depth of 55 cm to estimate the relative nutrient uptake capacity of the trees from different soil layers. In addition, a root bioassay was performed to estimate the nutrient uptake capacity of Rb+ and NH4+ by these fine roots under standardized conditions in the laboratory. The study was performed in monocultures of oak (Quercus robur L.), European beech (Fagus sylvatica L.) and Norway spruce [Picea abies (L.) Karst.] on sandy soil in a tree species trial in Denmark. The distribution of spruce roots was found to be more concentrated to the top layer (0-11 cm) than that of oak and beech roots, and the amount of external ectomycorrhizal mycelia was correlated to the distribution of the roots. The uptake rate of [86 Rb+] by oak roots declined with soil depth, while that of beech or spruce roots was not influenced by soil depth. In modelling the nutrient sustainability of forest soils, the utilization of nutrient resources in deep soil layers has been found to be a key factor. The present study shows that the more shallow-rooted spruce can have a similar capacity to take up nutrients from deeper soil layers than the more deeply rooted oak. The distribution of roots and mycelia may therefore not be a reliable parameter for describing nutrient uptake capacity by tree roots at different soil depths.
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| 8. |
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| 9. |
- Husted, Søren, et al.
(author)
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Influence of nitrogen and sulphur form on manganese acquisition by barley (Hordeum vulgare)
- 2005
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In: Plant and Soil. - : Springer Netherlands. - 0032-079X .- 1573-5036. ; 268:1, s. 309-317
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Journal article (peer-reviewed)abstract
- The influence of various nitrogen (N) and sulphur (S) forms on the uptake of manganese (Mn) in young spring barley (Hordeum vulgare L cv Golf) plants was examined in both a hydroponic system and in a soil-based system. The soil was a typical Danish Mn-deficient soil viz. a sandy loam soil developed on old marine sediments. Plants growing in solution culture with NO3– as the only N source had a higher Mn uptake than plants receiving mixtures of NO3– and NH4+. These findings were opposite to the results obtained in the soil-based experiments, where plants fertilized with NO3– as the only N source accumulated much less Mn than plants fertilized with NH4+. Combining the results of these experiments confirmed that NH4+ acted as a powerful antagonist to Mn2+ during uptake but that this antagonistic effect was more than compensated for by the influence of NH4+ in reducing plant-unavailable Mn(IV) to plant-available Mn(II) in the soil. Furthermore the soil experiments showed that fertilizers containing sulphur in the form of reduced S (thiosulphate) had a strong mobilizing effect on Mn, and enabled the plants to accumulate large amounts of Mn in the biomass compared with oxidized S (sulphate). Thus, fertilization with thiosulphate may be very effective in alleviating Mn-deficiency in soils developed on old marine sediments where Mn availability is limiting plant growth.
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| 10. |
- Johansson, Emma M., et al.
(author)
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Quantitative analysis of root and ectomycorrhizal exudates as a response to Pb, Cd and As stress
- 2008
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In: Plant and Soil. - Berlin : Springer. - 0032-079X .- 1573-5036. ; 313:1-2, s. 39-54
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Journal article (peer-reviewed)abstract
- We examined exudation of low molecular weight (LMW) organic compounds of ectomycorrhizal (ECM) and non-mycorrhizal (NM) seedlings in relation to metals. Scots pine seedlings, either colonized by one of six different ECM fungi or NM, were grown in Petri dishes containing glass beads and liquid growth medium and exposed to elevated concentrations of Pb, Cd and As. Exudation of LMW organic compounds (LMW organic acids (LMWOAs), amino acids and dissolved monosaccharides) and dissolved organic carbon (DOC) was determined qualitatively and quantitatively and exudation rates were calculated. Metals had a significant impact on exudation, especially of oxalate. For Pb and Cd treatments, exudation of oxalate and total LMWOAs generally increased by 15–45% compared to nutrient controls. Production of amino acids, dissolved monosaccharides and DOC was not significantly stimulated by exposure to metals; however, there were non-significant trends towards increased exudation. Finally, exudation generally increased in the presence of mycorrhizal seedlings compared to NM seedlings. The results suggest that ECM fungi may reduce the toxicity of metals to plants through significant increases in the production of organic chelators. Axenic conditions are required to assess the full potential for production of these molecules but their overall significance in soil ecosystems needs to be determined using additional experiments under more ecologically realistic conditions.
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