Effects of climate and forest age on the ecosystem carbon exchange of afforestation

Afforestation is believed to be an effective practice to reduce global warming by sequestering large amounts of carbon in plant biomass and soil.However,the factors that determine the rate of carbon sequestration with afforestation are still poorly understood.We analyzed ecosystem carbon exchange after afforestation based on eddy covariance measurements with the aim to identify factors responsible for the rate of carbon exchange following afforestation.The results indicated that afforestation in the tropical/subtropical and temperate climate zones had greater capacities for carbon sequestration than those in boreal zones.Net ecosystem production(NEP),gross primary production(GPP)and ecosystem respiration(RE)varied greatly with age groups over time.Specifically,NEP was initially less than zero in the\10 year group and then increased to its peak in the 10-20 year group.Afforestation of varied previous land use types and planting of diverse tree species did not result in different carbon fluxes.The general linear model showed that climate zone and age of afforestation were the dominant factors influencing carbon sequestration.These factors jointly controlled 51%,61%and 63%of the variation in NEP,GPP and RE,respectively.Compared to the strong regulation of climate on GPP and RE,NEP showed greater sensitivity to the age of afforestation.These results increase our understanding of the variation in ecosystem carbon exchange of afforestation and suggest that afforestation in subtropical and temperate areas after 20 years would yield greater carbon sink benefits than would afforestation of boreal regions.

Moving toward a new era of ecosystem science

Ecosystem is a fundamental organizational unit of the biosphere in which biological communities interact with their non-biological environment through energy flows and material cycles.Ecosystem science is the study of patterns,processes,and services of ecosystems.Since the 1990s,rising concerns regarding global climate change,biodiversity loss,ecosystem degradation,and sustainability of the human-dominated biosphere have stimulated the growth of ecosystem science,which is expected to provide systematic solutions to many of these major issues facing human societies.This paper provides a comprehensive review of the current progress in ecosystem science and identifies some key research challenges facing this discipline.We demonstrate that a key feature of the current progress in ecosystem science is its evolution from primarily theoretical explorations toward more systematic,integrative and application-oriented studies.Specifically,five major changes in the discipline over the past several decades can be identified.These include:(1)the expansion of the primary goal from understanding nature to include human activities;(2)the broadening of the research focus from single ecosystem types to macro-ecosystems comprising multiple regional ecosystems;(3)the shifting of research methods from small-scale observations and experiments to large-scale observations,network experiments,and model simulations;(4)the increasing attention to comprehensive integration of ecosystem components,processes,and scales;and(5)the shifting from a primarily biology-oriented focus to an integrated multi-disciplinary scientific field.While ecosystem science still faces many challenges in the future,these directional changes,along with the rapidly enriched research tools and data acquisition capabilities,lay a promising ground for the discipline’s future as a fundamental scientific basis for solving many environmental challenges facing human societies.

中国碳收支:1980~2021年

As one of the world's largest emitters of greenhouse gases,China has set itself the ambitious goal of achieving carbon peaking and carbon neutrality.Therefore,it is crucial to quantify the magnitude and trend of sources and sinks of atmospheric carbon dioxide(CO_(2)),and to monitor China's progress toward these goals.Using state-of-the-art datasets and models,this study comprehensively estimated the anthropogenic CO_(2)emissions from energy,industrial processes and product use,and waste along with natural sources and sinks of CO_(2)for all of China during 1980-2021.To recognize the differences among various methods of estimating greenhouse emissions,the estimates are compared with China's National Greenhouse Gas Inventories(NGHGIs)for 1994,2005,2010,2012,and 2014.Anthropogenic CO_(2)emissions in China have increased by 7.39 times from 1980 to 12.77 Gt CO_(2)a^(-1)in 2021.While benefiting from ecological projects(e.g.,Three Norths Shelter Forest System Project),the land carbon sink in China has reached 1.65 Gt CO_(2)a^(-1)averaged through 2010-2021,which is almost 15.81 times that of the carbon sink in the 1980s.On average,China's terrestrial ecosystems offset 14.69%±2.49%of anthropogenic CO_(2)emissions through 2010-2021.Two provincial-level administrative regions of China,Xizang and Qinghai,have achieved carbon neutrality according to our estimates,but nearly half of the administrative regions of China have terrestrial carbon sink offsets of less than 10%of anthropogenic CO_(2)emissions.This study indicated a high level of consistency between NGHGIs and various datasets used for estimating fossil CO_(2)emissions,but found notable differences for land carbon sinks.Future estimates of the terrestrial carbon sinks of NGHGIs urgently need to be verified with process-based models which integrate the comprehensive carbon cycle processes.

Achieving accurate regional carbon-sink accounting and its significance for “missing” carbon sinks

In the 2019 revision of the IPCC’s 2006 national inventory guidelines,the atmospheric inversion of greenhouse gas(GHG)emissions based on atmospheric concentrations was proposed for the first time to better support inventory verifi-cation initiatives.Thus,a globally unified verification reference standard was formulated,commonly known as the“top-down inversion”method.1 The characteristics of this method are its thorough coverage,strong timeliness,and low bias.The 2019 IPCC guideline’s“refinement”can effectively improve the accuracy and credibility of the bottom-up method that is currently being used to account for the carbon(C)source/sink status of various ecosystem types.It will be necessary to couple and synchronize atmospheric and ecological C processes to accurately calculate the status of ecosystem C sinks while also reducing errors introduced by anthropogenic-based emission uncertainties.

Ecosystem quality-based management and the development of a new eco-friendly economy

(The Innovation 4,100491;September 11,2023)In Figure 1 of this commentary as originally published,the labels“Technological system”and“Industry system”should have been interchanged.Figure 1 has now been corrected online.The authors regret this error and any confusion that may have resulted.

Dynamic carbon-nitrogen coupling under global change

Carbon-nitrogen coupling is a fundamental principle in ecosystem ecology.However,how the coupling responds to global change has not yet been examined.Through a comprehensive and systematic literature review,we assessed how the dynamics of carbon processes change with increasing nitrogen input and how nitrogen processes change with increasing carbon input under global change.Our review shows that nitrogen input to the ecosystem mostly stimulates plant primary productivity but inconsistently decreases microbial activities or increases soil carbon sequestration,with nitrogen leaching and nitrogenous gas emission rapidly increasing.Nitrogen fixation increases and nitrogen leaching decreases to improve soil nitrogen availability and support plant growth and ecosystem carbon sequestration under elevated CO_(2)and temperature or along ecosystem succession.We conclude that soil nitrogen cycle processes continually adjust to change in response to either overload under nitrogen addition or deficiency under CO_(2)enrichment and ecosystem succession to couple with carbon cycling.Indeed,processes of both carbon and nitrogen cycles continually adjust under global change,leading to dynamic coupling in carbon and nitrogen cycles.The dynamic coupling framework reconciles previous debates on the“uncoupling”or“decoupling”of ecosystem carbon and nitrogen cycles under global change.Ecosystem models failing to simulate these dynamic adjustments cannot simulate carbonnitrogen coupling nor predict ecosystem carbon sequestration well.

China's current forest age structure will lead to weakened carbon sinks in the near future

Forests are chiefly responsible for the terrestrial carbon sink that greatly re duces the buildup of CO_(2)concentrations in the atmosphere and alleviates climate change.Current predictions of terrestrial carbon sinks in the future have so far ignored the variation of forest carbon uptake with forest age.Here,we predict the role of China's current forest age in future carbon sink capacity by generating a high-resolution(30 m)forest age map in 2019 over China's landmass using satellite and forest inventory data and deriving forest growth curves using measurements of forest biomass and age in 3,121 plots.As China's forests currently have large proportions of young and middle-age stands,we project that China's forests will maintain high growth rates for about 15 years.However,as the forests grow older,their net primary productivity will decline by 5.0%±1.4%in 2050,8.4%±1.6%in 2060,and 16.6%±2.8%in 2100,indicating weakened carbon sinks in the near future.The weakening of forest carbon sinks can be potentially mitigated by optimizing forest age structure through selective logging and implementing new or improved afforestation.This finding is important not only for the global carbon cycle and climate projections but also for developing forest management strategies to enhance land sinks by alleviating the age effect.

青藏高原植被结构变化反映环境变迁

草地植被结构对于其生产和生态功能至关重要,但大尺度信息严重匮乏.本研究结合多源遥感数据和深度学习,在区域尺度上厘清了青藏高原高寒草地基于群系的植物群落结构空间格局,并比较了其历史变化.过去40年,高寒草甸在高寒草地中的比例从50%上升到69%,反映了变暖变湿的环境变化.此外,高寒草甸和高寒草原中高山嵩草草甸和紫花针茅草原的优势度分别增强到76%和92%.其中,气候因子驱动了紫花针茅草原近些年的分布;高山嵩草草甸近些年的分布则并非完全由气候驱动,人类活动可能起重要作用.本研究首次探索了区域尺度植被结构特征与历史变化,为认识青藏高原草地变化的驱动力及其空间异质性提供了新视角.

Ecosystem quality-based management and the development of a new eco-friendly economy

A harmonious“nature–society–economy”system can improve human welfare if ecological products are valued and an ecologically self-aware economy is created.Natural ecosystems provide abundant,high-quality ecological products,as well as stable and sustainable ecological services for the Earth’s life support system.Maintaining healthy,functional environments can facilitate the survival and development of human societies.1 In the previous era of agricultural civilization,agricultural products and handicrafts were the main commodities,and the agricultural economy determined socioeconomic development.Since the Industrial Revolution,the production,circulation,trade,and application of products related to industry,including machines,steel,and coal,have resulted in the agricultural economy gradually being replaced with the industrial economy.With information technology development,electronic products and e-commerce,as well as other new economic products and relationships,have become the most important part of the social economy.However,traditional industrial production and industrial economic development are impacted by limited resources and strict environmental protections.

Spatio-temporal patterns of forest carbon dioxide exchange based on global eddy covariance measurements

Spatio-temporal patterns and driving mechanisms of forest carbon dioxide (CO2) exchange are the key issues on terrestrial ecosystem carbon cycles, which are the basis for developing and validating ecosystem carbon cycle models, assessing and predicting the role of forests in global carbon balance. Eddy covariance (EC) technique, an important method for measuring energy and material exchanges between terrestrial ecosystems and the atmosphere, has made a great contribution to understanding CO2 exchanges in the biosphere during the past decade. Here, we synthesized published EC flux measurements at various forest sites in the global network of eddy flux tower sites (FLUXNET) and regional flux networks. Our objective was to explore spatio-temporal patterns and driving factors on forest carbon fluxes, i.e. net ecosystem productivity (NEP), gross primary productivity (GPP) and total ecosystem respiration (TER). Globally, forest NEP exhibited a significant latitudinal pattern jointly controlled by GPP and TER. The NEP decreased in an order of warm temperate forest > cold temperate and tropical rain forests > boreal and subalpine forests. Mean annual temperature (MAT) made a greater contribution to forest carbon fluxes than sum of annual precipitation (SAP). As MAT increased, the GPP increased linearly, whereas the TER increased exponentially, resulting in the NEP decreasing beyond an MAT threshold of 20°C. The GPP, TER and NEP varied substantially when the SAP was less than 1500 mm, but tended to increase with increasing SAP. Temporal dynamics in forest carbon fluxes and determinants depended upon time scales. NEP showed a significant interannual variability mainly driven by climate fluctuations and different responses of the GPP and TER to environmental forcing. In a longer term, forest carbon fluxes had a significant age effect. The ecosystem was a net carbon source right after clearcutting, gradually switched to a net carbon sink when the relative stand age (i.e. ratio of actual stand age to the stand rotation age) approached 0.3, and maximized carbon sequestration capacity at premature or mature stand stages. This temporal pattern of NEP was correlated with stand leaf area index and associated GPP. This study highlights the significance of spatio-temporal dynamics in the CO2 exchange in forest carbon cycling studies. It is also suggested that in addition to forest biomes, interannual variations and stand age effects of forest carbon fluxes should be considered in the global carbon balance.

2010~2060年中国森林碳汇的时空动态及其调控策略

造林是陆地生态系统吸收二氧化碳和增加碳汇最有效和生态友好的方式.本文假定在适宜造林土地上造林的条件下,利用森林固碳(FCS)模型和中国区域内3365块森林样地的调查数据,估算了中国现存森林和新造林2010~2060年在3种造林情景和3种气候情景下的固碳速率(CSR).在不考虑极端事件和人为干扰的情况下,中国森林生态系统的平均CSR为0.358±0.016 Pg C a^(-1),植被和土壤碳库的CSR分别为0.211±0.016和0.147±0.005 Pg C a^(-1).现存森林约占整体CSR的93.5%,在2035年前后达到峰值,2035年以后总体呈下降趋势.2035年以后,需要有效的抚育管理来维持较高的CSR,如择伐、间伐等;而新造林在整体CSR增长中发挥很小的作用.总体来看,CSR在东北、西南和中南地区较高,在西北地区较低.2010~2060年期间,中国森林通过固碳可以抵消14.1%的人为碳排放.但是,要达到森林预期的固碳潜力,需要国家实施有效的现存森林管理策略和制定合适的造林政策.

Primary estimation of Chinese terrestrial carbon sequestration during 2001-2010

在重新审视生态系统生产力概念体系的基础上,将中国的陆地区域假设为一个大尺度的生物-社会群区生态系统,采用不同时空尺度多源数据的整合分析方法,定量评估了中国区域陆地生态系统生产力及其在各种生态过程中的分配和消耗量,进而分析评价了中国区域陆地生态系统潜在的碳源/汇强度.统计分析结果表明,中国区域的陆地生态系统具有较高的碳吸收能力,该研究结果可以为中国区域陆地碳收支现状和增汇潜力的评估分析提供参考信息,也可作为中国区域碳管理决策分析的重要依据.

Integrative ecology in the era of big data——From observation to prediction

Most ecological and environmental issues faced by human society can only be solved at the ecosystem,watershed,regional and even global scale.Thus,ecological research is developing rapidly towards macro-scale studies.With the rapid development of observational networks and information technology,the spaceborne-aircraft-ground based observation system is becoming an important feature of ecosystem monitoring in the new era.With the gradual formation of the global new-generation observational systems and the rapid expansion of massive multi-source heterogeneous data,ecology has entered the era of big data,big science,and big theory.How to integrate ecological big data,discover valuable ecological laws and mechanisms,and further expand them to solve eco-environmental issues that closely relate to human development are the major opportunities and challenges in this field.In this paper,we systematically summarized the research progresses in ecological big data,reviewed the opportunity and demand of integrative ecology,and further discussed the main approaches of ecological big data integration by using meta-analysis,data mining,and data-model fusion.Finally,we proposed the prospects and research directions of integrative ecology and suggested that future researches need to integrate big data into land models so as to improve the accuracy of ecological forecasting.It can be foreseen that under the background of global change and the rapid development of big data in the future,integrative ecology will be extensively applied and developed to serve the sustainable development of human society.

Grazing alters environmental control mechanisms of evapotranspiration in an alpine meadow of the tibetan Plateau

Aims Evapotranspiration(Et)is an important component of the terrestrial water cycle and is easily affected by external disturbances,such as climate change and grazing.Identifying Et responses to grazing is instructive for determining grazing activity and informative for understanding the water cycle.Methods this study utilized 2 years(2014 and 2017)of eddy covariance data to test how grazing regulated Et for an alpine meadow ecosystem on the tibetan Plateau(tP)by path analysis.Important Findings Radiation dominated Et with a decision coefficient of 64-74%.the soil water content(SWc)worked as the limiting factor in the fenced site.However,in the grazing site,the limiting factor was the vapor pressure deficit(VPD).Grazing had large effects on Et because it greatly affected the water conditions.the SWc and VPD were enhanced by 14.63%and 4.36%in the grazing site,respectively.therefore,sufficient water was supplied to Et,especially during drought,and strengthened the transpiration pull.As a result,a favorable micrometeorological environment was created for Et.Grazing shifted the limiting factor of Et from the SWc to VPD,which weakened the limiting effect of the water conditions on Et and advanced the Et peak time.In addition,grazing altered the compositions of Et by changing the community structure,which directly resulted in an increased Et.In summary,grazing enhanced Et through altering the community structure and micrometeorological environments.the findings of this study further improve our understanding of the driving mechanisms of grazing on Et and will improve our predictions for the global water cycle.

Towards a paradigm for open and free sharing of scientific data on global change science in China

Despite great progress in data sharing that has been made in China in recent decades,cultural,policy,and technological challenges have prevented Chinese researchers from maximizing the availability of their data to the global change science community.To achieve full and open exchange and sharing of scientific data,Chinese research funding agencies need to recognize that preserva-tion of,and access to,digital data are central to their mission,and must support these tasks accord-ingly.The Chinese government also needs to develop better mechanisms,incentives,and rewards,while scientists need to change their behavior and culture to recognize the need to maximize the usefulness of their data to society as well as to other researchers.The Chinese research communi-ty and individual researchers should think globally and act personally to promote a paradigm of open,free,and timely data sharing,and to increase the effectiveness of knowledge development.

Fate of river‐transported carbon in china:implications for carbon cycling in coastal ecosystems

Rivers play an important role in carbon(C)exchange between terrestrial and oceanic water bodies and the atmosphere.The aim of this study was to systematically quantify fluxes in riverine C export and C exchange in the air-sea interface of marine ecosystems in China.Results show that annual C transport from rivers to coastal ecosystems in China can reach up to 64.35 TgC,which accounts for approximately 4.8%-8.1%of global C transport from river systems.In the Bohai Sea,particulate inorganic carbon is the main form of C influx,and it can reach up to 20.79 TgC/yr.Conversely,dissolved inorganic carbon is the main form of C influx into the East China Sea,and it can reach up to 10.52 TgC/yr,which is 42.6%of the total annual C imported into the East China Sea.China’s marine ecosystems including the Yellow Sea,the Bohai Sea,the East China Sea,and the South China Sea can absorb 65.06 TgC/yr from the atmosphere.

Climate warming increases biodiversity of small rodents by favoring rare or less abundant species in a grassland ecosystem

Our Earth is facing the challenge of accelerating climate change,which imposes a great threat to biodiversity.Many published studies suggest that climate warming may cause a dramatic decline in biodiversity,especially in colder and drier regions.In this study,we investigated the effects of temperature,precipitation and a normalized difference vegetation index on biodiversity indices of rodent communities in the current or previous year for both detrended and nondetrended data in semi-arid grassland of Inner Mongolia during 1982-2006.Our results demonstrate that temperature showed predominantly positive effects on the biodiversity of small rodents;precipitation showed both positive and negative effects;a normalized difference vegetation index showed positive effects;and cross-correlation function values between rodent abundance and temperature were negatively correlated with rodent abundance.Our results suggest that recent climate warming increased the biodiversity of small rodents by providing more benefits to population growth of rare or less abundant species than that of more abundant species in Inner Mongolia grassland,which does not support the popular view that global warming would decrease biodiversity in colder and drier regions.We hypothesized that higher temperatures might benefit rare or less abundant species(with smaller populations and more folivorous diets)by reducing the probability of local extinction and/or by increasing herbaceous food resources.

Divergent apparent temperature sensitivity of terrestrial ecosystem respiration

Aims Recent studies revealed convergent temperature sensitivity of ecosys-tem respiration(Re)within aquatic ecosystems and between terrestrial and aquatic ecosystems.We do not know yet whether various terres-trial ecosystems have consistent or divergent temperature sensitivity.Here,we synthesized 163 eddy covariance flux sites across the world and examined the global variation of the apparent activation energy(Ea),which characterizes the apparent temperature sensitivity of and its interannual variability(IAV)as well as their controlling factors.Methods We used carbon fluxes and meteorological data across FLUXNET sites to calculate mean annual temperature,tempera-ture range,precipitation,global radiation,potential radiation,gross primary productivity and Re by averaging the daily values over the years in each site.Furthermore,we analyzed the sites with>8 years data to examine the IAV of Ea and calculated the standard deviation of Ea across years at each site to character-ize IAV.Important Findings The results showed a widely global variation of Ea,with significantly lower values in the tropical and subtropical areas than in temperate and boreal areas,and significantly higher values in grasslands and wetlands than that in deciduous broadleaf forests and evergreen for-ests.Globally,spatial variations of Ea were explained by changes in temperature and an index of water availability with differing contribution of each explaining variable among climate zones and biomes.IAV and the corresponding coefficient of variation of Ea decreased with increasing latitude,but increased with radiation and corresponding mean annual temperature.The revealed patterns in the spatial and temporal variations of Ea and its controlling factors indicate divergent temperature sensitivity of Re,which could help to improve our predictive understanding of Re in response to climate change.

干旱条件下蒸散变异由气象因子主控转变为生物因子主控

青藏高原被称为中国水塔,其蒸散(evapotranspiration,ET)影响着青藏高原的水分平衡及高寒草甸生态系统的稳定性。然而,全球变化进程对青藏高原蒸散的变异及其控制机制的影响尚不明晰。因此,本研究旨在明晰不同水分条件下,青藏高原高寒草甸生态系统蒸散变异受气象因子主控亦或是受生物因子主控。基于6年(2013-2018)的碳通量与气象因子和生物因子数据,采用线性扰动分析法量化了各气象因子和生物因子对蒸散变异的贡献。研究结果表明,在湿润年的生长旺季(7-8月),气象因子主控蒸散的变异。能量供应的不足限制了蒸散,因此净辐射和温度主控了蒸散的变异。在干旱年的生长旺季,蒸散变异由气象因子主控转变为生物因子主控,蒸散变异主要受到冠层导度和叶面积指数的控制。此时,生态系统受水分限制。本研究为深入研究不同水分条件下气象和生物因子如何控制蒸散变异提供了经验:有助于深刻理解水循环过程,可为未来气候变化条件下有效管理高寒草甸生态系统水资源提供理论基础。

Lagged climatic effects on carbon fluxes over three grassland ecosystems in China

Aims The plasticity of ecosystem responses could buffer and post-pone the effects of climates on ecosystem carbon fluxes,but this lagged effect is often ignored.In this study,we used carbon flux data collected from three typical grassland ecosystems in China,including a temperate semiarid steppe in Inner mongolia(Neimeng site,Nm),an alpine shrub-meadow in Qinghai(Haibei site,Hb)and an alpine meadow steppe in Tibet(Dangxiong site,DX),to examine the time lagged effects of environmental factors on CO_(2) exchange.Methods Eddy covariance data were collected from three typical Chinese grasslands.In linking carbon fluxes with climatic factors,we used their averages or cumulative values within each 12-month period and we called them‘yearly’statistics in this study.To investigate the lagged effects of the climatic factors on the car-bon fluxes,the climatic‘yearly’statistics were kept still and the‘yearly’statistics of the carbon fluxes were shifted backward 1 month at a time.Important Findingssoil moisture and precipitation was the main factor driving the annual variations of carbon fluxes at the alpine Hb and DX,respectively,while the Nm site was under a synthetic impact of each climatic factor.The time lagged effect analysis showed that temperature had several months,even half a year lag effects on Co2 exchange at the three studied sites,while moisture’s effects were mostly exhibited as an immediate manner,except at Nm.In general,the lagged climatic effects were relatively weak for the alpine ecosystem.our results implied that it might be months or even 1 year before the variations of ecosystem carbon fluxes are adjusted to the current climate,so such lag effects could be resistant to more frequent climate extremes and should be a critical component to be considered in evaluating ecosystem stability.an improved knowledge on the lag effects could advance our understanding on the driving mechanisms of climate change effects on ecosystem carbon fluxes.