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Latest Results for Ecosystems
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The Influence of Climate Change on the Restoration Trajectory of a Nutrient-Rich Deep Lake
20. September 2019
Abstract Nutrient reduction in impacted lowland freshwater systems is ecologically and culturally important. Gaining a greater insight into how lakes respond to lowering nutrient loads and how climate-driven physical limnology affects present and future cycling of available nutrients is important for ecosystem resource management. This study examines the nutrient decline in a hypereutrophic freshwater lake (Rostherne Mere, Cheshire, UK) 25 years after sewage effluent diversion, a uniquely long-term analysis of a recovering nutrient-rich deep lake. Using nutrient...
Tall Shrubs Mediate Abiotic Conditions and Plant Communities at the Taiga–Tundra Ecotone
18. September 2019
Abstract Shrub expansion has occurred across much of the arctic tundra over the past century. Increasing dominance of woody vegetation is expected to have global influences on climate patterns and lead to local changes in hydrological function and nutrient cycling. Changing abiotic conditions associated with shrubs will likely alter the relative fitness of neighbouring plants resulting in distinct community composition. Here, we use an extensive set of paired abiotic and biotic data to investigate the capacity for Alnus alnobetula (green alder) patches to modify the...
Varying Vegetation Composition, Respiration and Photosynthesis Decrease Temporal Variability of the CO 2 Sink in a Boreal Bog
16. September 2019
Abstract We quantified the role of spatially varying vegetation composition in seasonal and interannual changes in a boreal bog’s CO2 uptake. We divided the spatially heterogeneous site into six microform classes based on plant species composition and measured their net ecosystem exchange (NEE) using chamber method over the growing seasons in 2012–2014. A nonlinear mixed-effects model was applied to assess how the contributions of microforms with different vegetation change temporally, and to upscale NEE to the ecosystem level to be compared with eddy covariance (EC...
Fungi in the Canopy: How Soil Fungi and Extracellular Enzymes Differ Between Canopy and Ground Soils
16. September 2019
Abstract Tropical montane cloud forests contain a large abundance and diversity of canopy epiphytes, which depend on canopy soil to retain water and nutrients. We lack an in depth understanding of how these soils contribute to ecosystem processes and soil diversity and how sensitive they may be to projected climate change. We compared canopy and ground soils in Monteverde, Costa Rica, to determine how these two soil types differ in their extracellular enzyme activity (EEA) and fungal communities. Samples were also collected along two elevation gradients to reveal if...
Alleviation of Plant Stress Precedes Termination of Rich Fen Stages in Peat Profiles of Lowland Mires
16. September 2019
Abstract Mesotrophic rich fens, that is, groundwater-fed mires, may be long-lasting, as well as transient ecosystems, displaced in time by poor fens, bogs, forests or eutrophic reeds. We hypothesized that fen stability is controlled by plant stress caused by waterlogging with calcium-rich and nutrient-poor groundwater, which limits expansion of hummock mosses, tussock sedges and trees. We analysed 32 European Holocene macrofossil profiles of rich fens using plant functional traits (PFTs) which indicate the level of plant stress in the environment: canopy height, clonal...
Accounting for Carbon Flux to Mycorrhizal Fungi May Resolve Discrepancies in Forest Carbon Budgets
16. September 2019
Abstract Carbon (C) fluxes among different components of plant growth are important to forest ecosystem C cycling and are strongly influenced by species composition and resource availability. Although mycorrhizal fungi are crucial for nutrient acquisition and can receive a large fraction of annual net primary production, most studies do not explicitly include carbon flux to mycorrhizal fungi in ecosystem C budgets. We measured annual production of plant components (foliage, wood, fine roots) and mycorrhizal fungi across temperate forest stands varying in species...
Droughts Decouple African Savanna Grazers from Their Preferred Forage with Consequences for Grassland Productivity
13. September 2019
Abstract Grazing lawn and flammable-tussock grass communities are contrasting resource pools for mammalian grazers in terms of forage quantity and quality. Drought events fundamentally alter forage availability within these communities and therefore should alter herbivore use with repercussions for the recovery and functioning of ecosystems after drought. During and after an intense El Niño drought (2014–2017) in Kruger National Park, South Africa, we addressed two questions: (1) how does herbivore use of different grass types change during a drought and (2) how do...
Effects of Nitrogen Deposition on the Abundance and Metabolism of Lichens: A Meta-analysis
12. September 2019
Abstract Lichens are the key to nutrient cycling and trophic networks in many terrestrial ecosystems and are good bioindicators of air pollution, including nitrogen (N) deposition. Experimental studies have shown that N deposition can reduce the abundance of lichens and alter their thallus chemistry and metabolism, but we currently lack information about how widespread this effect is and what are the environmental factors modulating the response of lichens to N. We carried out a meta-analysis of the literature about the effects of experimental N fertilization on lichen...
Nitrogen Enrichment Accelerates Mangrove Range Expansion in the Temperate–Tropical Ecotone
12. September 2019
Abstract Climate change and nutrient enrichment are two phenomena impacting coastal ecosystems. In coastal wetlands, mangroves in temperate–tropical ecotones are encroaching on adjacent saltmarshes, a pattern that is primarily attributed to warmer winter temperatures. Climate change is also expected to increase the vulnerability of coastal wetlands to eutrophication, and increases in nutrient availability may further mediate the rate of mangrove expansion. We investigated the consequences of nutrient enrichment on coastal wetlands in the mangrove–saltmarsh ecotone...
Cumulative Effects of Disturbances on Soil Nutrients: Predominance of Antagonistic Short-Term Responses to the Salvage Logging of Insect-Killed Stands
12. September 2019
Abstract Nutrient cycling generally recovers rapidly following disturbance in forest ecosystems. Concerns have been expressed that the resilience of this function may be altered by enhanced disturbance frequency, and especially by the use of salvage logging. A sudden hemlock looper (Lambdina fiscellaria) outbreak in a boreal forest leading to tree mortality in discrete patches allowed us to evaluate the impact of disturbance type (logging vs insect defoliation) as well as the cumulative effects of both disturbances (that is, salvage logging of defoliated sites) on soil...
Nitrogen Identity Drives Differential Impacts of Nutrients on Coral Bleaching and Mortality
11. September 2019
Abstract Nitrogen pollution increases the susceptibility of corals to heat-induced bleaching. However, different forms of nitrogen (nitrate vs. ammonium/urea) may have different impacts on thermal tolerance of corals. We used an 18-month field experiment on the oligotrophic fore reef of Moorea, French Polynesia, to test how different forms of nitrogen (nitrate vs. urea) impacted coral bleaching. The experiment spanned two moderate thermal stress events in 2016 and 2017. Nitrate increased bleaching prevalence in Acropora by up to 100% and in Pocillopora by up to 60...
Permafrost Hydrology Drives the Assimilation of Old Carbon by Stream Food Webs in the Arctic
03. September 2019
Abstract Permafrost thaw in the Arctic is mobilizing old carbon (C) from soils to aquatic ecosystems and the atmosphere. Little is known, however, about the assimilation of old C by aquatic food webs in Arctic watersheds. Here, we used C isotopes (δ13C, Δ14C) to quantify C assimilation by biota across 12 streams in arctic Alaska. Streams spanned watersheds with varying permafrost hydrology, from ice-poor bedrock to ice-rich loess (that is, yedoma). We measured isotopic content of (1) C sources including dissolved organic C (DOC), dissolved inorganic C (DIC), and soil C...
Advancing Our Understanding of Woody Debris in Tropical Forests
01. September 2019
Nitrogen Retention of Terricolous Lichens in a Northern Alberta Jack Pine Forest
01. September 2019
Abstract The Athabasca Oil Sands in Alberta, Canada, is one of the largest point sources of nitrogen oxides in Canada. There are concerns that elevated nitrogen (N) deposition will adversely impact forest ecosystems located downwind of emission sources. The role of the forest floor in regulating these potential eutrophication effects was investigated following a 5-year enrichment study in which N was applied as NH4NO3 above the canopy of a jack pine (Pinus banksiana Lamb) stand in northern Alberta close to Fort McMurray at rates ranging from 5 to 25 kg N ha−1 y−1...
Boreal Forest Floor Greenhouse Gas Emissions Across a Pleurozium schreberi -Dominated, Wildfire-Disturbed Chronosequence
01. September 2019
Abstract The boreal forest is a globally critical biome for carbon cycling. Its forests are shaped by wildfire events that affect ecosystem properties and climate feedbacks including greenhouse gas (GHG) emissions. Improved understanding of boreal forest floor processes is needed to predict the impacts of anticipated increases in fire frequency, severity, and extent. In this study, we examined relationships between time since last wildfire (TSF), forest floor soil properties, and GHG emissions (CO2, CH4, N2O) along a Pleurozium schreberi-dominated chronosequence in mid...
N-Isotopes in Feathers and Abundance of Eiders Respond to Nutrients in Seawater
01. September 2019
Abstract Nitrification of the environment has resulted from tremendous increases in the use of fertilizers for crop plants. This has increased runoff to coastal marine areas with consequences for primary production, benthos and upper trophic-level consumers, including sea ducks such as eiders Somateria mollissima. This species primarily relies on filter-feeding bivalves, especially blue mussels Mytilus edulis. Stable isotopes of nitrogen (measured as δ15N) are incorporated in the feathers of eiders during molt at a constant rate reflecting the amount in food eaten. We...
Coastal Wetland Distributions: Delineating Domains of Macroscale Drivers and Local Feedbacks
01. September 2019
Abstract How do multiple stable states influence local and macroscale ecological patterns? Understanding how local feedbacks operate within heterogeneous coastal environments is essential to forecasting marsh persistence and loss in response to sea level rise, river impoundment, and other environmental changes. In coastal lagoons, feedbacks between open water, wind erosion, and stabilizing effects from wetland vegetation produce two states: open water with fringing marshes, and marsh-dominated basins. Unknown is whether, how, and at what scales these feedbacks affect...
The Spatial Heterogeneity of Vegetation, Hydrology and Water Chemistry in a Peatland with Open-Water Pools
01. September 2019
Abstract Ombrotrophic bogs can comprise a mosaic of vegetation patches and open-water pools, with hydrological and biogeochemical connections between pools and the surrounding peat and vegetation. To establish these connections, we studied the spatial heterogeneity of hydrology and water chemistry in two zones of distinct vegetation assemblages in the subboreal Grande plée Bleue peatland, southern Québec, Canada. We show that seasonal water-level fluctuations are greater and organic C, N and P concentrations are higher in the peat pore water of a forested zone than in...
The Effect of Land-Use Change on Soil CH 4 and N 2 O Fluxes: A Global Meta-Analysis
01. September 2019
Abstract Land-use change is a prominent feature of the Anthropocene. Transitions between natural and human-managed ecosystems affect biogeochemical cycles in many ways, but soil processes are among the least understood. We used a global meta-analysis (62 studies, 1670 paired comparisons) to examine effects of land conversion on soil–atmosphere fluxes of methane (CH4) and nitrous oxide (N2O) from upland soils, and determine soil and environmental factors driving these effects. Conversion from a natural ecosystem to any anthropogenic land use increased soil CH4 and N2O...
Effects of Duration, Frequency, and Severity of the Non-flow Period on Stream Biofilm Metabolism
01. September 2019
Abstract Temporary streams make up the majority of river networks in many regions around the world. Although they are known to have non-flow periods, it is uncertain in what ways the temporal components of the non-flow period affect stream ecosystems. We analyzed how duration and frequency of the non-flow period influence the biofilm metabolism of 33 Mediterranean streams in NE Iberian Peninsula. Selected streams ranged from perennial to ephemeral, and their hydrology was characterized during a period of 150 days before the sampling. Cobbles were collected from the...