The response and feedback of ecosystems to global change is a scientific frontier in ecosystem ecology, which combines macro- and micro-level studies across multidisciplines. It focuses on the responses of ecosystem structure and function to global change, and its objective is to achieve sustainable use of ecosystem services. Based on the review of previous studies, we summarized the major progress and main achievements in this field and made an outlook for future challenges. According to the research content and object, this special issue systematically reviewed the effects of different global change factors, including increasing atmospheric CO₂ and O₃ concentration, global warming, precipitation change, increasing nitrogen deposition and land use change, on terrestrial plant ecophysiology, community structure, and ecosystem functions, and global change impacts on marine ecosystems. It mainly discussed the changes in biogeochemical cycles and biodiversity under global change, and clarified the mechanisms underlying feedback between ecosystem and climate change. The study of this research area could provide theoretical basis for the construction of global change adaptation strategies.

Characterizing ecosystem responses to past, present and future changes in atmopsheric carbon dioxide (CO₂) concentration is critical for understanding and predicting the consequences of global change over evolutionary and ecological timescales. Over the past two decades, CO₂ studies have provided great insights into the effects of rising CO₂ concentration on plant growth and productivity, carbon-nitrogen turnover, the formation of progressive nitrogen limitation (PNL) in ecosystems, and the interaction between elevated CO₂ concentration and other envrionmental factors (O₃ pollution, N deposition, warming and drought). However, scaling CO₂ effects across wide spatial and temporal scales, especially at belowground part, has many uncertainties. Here we explore major research areas and hotspots of CO₂ studies on plants and ecosystems from 1990 to 2018, and review the development of manipulated experiments in the field of elevated CO₂ impacts. In detail, we discussed the states of art in five international frontiers research directions: crop yield and quality, carbon fixation, water use efficiency, ecosystem nitrogen use and soil microorganism. Finally, we identify several topics and research outlooks to facilitate further developments in the field of CO₂ effects on ecosystems.

Due to huge consumption of fossil fuels and chemical fertilizers, substantial amount of anthropogenic reactive nitrogen (N) has been released into the environment. Therefore, N deposition has gradually increased worldwide and become one of the most important issues of global change. China has been a N deposition hotspot, and N deposition is projected to last long duration, which poses serious threats to ecosystem stability and functionality. In this synthesis paper, we summarized the impacts of N deposition on aboveground vegetation, soil microorganisms and biogeochemical cycling of major elements (carbon, N and phosphorus) in terrestrial ecosystems by outlining the progresses in the research field during the past 40 years. Results indicate that the accumulation of reactive N compounds induced by N deposition alters the soil environment, ecological stoichiometric balance and species co-occurrence patterns, thereby changing biodiversity and ecosystem functions. The rates, forms and duration of N deposition and the homeostasis of biosystem together with abiotic environments determine the direction and extent of the ecosystem response to N deposition. Through analysing local and foreign studies in this research area, we explore the weaknesses of relevant research that are being conducted in China. To advance the basic research on and risk management of N deposition, we propose the establishment of a N deposition monitoring and research network across the country with consideration of different ecosystems to promote regional and global risk assessments. Future research should highlight the combined multiple factors with N deposition and conduct direct and in-depth mechanism studies.

Terrestrial ecosystems are characterized by a series of spatiotemporally continuous, multiple scaled, and mutually connected processes. Since most of these ecological processes are regulated by temperature, climate warming will profoundly impact terrestrial ecosystems at global scale. Recently, how key processes in terrestrial ecosystems respond and/or adapt to climate warming has become a fundamental question in global change ecology. Here, we reviewed the recent research progress related to such question. This review focuses on key ecosystem processes, such as plant ecophysiological processes, phenology, community dynamics, productivity and carbon allocation, decomposition of litter and soil organic carbon, nutrient cycling, and carbon-nitrogen coupling. Based on a literature review, we propose perspectives for future research to tackle fundamental questions, such as the predictability of plant traits on ecosystem processes, coupling between biogeochemical cycles, mechanisms driving ecosystem responses to extreme climate and asymmetric warming, and ecological forecasting with models. We finally suggest more research efforts on warming adaptation rather than response on China’s specific ecosystems, and on the integration of experiments, observations, and models for coordinating studies across scales.

As an important compartment of the Earthʼs surface, terrestrial ecosystems act as a vital harbor for human survival and development. Climate change significantly increased the frequency, intensity and duration of drought since the beginning of the 21st century, which have marked impact on ecosystems, leading to serious restriction or even threat on the sustainable development of human beings. Therefore, developing integrative research on effects of drought on terrestrial ecosystems and assessing the associated ecological risk are impressive in global change field. This study reviewed the effects of drought on plant physiological and ecological processes, biogeochemical cycles, biodiversity, and ecosystem structure and functions in terrestrial ecosystems, and discussed current hotspot issues in this field as well as deeply analyzing the existing problems and the potential development direction. This study aims to provide some suggestions for the future observation, manipulative experiments, and modeling prediction on effects of drought on terrestrial ecosystems, and offer new insights to enhance risk assessment and management under drought.

Rising ground-level ozone (O₃) is currently an essential environmental issue in the world, especially in China. While research on the effects of O₃ on leaf photosynthetic gas exchange, plant growth and biomass has received a lot of attention, ecosystem-scale studies are however scarce and subject to great uncertainties. This article combs trends and hotpots of ground-level O₃ concentration and its effects on plants and ecosystems over the past 40 years. Research techniques and assessment methods for studying the ecological effects of ozone pollution are covered. The most important advances on the impacts of elevated ozone on terrestrial ecosystem are reviewed: plant response mechanisms, effects on grain yield, crop quality, carbon sequestration capacity, community structure and below-ground processes of different terrestrial ecosystems. Finally, regional risk assessment of the O₃ pollution is discussed. Considering the main knowledge gaps, future research should focus on belowground ecosystem response to elevated O₃ and should also incorporate O₃ and multi-factor experiments using Free-Air Ozone Concentration Elevation (FACE) system. More attention should also be paid on food security, establishment of Asian ozone network, standardization of risk assessment approach, and exploration of ecological measures to reduce the negative effects of O₃ pollution. This review can help to promote more studies on the ecological effects of ground-level O₃ pollution.

With the growth of human population and the development of human society, land use and land cover change (LUCC) is inevitable. LUCC not only has a far-reaching impact on the elements, structure and functions of ecosystems, but also has a feedback effect on global climate change. Scientific research has been carried out on the processes of land use change, the driving mechanisms, and the possible ecological and environmental effects in various aspects. This paper reviews the research progress on the impacts of land use change on climate, soil, biogeochemical cycle, biodiversity and regional ecological environment, and puts forward the prospects for the frontier research. With the continuous development of new technologies, scholars will focus more on the prediction of the future development, rationality and adaptability of LUCC in the context of future global change, providing basic information and theoretical basis for sustainable development.

As an important component of terrestrial ecosystems, natural grasslands cover 30% of the global land. Thus, grasslands play a significant role in global carbon cycle, climate change, water retention, soil and water conservation, livestock production and so on. Grazing, as one common use of grasslands, brings fundamental impacts on plant individuals, populations, communities, biodiversity, soil quality and microbes, and then affects structural and functional processes of grassland ecosystems through different kinds of grazing livestock, grazing intensity, period, and system. We explored the effects of grazing on grassland ecosystem by using the methods of bibliometric analysis and literature review. To summarize the effects of grazing on grassland structure and functional processes, our study 1) reviewed the research stages on the impacts of grazing on grassland ecosystems since the 1950s; 2) extracted the hot topics, important research areas and keywords of previous research; 3) revealed the cutting-edge and limitations of domestic research on the effects of grazing on plants growth, community characteristics, carbon, nitrogen and nutrient cycling, productivity and soil quality; 4) proposed the future research directions and priority areas from the aspects of precise grazing management, validation of related hypothesis, and global change research. This study can provide scientific basis for grassland grazing ecology research, adaptive management and sustainable development in China.

Global change has already posed a serious threat to different freshwater ecosystems by raising water temperatures, changing precipitation patterns and water flow conditions, enhancing species invasion, and increasing extreme events. In order to identify the major works carried out and highlights of the outcomes of research in freshwater ecology in the context of global change, we conducted literature search and analysis of papers published during 1900-2018 via Web of Science. In this review, the major researches in freshwater ecology in the context of global change are categorized into: (1) the effects of various global change factors on individuals, populations, communities and ecosystems; (2) changes in biogeochemical cycles of ecosystems in the process of global change; and (3) adaptation strategies of freshwater ecosystems to global changes. Over the past 10-15 years, research in freshwater ecosystems and global change progressed rapidly and showed breakthroughs in the following aspects: (1) elucidated the response processes and mechanisms of the structure and function of freshwater ecosystems to global climate change, in particular rising water temperatures; (2) revealed that freshwater ecosystems (wetlands, lakes, rivers, etc.) are important components of the global carbon cycle, such that under the influence of global change factors organic carbon burial decreased and mineralization rate increased. In future research, it is necessary to strengthen the systematic observations and integration of the total elements of freshwater ecosystems, to conduct research on carbon transport and transformation processes mediated by the river-connected multi-systems, and to strengthen basic theoretical research for uncovering the adaptation mechanisms of freshwater ecosystems to global change.

Since the industrial revolution, marine ecosystems have faced unprecedented stress caused by increasing temperature and atmospheric CO₂ concentration as a result of anthropogenic activities. In this review, we analyzed the domestic and international research status about impacts of global change on marine ecosystems by bibliometrics, briefly introduced the history of the research on marine ecosystems under global change, and reviewed the main progress in studies about the effects of global change on key processes of marine primary production, focusing on the impacts of ocean warming, ocean acidification, and eutrophication and hypoxia. We also summarized the major issues in current studies and proposed future research directions in the field.