| 1. |
- Duran, J., et al.
(författare)
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Different Cerrado Ecotypes Show Contrasting Soil Microbial Properties, Functioning Rates, and Sensitivity to Changing Water Regimes
- 2023
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Ingår i: Ecosystems. - : SPRINGER. - 1432-9840 .- 1435-0629.
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Tidskriftsartikel (refereegranskat)abstract
- Soil moisture is among the most important factors regulating soil biodiversity and functioning. Models forecast changes in the precipitation regime in many areas of the planet, but how these changes will influence soil functioning, and how biotic drivers modulate such effects, is far from being understood. We evaluated the responses of C and N fluxes, and soil microbial properties to different soil water regimes in soils from the main three ecotypes of the worlds largest and most diverse tropical savanna. Further, we explored the direct and indirect effects of changes in the ecotype and soil water regimes on these key soil processes. Soils from the woodland savanna showed a better nutritional status than the other ecotypes, as well as higher potential N cycling rates, N2O emissions, and soil bacterial abundance but lower bacterial richness, whereas potential CO2 emissions and CH4 uptake peaked in the intermediate savanna. The ecotype also modulated the effects of changes in the soil water regime on nutrient cycling, greenhouse gas fluxes, and soil bacterial properties, with more intense responses in the intermediate savanna. Further, we highlight the existence of multiple contrasting direct and indirect (via soil microbes and abiotic properties) effects of an intensification of the precipitation regime on soil C- and N-related processes. Our results confirm that ecotype is a fundamental driver of soil properties and functioning in the Cerrado and that it can determine the responses of key soil processes to changes in the soil water regime.
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| 2. |
- Hargeby, Anders, et al.
(författare)
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Long-term patterns of shifts between clear and turbid states in Lake Krankesjon and Lake Takern
- 2007
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 10:1, s. 29-36
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Tidskriftsartikel (refereegranskat)abstract
- During the past century, Lake Takern and Lake Krankesjon, southern Sweden, have shifted repeatedly between a state of clear water and abundant submerged vegetation, and a state of turbid water and sparse vegetation. Long-term empirical data on such apparently alternative stable state dynamics are valuable as complements to modeling and experiments, although the causal mechanisms behind shifts are often difficult to identify in hindsight. Here, we summarize previous studies and discuss possible mechanisms behind the shifts. The most detailed information comes from monitoring of two recent shifts, one in each lake. In the 1980s, L. Krankesjon shifted to clear water following an expansion of sago pondweed, Potamogeton pectinatus. Water clarity increased when the pondweed was replaced by characeans. Zooplankton biomass in summer declined and the concentration of total phosphorus (TP) was reduced to half the previous level. The fish community changed over several years, including an increasing recruitment of piscivorous perch (Perca fluviatilis). An opposite directed shift to turbid water occurred in Lake Takern in 1995, when biomass of phytoplankton increased in spring, at the expense of submerged vegetation. Consistent with the findings in L. Krankesjon, phyto- and zooplankton biomass increased and the average concentration of TP doubled. After the shift to clear water in L. Krankesjon, TP concentration has increased during the latest decade, supporting the idea that accumulation of nutrients may lead to a long-term destabilization of the clear water state. In L. Takern, data on TP are inconclusive, but organic nitrogen concentrations oscillated during a 25-year period of clear water. These observations indicate that intrinsic processes cause gradual or periodic changes in system stability, although we cannot exclude the possibility that external forces are also involved. During such phases of destabilization of the clear water state, even small disturbances could possibly trigger a shift, which may explain why causes behind shifts are hard to identify even when they occur during periods of extensive monitoring.
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| 3. |
- Peixoto, R. B., et al.
(författare)
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Floating Aquatic Macrophytes Can Substantially Offset Open Water CO2 Emissions from Tropical Floodplain Lake Ecosystems
- 2016
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Ingår i: Ecosystems (New York. Print). - : SPRINGER. - 1432-9840 .- 1435-0629. ; 19:4, s. 724-736
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Tidskriftsartikel (refereegranskat)abstract
- Tropical floodplain lake ecosystems are recognized as important sources of carbon (C) from the water to the atmosphere. They receive large amounts of organic matter and nutrients from the watershed, leading to intense net heterotrophy and carbon dioxide (CO2) emission from open waters. However, the role of extensive stands of floating macrophytes colonizing floodplains areas is still neglected in assessments of net ecosystem exchange of CO2 (NEE). We assessed rates of air-lake CO2 flux using static chambers in both open waters and waters covered by the widespread floating aquatic macrophyte (water hyacinth; Eichornia sp.) in two tropical floodplain lakes in Pantanal, Brazil during different hydrological seasons. In both lakes, areas colonized by floating macrophytes were a net CO2 sink during all seasons. In contrast, open waters emitted CO2, with higher emissions during the rising and high water periods. Our results indicate that the lake NEE can be substantially overestimated (fivefold or more in the studied lakes) if the carbon fixation by macrophytes is not considered. The contribution of these plants can lead to neutral or negative NEE (that is, net uptake of CO2) on a yearly basis. This highlights the importance of floating aquatic macrophytes for the C balance in shallow lakes and extensive floodplain areas.
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