Showing papers on "Ecosystem published in 2022"

Rhizosphere bacteriome structure and functions

Abstract: Microbial composition and functions in the rhizosphere-an important microbial hotspot-are among the most fascinating yet elusive topics in microbial ecology. We used 557 pairs of published 16S rDNA amplicon sequences from the bulk soils and rhizosphere in different ecosystems around the world to generalize bacterial characteristics with respect to community diversity, composition, and functions. The rhizosphere selects microorganisms from bulk soil to function as a seed bank, reducing microbial diversity. The rhizosphere is enriched in Bacteroidetes, Proteobacteria, and other copiotrophs. Highly modular but unstable bacterial networks in the rhizosphere (common for r-strategists) reflect the interactions and adaptations of microorganisms to dynamic conditions. Dormancy strategies in the rhizosphere are dominated by toxin-antitoxin systems, while sporulation is common in bulk soils. Functional predictions showed that genes involved in organic compound conversion, nitrogen fixation, and denitrification were strongly enriched in the rhizosphere (11-182%), while genes involved in nitrification were strongly depleted.

The biodiversity and ecosystem service contributions and trade-offs of forest restoration approaches

Abstract: Forest restoration is being scaled up globally to deliver critical ecosystem services and biodiversity benefits; however, there is a lack of rigorous comparison of cobenefit delivery across different restoration approaches. Through global synthesis, we used 25,950 matched data pairs from 264 studies in 53 countries to assess how delivery of climate, soil, water, and wood production services, in addition to biodiversity, compares across a range of tree plantations and native forests. Benefits of aboveground carbon storage, water provisioning, and especially soil erosion control and biodiversity are better delivered by native forests, with compositionally simpler, younger plantations in drier regions performing particularly poorly. However, plantations exhibit an advantage in wood production. These results underscore important trade-offs among environmental and production goals that policy-makers must navigate in meeting forest restoration commitments. Description Benefits of forest restoration Reforestation is promoted globally as one way to mitigate climate change through the storage of carbon in woody growth and ecosystem services such as control of soil erosion and management of water supplies. Hua et al. assessed the relative performance of plantation and native forest in achieving these goals (see the Perspective by Gurevitch). Synthesizing data from the world’s major forest biomes, they found that native forests consistently delivered better performance than plantations in the provision of the three major ecosystem services, with additional benefits for biodiversity. The discrepancy was particularly marked in in warmer and drier regions. These findings show that the benefits of reforestation will be best achieved through the restoration of native forests rather than extensive plantation programs. —AMS Critical ecosystem services and biodiversity are typically delivered more effectively by native forests than by plantations.

Soil microbiota as game-changers in restoration of degraded lands

Abstract: Land degradation reduces soil functioning and, consequently, the services that soil provides. Soil hydrological functions are critical to combat soil degradation and promote soil restoration. Soil microorganisms affect soil hydrology, but the role of soil microbiota in forming and sustaining soil is not well explored. Case studies indicate the potential of soil microorganisms as game-changers in restoring soil functions. We review the state of the art of microorganism use in land restoration technology, the groups of microorganisms with the greatest potential for soil restoration, knowledge of the effect of microorganisms on soil physical properties, and proposed strategies for the long-term restoration of degraded lands. We also emphasize the need to advance the emerging research field of biophysical landscape interactions to support soil-plant ecosystem restoration practices. Description Microbes repairing degraded soils Soils worldwide have become increasingly degraded by human activities, especially in drylands. Land degradation negatively affects soil hydrological functioning and thereby the ecosystem services that soil provides. Soil microbes may play an important part in the restoration of degraded soils, positively influencing moisture content and other physical features of soil. Coban et al. reviewed recent work on soil hydraulic properties, potential groups of microorganisms for hydrological soil restoration based on their resilience in dry soils, and future strategies for long-term restoration of degraded lands. —AMS A review suggests that soil microorganisms may be the key to the restoration of hydraulic function in soils degraded by human activities. BACKGROUND Soil, the living skin of Earth, provides ecosystem services critical for life: Soil acts as a filter and store of water, provides a growing medium that supplies plants and heterotrophs with water and nutrients, offers habitat for a large diversity of organisms, and is the source of most of our antibiotics. Humanity is increasingly challenged by the combination of climate change, population growth, and land degradation, including carbon loss, biodiversity decline, and erosion. In particular, land degradation reduces soil hydrological functioning and thereby several other ecosystem services. Such impacts occur through alterations of hydraulic functioning, infiltration and soil moisture storage, carbon cycling, biological activity, transport of nutrients and contaminants, and plant growth. Impacts of global environmental change and associated soil degradation need to be understood and reversed as biodiversity, food production, climate regulation, and people’s livelihoods are increasingly affected by soil ecosystem degradation. The interplay between soil biota and soil hydrological functioning plays an essential role in many biogeochemical cycles, including the water and carbon cycles. Microorganisms dominate soil life and perform an array of vital soil functions by regulating nutrient cycling, decomposing organic matter, defining soil structure, suppressing plant diseases, and supporting plant productivity. The presence of microorganisms and their activity can affect soil structure and hydraulic properties in multiple ways. Case studies indicate the potential of microorganisms as game-changers toward the restoration of soil functioning. However, the role of soil microbiota in forming and sustaining soils has historically been overlooked. ADVANCES It has been proposed that microbial communities not only are an indicator of ecosystem health and restoration level but also can be manipulated to enhance the recovery of degraded ecosystems. In the past decade, there have been an increasing number of studies suggesting the use of microorganisms as ecosystem mediators, particularly to enhance crop production and to engineer microorganisms for dryland restoration. Most current experimental approaches focus on monitoring changes in the microbial community that can be correlated with land restoration; however, microorganisms are also facilitators of ecosystem change, not just followers. We review how microorganisms can help address different types of land degradation, with a focus on physical soil loss and transformation, loss of soil chemical properties, and contamination. We discuss potentially the most valuable groups of microorganisms for soil restoration (namely, plant growth–promoting rhizobacteria, nitrogen-fixing bacteria, and mycorrhizal fungi), emphasizing drylands and advances in plant-microbe interaction studies. We review known effects of microorganisms on soil physical and, specifically, hydraulic properties at pore scale and discuss future strategies for the long-term restoration of degraded lands. We also identify the methodological challenges that have so far hampered progress in understanding soil biophysical processes. OUTLOOK Microorganisms can play the leading role in restoring degraded lands, improving soil hydraulic properties such as infiltration and water retention and reducing soil hydrophobicity, which together can facilitate ecosystem restoration. We advocate for research on mechanisms to restore degraded soils with the use of microorganisms. Given the critical role of freshwater availability to terrestrial life and the paucity of studies on hydrological restoration, we especially advocate for research on the hydrological restoration of degraded soil using microorganisms. We propose that microorganisms can improve soil hydraulic properties such as infiltration and water retention and reduce soil hydrophobicity. Along with new organic matter derived from microbes, this will promote plant growth and facilitate further ecosystem restoration. Such a restoration strategy requires collaboration across the research fields of microbiology and soil hydrology, of which there has been very little to date. Understanding the dynamics of soil microbes and connected hydrological processes would create the foundation for restoration practices that can return resilience to the soil ecosystem. Degraded land in Libya. In degraded lands, a decrease in soil nutrients and organic matter, deterioration of soil structure, increase in salinity, water deficiency, and physical instability can be observed. Credit:cinoby/istockphoto

Plant-microbiome interactions under a changing world: responses, consequences, and perspective.

Abstract: Climate change is increasing global temperatures and the frequency and severity of droughts in many regions. These anthropogenic stresses pose a significant threat to plant performance and crop production. The plant-associated microbiome modulates the impacts of biotic and abiotic stresses on plant fitness. However, climate change induced change in composition and activities of plant microbiomes, can affect host functions. Here, we highlight recent advancements in our understanding of the impact of climate change (warming and drought) on plant-microbiome interactions and on their ecological functions from genome to ecosystem scales. We identify knowledge gaps, propose new concepts, and make recommendations for future research directions. It is proposed that in short-term (years to decades) adaptation of plants to climate change is mainly driven by the plant microbiome, while long-term (century to millennia) adaptation of plants will be driven equally by eco-evolutionary interactions between the plant microbiome and its host. A better understanding of the response of plant and its microbiome interactions to climate change and the ways in which microbiomes can mitigate the negative impacts will better inform predictions of climate change impacts on primary productivity and aid in developing management and policy tools to improve the resilience of plant systems.

The land-to-ocean loops of the global carbon cycle

Abstract: Carbon storage by the ocean and by the land is usually quantified separately, and does not fully take into account the land-to-ocean transport of carbon through inland waters, estuaries, tidal wetlands and continental shelf waters—the ‘land-to-ocean aquatic continuum’ (LOAC). Here we assess LOAC carbon cycling before the industrial period and perturbed by direct human interventions, including climate change. In our view of the global carbon cycle, the traditional ‘long-range loop’, which carries carbon from terrestrial ecosystems to the open ocean through rivers, is reinforced by two ‘short-range loops’ that carry carbon from terrestrial ecosystems to inland waters and from tidal wetlands to the open ocean. Using a mass-balance approach, we find that the pre-industrial uptake of atmospheric carbon dioxide by terrestrial ecosystems transferred to the ocean and outgassed back to the atmosphere amounts to 0.65 ± 0.30 petagrams of carbon per year (±2 sigma). Humans have accelerated the cycling of carbon between terrestrial ecosystems, inland waters and the atmosphere, and decreased the uptake of atmospheric carbon dioxide from tidal wetlands and submerged vegetation. Ignoring these changing LOAC carbon fluxes results in an overestimation of carbon storage in terrestrial ecosystems by 0.6 ± 0.4 petagrams of carbon per year, and an underestimation of sedimentary and oceanic carbon storage. We identify knowledge gaps that are key to reduce uncertainties in future assessments of LOAC fluxes.

High-resolution mapping of losses and gains of Earth’s tidal wetlands

Abstract: Tidal wetlands are expected to respond dynamically to global environmental change, but the extent to which wetland losses have been offset by gains remains poorly understood. We developed a global analysis of satellite data to simultaneously monitor change in three highly interconnected intertidal ecosystem types—tidal flats, tidal marshes, and mangroves—from 1999 to 2019. Globally, 13,700 square kilometers of tidal wetlands have been lost, but these have been substantially offset by gains of 9700 km2, leading to a net change of −4000 km2 over two decades. We found that 27% of these losses and gains were associated with direct human activities such as conversion to agriculture and restoration of lost wetlands. All other changes were attributed to indirect drivers, including the effects of coastal processes and climate change. Description Global shifts in tidal wetlands Ecologically and economically important coastal wetlands are threatened by sea level rise and land use change. Murray et al. used high-resolution satellite imagery to assess the global extent of tidal wetlands and changes in wetland extent and distribution over the past two decades. They found that although over 13,000 square kilometers of tidal wetland have recently been lost, much of this decreasing extent has been offset by the creation of new wetlands. The greatest losses and gains were in tidal flats, but mangrove ecosystems showed the largest net decline in area globally. Direct human impacts on wetlands, including land transformation and restoration, are detectable from satellite imagery and account for 27% of wetland losses and gains. —BEL High-resolution satellite imagery reveals that substantial global losses of tidal wetlands are largely offset by new wetland formation.

Feeding habits and multifunctional classification of soil‐associated consumers from protists to vertebrates

Abstract: Soil organisms drive major ecosystem functions by mineralising carbon and releasing nutrients during decomposition processes, which supports plant growth, aboveground biodiversity and, ultimately, human nutrition. Soil ecologists often operate with functional groups to infer the effects of individual taxa on ecosystem functions and services. Simultaneous assessment of the functional roles of multiple taxa is possible using food‐web reconstructions, but our knowledge of the feeding habits of many taxa is insufficient and often based on limited evidence. Over the last two decades, molecular, biochemical and isotopic tools have improved our understanding of the feeding habits of various soil organisms, yet this knowledge is still to be synthesised into a common functional framework. Here, we provide a comprehensive review of the feeding habits of consumers in soil, including protists, micro‐, meso‐ and macrofauna (invertebrates), and soil‐associated vertebrates. We have integrated existing functional group classifications with findings gained with novel methods and compiled an overarching classification across taxa focusing on key universal traits such as food resource preferences, body masses, microhabitat specialisation, protection and hunting mechanisms. Our summary highlights various strands of evidence that many functional groups commonly used in soil ecology and food‐web models are feeding on multiple types of food resources. In many cases, omnivory is observed down to the species level of taxonomic resolution, challenging realism of traditional soil food‐web models based on distinct resource‐based energy channels. Novel methods, such as stable isotope, fatty acid and DNA gut content analyses, have revealed previously hidden facets of trophic relationships of soil consumers, such as food assimilation, multichannel feeding across trophic levels, hidden trophic niche differentiation and the importance of alternative food/prey, as well as energy transfers across ecosystem compartments. Wider adoption of such tools and the development of open interoperable platforms that assemble morphological, ecological and trophic data as traits of soil taxa will enable the refinement and expansion of the multifunctional classification of consumers in soil. The compiled multifunctional classification of soil‐associated consumers will serve as a reference for ecologists working with biodiversity changes and biodiversity–ecosystem functioning relationships, making soil food‐web research more accessible and reproducible.

Global maps of soil temperature

Abstract: Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.

Gradients and consequences of heterogeneity in biofilms

Abstract: Historically, appreciation for the roles of resource gradients in biology has fluctuated inversely to the popularity of genetic mechanisms. Nevertheless, in microbiology specifically, widespread recognition of the multicellular lifestyle has recently brought new emphasis to the importance of resource gradients. Most microorganisms grow in assemblages such as biofilms or spatially constrained communities with gradients that influence, and are influenced by, metabolism. In this Review, we discuss examples of gradient formation and physiological differentiation in microbial assemblages growing in diverse settings. We highlight consequences of physiological heterogeneity in microbial assemblages, including division of labour and increased resistance to stress. Our impressions of microbial behaviour in various ecosystems are not complete without complementary maps of the chemical and physical geographies that influence cellular activities. A holistic view, incorporating these geographies and the genetically encoded functions that operate within them, will be essential for understanding microbial assemblages in their many roles and potential applications.

Protecting ice from melting under sunlight via radiative cooling

Abstract: As ice plays a critical role in various aspects of life, from food preservation to ice sports and ecosystem, it is desirable to protect ice from melting, especially under sunlight. The fundamental reason for ice melt under sunlight is related to the imbalanced energy flows of the incoming sunlight and outgoing thermal radiation. Therefore, radiative cooling, which can balance the energy flows without energy consumption, offers a sustainable approach for ice protection. Here, we demonstrate that a hierarchically designed radiative cooling film based on abundant and eco-friendly cellulose acetate molecules versatilely provides effective and passive protection to various forms/scales of ice under sunlight. This work provides inspiration for developing an effective, scalable, and sustainable route for preserving ice and other critical elements of ecosystems.

Recovering wetland biogeomorphic feedbacks to restore the world’s biotic carbon hotspots

Abstract: Biogeomorphic wetlands cover 1% of Earth’s surface but store 20% of ecosystem organic carbon. This disproportional share is fueled by high carbon sequestration rates and effective storage in peatlands, mangroves, salt marshes, and seagrass meadows, which greatly exceed those of oceanic and forest ecosystems. Here, we review how feedbacks between geomorphology and landscape-building vegetation underlie these qualities and how feedback disruption can switch wetlands from carbon sinks into sources. Currently, human activities are driving rapid declines in the area of major carbon-storing wetlands (1% annually). Our findings highlight the urgency to stop through conservation ongoing losses and to reestablish landscape-forming feedbacks through restoration innovations that recover the role of biogeomorphic wetlands as the world’s biotic carbon hotspots. Description Restoring wetlands for carbon Wetlands disproportionately contribute to carbon sequestration globally. However, the ability of wetlands to store carbon depends on feedbacks between vegetation and geomorphology that allow wetlands to continue to develop over long time periods. When these feedbacks break down, wetlands can become carbon sources. Temmink et al. reviewed recent research on the role of plant-landform interactions in wetland carbon storage and the potential for restoration to restore these critical processes. —BEL A review explains that restoring plant-landform linkages is critical to harnessing the carbon sequestration potential of wetlands. BACKGROUND Evaluating effects of global warming from rising atmospheric carbon dioxide (CO2) concentrations requires resolving the processes that drive Earth’s carbon stocks and flows. Although biogeomorphic wetlands (peatlands, mangroves, salt marshes, and seagrass meadows) cover only 1% of Earth’s surface, they store 20% of the global organic ecosystem carbon. This disproportionate share is fueled by high carbon sequestration rates per unit area and effective storage capacity, which greatly exceed those of oceanic and forest ecosystems. We highlight that feedbacks between geomorphology and landscape-building wetland vegetation underlie these critical qualities and that disruption of these biogeomorphic feedbacks can switch these systems from carbon sinks into sources. ADVANCES A key advancement in understanding wetland functioning has been the recognition of the role of reciprocal organism-landform interactions, “biogeomorphic feedbacks.” Biogeomorphic feedbacks entail self-reinforcing interactions between biota and geomorphology, by which organisms—often vegetation—engineer landforms to their own benefit following a positive density-dependent relationship. Vegetation that dominates major carbon-storing wetlands generate self-facilitating feedbacks that shape the landscape and amplify carbon sequestration and storage. As a result, per unit area, wetland carbon stocks and sequestration rates greatly exceed those of terrestrial forests and oceans, ecosystems that worldwide harbor large stocks because of their large areal extent. Worldwide biogeomorphic wetlands experience human-induced average annual loss rates of around 1%. We estimate that associated carbon losses amount to 0.5 Pg C per year, levels that are equivalent to 5% of the estimated overall anthropogenic carbon emissions. Because carbon emissions from degraded wetlands are often sustained for centuries until all organic matter has been decomposed, conserving and restoring biogeomorphic wetlands must be part of global climate solutions. OUTLOOK Our work highlights that biogeomorphic wetlands serve as the world’s biotic carbon hotspots, and that conservation and restoration of these hotspots offer an attractive contribution to mitigate global warming. Recent scientific findings show that restoration methods aimed at reestablishing biogeomorphic feedbacks can greatly increase establishment success and restoration yields, paving the way for large-scale restoration actions. Therefore, we argue that implementing such measures can facilitate humanity in its pursuit of targets set by the Paris Agreement and the United Nations Decade on Ecosystem Restoration. Carbon storage in biogeomorphic wetlands. Organic carbon (A) stocks, (B) densities, and (C) sequestration rates in the world’s major carbon-storing ecosystems. Oceans hold the largest stock, peatlands (boreal, temperate, and tropical aggregated) store the largest amount per unit area, and coastal ecosystems (mangroves, salt marshes, and seagrasses aggregated) support the highest sequestration rates. (D and E) Biogeomorphic feedbacks, indicated with arrows, can be classified as productivity stimulating or decomposition limiting. Productivity-stimulating feedbacks increase resource availability and thus stimulate vegetation growth and organic matter production. Although production is lower in wetlands with decomposition-limiting feedbacks, decomposition is more strongly limited, resulting in net accumulation of organic matter. (D) In fens, organic matter accumulation from vascular plants is amplified by productivity-stimulating feedbacks. Once the peat rises above the groundwater and is large enough to remain waterlogged by retaining rainwater, the resulting bog maintains being waterlogged and acidic, resulting in strong decomposition-limiting feedbacks. (E) Vegetated coastal ecosystems generate productivity-stimulating feedbacks that enhance local production and trapping of external organic matter.

Global Trends of Forest Loss Due to Fire From 2001 to 2019

Abstract: Forest fires contribute to global greenhouse gas emissions and can negatively affect public health, economic activity, and provision of ecosystem services. In boreal forests, fires are a part of the ecosystem dynamics, while in the humid tropics, fires are largely human-induced and lead to forest degradation. Studies have shown changing fire dynamics across the globe due to both climate and land use change. However, global trends in fire-related forest loss remain uncertain due to the lack of a globally consistent methodology applied to high spatial resolution data. Here, we create the first global 30-m resolution satellite-based map of annual forest loss due to fire. When producing this map, we match the mapped area of forest loss due to fire to the reference area obtained using a sample-based unbiased estimator, thus enabling map-based area reporting and trend analysis. We find an increasing global trend in forest loss due to fire from 2001 to 2019, driven by near-uniform increases across the tropics, subtropical, and temperate Australia, and boreal Eurasia. The results quantify the increasing threat of fires to remaining forests globally and may improve modeling of future forest fire loss rates under various climate change and development scenarios.

Biomineralization: Integrating mechanism and evolutionary history

Abstract: Calcium carbonate (CaCO3) biomineralizing organisms have played major roles in the history of life and the global carbon cycle during the past 541 Ma. Both marine diversification and mass extinctions reflect physiological responses to environmental changes through time. An integrated understanding of carbonate biomineralization is necessary to illuminate this evolutionary record and to understand how modern organisms will respond to 21st century global change. Biomineralization evolved independently but convergently across phyla, suggesting a unity of mechanism that transcends biological differences. In this review, we combine CaCO3 skeleton formation mechanisms with constraints from evolutionary history, omics, and a meta-analysis of isotopic data to develop a plausible model for CaCO3 biomineralization applicable to all phyla. The model provides a framework for understanding the environmental sensitivity of marine calcifiers, past mass extinctions, and resilience in 21st century acidifying oceans. Thus, it frames questions about the past, present, and future of CaCO3 biomineralizing organisms.

Evidence, causes, and consequences of declining nitrogen availability in terrestrial ecosystems

Abstract: The productivity of ecosystems and their capacity to support life depends on access to reactive nitrogen (N). Over the past century, humans have more than doubled the global supply of reactive N through industrial and agricultural activities. However, long-term records demonstrate that N availability is declining in many regions of the world. Reactive N inputs are not evenly distributed, and global changes—including elevated atmospheric carbon dioxide (CO2) levels and rising temperatures—are affecting ecosystem N supply relative to demand. Declining N availability is constraining primary productivity, contributing to lower leaf N concentrations, and reducing the quality of herbivore diets in many ecosystems. We outline the current state of knowledge about declining N availability and propose actions aimed at characterizing and responding to this emerging challenge. Description Declining nitrogen in natural ecosystems Nitrogen (N) availability is key to the functioning of ecosystems and the cycling of nutrients and energy through the biosphere. However, there is growing evidence that N availability is decreasing in many terrestrial ecosystems. The consequences of declining N availability will be widespread. For example, a decreased concentration of N in leaves reduces the availability of N to insects, contributing to population declines that may then cascade through higher trophic levels. Mason et al. reviewed the extent of this phenomenon, and the anthropogenic factors that might be driving it (including climate change and increasing atmospheric carbon dioxide), and discuss how its damaging effects might be mitigated. —AMS A review explains that a global decline in nitrogen availability is affecting ecosystems, with consequences for biodiversity and ecosystem function. BACKGROUND The availability of nitrogen (N) to plants and microbes has a major influence on the structure and function of ecosystems. Because N is an essential component of plant proteins, low N availability constrains the growth of plants and herbivores. To increase N availability, humans apply large amounts of fertilizer to agricultural systems. Losses from these systems, combined with atmospheric deposition of fossil fuel combustion products, introduce copious quantities of reactive N into ecosystems. The negative consequences of these anthropogenic N inputs—such as ecosystem eutrophication and reductions in terrestrial and aquatic biodiversity—are well documented. Yet although N availability is increasing in many locations, reactive N inputs are not evenly distributed globally. Furthermore, experiments and theory also suggest that global change factors such as elevated atmospheric CO2, rising temperatures, and altered precipitation and disturbance regimes can reduce the availability of N to plants and microbes in many terrestrial ecosystems. This can occur through increases in biotic demand for N or reductions in its supply to organisms. Reductions in N availability can be observed via several metrics, including lowered nitrogen concentrations ([N]) and isotope ratios (δ15N) in plant tissue, reduced rates of N mineralization, and reduced terrestrial N export to aquatic systems. However, a comprehensive synthesis of N availability metrics, outside of experimental settings and capable of revealing large-scale trends, has not yet been carried out. ADVANCES A growing body of observations confirms that N availability is declining in many nonagricultural ecosystems worldwide. Studies have demonstrated declining wood δ15N in forests across the continental US, declining foliar [N] in European forests, declining foliar [N] and δ15N in North American grasslands, and declining [N] in pollen from the US and southern Canada. This evidence is consistent with observed global-scale declines in foliar δ15N and [N] since 1980. Long-term monitoring of soil-based N availability indicators in unmanipulated systems is rare. However, forest studies in the northeast US have demonstrated decades-long decreases in soil N cycling and N exports to air and water, even in the face of elevated atmospheric N deposition. Collectively, these studies suggest a sustained decline in N availability across a range of terrestrial ecosystems, dating at least as far back as the early 20th century. Elevated atmospheric CO2 levels are likely a main driver of declines in N availability. Terrestrial plants are now uniformly exposed to ~50% more of this essential resource than they were just 150 years ago, and experimentally exposing plants to elevated CO2 often reduces foliar [N] as well as plant-available soil N. In addition, globally-rising temperatures may raise soil N supply in some systems but may also increase N losses and lead to lower foliar [N]. Changes in other ecosystem drivers—such as local climate patterns, N deposition rates, and disturbance regimes—individually affect smaller areas but may have important cumulative effects on global N availability. OUTLOOK Given the importance of N to ecosystem functioning, a decline in available N is likely to have far-reaching consequences. Reduced N availability likely constrains the response of plants to elevated CO2 and the ability of ecosystems to sequester carbon. Because herbivore growth and reproduction scale with protein intake, declining foliar [N] may be contributing to widely reported declines in insect populations and may be negatively affecting the growth of grazing livestock and herbivorous wild mammals. Spatial and temporal patterns in N availability are not yet fully understood, particularly outside of Europe and North America. Developments in remote sensing, accompanied by additional historical reconstructions of N availability from tree rings, herbarium specimens, and sediments, will show how N availability trajectories vary among ecosystems. Such assessment and monitoring efforts need to be complemented by further experimental and theoretical investigations into the causes of declining N availability, its implications for global carbon sequestration, and how its effects propagate through food webs. Responses will need to involve reducing N demand via lowering atmospheric CO2 concentrations, and/or increasing N supply. Successfully mitigating and adapting to declining N availability will require a broader understanding that this phenomenon is occurring alongside the more widely recognized issue of anthropogenic eutrophication. Intercalibration of isotopic records from leaves, tree rings, and lake sediments suggests that N availability in many terrestrial ecosystems has steadily declined since the beginning of the industrial era. Reductions in N availability may affect many aspects of ecosystem functioning, including carbon sequestration and herbivore nutrition. Shaded areas indicate 80% prediction intervals; marker size is proportional to the number of measurements in each annual mean. Isotope data: (tree ring) K. K. McLauchlan et al., Sci. Rep. 7, 7856 (2017); (lake sediment) G. W. Holtgrieve et al., Science 334, 1545–1548 (2011); (foliar) J. M. Craine et al., Nat. Ecol. Evol. 2, 1735–1744 (2018)

Geological evolution of offshore pollution and its long-term potential impacts on marine ecosystems

Abstract: • Increasing global offshore pollution as a worldwide problem. • Coastal geological disasters due to global offshore pollution. • Complex offshore sedimentary dynamics through long-term accumulating pollutants. • The stable succession and development trend of marine ecosystems was significantly interrupted. Populations and metropolitan centers are accumulated in coastal areas around the world. In view of the fact that they are geographically adjacent to coasts and intense anthropogenic activities, increasing global offshore pollution has been an important worldwide concern over the past several decades and has become a very serious problem that needs to be addressed urgently. Due to offshore pollution, various geological disasters occur in high frequency, including intensified erosion and salinization of coastal soils, frequent geological collapses and landslides and increasing seismic activities. Moreover, offshore pollution shows increasingly serious impacts on the topography and geomorphology of offshore and coastal areas, including coastal degradation, retreating coastlines and estuary delta erosion. Offshore sedimentation processes are strongly influenced by the pH changes of terrestrial discharges, and sedimentary dynamics have become extremely acute and complex due to offshore pollution. The seabed topography and hydrodynamic environment determine the fate and transport of pollutants entering offshore regions. Coastal estuaries, port basins and lagoons that have relatively moderate ocean currents and winds are more likely to accumulate pollutants. Offshore regions and undersea canyons can be used as conduits for transporting pollutants from the continent to the seabed. It is particularly noteworthy that the spatial/temporal distribution of species, community structures, and ecological functions in offshore areas have undergone unprecedented changes in recent decades. Due to increasing offshore pollution, the stable succession and development trend of marine ecosystems has been broken. It is thus important to identify and regulate the quantity, composition and transportation of pollutants in offshore regions and their behavior in marine ecosystems. In particular, crucial actions for stabilizing marine ecosystems, including increasing species and biodiversity, should be implemented to enhance their anti-interference capabilities. This review provides an overview of the current situation of offshore pollution, as well as major trends of pollutant fate and transportation from continent to marine ecosystems, transformation of pollutants in sediments, and their bioaccumulation and diffusion. This study retrospectively reviews the long-term geological evolution of offshore pollution from the perspective of marine geology, and analyses their long-term potential impacts on marine ecosystems. Due to ecological risks associated with pollutants released from offshore sediments, more research on the influence of global offshore pollution based on marine geology is undoubtedly needed.

Best practices in metabarcoding of fungi: From experimental design to results

Abstract: The development of high‐throughput sequencing (HTS) technologies has greatly improved our capacity to identify fungi and unveil their ecological roles across a variety of ecosystems. Here we provide an overview of current best practices in metabarcoding analysis of fungal communities, from experimental design through molecular and computational analyses. By reanalysing published data sets, we demonstrate that operational taxonomic units (OTUs) outperform amplified sequence variants (ASVs) in recovering fungal diversity, a finding that is particularly evident for long markers. Additionally, analysis of the full‐length ITS region allows more accurate taxonomic placement of fungi and other eukaryotes compared to the ITS2 subregion. Finally, we show that specific methods for compositional data analyses provide more reliable estimates of shifts in community structure. We conclude that metabarcoding analyses of fungi are especially promising for integrating fungi into the full microbiome and broader ecosystem functioning context, recovery of novel fungal lineages and ancient organisms as well as barcoding of old specimens including type material.

The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Abstract: Abstract Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.