| 1. |
- Akselsson, Cecilia, et al.
(författare)
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The influence of N load and harvest intensity on the risk of P limitation in Swedish forest soils
- 2008
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 1879-1026 .- 0048-9697. ; 404, s. 284-289
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) is often considered to be the major factor limiting tree growth in northern forest ecosystems. An increased N availability, however, increases the demand for other nutrients such as base cations and phosphorous (P) which in turn may change which nutrient is the limiting factor. If P or base cations become limiting, N will start to leach which means a risk of increased eutrophication of surface waters. As many studies focus on base cations, this study instead aims at estimating P budgets on a regional scale for different harvesting scenarios relevant for Swedish conditions. P budget calculations were carried out for 14,550 coniferous sites from the Swedish National Forest Inventory, as weathering+deposition–harvesting–leaching. Three scenarios with different harvest intensities were used: 1) no harvesting, 2) stem harvesting and 3) wholetree harvesting. The input data were derived from measurements and model results. The P budget estimates indicate that harvesting, especially whole-tree harvesting, result in net losses of P in large parts of Sweden. The highest losses were found in southern Sweden due to high growth rate in this area. In the whole-tree harvesting scenario the losses exceeded 1 kg ha−1 y−1 on many sites. N budget calculations on the same sites indicate that N generally accumulates in the whole country and especially in the southern parts. Consequently, the N and P budget calculations indicate that the forests in southern Sweden are in a transition phase from N-to P-limitation to growth. This transition will proceed as long as the accumulation of N continues. These results are important in a sustainable forestry context, as a basis for assessing the risk of future N leaching, and in designing recommendations for abatement strategies of N deposition and for application of wood ash recycling and N fertilization.
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| 2. |
- Fransson, Ann-Mari, et al.
(författare)
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Phosphatase activity does not limit the microbial use of low molecular weight organic-P substrates in soil
- 2007
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 39:5, s. 1213-1217
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Tidskriftsartikel (refereegranskat)abstract
- Plant roots and soil microorganisms contain significant quantities of low molecular weight (MW) phosphorylated nucleosides and sugars. Consequently.. upon death these can represent a significant input of organic-P to the soil. Some of these organic-P substrates must first be dephosphorylated by phosphatases before being assimilated by the soil microbial community while others can be taken up directly from soil solution. To determine whether sorption or phosphatase activity was limiting the bioavailability of low MW organic-P in soil we compared the microbial uptake and C mineralization of a range of C-14-labeled organic-P substrates [glucose-6-phosphate, adenosine monophosphate (AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP)] to that of the parent compounds (adenosine and glucose). In a fertile grassland soil we showed that at low organic-P substrate concentrations (< 0.5 mM) phosphatase activity did not limit microbial uptake or mineralization in comparison to their non-phosphorylated counterparts. However, at high substrate concentrations (1-10 mM) the mineralization of the organic-P compounds was significantly lower than that of the nonphosphorylated compounds suggesting that phosphatase activity or microbial transporter capacity limited bioavailability. Sorption to the solid phase followed the series glucose < adenosine < G-6-P < AMP < ADP=ATP. However, sorption of the organic-P compounds to the solid phase did not appear to greatly affect bioavailability. The high adenosine mineralization capacity of the microbial biomass suggests that nucleosides may represent a significant source of C and N to the soil microbial biomass. We conclude that at low organic-P substrate concentrations typical of those in soil, neither phosphatase activity nor sorption greatly limits their bioavailability.
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| 3. |
- Göransson, Hans, et al.
(författare)
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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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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 297:1-2, s. 119-125
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Göransson, Hans, et al.
(författare)
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Nutrient acquisition from different soil depths by pedunculate oak
- 2006
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Ingår i: Trees. - : Springer Science and Business Media LLC. - 1432-2285 .- 0931-1890. ; 20:3, s. 292-298
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Tidskriftsartikel (refereegranskat)abstract
- Eight oak trees (Quercus robur L.) received P-32 at a soil depth of 50 cm and P-33 at a soil depth of 15 cm at the end of June 2002 through plastic tubes inserted into the mineral soil. The phosphorus uptake from different soil depths was estimated by analysing the concentration of P-32 and P-33 in the foliage of oak growing in a mixed stand in southern Sweden. P-32 and P-33 were recovered in the leaves/needles after 21 and 39 days. The recovery of labelled P in oak was higher from 15 cm soil depth than from 50 cm, however, more than 4% of the total amount of labelled P was taken up from 50 cm. This indicates that oak can utilize deep soil layers for nutrient uptake. A study on the uptake of Cs (as an analogue to K) and N-15 into the leaves was performed on the same trees and detectable amounts of N-15 and Cs were recovered in leaves and buds. This indicates that N-15 and Cs can be used to study nutrient uptake of mature trees from the mineral soil.
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| 5. |
- Rousk, Johannes, et al.
(författare)
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Assessing plant-microbial competition for P-33 using uptake into phospholipids
- 2007
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Ingår i: Applied Soil Ecology. - : Elsevier BV. - 0929-1393. ; 36:2-3, s. 233-237
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Tidskriftsartikel (refereegranskat)abstract
- A novel method of estimating soil microbial P uptake, using P-33 incorporation into the phospholipids in soil microbial biomass, was used in a study of P-competition between plants and microorganisms. The microbial biomass, and thus the competition for the added P-33, was altered by using different glucose treatments in a microcosm set-up. There was obvious competition for P-33, as shown by the negative relationship between P-33 uptake by the plant and P-33 incorporation into microbial phospholipids. The data thus indicate that soil microorganisms partly control P-33 uptake by the plant. The suggested method of measuring P-33 in phospholipids appears to have the potential to provide a rapid alternative to techniques such as chloroform fumigation-extraction for the determination of microbial P uptake, although at present the method will only give relative estimates of P uptake.
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| 6. |
- Sandberg, Jakob, et al.
(författare)
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Despite high uptake efficiency, non-mycorrhizal Rumex acetosella increases available phosphorous in the rhizosphere soil, whereas Viscaria vulgaris, Plantago lanceolata and Achillea millefolium does not
- 2009
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Ingår i: Nordic Journal of Botany. - : John Wiley & Sons. - 0107-055X .- 1756-1051. ; 27:5, s. 444-448
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Tidskriftsartikel (refereegranskat)abstract
- The phosphorous (P) uptake efficiency, reduction of the soil extractable P, and the root morphology was determined for the four common grassland species Rumex acetosella, Viscaria vulgaris, Plantago lanceolata and Achillea millefolium in one pot cultivation and one microcosm experiment. Rumex acetosella produced more than tree times as much biomass as each of V. vulgaris, P. lanceolata and A. millefolium, and could maintain a P concentration in the tissue that was twice as high as in the other species. R. acetosella was able to take up 10 times more phosphorous than the other species but the high uptake was not reflected in reduced Olsen P levels in the root affected soil. Calculating the uptake efficiency of the roots with a diameter less than 0.5 mm showed that the P uptake, calculated per root area, had been more efficient in R. acetosella than in the other species. The calculated rhizosphere volume (explored by the plant) seemed to correlate with the higher uptake efficiency of R. acetosella. We can conclude that R. acetosella have mechanisms to maintain a high P availability in the soil and may sustain a high uptake without any mycorrhizal interactions.
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