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Ecosystems 

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Consequences of Piñon-Juniper Woodland Fuel Reduction: Prescribed Fire Increases Soil Erosion While Mastication Does Not
07. Mai 2021
Abstract Fire suppression has increased fuel load and the risk of catastrophic wildfire in forest and woodland ecosystems across the Western United States. In an effort to reduce fuel load and restore historical structure and function, land managers have implemented fuel reduction treatments on millions of acres. Reducing fuel loads protects people, structures, and in some cases, improves ecosystem health. However, the ecological risks of soil surface disturbance related to fuel reduction strategies, and subsequent soil erosion, may be significant in some cases. Here, we...
Foliar Stoichiometry is Marginally Sensitive to Soil Phosphorus Across a Lowland Tropical Rainforest
07. Mai 2021
Abstract The distribution of nutrients, both vertically and horizontally in a forest, has long been theorized to influence primary productivity. Working at La Selva Biological Station, Costa Rica, we gathered the most comprehensive foliar samples to date for a lowland tropical rainforest to measure horizontal and vertical trends in foliar nutrients. The mean traits of foliage from forest floor to top-of-canopy were determined at 45 plots placed across the landscape in a stratified random design. Area-basis foliar N and P for these vertically integrated columns varied by a...
Temperature Increases Soil Respiration Across Ecosystem Types and Soil Development, But Soil Properties Determine the Magnitude of This Effect
07. Mai 2021
Abstract Soil carbon losses to the atmosphere, via soil heterotrophic respiration, are expected to increase in response to global warming, resulting in a positive carbon-climate feedback. Despite the well-known suite of abiotic and biotic factors controlling soil respiration, much less is known about how the magnitude of soil respiration responses to temperature changes over soil development and across contrasting soil properties. Here we investigated the role of soil development stage and soil properties in driving the responses of soil heterotrophic respiration to...
Meta-analysis Reveals Different Competition Effects on Tree Growth Resistance and Resilience to Drought
06. Mai 2021
Abstract Drought will increasingly threaten forest ecosystems worldwide. Understanding how competition influences tree growth response to drought is essential for forest management aiming at climate change adaptation. However, published results from individual case studies are heterogeneous and sometimes contradictory. We reviewed 166 cases from the peer-reviewed literature to assess the influence of stand-level competition on tree growth response to drought. We monitored five indicators of tree growth response: mean sensitivity (inter-annual tree ring width variability...
Species Climatic Suitability Explains Insect–Host Dynamics in the Southern Rocky Mountains, USA
06. Mai 2021
Abstract Recent extreme events of drought and heat have been associated with insect-driven tree mortality. However, there is substantial uncertainty about the impact of climate variability and extreme climatic episodes on insect–host dynamics, especially over species biogeographical ranges. Here, we use climatic suitability indices derived from species distribution models to analyze the spruce beetle (Dendroctonus rufipennis) outbreak dynamics in spruce-fir forests across the Southern Rocky Mountains (USA) during a warm and dry episode (2000–2013). We estimated the...
Increased Above- and Belowground Plant Input Can Both Trigger Microbial Nitrogen Mining in Subarctic Tundra Soils
05. Mai 2021
Abstract Low nitrogen (N) availability in the Arctic and Subarctic constrains plant productivity, resulting in low litter inputs to soil. Increased N availability and litter inputs as a result of climate change, therefore, have the potential to impact the functioning of these ecosystems. We examined plant and microbial responses to chronic inorganic N (5 g m−2 year−1) and/or litter (90 g m−2 year−1), supplied during three growing seasons. We also compared the response to more extreme additions, where the total cumulative additions of N (that is, 15 g m−2...
Submerged Rootless Macrophytes Sustain a Stable State Against Free-Floating Plants
04. Mai 2021
Abstract Both non-rooted submerged vegetation dominated by coontail (Ceratophyllum demersum) and non-rooted floating duckweed vegetation (Lemna gibba) can maintain their stable dominance in small ponds and channels. We examined the competitive interactions between them and how Ceratophyllum can sustain its stable state against floating plants in a range of nutrient concentrations. Coontail and duckweed were co-cultured in static and semi-static microcosm experiments, and their impact on the nutrients (N, P, Fe, Mn) in the water column was analysed. Coontail strongly...
Warming Stimulates Iron-Mediated Carbon and Nutrient Cycling in Mineral-Poor Peatlands
04. Mai 2021
Abstract Iron (Fe) plays a key role in elemental cycling at terrestrial–aquatic interfaces by stabilizing carbon (C), phosphorus (P), and nutrient cations through physicochemical associations and by potentially releasing these elements following the reduction of Fe(III) to Fe(II). However, the ecosystem-scale importance of Fe redox cycling and its responses to climate change remain unclear in precipitation-fed peatlands (bogs), C-rich wetlands with very low mineral content. We tested impacts of Fe redox cycling on C and nutrient release in two bogs in northern Minnesota...
Land Use History Mediates Soil Biogeochemical Responses to Drought in Temperate Forest Ecosystems
03. Mai 2021
Abstract Terrestrial ecosystems are experiencing increasing frequency and intensity of droughts as a result of climate change. Despite a wealth of previous studies investigating soil responses to drought, the importance of historical land use in mediating drought effects remains poorly understood. To identify interactions between drought and historical land use, we sampled soils from two adjacent forested watersheds at the USFS Coweeta Hydrologic Laboratory: a ‘reference’ forest that has remained undisturbed for approximately a century and a ‘disturbed’ forest...
Coupled Shifts in Ectomycorrhizal Communities and Plant Uptake of Organic Nitrogen Along a Soil Gradient: An Isotopic Perspective
26. April 2021
Abstract Plants associating with mutualistic ectomycorrhizal (ECM) fungi may directly obtain nitrogen (N) bound in soil organic matter (N-SOM). However, the contribution of N-SOM to plant growth under field conditions remains poorly constrained. We tested the hypothesis that turnover in ECM communities along soil inorganic N gradients mediates a functional transition from plant reliance on N-SOM in low inorganic N soils, to primarily inorganic N uptake in inorganic N-rich condition soils. We quantified the δ 15 N of Q. rubra foliage and roots, organic and...
Legacies of Nutrient Accumulation and Depletion in Residential Ecosystems
12. April 2021
Abstract In residential ecosystems, land management can help regulate climate and improve water quality by promoting the accumulation of nutrients in the soil. We tested how varying intensity of residential land use and management altered nutrient (Ca, K, Mg, P, S) pools. We studied soils and vegetation across twelve land use-intensity gradients (yards-perennial old fields-forests) established 15–227 y. ago in the native ecosystems of temperate forests. We found that yard soils were enriched with nutrients relative to fields and forests, regardless of recent yard...
How Are Greenhouse Gases Coupled Across Seasons in a Large Temperate River with Differential Land Use?
12. April 2021
Abstract Rivers are known to emit large amounts of greenhouse gases globally, however, few studies have evaluated the interacting influence of land use, within river features (for example, sites of major confluence, changes in shape), and hydrology on the coupled dynamics of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Here, we measured CO2, CH4 and N2O concentrations and fluxes at 15 sites along a 146.6 km stretch of the main stem of a large north temperate river: the Rivière du Nord, which experiences an abrupt change in geology and land use and winter...
Methane and Carbon Dioxide Flux Heterogeneity Mediated by Termite Mounds in Moist Tropical Forest Soils of Himalayan Foothills, India
09. April 2021
Abstract Termites are dominant soil macro-fauna in tropical forests, yet remain an uncertain component of the carbon budget in many regions. We investigated CH4 and CO2 flux patterns from termite mounds and background soils of moist tropical deciduous forests in Indian lower Himalaya from April 2015 till March 2016 using static closed chamber technique. The relation between gas fluxes and soil moisture as well as temperature were examined. Termite (Odontotermes obesus) mounds were significant localized source of CH4 (0.38 ± 0.01 mg m−2 h−1) and CO2...
Decomposition in Mixed Beech Forests in the South-Western Alps Under Severe Summer Drought
08. April 2021
Abstract Climate and plant litter diversity are major determinants of carbon (C) and nitrogen (N) cycling rates during decomposition. Yet, how these processes will be modified with combined changes in climate and biodiversity is poorly understood. With a multisite field experiment, we studied the interactive effects of reinforced and prolonged summer drought (using rainout shelters) and tree species mixing on leaf litter decomposition in beech forests in the French Alps. Forests included monospecific stands of Fagus sylvatica, Abies alba and Quercus pubescens and...
Soil Organic Carbon Content Decreases in Both Surface and Subsoil Mineral Horizons by Simulated Future Increases in Labile Carbon Inputs in a Temperate Coniferous Forest
07. April 2021
Abstract Soils represent important pools of soil organic carbon (SOC) that can be greatly influenced by labile C inputs, which are expected to increase in future due to CO2 enrichment of atmosphere and a concomitant rise in plant primary productivity. Studying effects of variable labile C inputs on SOC pool helps to understand how soils respond to global change. However, this knowledge is missing for coniferous forest soils despite being widespread throughout the northern temperate zone. We conducted a 7-month field manipulation experiment to study the effects of variable...
Differential Resilience of Soil Microbes and Ecosystem Functions Following Cessation of Long-Term Fertilization
07. April 2021
Abstract Nitrogen (N) from anthropogenic sources has dramatically increased in terrestrial ecosystems globally. Although belowground microbial processes and events that release N into the atmosphere, such as fire, could support ecosystem resilience to eutrophication, little is known about how these factors might affect N loss following chronic fertilization, thus promoting ecosystem recovery. We studied how N pools, N-cycling potential rates and their affiliated microbial populations, and microbial community composition responded to the factorial effects of cessation of...
Global Warming Potential Is Not an Ecosystem Property
05. April 2021
Abstract Greenhouse gas metrics and ecosystem greenhouse gas fluxes should not be confounded with each other, either conceptually or in the language that we use to describe them. The global warming potential (GWP) and sustained-flux global warming potential (SGWP) are metrics that describe the relative radiative impact of different greenhouse gases and have been widely used to normalize greenhouse gas fluxes as CO2 equivalents to facilitate comparisons. A clear application of definitions, the pursuit of scientific clarity, and the ability of language to influence our...
The Metabolic Regimes at the Scale of an Entire Stream Network Unveiled Through Sensor Data and Machine Learning
02. April 2021
Abstract Streams and rivers form dense networks that drain the terrestrial landscape and are relevant for biodiversity dynamics, ecosystem functioning, and transport and transformation of carbon. Yet, resolving in both space and time gross primary production (GPP), ecosystem respiration (ER) and net ecosystem production (NEP) at the scale of entire stream networks has been elusive so far. Here, combining Random Forest (RF) with time series of sensor data in 12 reach sites, we predicted annual regimes of GPP, ER, and NEP in 292 individual stream reaches and disclosed...
Local and Regional Drivers of Environmental Changes in Two Subtropical Montane Ponds (Central China) Over the Last Two Centuries
01. April 2021
Abstract Central China, one of the Earth’s distinctive ecoregions due to its endemic subtropical biota, has been subjected to enhanced nitrogen deposition and climate warming during recent decades. However, the extent and timescale of ecological changes are largely unexplored. Multiproxy analyses (diatoms, photosynthetic pigments and geochemistry) of 210Pb-dated sediment cores from two shallow ponds within an alpine basin (central China) were used to investigate the response of primary producer communities to external stressors during the last two centuries. The study...
Ecosystem Recovery from Disturbance is Constrained by N Cycle Openness, Vegetation-Soil N Distribution, Form of N Losses, and the Balance Between Vegetation and Soil-Microbial Processes
01. April 2021
Abstract We present a framework for assessing biogeochemical recovery of terrestrial ecosystems from disturbance. We identify three recovery phases. In Phase 1, nitrogen is redistributed from soil organic matter to vegetation, but the ecosystem continues to lose nitrogen because the recovering vegetation cannot take up nitrogen as fast as it is released from soil. In Phase 2, the ecosystem begins re-accumulating nitrogen and converges on a quasi-steady state in which vegetation and soil-microbial processes are in balance. In Phase 3, vegetation and soil-microbial...