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Latest Results for Ecosystems
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Free-living N 2 Fixation in Three Karst Shrublands, Southwest China
12. November 2018
Abstract Free-living N2 fixation is an important pathway of external nitrogen input to natural terrestrial ecosystems. However, few measurements of N2 fixation have been conducted in shrublands. Here, free-living N2 fixation in soil (or soil N2 fixation) and litter (or litter N2 fixation) in three shrublands was measured in a karst catchment, southwest China. The three shrublands were dominated by Pterolobium punctatum Hemsl., Vitex negundo Linn. and Rhus chinensis Mill., respectively. Field measurements were carried out in January and July 2016, respectively, using...
Temporal Shifts in Plant Diversity Effects on Carbon and Nitrogen Dynamics During Litter Decomposition in a Mediterranean Shrubland Exposed to Reduced Precipitation
12. November 2018
Abstract Climate and plant diversity are major determinants of carbon (C) and nitrogen (N) dynamics in decomposing plant litter. However, the direction and extent to which these dynamics are affected by combined changes in climate and biodiversity are not well understood. We used a field experiment in a Mediterranean shrubland ranging from one to four shrub species with partial rain exclusion (− 12%) to test how lower precipitation interacts with shrub species diversity to influence C and N release during decomposition. We also distinguished between first-year...
Community Trait Distribution Across Environmental Gradients
07. November 2018
Abstract Variability in community composition is often attributed to underlying differences in physical environments. However, predator–prey interactions can play an equally important role in structuring communities. Although environmental differences select for different species assemblages, less is known about their impacts on trait compositions. We develop a trait-based analysis of plankton communities of the southern California Current System across multiple trophic levels, from bacteria to mesozooplankton, and over a gradient of environmental conditions, from the...
Disentangling Climate and Disturbance Effects on Regional Vegetation Greening Trends
05. November 2018
Abstract Productivity of northern latitude forests is an important driver of the terrestrial carbon cycle and is already responding to climate change. Studies of the satellite-derived Normalized Difference Vegetation Index (NDVI) for northern latitudes indicate recent changes in plant productivity. These detected greening and browning trends are often attributed to a lengthening of the growing season from warming temperatures. Yet, disturbance-recovery dynamics are strong drivers of productivity and can mask direct effects of climate change. Here, we analyze 1-km...
Correction to: Headwater Mires Constitute a Major Source of Nitrogen (N) to Surface Waters in the Boreal Landscape
01. November 2018
The authors discovered an error in the discharge calculation for the mire outlet stream (MC4) that led to an underestimation of nitrogen (N) export from this catchment. This error has no influence on the overall message or conclusions of the paper but does suggest even greater relative N losses from the mire-dominated catchment.
Does Nutrient Availability Regulate Seagrass Response to Elevated CO 2 ?
01. November 2018
Abstract Future increases in oceanic carbon dioxide concentrations (CO2(aq)) may provide a benefit to submerged plants by alleviating photosynthetic carbon limitation. However, other environmental factors (for example, nutrient availability) may alter how seagrasses respond to CO2(aq) by regulating the supply of additional resources required to support growth. Thus, questions remain in regard to how other factors influence CO2(aq) effects on submerged vegetation. This study factorially manipulated CO2(aq) and nutrient availability, in situ, within a subtropical seagrass...
Stand Age Influence on Potential Wildfire Ignition and Spread in the Boreal Forest of Northeastern Canada
01. November 2018
Abstract Although it has long been assumed that wildfire occurrence is independent of stand age in the North American boreal forest, recent studies indicate that young forests may influence burn rates by limiting the ignition and spread of fires for several years. Wildfires not only structure the stand-age mosaic of boreal landscapes, but also alter the likelihood and behavior of subsequent fires. Using a fire simulation model, we evaluated the effect of stand age on the magnitude and spatial patterns of burn probability (BP) in the boreal forest of northeastern Canada...
Rapid Recovery of Gross Production and Respiration in a Mesic Mountain Big Sagebrush Ecosystem Following Prescribed Fire
01. November 2018
Abstract The impact of land management actions such as prescribed fire remains a key uncertainty in understanding the spatiotemporal patterns of carbon cycling in the Western USA. We therefore quantified carbon exchange and aboveground carbon stocks following a prescribed fire in a mountain big sagebrush ecosystem located in the northern Great Basin, USA. Specifically, we examined the changes in plant functional type, leaf area index, standing aboveground carbon stocks, net ecosystem production (NEP), gross ecosystem production (GEP), and ecosystem-level respiration...
Vegetation Cover, Tidal Amplitude and Land Area Predict Short-Term Marsh Vulnerability in Coastal Louisiana
01. November 2018
Abstract The loss of coastal marshes is a topic of great concern, because these habitats provide tangible ecosystem services and are at risk from sea-level rise and human activities. In recent years, a significant effort has gone into understanding and modeling the relationships between the biological and physical factors that contribute to marsh stability. Simulation-based process models suggest that marsh stability is the product of a complex feedback between sediment supply, flooding regime and vegetation response, resulting in elevation gains sufficient to match the...
Fire and Grazing Influence Site Resistance to Bromus tectorum Through Their Effects on Shrub, Bunchgrass and Biocrust Communities in the Great Basin (USA)
01. November 2018
Abstract Shrubs, bunchgrasses and biological soil crusts (biocrusts) are believed to contribute to site resistance to plant invasions in the presence of cattle grazing. Although fire is a concomitant disturbance with grazing, little is known regarding their combined impacts on invasion resistance. We are the first to date to test the idea that biotic communities mediate the effects of disturbance on site resistance. We assessed cover of Bromus tectorum, shrubs, native bunchgrasses, lichens and mosses in 99 burned and unburned plots located on similar soils where fires...
A Framework for Understanding Variation in Pelagic Gross Primary Production of Lake Ecosystems
01. November 2018
Abstract Light and nutrient availability are key physiological constraints for primary production. Widespread environmental changes are causing variability in loads of terrestrial dissolved organic carbon (DOC) and nutrients from watersheds to lakes, contributing to simultaneous changes in both light and nutrient supply. Experimental evidence highlights the potential for these watershed loads to create complex and context-dependent responses of within-lake primary production; however, the field lacks a predictive model to investigate these responses. We embedded a...
Allochthonous Organic Matter Supports Benthic but Not Pelagic Food Webs in Shallow Coastal Ecosystems
01. November 2018
Abstract Rivers transport large amounts of allochthonous organic matter (OM) to the ocean every year, but there are still fundamental gaps in how allochthonous OM is processed in the marine environment. Here, we estimated the relative contribution of allochthonous OM (allochthony) to the biomass of benthic and pelagic consumers in a shallow coastal ecosystem in the northern Baltic Sea. We used deuterium as a tracer of allochthony and assessed both temporal variation (monthly from May to August) and spatial variation (within and outside river plume). We found variability...
Long-Term Grazing Accelerated Litter Decomposition in Northern Temperate Grasslands
01. November 2018
Abstract Livestock grazing affects plant community composition, diversity, and carbon (C) and nutrient cycling in grasslands. Grazing leads to plant communities that have higher relative abundance of grazing-tolerant species, which in turn may alter the chemical composition of biomass and subsequent litter decomposition rates. To better understand the effects of long-term grazing and associated vegetation shifts on biogeochemical cycling in northern temperate grasslands of western Canada, we studied litter decomposition over 18 months at 15 locations, stratified across...
The Effects of Differences in Vegetation on Calcium Dynamics in Headwater Streams
01. November 2018
Abstract Although organisms can alter dynamics of elements in ecosystems via physiological results, the effects of tree species on ecosystem nutrient dynamics are highly uncertain. A four-fold variation in the calcium concentrations of streams, soils and leaf litters were caused by the planting of Cryptomeria japonica in south-central Japan. In this study, we examined how the calcium dynamics were affected by the planting of C. japonica through strontium isotope analysis. We predicted the planting of C. japonica would result in the calcium concentration increasing...
Aridity Induces Nonlinear Effects of Human Disturbance on Precipitation-Use Efficiency of Iberian Woodlands
01. November 2018
Abstract The effects of ecosystem degradation are pervasive worldwide and increasingly concerning under the present context of global changes in climate and land use. Theoretical studies and empirical evidence increasingly suggest that drylands are particularly prone to develop nonlinear functional changes in response to climate variations and human disturbance. Precipitation-use efficiency (PUE) represents the ratio of vegetation production to precipitation and provides a tool for evaluating human and climate impacts on landscape functionality. Holm oak (Quercus ilex...
Phenological Sensitivity of Early and Late Flowering Species Under Seasonal Warming and Altered Precipitation in a Seminatural Temperate Grassland Ecosystem
01. November 2018
Abstract Shifts in flowering phenology of plants are indicators of climate change. The great majority of existing phenological studies refer solely to gradual warming. However, knowledge on how flowering phenology responds to changes in seasonal variation of warming and precipitation regimes is missing. We report the onset of 22 early (flowering before/within May) and 23 late flowering (flowering after May) species in response to manipulated seasonal warming (equal to + 1.2°C; last 100-year summer/winter warming), additional winter rainfall, and modified precipitation...
Increased Soil Frost Versus Summer Drought as Drivers of Plant Biomass Responses to Reduced Precipitation: Results from a Globally Coordinated Field Experiment
01. November 2018
Abstract Reduced precipitation treatments often are used in field experiments to explore the effects of drought on plant productivity and species composition. However, in seasonally snow-covered regions reduced precipitation also reduces snow cover, which can increase soil frost depth, decrease minimum soil temperatures and increase soil freeze–thaw cycles. Therefore, in addition to the effects of reduced precipitation on plants via drought, freezing damage to overwintering plant tissues at or below the soil surface could further affect plant productivity and relative...
Initial Soil Organic Matter Content Influences the Storage and Turnover of Litter, Root and Soil Carbon in Grasslands
01. November 2018
Abstract Grassland degradation is a worldwide problem that often leads to substantial loss of soil organic matter (SOM). To estimate the potential for carbon (C) accumulation in degraded grassland soils, we first need to understand how SOM content influences the transformation of plant C and its stabilization within the soil matrix. We conducted a greenhouse experiment using C3 soils with six levels of SOM content; we planted the C4 grass Cleistogenes squarrosa or added its litter to the soils to investigate how SOM content regulates the storage of new soil C derived...
Change in Vegetation Patterns Over a Large Forested Landscape Based on Historical and Contemporary Aerial Photography
01. November 2018
Abstract Changes to vegetation structure and composition in forests adapted to frequent fire have been well documented. However, little is known about changes to the spatial characteristics of vegetation in these forests. Specifically, patch sizes and detailed information linking vegetation type to specific locations and growing conditions on the landscape are lacking. We used historical and recent aerial imagery to characterize historical vegetation patterns and assess contemporary change from those patterns. We created an orthorectified mosaic of aerial photographs...
Spatial Variation of Soil CO 2 , CH 4 and N 2 O Fluxes Across Topographical Positions in Tropical Forests of the Guiana Shield
01. November 2018
Abstract The spatial variation of soil greenhouse gas fluxes (GHG; carbon dioxide—CO2, methane—CH4 and nitrous oxide—N2O) remains poorly understood in highly complex ecosystems such as tropical forests. We used 240 individual flux measurements of these three GHGs from different soil types, at three topographical positions and in two extreme hydric conditions in the tropical forests of the Guiana Shield (French Guiana, South America) to (1) test the effect of topographical positions on GHG fluxes and (2) identify the soil characteristics driving flux variation in...