Interaction of climate change, potentially toxic elements (PTEs), and topography on plant diversity and ecosystem functions in a high-altitude mountainous region of the Tibetan Plateau

Terrestrial ecosystems are increasingly confronted with environmental changes such as climate change, natural disasters, or anthropogenic disturbances. Prolonged droughts, heat waves and increasing aridity are generally considered major consequences of ongoing global climate change and are expected to produce widespread changes in key ecosystem attributes, functions, and dynamics. Europe has been heavily affected by consecutive and increasingly severe droughts in the past decades, leading to large-scale vegetation die-offs and land degradation. This enhanced frequency in the past, combined with potential impacts of future climate change, makes it important to understand how these droughts affect ecosystem stability functioning and induce changes in ecosystem functioning, which is the aim of the DRYTIP project.  As carbon gain in terrestrial ecosystems is a compromise between photosynthesis and transpiration, a ratio that is also known as water-use-efficiency (WUE), assessing changes in WUE plays a key role in assessing changes in terrestrial ecosystem functioning. We used a remote sensing-based approach to describe changes in ecosystem functioning (similar to the approach suggested in Horion et al. (2019)) across Europe between 2000 and 2023.  We investigate how the severity and duration of droughts relates to the intensity of the change in ecosystem functioning, as well as what are the characteristics of ecosystems where abrupt changes in WUE were observed as a result of drought. We expect to find regional differences in the WUE response scenarios to drought and we will explore the underlying ecosystem conditions in exemplary cases. We finally hypothesise that these differences in ecosystem response to drought can be linked to ecosystem resilience.  We are looking forward to presenting and discussing preliminary results at the General Assembly.  

Summary Trait‐based approaches evaluate ecosystem functioning under environmental change by relating traits predicting changes in species densities (response traits) to traits driving ecosystem functioning (effect traits). Stressors can, however, affect ecosystem functioning not only by altering species densities but also by directly changing species effect traits. We first identified the response traits predicting the cell density of 18 marine benthic diatom strains along gradients of two chemical stressors (a pesticide and a metal, atrazine and copper). We then tested if response traits could predict stressor‐induced changes in ecosystem functioning, i.e. changes in the effect traits driving the diatoms’ potential contribution to primary production, sediment stabilization and energy content in intertidal systems. Finally, we examined if changes in density and changes in ecosystem functioning were correlated, to assess whether species capable of growing under stressful conditions could maintain their contribution to ecosystem functioning. The relationship between response traits and stressor‐induced changes in density and ecosystem functioning was different depending on stressor type: a set of intercorrelated morphological traits predicted changes in both density and ecosystem functioning under metal stress, with large cells being more stress resistant. Changes in density and changes in ecosystem functioning were positively related: diatoms whose density was least affected by the metal were also able to sustain functioning under metal exposure. In contrast, the capacity for mixotrophic growth predicted changes in density, but not changes in ecosystem functioning under pesticide stress. Pesticide effects on density and on ecosystem functioning were negatively related for energy content and sediment stabilization, indicating a limited capacity of pesticide‐tolerant diatoms to maintain their contribution to ecosystem functioning. Synthesis. Ecosystem functioning under stress can depend on whether the response traits driving changes in species densities also predict direct stress effects on the species’ contribution to functioning. Based on our results, we expect a disproportionate loss of functioning when traits driving species densities do not allow to maintain ecosystem functioning under stress.

The effect of sheep grazing abandonment on soil bacterial communities in productive mountain grasslands

Ecosystem coupling: A unifying framework to understand the functioning and recovery of ecosystems

The introduction of non-native predators is a matter of great concern, but their impacts on ecosystem functions remain poorly understood. We investigated how changes in fish diversity following the invasion of Cichla kelberi affected ecosystem functions generated by fish populations. Fish assemblages were sampled in macrophyte patches in a Neotropical impoundment over a 5-year period, before and after the introduction of the predator. We assigned seven ecosystem functions (26 trait-states) to each fish species, and examined how these functions behaved after the invasion. We collected 577 fish belonging to 25 species. Species richness, fish biomass and main species declined significantly over periods. The biomass of ecosystem functions changed significantly over time, and most trait-states declined. Few trait-states were lost, but all functions had at least one trait-state reduced by more than 85%. A null model analysis showed that changes in functions were not driven by species identities, while species richness correlated positively with total biomass and with most functions, suggesting that the loss of taxa and biomass drove observed changes in ecosystem functions. Our study provided evidence that community disassembly associated with the invasion of C. kelberi translated to the decline of several ecosystem functions, affecting energy mobilization and transference.

Research Highlights: A small, long-term decrease in the water availability in a Mediterranean holm oak forest elicited strong effects on tree stem growth, mortality, and species composition, which led to changes in the ecosystem function and service provision. Background and Objectives: Many forest ecosystems are increasingly challenged by stress conditions under climate change. These new environmental constraints may drive changes in species distribution and ecosystem function. Materials and Methods: An evergreen Mediterranean holm oak (Quercus ilex L.) forest was subjected to 21 consecutive years of experimental drought (performing 30% of rainfall exclusion resulted in a 15% decrease in soil moisture). The effects of the annual climatic conditions and the experimental drought on a tree and shrub basal area increment were studied, with a focus on the two most dominant species (Q. ilex and the tall shrub Phillyrea latifolia L.). Results: Stem growth decreased and tree mortality increased under the experimental drought conditions and in hot and dry years. These effects differed between the two dominant species: the basal area of Q. ilex (the current, supradominant species) was dependent on water availability and climatic conditions, whereas P. latifolia was more tolerant to drought and experienced increased growth rates in plots where Q. ilex decay rates were high. Conclusions: Our findings reveal that small changes in water availability drive changes in species growth, composition, and distribution, as demonstrated by the continuous and ongoing replacement of the current supradominant Q. ilex by the subdominant P. latifolia, which is better adapted to tolerate hot and dry environments. The consequences of these ecological transformations for ecosystem function and service provision to human society are discussed.

The recognition that the numbers and types of species in a community influence the functioning of ecosystems has catalyzed the research of a generation of scientists. The relationship between biodiversity and ecosystem functioning (BEF) is most often examined by controlling species richness and randomizing community composition. In natural systems, biodiversity changes occur as part of metacommunity assembly processes. Focusing on community assembly and the functioning of ecosystems (CAFE), by integrating both species richness and composition changes through species gains, losses, and changes in abundance, will better reveal how changes to communities will impact ecosystem function. We synthesize the BEF and CAFE perspectives using an ecological application of the Price equation (Fox and Kerr 2012), which partitions the contributions of richness and composition to ecosystem function. We demonstrate the utility of this method with a novel graphical approach and empirical examples of environmental perturbations in terrestrial and marine ecosystems affecting plant and mammal communities. The CAFE approach reveals important contributions of composition, over and above species richness changes, to ecosystem function. Examples of species invasions showed that changes in species richness and composition can work in concert to magnify ecosystem function changes or antagonistically to minimize ecosystem function impacts. Furthermore, we show how the CAFE approach can highlight, through time, the compositional and abundance-based changes that allow for the recovery of pre-disturbance levels of ecosystem function in small rodent communities. Considering how communities change in an integrative fashion, rather than focusing on one axis of community structure at a time, will improve our ability to anticipate and predict changes in ecosystem function. Considering the CAFE approach in studies of ecosystem function illustrates the importance of metacommunity processes for explaining the linkages between diversity, ecosystem function, and bridges knowledge derived from experimental and naturally-occurring communities.

Wildfires subject soil microbes to extreme temperatures and modify their physical and chemical habitat. This might immediately alter their community structure and ecosystem functions. We burned a fire-prone shrubland under controlled conditions to investigate (1) the fire-induced changes in the community structure of soil archaea, bacteria and fungi by analysing 16S or 18S rRNA gene amplicons separated through denaturing gradient gel electrophoresis; (2) the physical and chemical variables determining the immediate shifts in the microbial community structure; and (3) the microbial drivers of the change in ecosystem functions related to biogeochemical cycling. Prokaryotes and eukaryotes were structured by the local environment in pre-fire soils. Fire caused a significant shift in the microbial community structure, biomass C, respiration and soil hydrolases. One-day changes in bacterial and fungal community structure correlated to the rise in total organic C and NO(3)(-)-N caused by the combustion of plant residues. In the following week, bacterial communities shifted further forced by desiccation and increasing concentrations of macronutrients. Shifts in archaeal community structure were unrelated to any of the 18 environmental variables measured. Fire-induced changes in the community structure of bacteria, rather than archaea or fungi, were correlated to the enhanced microbial biomass, CO(2) production and hydrolysis of C and P organics. This is the first report on the combined effects of fire on the three biological domains in soils. We concluded that immediately after fire the biogeochemical cycling in Mediterranean shrublands becomes less conservative through the increased microbial biomass, activity and changes in the bacterial community structure.

Disturbance-mediated species loss has prompted research considering how ecosystem functions are changed when biota is impaired. However, there is still limited empirical evidence from natural environments evaluating the direct and indirect (i.e. via biota) effects of disturbance on ecosystem functioning. Oxygen deficiency is a widespread threat to coastal and estuarine communities. While the negative impacts of hypoxia on benthic communities are well known, few studies have assessed in situ how benthic communities subjected to different degrees of hypoxic stress alter their contribution to ecosystem functioning. We studied changes in sediment ecosystem function (i.e. oxygen and nutrient fluxes across the sediment water-interface) by artificially inducing hypoxia of different durations (0, 3, 7 and 48 days) in a subtidal sandy habitat. Benthic chamber incubations were used for measuring responses in sediment oxygen and nutrient fluxes. Changes in benthic species richness, structure and traits were quantified, while stress-induced behavioral changes were documented by observing bivalve reburial rates. The initial change in faunal behavior was followed by non-linear degradation in benthic parameters (abundance, biomass, bioturbation potential), gradually impairing the structural and functional composition of the benthic community. In terms of ecosystem function, the increasing duration of hypoxia altered sediment oxygen consumption and enhanced sediment effluxes of NH4 + and dissolved Si. Although effluxes of PO4 3− were not altered significantly, changes were observed in sediment PO4 3− sorption capability. The duration of hypoxia (i.e. number of days of stress) explained a minor part of the changes in ecosystem function. Instead, the benthic community and disturbance-driven changes within the benthos explained a larger proportion of the variability in sediment oxygen- and nutrient fluxes. Our results emphasize that the level of stress to the benthic habitat matters, and that the link between biodiversity and ecosystem function is likely to be affected by a range of factors in complex, natural environments.

Global environmental change and the uncertain fate of biodiversity

Mangrove forest coverage is increasing in the estuaries of the North Island of New Zealand, causing changes in estuarine ecosystem structure and function. Sedimentation and associated nutrient enrichment have been proposed to be factors leading to increases in mangrove cover, but the relative importance of each of these factors is unknown. We conducted a fertilization study in estuaries with different sedimentation histories in order to determine the role of nutrient enrichment in stimulating mangrove growth and forest development. We expected that if mangroves were nutrient-limited, nutrient enrichment would lead to increases in mangrove growth and forest structure and that nutrient enrichment of trees in our site with low sedimentation would give rise to trees and sediments that converged in terms of functional characteristics on control sites in our high sedimentation site. The effects of fertilizing with nitrogen (N) varied among sites and across the intertidal zone, with enhancements in growth, photosynthetic carbon gain, N resorption prior to leaf senescence and the leaf area index of canopies being significantly greater at the high sedimentation sites than at the low sedimentation sites, and in landward dwarf trees compared to seaward fringing trees. Sediment respiration (CO(2) efflux) was higher at the high sedimentation site than at the low one sedimentation site, but it was not significantly affected by fertilization, suggesting that the high sedimentation site supported greater bacterial mineralization of sediment carbon. Nutrient enrichment of the coastal zone has a role in facilitating the expansion of mangroves in estuaries of the North Island of New Zealand, but this effect is secondary to that of sedimentation, which increases habitat area and stimulates growth. In estuaries with high sediment loads, enrichment with N will cause greater mangrove growth and further changes in ecosystem function.

In the coming decade, accelerating climate change and human modification of both landscapes and oceans will cause tremendous changes in ecosystem distribution and function. These changes will affect the capacity of ecosystems to provide food, water, healthy living environments, and a range of other services, and they will also affect the rate at which global warming continues to increase. Changes are already occurring in many parts of the world, notably in coastal zones where much of the world's population lives, at high latitudes where climate change is lengthening the snow-free season, and in tropical forests undergoing massive conversions for agricultural expansion and timber extraction. The vast, remote open ocean is experiencing increasing acidity as a result of higher levels of atmospheric CO2 while over-harvesting of fish is leading to global changes in marine ecosystems. Global ecosystem management is a growing challenge for the future. In order to understand and manage ecosystem changes and their feedback to the Earth's climate system, continuous global observations are critical. Space-based observations of ecosystems now span decades and capture variability and trends in ecosystems by studying large areas repeatedly. Observations of the physical environment provide the context for understanding ecosystems' sensitivity to climate change. Measurements such as soil moisture, ocean topography, ocean vector winds, earth radiation, and precipitation are among those needed. The Space Studies Board of the National Research Council has organized a decadal survey study, “Earth observations from space: a community assessment and strategy for the future” (http://qp.nas.edu/decadalsurvey). NASA has used decadal surveys in other disciplines to establish a framework for science priorities and missions, but this is the first attempt to use the process for the Earth sciences, including ecology. Satellite observations and the analyses they provide have an important and growing role in environmental science and management, so the decadal survey will have a major impact in ecology and environmental management. Within this process, the Earth Science and Applications Panel on Ecosystems was appointed to address terrestrial, aquatic, and marine environments. (Although the authors are members of this panel, the views in this editorial are based on personal observations of the process.) The survey will generate recommendations regarding science and applications priorities, identify opportunities afforded by new measurement types and new vantage points, and take a systems approach to observations that encompass the research programs of NASA and the related operational programs of NOAA and the USGS. This study will recommend priority measurements to support research, monitoring, and management during the decade 2005–2015 and beyond. In addition to elucidating fundamental Earth system processes and those underlying environmental change, applications needs also include weather and hydrological forecasting, climate prediction, aviation safety, earthquake prediction, natural resources management, agricultural assessment, homeland security, and infrastructure planning. The ecosystems panel evaluated ecological, technical, and management challenges, identified the contribution of remote observations to research and applications, and reviewed existing plans for ongoing ecologically relevant measurements. The panel strongly supports continuity of critical time series begun with LANDSAT, MODIS, and other sensors, and has tentatively identified four high-priority satellite missions. These research missions will employ new technologies to add new observations. The first new mission focuses on the detection and diagnosis of changes in ecosystem function (productivity, nutrient and water status, invasive species distributions, and coral reef status). The second focuses on terrestrial ecosystem structure and biomass, providing information on woody biomass, horizontal and vertical heterogeneity of forest habitat, and the effects of land use and deforestation on carbon stocks. A third mission will detail changes in CO2 concentration profiles above land and oceans, to quantify the global carbon budget. The fourth will view the coastal zone diurnally from a geostationary orbit to measure coastal ecosystem dynamics, including instances of harmful algal blooms, transport of organic matter, productivity, fisheries, and impacts of pollution episodes. The panel will also make recommendations about the need for new in situ and airborne capability. Remote sensing is used to address global-change ecology, conservation biology and planning, invasive species management, fisheries, wildfire management, precision agriculture, water resource planning, and a host of other ecological problems. The outcome of the decadal survey will influence the ecological satellite data resources available for the future. Interested scientists are strongly encouraged to contact the authors of this editorial or the NRC directly with their views. Bringing the next decade's ecological remote sensing program to fruition will require input, involvement, and support for spaced-based science and funding by ecologists and managers in an environment where many needs compete for limited opportunities. David Schimel, Senior Scientist, National Center for Atmospheric Research, Boulder, CO Inez Fung, Co-Director, Berkeley Institute of the Environment, CA Ruth Defries, Associate Professor, University of Maryland, MD

The research of a generation of ecologists was catalysed by the recognition that the number and identity of species in communities influences the functioning of ecosystems. The relationship between biodiversity and ecosystem functioning (BEF) is most often examined by controlling species richness and randomising community composition. In natural systems, biodiversity changes are often part of a bigger community assembly dynamic. Therefore, focusing on community assembly and the functioning of ecosystems (CAFE), by integrating both species richness and composition through species gains, losses and changes in abundance, will better reveal how community changes affect ecosystem function. We synthesise the BEF and CAFE perspectives using an ecological application of the Price equation, which partitions the contributions of richness and composition to function. Using empirical examples, we show how the CAFE approach reveals important contributions of composition to function. These examples show how changes in species richness and composition driven by environmental perturbations can work in concert or antagonistically to influence ecosystem function. Considering how communities change in an integrative fashion, rather than focusing on one axis of community structure at a time, will improve our ability to anticipate and predict changes in ecosystem function.

Mining activities are not only sources of potentially toxic element (PTE) pollution, but are also closely associated with natural radioisotopes. This study combined uranium radioisotopes to better understand the behavior of mine-derived PTEs in lake sediments. We collected surface sediments near an abandoned mine in Lake Daecheong, South Korea, and determined the concentration distribution of PTEs (Pb, Zn, Cu, Cr, Ni, As, Cd, and Hg) and uranium radioisotopes (235U and 238U) using an inductively coupled plasma mass spectrometer and a gamma spectrometer, respectively. The mean Zn, Cu, Ni, and Cd concentrations in the tributary near the mine were significantly higher than those of other PTEs, and their distributions tended to decrease downstream. The mean concentrations and distributions of 235U and 238U showed a consistent trend similar to that of PTEs. PTE pollution was extremely high only in sites downstream of the tributary directly affected by the mine. Zn, Cu, Ni, Cd, 235U, and 238U were closely related and were the most important factors controlling PTE origin. Consequently, the surface sediments were dominated by mine-derived PTEs (Zn, Cu, Ni, and Cd), suggesting a close relationship between the locations and PTE concentrations, highlighting mines as sources. Moreover, uranium radioisotopes were highly correlated with mine-derived PTEs, which will help improve our understanding of PTE behavior. Therefore, uranium radioisotopes can be used as tracers to assess the origin of PTEs from mining activities.

Functional traits, short life cycles, and the pivotal role in the ocean make copepod diversity a solid foundation for assessing the effect of global changes in marine food webs and ecosystem functioning. Climate change and extreme events, particularly El Niño, can affect coastal ecosystems. The Arvoredo Marine Biological Reserve (MPA), located in highly productive coastal waters of the Southern Brazilian Bight, presents complex climate and oceanographic conditions. This study investigates the influence of oceanographic processes and El Niño 2015-2016 on the copepod functional diversity from 2014 to 2016 in the Arvoredo MPA. Horizontal tows were performed using a WP2 net with a mesh size of 200 µm. The 41 species accounted for 19 functional entities and four functional groups. Our findings reveal that the seasonal intrusion of water masses influenced copepod functional diversity. During summer, the upwelling of South Atlantic Central Water increased nutrient availability and favored large herbivore-omnivores and carnivores. The Plata Plume Water enrichment during winter coincided with a decline in functional richness and abundance, leading to the predominance of the Oithona nana, a small-sized omnivore. Compensatory mechanisms were observed as functional equivalence and species composition shifts. Acartia lilljeborgii and Temora turbinata exhibited functional equivalence and compensated for each other in response to salinity changes associated with upwelling and El Niño. The copepod assemblage demonstrated the ability to maintain functional diversity despite changes in copepod abundance. However, the decline in functional diversity and abundance during the intense winter indicated potential disruption in trophic dynamics and ecosystem functioning. Maintaining balance and compensating for disturbances such as El Niño is crucial for marine food web resilience. The functional trait approach provided a comprehensive understanding of the copepod assemblage in Arvoredo MPA, contributing to a broader knowledge of the impact of oceanographic processes intensification. Monitoring functional diversity and abundance is crucial for evaluating the effects of copepod assemblage changes in ecosystem functionings.