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Ecosystems 

Latest Results for Ecosystems
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Biological Nitrogen Fixation Does Not Replace Nitrogen Losses After Forest Fires in the Southeastern Amazon
11. November 2019
Abstract Tropical forest fires have become more common due to interactions between deforestation, land clearing, and drought. Forest recovery following fires may be limited by nitrogen. Biological nitrogen fixation (BNF) is the main pathway for new nitrogen (N) to enter most ecosystems, but BNF may be constrained by other nutrients, such as molybdenum and phosphorus, which are required for the process. We studied the role of BNF 7 years into the recovery of southeastern Amazon tropical forests that were burned experimentally either annually or every 3 years between 2004...
Food Web Complexity of High Mountain Lakes is Largely Affected by Glacial Retreat
08. November 2019
Abstract High mountain lakes provide essential ecosystem services and have a high conservation value. Therefore, understanding how glacier retreat will affect their ecological functioning and water quality is crucial. Here, we tested how shallow high mountain lakes having different glacial influences differ in their abiotic main features and food web structure using a multiple ecological indicator approach. We identified 13 functional groups within the planktonic and littoral communities, each one representing a biotic indicator and a node in a simplified food web network...
Effects of Mineral Nitrogen Partitioning on Tree–Grass Coexistence in West African Savannas
01. November 2019
Abstract Coexistence between trees and grasses in savannas is generally assumed to be due to a combination of partial niche separation for water acquisition and disturbances impacting the demography of trees and grasses. We propose a mechanism of coexistence solely based on the partitioning of the two dominant forms of mineral nitrogen (N), ammonium (NH4+) and nitrate (NO3−). We built a mean-field model taking into account the capacity of grasses and trees to alter nitrification fluxes as well as their relative preferences for NH4+ versus NO3−. Two models were...
Livestock Herbivory Shapes Fire Regimes and Vegetation Structure Across the Global Tropics
01. November 2019
Abstract Livestock grazing is the most extensive human land use and one of the key drivers of the conversion of tropical forests into grasslands. Livestock effects on vegetation structure are complex, as they can prevent tree recruitment and growth through browsing and trampling, but they can also affect vegetation indirectly through fire interactions. However, a systematic analysis of the overall effects of livestock across the global tropics is lacking. We analyzed remote sensing data on vegetation height and cover, climate, and fire as well as ground data on...
Effects of Epixylic Vegetation Removal on the Dynamics of the Microbial Community Composition in Decaying Logs in an Alpine Forest
01. November 2019
Abstract Epixylic vegetation may be important in dead wood decay by altering the microenvironment and, thereby, microbial communities in logs. However, the interaction between epixylic vegetation and dead wood microbial communities remains poorly known. Therefore, repeated experimental epixylic (bryophyte-dominated) vegetation removal (ERM) from logs of the fir Abies faxoniana across a wide range of decay classes (I–V) was conducted on the eastern Tibetan Plateau. The dynamics of the microbial community were separately measured in heartwood, sapwood and bark using the...
Ectomycorrhiza, Friend or Foe?
01. November 2019
Abstract Many ecology textbooks present the interaction between mycorrhizal fungi and their host plants as the archetype of symbiosis or mutualism. However, mycorrhiza drains carbon directly from the plant and also competes with the plant for soil inorganic nitrogen. We developed hypotheses based on a simple model to qualitatively investigate when, in a nitrogen-limited system, the fungal partner returns sufficient extra nitrogen to compensate for the amount of carbon allocated to it by the plant. We showed when the mycorrhizal association can be beneficial to the plant...
Nitrous Oxide (N 2 O) Emissions from Subsurface Soils of Agricultural Ecosystems
01. November 2019
Abstract Nitrous oxide (N2O) is a major greenhouse gas and cultivated soils are the most important anthropogenic source. N2O production and consumption are known to occur at depths below the A or Ap horizon, but their magnitude in situ is largely unknown. At a site in SW Michigan, USA, we measured N2O concentrations at different soil depths and used diffusivity models to examine the importance of depth-specific production and consumption. We also tested the influence of crop and management practices on subsurface N2O production in (1) till versus no-till, (2) a nitrogen...
Natural Land Cover in Agricultural Catchments Alters Flood Effects on DOM Composition and Decreases Nutrient Levels in Streams
01. November 2019
Abstract A shift in natural hydrologic patterns, such as increases in the frequency, and changes in the magnitude of flood events are expected with climate change. A better understanding of how land use and hydrological patterns interact to affect solute levels in aquatic systems is needed so we can better navigate expected climatic changes. Here we analyzed spatiotemporal event-based data from 21 predominantly agricultural catchments with varying contributions of natural land cover. We studied the effect of hydrological events on stream dissolved phosphorus and...
Quantitative Analysis of Pedogenic Thresholds and Domains in Volcanic Soils
01. November 2019
Abstract Pedogenic thresholds describe where soil properties or processes change in an abrupt/nonlinear fashion in response to small changes in environmental forcing. Contrastingly, soil process domains refer to the space between thresholds where soil properties are either unchanged, or change gradually, across a broad range of environmental forcing. Here, we test quantitatively for the presence of thresholds in patterns of soil properties across a climatic gradient on soils developed from about 20-ky-old basaltic substrate on the Island of Hawai’i. From multiple soil...
Connectivity-Mediated Ecohydrological Feedbacks and Regime Shifts in Drylands
01. November 2019
Abstract Identified as essential mechanisms promoting alternative stable states, positive feedbacks have been the focus of most former studies on the potential for catastrophic shifts in drylands. Conversely, little is known about how negative feedbacks could counterbalance the effects of positive feedbacks. A decrease in vegetation cover increases the connectivity of bare-soil areas and entails a global loss of runoff-driven resources from the ecosystem but also a local increase in runoff transferred from bare-soil areas to vegetation patches. In turn, these global...
Legacies of Historical Exploitation of Natural Resources Are More Important Than Summer Warming for Recent Biomass Increases in a Boreal–Arctic Transition Region
01. November 2019
Abstract Eurasian forest cover at high northern latitudes (> 67°N) has increased in recent decades due to stimulatory effects of global warming, but other factors may be important. The objective of this study is to compare the importance of historical human exploitation and climate change. Periodic information on forest and tundra resources along with human and domestic animal populations and forest harvesting was collected from sources like official statistics and maps and compiled for joint analysis. Our results show that the northernmost birch and Scots pine...
Long-Term Nitrogen Addition Does Not Increase Soil Carbon Storage or Cycling Across Eight Temperate Forest and Grassland Sites on a Sandy Outwash Plain
01. November 2019
Abstract Experimental nitrogen (N) deposition generally inhibits decomposition and promotes carbon (C) accumulation in soils, but with substantial variation among studies. Differences in ecosystem properties could help explain this variability: N could have distinct effects on decomposition and soil C due to differences in vegetation characteristics (that is, root C inputs and chemistry) that influence microbial biomass or soil properties like pH that can affect organic matter stabilization. We used a 12-year N addition experiment to determine effects of sustained N...
Seasonal Patterns of Root Production with Water and Nitrogen Additions Across Three Dryland Ecosystems
01. November 2019
Abstract Root production is known to contribute at least 50% of total net primary production in dryland ecosystems, yet few studies have addressed seasonal dynamics of root production or the belowground response to altered resource availability. We aimed to identify how root production varies across three dryland ecosystems dominated by different plant functional types: the shortgrass steppe, dominated by C4 perennial bunchgrasses, the northern mixed-grass prairie, co-dominated by perennial C3 and C4 grasses, and the sagebrush steppe, dominated by a perennial shrub with...
Summer Redox Dynamics in a Eutrophic Reservoir and Sensitivity to a Summer’s End Drawdown Event
01. November 2019
Abstract In eutrophic lakes and reservoirs, reduced mixing during stratified conditions limits oxygen (O2) supply to the hypolimnion (that is, bottom waters). In the absence of an O2 supply, microbial decomposers consume alternative electron acceptors, generally in order of their thermodynamic favorability, releasing soluble, reduced manganese (Mn), iron (Fe) and methane (CH4) to the water column with implications for reservoir water quality and greenhouse gas dynamics. Still, there are very few studies that quantify intra- and inter-annual controls on lake and...
Biotic and Abiotic Drivers of Topsoil Organic Carbon Concentration in Drylands Have Similar Effects at Regional and Global Scales
01. November 2019
Abstract Drylands contain 25% of the world’s soil organic carbon (SOC), which is controlled by many factors, both abiotic and biotic. Thus, understanding how these factors control SOC concentration can help to design more sustainable land-use practices in drylands aiming to foster and preserve SOC storage, something particularly important to fight ongoing global warming. We use two independent, large-scale databases with contrasting geographic coverage (236 sites in global drylands and 185 sites in Patagonia, Argentina) to evaluate the relative importance of abiotic...
Belowground Biomass Response to Nutrient Enrichment Depends on Light Limitation Across Globally Distributed Grasslands
01. November 2019
Abstract Anthropogenic activities are increasing nutrient inputs to ecosystems worldwide, with consequences for global carbon and nutrient cycles. Recent meta-analyses show that aboveground primary production is often co-limited by multiple nutrients; however, little is known about how root production responds to changes in nutrient availability. At twenty-nine grassland sites on four continents, we quantified shallow root biomass responses to nitrogen (N), phosphorus (P) and potassium plus micronutrient enrichment and compared below- and aboveground responses. We...
Spiraling Down Hillslopes: Nutrient Uptake from Water Tracks in a Warming Arctic
01. November 2019
Abstract Hydrologic flowpaths might propagate biogeochemical signals among connected ecosystems or alter and dampen signals because of reactions or retention occurring during transport. In the Arctic, experimentally warmed terrestrial tundra releases inorganic nitrogen (N), but the fate of this newly released N remains unclear. Nitrogen could be passively transported downslope in flowing water, or retained when flowpaths intercept N-limited ecosystems. We applied nutrient spiraling theory to simultaneously measure reaction and transport of ammonium (NH4+) and phosphate...
Structured Decision-Making Identifies Effective Strategies and Potential Barriers for Ecosystem-Based Management of a Range-Extending Species in a Global Marine Hotspot
01. November 2019
Abstract Climate-driven changes in ocean currents have facilitated the range extension of the long-spined sea urchin (Centrostephanus rodgersii) from Australia’s mainland to eastern Tasmania over recent decades. Since its arrival, destructive grazing by the urchin has led to widespread formation of sea urchin ‘barrens’. The loss of habitat, biodiversity and productivity for important commercial reef species in conjunction with the development of an urchin fishery has led to conflicting objectives among stakeholders, which poses complex challenges for regional...
Apex Predators Decouple Population Dynamics Between Mesopredators and Their Prey
01. November 2019
Abstract The mesopredator release hypothesis (MRH) predicts that the removal of apex predators should lead to increased abundance of smaller predators through relaxation of suppressive, top-down effects. However, apex predators’ effects on mesopredators are also likely to be modulated by interactions with human activities and ecosystem productivity. The exploitation ecosystems hypothesis (EEH) predicts that biomass of apex predators will scale with primary productivity but herbivore and mesopredator biomass will remain constant due to top-down control. Here, we take...
Long-Term Steady-State Dry Boreal Forest in the Face of Disturbance
30. Oktober 2019
Abstract We used bioproxies from paleosoils buried within two aeolian dunes to test hypotheses concerning the origin of dry sandy boreal forests in Canada. These forests are dominated today by Pinus banksiana Lamb. One hypothesis is that too frequent Holocene stand-replacing fires would have transformed the original vegetation through extirpation of susceptible species to fire in water stress habitat. Alternatively, the ecosystem would have not changed since the dunes stabilized enough to support forest establishment. The vegetation composition and richness were determined...