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Abstract Coastal ecosystems are exposed to saltwater intrusion but differential effects on biogeochemical cycling are uncertain. We tested how elevated salinity and phosphorus (P) individually and interactively affect microbial activities and biogeochemical cycling in freshwater and brackish wetland soils. In experimental mesocosms, we added crossed gradients of elevated concentrations of soluble reactive P (SRP) (0, 20, 40, 60, 80 μg/L) and salinity (0, 4, 7, 12, 16 ppt) to freshwater and brackish peat soils (10, 14, 17, 22, 26 ppt) for 35 d. We quantified changes in water chemistry [dissolved organic carbon (DOC), ammonium (), nitrate + nitrite (N + N), SRP concentrations], soil microbial extracellular enzyme activities, respiration rates, microbial biomass C, and soil chemistry (%C, %N, %P, C:N, C:P, N:P). DOC, , and SRP increased in freshwater but decreased in brackish mesocosms with elevated salinity. DOC similarly decreased in brackish mesocosms with added P, and N + N decreased with elevated salinity in both freshwater and brackish mesocosms. In freshwater soils, water column P uptake occurred only in the absence of elevated salinity and when P was above 40 µg/L. Freshwater microbial EEAs, respiration rates, and microbial biomass C were consistently higher compared to those from brackish soils, and soil phosphatase activities and microbial respiration rates in freshwater soils decreased with elevated salinity. Elevated salinity increased arylsulfatase activities and microbial biomass C in brackish soils, and elevated P increased microbial respiration rates in brackish soils. Freshwater soil %C, %N, %P decreased and C:P and N:P increased with elevated salinity. Elevated P increased %C and C:N in freshwater soils and increased %P but decreased C:P and N:P in brackish soils. Freshwater soils released more C and nutrients than brackish soils when exposed to elevated salinity, and both soils were less responsive to elevated P than expected. Freshwater soils became more nutrient‐depleted with elevated salinity, whereas brackish soils were unaffected by salinity but increased P uptake. Microbial activities in freshwater soils were inhibited by elevated salinity and unaffected by added P, but brackish soil microbial activities slightly increased with elevated salinity and P.
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A genetically based ecological trade‐off contributes to setting a geographic range limit
Abstract Understanding the ecological factors that shape geographic range limits and the evolutionary constraints that prevent populations from adaptively evolving beyond these limits is an unresolved question. Here, we investigated why the euryhaline fish,Poecila reticulata, is confined to freshwater within its native range, despite being tolerant of brackish water. We hypothesised that competitive interactions with a close relative,Poecilia picta, in brackish water preventsP.reticulatafrom colonising brackish water. Using a combination of field transplant, common garden breeding, and laboratory behaviour experiments, we find support for this hypothesis, asP.reticulataare behaviourally subordinate and have lower survival in brackish water withP.picta. We also found a negative genetic correlation betweenP.reticulatagrowth in brackish water versus freshwater in the presence ofP.picta, suggesting a genetically based trade‐off between salinity tolerance and competitive ability could constrain adaptive evolution at the range limit.
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- Award ID(s):
- 1450032
- PAR ID:
- 10366387
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 24
- Issue:
- 12
- ISSN:
- 1461-023X
- Page Range / eLocation ID:
- p. 2739-2749
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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