36 research outputs found
Denitrification and nitrous oxide emissions from riparian forests soils exposed to prolonged nitrogen runoff
Compared to upland forests, riparian forest soils have greater potential to remove nitrate (NO3) from agricultural run-off through denitrification. It is unclear, however, whether prolonged exposure of riparian soils to nitrogen (N) loading will affect the rate of denitrification and its end products. This research assesses the rate of denitrification and nitrous oxide (N2O) emissions from riparian forest soils exposed to prolonged nutrient run-off from plant nurseries and compares these to similar forest soils not exposed to nutrient run-off. Nursery run-off also contains high levels of phosphate (PO4). Since there are conflicting reports on the impact of PO4 on the activity of denitrifying microbes, the impact of PO4 on such activity was also investigated. Bulk and intact soil cores were collected from N-exposed and non-exposed forests to determine denitrification and N2O emission rates, whereas denitrification potential was determined using soil slurries. Compared to the non-amended treatment, denitrification rate increased 2.7- and 3.4-fold when soil cores collected from both N-exposed and non-exposed sites were amended with 30 and 60 μg NO3-N g-1 soil, respectively. Net N2O emissions were 1.5 and 1.7 times higher from the N-exposed sites compared to the non-exposed sites at 30 and 60 μg NO3-N g-1 soil amendment rates, respectively. Similarly, denitrification potential increased 17 times in response to addition of 15 μg NO3-N g-1 in soil slurries. The addition of PO4 (5 μg PO4–P g-1) to soil slurries and intact cores did not affect denitrification rates. These observations suggest that prolonged N loading did not affect the denitrification potential of the riparian forest soils; however, it did result in higher N2O emissions compared to emission rates from non-exposed forests
Fast and furious: Early differences in growth rate drive short-term plant dominance and exclusion under eutrophication
The reduction of plant diversity following eutrophication threatens many ecosystems worldwide. Yet, the mechanisms by which species are lost following nutrient enrichment are still not completely understood, nor are the details of when such mechanisms act during the growing season, which hampers understanding and the development of mitigation strategies.
Using a common garden competition experiment, we found that early‐season differences in growth rates among five perennial grass species measured in monoculture predicted short‐term competitive dominance in pairwise combinations and that the proportion of variance explained was particularly greater under a fertilization treatment.
We also examined the role of early‐season growth rate in determining the outcome of competition along an experimental nutrient gradient in an alpine meadow. Early differences in growth rate between species predicted short‐term competitive dominance under both ambient and fertilized conditions and competitive exclusion under fertilized conditions.
The results of these two studies suggest that plant species growing faster during the early stage of the growing season gain a competitive advantage over species that initially grow more slowly, and that this advantage is magnified under fertilization. This finding is consistent with the theory of asymmetric competition for light in which fast‐growing species can intercept incident light and hence outcompete and exclude slower‐growing (and hence shorter) species. We predict that the current chronic nutrient inputs into many terrestrial ecosystems worldwide will reduce plant diversity and maintain a low biodiversity state by continuously favoring fast‐growing species. Biodiversity management strategies should focus on controlling nutrient inputs and reducing the growth of fast‐growing species early in the season
Snow cover manipulation effects on microbial community structure and soil chemistry in a mountain bog
Background and Aims: Alterations in snow cover driven
by climate change may impact ecosystem functioning,
including biogeochemistry and soil (microbial)
processes. We elucidated the effects of snow cover
manipulation (SCM) on above-and belowground processes
in a temperate peatland.
Methods: In a Swiss mountain-peatland we manipulated
snow cover (addition, removal and control), and
assessed the effects on Andromeda polifolia root enzyme
activity, soil microbial community structure, and
leaf tissue and soil biogeochemistry.
Results: Reduced snow cover produced warmer soils
in our experiment while increased snow cover kept
soil temperatures close-to-freezing. SCM had a major
influence on the microbial community, and prolonged
‘close-to-freezing’ temperatures caused a shift in microbial
communities toward fungal dominance. Soil
temperature largely explained soil microbial structure,
while other descriptors such as root enzyme activity
and pore-water chemistry interacted less with the soil
microbial communities.
Conclusions: We envisage that SCM-driven changes
in the microbial community composition could lead to substantial changes in trophic fluxes and associated
ecosystem processes. Hence, we need to improve our
understanding on the impact of frost and freeze-thaw
cycles on the microbial food web and its implications
for peatland ecosystem processes in a changing climate;
in particular for the fate of the sequestered
carbon
Hotspots of anaerobic ammonium oxidation at land-freshwater interfaces
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