| 1. |
- Blaser, Wilma J., et al.
(författare)
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Facilitative or competitive effects of woody plants on understorey vegetation depend on N-fixation, canopy shape and rainfall
- 2013
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Ingår i: Journal of Ecology. - : John Wiley & Sons. - 0022-0477 .- 1365-2745. ; 101:6, s. 1598-1603
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Tidskriftsartikel (refereegranskat)abstract
- A recent meta-analysis suggested that differences in rainfall are a cause of variation in tree-grass interactions in savannas, with trees facilitating growth of understorey grasses in low-rainfall areas, but competing with them under higher rainfall. We hypothesized that this effect of rainfall upon understorey productivity is modified by differences in the growth form of the woody plants (i.e. the height of the lower canopy) or by their capacity to fix nitrogen. We performed a meta-analysis of the effects of woody plants on understorey productivity, incorporating canopy height and N-fixation, and their interaction with rainfall. N-fixing woody plants enhanced understorey productivity, whereas non-fixers had a neutral or negative effect, depending on high or low canopy, respectively. We found a strong negative correlation between rainfall and the degree to which trees enhanced understorey productivity, but only for trees with a high canopy.Synthesis. The effect of woody plants on understorey productivity depends not only on rainfall, but also on their growth form and their capacity to fix N. Facilitation occurs mostly when woody plants ameliorate both water and nitrogen conditions. However, a low canopy suppresses understorey vegetation by competing for light, regardless of water and nutrient relations.
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| 2. |
- Göransson, Hans, et al.
(författare)
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Soil bacterial growth and nutrient limitation along a chronosequence from a glacier forefield
- 2011
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 43:6, s. 1333-1340
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Tidskriftsartikel (refereegranskat)abstract
- Resource availability and limiting factors for bacterial growth during early stages of soil development (8-138 years) were studied along a chronosequence from the glacial forefield of the Damma glacier in the Swiss Alps. We determined bacterial growth (leucine incorporation) and we investigated which resource (C, N or P) limited bacterial growth in soils formed by the retreating glacier. The latter was determined by adding labile sources of C (glucose), N and P to soil samples and then measuring the bacterial growth response after a 40 h incubation period. Bacterial growth increased with increasing soil age in parallel with the build up of organic matter. However, lower bacterial growth, when standardized to the amount of organic C, was found with time since the glacier retreat, indicating decreasing availability of soil organic matter with soil age. Bacterial growth in older soils was limited by the lack of C. The bacteria were never found to be limited by only N, only P. or N + P. In the youngest soils, however, neither the addition of C, N nor P singly increased bacterial growth, while a combination of C and N did. Bacterial growth was relatively more limited by lack of N than P when the C limitation was alleviated, suggesting that N was the secondary limiting resource. The availability of N for bacterial growth increased with time, as seen by an increased bacterial growth response after adding only C in older soils. This study demonstrated that bacterial growth measurements can be used not only to indicate direct growth effects, but also as a rapid method to indicate changes in bacterial availability of nutrients during soil development. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
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| 3. |
- Koelbener, Albert, et al.
(författare)
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Plant species from mesotrophic wetlands cause relatively high methane emissions from peat soil
- 2010
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 326:1-2, s. 147-158
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Tidskriftsartikel (refereegranskat)abstract
- Plants can influence methane emissions from wetland ecosystems by altering its production, consumption and transport in the soil. The aim of this study was to investigate how eight vascular plant species from mesotrophic to eutrophic wetlands vary in their influence on CH4 emissions from peat cores, under low and high N supply. Additionally, we measured the production of low-molecular-weight organic acids (LOA) by the same species (also at low and high N supply), because LOA form a substrate for methanogenesis. There were considerable differences among species in their effects upon rates of CH4 emission. Six of the species (Eriophorum latifolium Hoppe, Potentilla palustris (L.) Scop., Anthoxanthum odoratum (L.) s. str., Carex rostrata Stokes, Carex elata All., Carex acutiformis Ehrh.) increased CH4 emissions up to five times compared to control peat cores without plants, whereas two species (Phalaris arundinacea L., Phragmites australis (Cav.) Trin. ex Steud.) had no effect. There was a weak negative correlation between plant biomass and CH4 emission. N addition had no significant general effect upon CH4 emission. LOA production varied considerably among species, and tended to be highest for species from mesotrophic habitats. LOA production was stimulated by N addition. We conclude that some species from mesotrophic wetlands tend to cause higher CH4 emissions than species from eutrophic wetlands. This pattern, which contradicts what is often mentioned in literature, may be explained by the higher LOA production rates of species adapted to less productive habitats.
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| 4. |
- Robroek, Bjorn J. M., et al.
(författare)
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How nitrogen and sulphur addition, and a single drought event affect root phosphatase activity in Phalaris arundinacea
- 2009
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 1879-1026 .- 0048-9697. ; 407:7, s. 2342-2348
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Tidskriftsartikel (refereegranskat)abstract
- Conservation and restoration of fens and fen meadows often aim to reduce soil nutrients, mainly nitrogen (N) andphosphorus (P). The biogeochemistry of P has received much attention as P-enrichment is expected to negatively impact on species diversity in wetlands. It is known that N, sulphur (S) and hydrological conditions affect the biogeochemistry of P, yet their interactive effects on P-dynamics are largely unknown. Additionally, in Europe, climate change has been predicted to lead to increases in summer drought. We performed a greenhouse experiment to elucidate the interactive effects of N, S and a single drought event on the P-availability for Phalaris arundinacea. Additionally, the response of plant phosphatase activity to these factors was measured over the two year experimental period. In contrast to results from earlier experiments, our treatments hardly affected soil P-availability. This may be explained by the higher pH in our soils, hampering the formation of Fe-P or Fe-Al complexes. Addition of S, however, decreased the plants N:P ratio, indicating an effect of S on the N:P stoichiometry and an effect on the plant's P-demand. Phosphatase activity increased significantly after addition of S, but was not affected by the addition of N or a single drought event. Root phosphatase activity was also positively related to plant tissue N and P concentrations, plant N and P uptake, and plant aboveground biomass, suggesting that the phosphatase enzyme influences P-biogeochemistry. Our results demonstrated that it is difficult to predict the effects of wetland restoration, since the involved mechanisms are not fully understood. Short-term and long-term effects on root phosphatase activity may differ considerably. Additionally, the addition of S can lead to unexpected effects on the biogeochemistry of P. Our results showed that natural resource managers should be careful when restoring degraded fens or preventing desiccation of fen ecosystems. (C) 2008 Elsevier B.V. All rights reserved.
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| 5. |
- Sitters, Judith, et al.
(författare)
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Increases of soil C, N, and P pools along an acacia tree density gradient and their effects on trees and grasses
- 2013
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 16:2, s. 347-357
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) fixing trees including many species of Acacia are an important though variable component of savanna ecosystems. It is known that these trees enrich the soil with carbon (C) and N, but their effect on the combined C:N:P stoichiometry in soil is less well understood. Theory suggests that they might reduce available phosphorus (P), creating a shift from more N-limited conditions in grass-dominated to more P-limited conditions in tree-dominated sites, which in turn could feed back negatively on the trees' capacity to fix N. We studied the effects of Acacia zanzibarica tree density upon soil and foliar N:P stoichiometry, and the N-2-fixation rates of trees and leguminous herbs in a humid Tanzanian savanna. Foliar N:P ratios and N-2-fixation rates of trees remained constant across the density gradient, whereas soil C, N and organic P pools increased. In contrast, the N:P ratio of grasses increased and N-2-fixation rates of leguminous herbs decreased with increasing tree density, indicating a shift towards more P-limited conditions for the understory vegetation. These contrasting responses suggest that trees and grasses have access to different sources of N and P, with trees being able to access P from deeper soil layers and perhaps also utilizing organic forms more efficiently.
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| 6. |
- Sitters, Judith, et al.
(författare)
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Interactions between C:N:P stoichiometry and soil macrofauna control dung decomposition of savanna herbivores
- 2014
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 28:3, s. 776-786
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Tidskriftsartikel (refereegranskat)abstract
- Although dung of mammalian herbivores is an important pathway for nutrient return in savanna ecosystems, differences in dung decomposition rates among species have been little studied. We measured the rates of dung deposition and decomposition for various herbivores in a moist Tanzanian savanna and the related differences among species to nutrient concentrations and the activities of soil macrofauna (e.g. different mesh sizes of decomposition bags, or presence and absence of dung beetles). Dung C:N:P stoichiometry varied widely among species, which could in part be explained by differences in feeding strategy (browsers vs. grazers) and digestive physiology (ruminants vs. non-ruminants). Rates of both decomposition and nutrient release were influenced by the C:N:P stoichiometry of dung, with lower relative losses of the least abundant nutrient in the dung. Surprisingly, soil macrofauna increased the relative losses of the least abundant nutrient, thereby stabilizing the ratio of N loss to P loss. Dung beetles increased rates of N and P release from wildebeest dung significantly and also increased N availability in the soil. We conclude that rates of nutrient return in dung depend not only on where herbivores deposit their dung, but also on its C:N:P stoichiometry, the activity of soil macrofauna and interactions between these factors. These factors may therefore influence the relative availabilities of N and P in the soil and hence the functioning of savanna ecosystems.
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