Impact of priming on global soil carbon stocks

Fresh carbon input (above and belowground) contributes to soil carbon sequestration, but also accelerates decomposition of soil organic matter through biological priming mechanisms. Currently, poor understanding precludes the incorporation of these priming mechanisms into the global carbon models used for future projections. Here, we show that priming can be incorporated based on a simple equation calibrated from incubation and verified against independent litter manipulation experiments in the global land surface model, ORCHIDEE. When incorporated into ORCHIDEE, priming improved the model's representation of global soil carbon stocks and decreased soil carbon sequestration by 51% (12 ± 3 Pg C) during the period 1901–2010. Future projections with the same model across the range of CO₂ and climate changes defined by the IPCC‐RCP scenarios reveal that priming buffers the projected changes in soil carbon stocks — both the increases due to enhanced productivity and new input to the soil, and the decreases due to warming‐induced accelerated decomposition. Including priming in Earth system models leads to different projections of soil carbon changes, which are challenging to verify at large spatial scales.     

Dynamic disequilibrium of the terrestrial carbon cycle under global change

In this review, we propose a new framework, dynamic disequilibrium of the carbon cycles, to assess future land carbon-sink dynamics. The framework recognizes internal ecosystem processes that drive the carbon cycle toward equilibrium, such as donor pool-dominated transfer; and external forces that create disequilibrium, such as disturbances and global change. Dynamic disequilibrium within one disturbance-recovery episode causes temporal changes in the carbon source and sink at yearly and decadal scales, but has no impacts on longer-term carbon sequestration unless disturbance regimes shift. Such shifts can result in long-term regional carbon loss or gain and be quantified by stochastic statistics for use in prognostic modeling. If the regime shifts result in ecosystem state changes in regions with large carbon reserves at risk, the global carbon cycle might be destabilized.     

全球和生物群系尺度土壤有机碳分布控制因子及其分异规律

土壤有机碳(SOC)是陆地生态系统碳库的核心组成部分,其动态平衡受气候、土壤、植被、地形及人类活动等的影响,但在不同的空间尺度上,这些影响因素的相对重要性和差异还不明确。为阐明不同尺度和不同土层深度土壤有机碳密度(SOCd,kg/m³土壤)的环境影响因子差异,选用全球113571个土壤剖面SOCd测量数据以及38个环境协变量数据,利用数据挖掘方法,分析了全球尺度和生物群系尺度不同土层深度SOCd的控制因子,并量化了空间自相关对相关结果的影响。研究结果表明:仅空间自相关就能解释全球尺度不同土壤深度13%-20%的SOCd空间变异,但是随土壤深度的增加,空间自相关的解释率降低。在剔除空间自相关的影响后,分析结果表明:全球尺度上,气候因素对SOCd空间变异的解释率最高,但只能解释17%-20%,这种解释率在不同土层之间没有显著差异。在生物群系尺度上,除北方森林地区,气候因素能够解释SOCd空间变异的24%-37%;而在北方森林地区,地形是影响SOCd空间变异的重要因素,对SOCd的解释率为21%-43%。这些结果表明,SOCd的控制因子在不同的尺度上明显不同。无论是在全球尺度上,还是生物群系尺度上,如果不考虑空间自相关,地形的影响会被低估,其他环境因素的影响被严重高估。为了准确计算全球与生物群系尺度上各土层SOCd分布的控制因子及其分异情况,空间自相关必须被考虑。     

农田土壤固碳措施的温室气体泄漏和净减排潜力

农田土壤固碳措施作为京都议定书认可的大气CO2减排途径受到了广泛关注.研究表明,农田土壤固碳措施在主要农业国家和全球都具有很大的固碳潜力.但是,实施农田土壤固碳措施有可能影响农业中化石燃料消耗和其他农业投入的CO2排放和非CO2温室气体排放.这些土壤碳库以外的温室气体排放变化可能抵消部分甚至全部土壤固碳效果,构成了农田土壤固碳措施的温室气体泄漏.因此,将土壤固碳和温室气体泄漏综合计算的净减排潜力成为了判定土壤固碳措施可行性的首要标准.综述总结了目前较受重视的一些农田措施(包括施用化学氮肥、免耕和保护性耕作、灌溉、秸秆还田、施用禽畜粪便以及污灌)的土壤固碳潜力,温室气体泄漏和净减排潜力研究成果.结果表明,温室气体泄漏可抵消以上措施土壤固碳效益的-241%～660%.建议在今后的研究中,应该关注土壤碳饱和、气候变化及土地利用变化对农田固碳措施温室气体泄漏和净减排潜力的评估结果的影响.     

Role of vegetation in determining carbon sequestration along ecological succession in the southeastern United States

Vegetation plays a central role in controlling terrestrial carbon (C) exchange, but quantifying its impacts on C cycling on time scales of ecological succession is hindered by a lack of long‐term observations. The net ecosystem exchange of carbon (NEE) was measured for several years in adjacent ecosystems that represent distinct phases of ecological succession in the southeastern USA. The experiment was designed to isolate the role of vegetation – apart from climate and soils – in controlling biosphere–atmosphere fluxes of CO₂ and water vapor. NEE was near zero over 5 years at an early successional old‐field ecosystem (OF). However, mean annual NEE was nearly equal, approximately ?450 g C m^?2 yr^?1, at an early successional planted pine forest (PP) and a late successional hardwood forest (HW) due to the sensitivity of the former to drought and ice storm damage. We hypothesize that these observations can be explained by the relationships between gross ecosystem productivity (GEP), ecosystem respiration (RE) and canopy conductance, and long‐term shifts in ecosystem physiology in response to climate to maintain near‐constant ecosystem‐level water‐use efficiency (EWUE). Data support our hypotheses, but future research should examine if GEP and RE are causally related or merely controlled by similar drivers. At successional time scales, GEP and RE observations generally followed predictions from E. P. Odum's ‘Strategy of Ecosystem Development’, with the surprising exception that the relationship between GEP and RE resulted in large NEE at the late successional HW. A practical consequence of this research suggests that plantation forestry may confer no net benefit over the conservation of mature forests for C sequestration.     

Variation in ecosystem carbon dynamics of saltwater marshes in the northern Gulf of Mexico

Wetlands are highly productive ecosystems that can sequester large quantities of carbon. However, variation in physiological potential can alter their capacity to sequester carbon. To examine variation in ecosystem physiological capacity, we established three coastal marsh sites in Mississippi and Alabama spanning a productivity gradient. Over 1 year, we measured ecophysiological activity and spectral indices in two vegetation zones within each marsh to develop a better understanding of variation in ecosystem responses and health. Gross ecosystem exchange of carbon and ecosystem respiration rates (R_eco) differed significantly among sites, with the highest activity at Grand Bay, Mississippi and Point Aux Pines, Alabama and lower ecophysiological activity at Dauphin Island, Alabama. Net ecosystem exchange was similar for all three study areas because greater carbon assimilation was negated by higher levels of respiration. Spectral indices and leaf area were significantly different by marsh vegetation zone, suggesting that alterations in species composition and plant productivity can have important implications for carbon sequestration. While limited to 1 year, this study establishes a foundation by which to evaluate future research conducted over greater temporal and spatial scales, thereby enhancing our understanding of marsh physiological activity.     

我国植被生态系统固碳能力提升潜力空间格局研究

通过植被的光合作用对大气中的CO₂进行收集与捕捉是当前实现“碳中和”目标的重要手段,目前的研究大多是聚焦于当前植被的固碳能力的强弱,而对于当下植被固碳能力提升潜力大小的研究相对较少。为此,基于1982—2017年全球陆表特征参量-植被净初级生产力(GLASS NPP)产品以及Miami模型分别构建遥感观测和气候模型模拟的全国NPP潜在最大值空间分布结果,通过与2017年实际监测的NPP进行比较,计算得到两种不同的全国植被固碳能力提升潜力结果,分别进行空间特征分析,并对比两者冷热点区域空间分布的差异性,最后与我国目前规划的重点生态功能区进行叠加对比,得出以下主要结论：(1)两种方法得到的全国固碳能力提升潜力空间分布整体趋势均表现为“南高北低”,且空间分布特征呈现出高度空间自相关特性(空间正相关性,表现为“高高聚集”“低低聚集”),但局部差异较大。(2)基于遥感观测为最大潜力值的方法所得到的全国固碳能力提升潜力热点区集中在三个区域,分别分布在四川省、广东省、浙江省以及江苏省境内。基于气候模型模拟为最大潜力值的方法所得到的固碳能力提升潜力热点区域主要分布在以江西省、广东...     

基于CASA模型的长江口崇明东滩湿地植被净初级生产力与固碳潜力

湿地生态系统具有很强的储碳、固碳能力,在全球碳循环中占有重要地位.为了解盐沼的固碳能力,以崇明东滩南部典型盐沼潮沟体系为对象,结合实验观测与遥感影像解译,估算了盐沼湿地的净初级生产力,并探讨了环境变化下盐沼湿地固碳潜力的变化.结果 表明:盐沼植物净初级生产力表现出显著的时空差异,时间差异体现在年际和季节差异,即2013...     

Exogenous carbon turnover within the soil food web strengthens soil carbon sequestration through microbial necromass accumulation

Exogenous carbon turnover within soil food web is important in determining the trade-offs between soil organic carbon (SOC) storage and carbon emission. However, it remains largely unknown how soil food web influences carbon sequestration through mediating the dual roles of microbes as decomposers and contributors, hindering our ability to develop policies for soil carbon management. Here, we conducted a ¹³C-labeled straw experiment to demonstrate how soil food web regulated the residing microbes to influence the soil carbon transformation and stabilization process after 11 years of no-tillage. Our work demonstrated that soil fauna, as a “temporary storage container,” indirectly influenced the SOC transformation processes and mediated the SOC sequestration through feeding on soil microbes. Soil biota communities acted as both drivers of and contributors to SOC cycling, with 32.0% of exogenous carbon being stabilizing in the form of microbial necromass as “new” carbon. Additionally, the proportion of mineral-associated organic carbon and particulate organic carbon showed that the “renewal effect” driven by the soil food web promoted the SOC to be more stable. Our study clearly illustrated that soil food web regulated the turnover of exogenous carbon inputs by and mediated soil carbon sequestration through microbial necromass accumulation.     

秦岭山地碳中和空间服务范围及其模拟预测

在当前碳中和背景下,秦岭山地碳中和的量化及其空间服务范围的测算对于碳中和合理规划和快速实现具有重要意义。采用IUEMS （Intelligent Urban Ecosystem Management System）系统对秦岭山地的固碳量进行核算,利用DMSP/OLS （Defense Meteorological Satellite Program/Operational Linescan System）和NPP-VIIRS （Net Primary Productivity-Visible infrared Imaging Radiometer）夜间灯光数据和各地市的能源消耗数据通过模型拟合对秦岭山地碳排放量进行空间量化,基于固碳量和碳排放量得到秦岭山地空间碳中和量。利用PLUS （Patch-generating Land Use Simulation Model）模型模拟了2030和2050年的碳中和空间分布,结合常见气体扩散系数计算得到常温常压下秦岭山地碳中和对周边区域的服务范围。结果表明：2000-2020年秦岭山地固碳量呈现上升的趋势,大部分区域不同时间尺度上的固碳速率呈正向趋势,空间上秦岭山地中西部区域固碳量整体较大;对秦岭固碳量影响较大的地形特征为海拔1200m左右、斜坡、半阳坡和半阴坡;研究区内碳排放量空间上整体较低,碳排放低值区面积占到了秦岭总面积的90%,碳排放较大区域主要位于秦岭北坡的城区区域,时间上碳排放量最大值为先增加后减少的变化趋势;2000-2050年秦岭山地碳汇服务范围为174-262.63km,服务范围在空间上呈逐渐扩大趋势,2030年后其扩大程度将略有减少。     

Changes in soil heterotrophic respiration,carbon availability,and microbial function in seven forests along a climate gradient

Soil microbial communities play an essential role in soil carbon (C) emission and C sequestration in forest ecosystems. However, little information is available regarding the relationship between soil C dynamics and microbial substrate utilization at large scales. Along the North–South Transect of Eastern China (NSTEC), seven forests representative of boreal, temperate and tropical biomes were examined. Soil heterotrophic respiration (R_h), soil dissolved organic C (DOC), microbial biomass C (MBC), and microbial community-level physiological profiles (CLPPs) were investigated using biochemical measurements, static chamber-gas chromatography analysis, and Biolog-Eco microplates, respectively. We found that soil R_h rates were significantly higher in subtropical and boreal forests than in temperate forests. Conversely, the concentrations of soil DOC and MBC, as well as microbial metabolic activity and functional diversity, were consistently higher in temperate forests than in subtropical forests. There were considerably different substrate utilization profiles among the boreal, temperate, and subtropical forests. Soil microorganisms from the temperate and boreal forests mainly metabolized high-energy substrates, while those from the subtropical forests used all substrates equally. In addition, soil R_h rates were significantly and negatively related to soil labile C concentrations, total metabolic activity, and the intensity of individual substrate utilization, indicating that soil microbes assimilated more soil substrates, thereby reducing CO₂ emissions. Overall, our study suggests that climate factors, as well as substrate availability, dominate the activities and functions of soil microbes at large scales.     

基于文献计量的居民食物消费碳排放研究进展及发展态势

食物是人类生存和发展的基础,然而城市化过程中食物消费产生的碳排放也影响着生态环境与人类福祉。双碳目标下,如何协调食物消费增长与低碳减排之间的矛盾,亟需从不同尺度制定绿色消费优化策略。基于此,从居民食物消费碳排放研究的发文态势、研究方法以及研究内容3个方面进行归纳和梳理。研究发现：①由居民食物消费引起的碳排放问题仍是未来学术界的研究热点之一;②从生产端、消费端及系统视角3个方面对居民食物消费碳排放概念和内涵进行理解,有助于界定碳排放核算边界;③目前居民食物消费碳排放核算的主流测算方法包括生命周期评价（LCA）、碳排放系数、投入产出分析（IOA）和物质流分析（MFA）方法这4种;④从碳排放分布特征看,国内外学者从不同尺度（全球、国家、地区、省域、城市）、不同方式（直接与间接）、不同环节（生产与消费等）、不同消费结构（植物型与动物型）等多角度对其进行探讨;⑤从影响机制来看,基于多尺度时空融合视角量化分析居民食物消费碳排放作用机理这一科学问题值得关注。因此,综合考虑人口、社会、经济等多要素,同时考虑空间异质性,识别居民食物消费碳排放关键机制,构建面向双碳目标的碳减排潜力情景并揭示不同情景下的碳减排贡献,将有助于提出最优的居民生活绿色消费模式。     

Assessing the effect of climate change on carbon sequestration in a Mexican dry forest in the Yucatan Peninsula

Assessing the effect of climate change on carbon sequestration in tropical forest ecosystems is important to inform monitoring, reporting, and verification (MRV) for reducing deforestation and forest degradation (REDD), and to effectively assess forest management options under climate change. Two process-based models, Forest-DNDC and Biome-BGC, with different spatial modeling scales were evaluated to estimate the potential effect of climate change on carbon sequestration in a tropical dry semi-deciduous forest in the Yucatan Peninsula of Mexico. The results from the simulations using the two models show that carbon sequestration in this dry forest is highly sensitive to warming. Carbon uptake in this forest may increase or decrease slightly with a corresponding increase or decrease in precipitation; however, with an increase in temperature, carbon uptake may decrease significantly, showing that warming may be the main climate factor that impacts carbon storage in this tropical dry forest. Model performance evaluation indicates that both models may be used to estimate C stocks, but DNDC may be better than BGC for assessing the effect of climate change on C dynamics.     

气候变化背景下农林复合系统碳汇功能研究进展

农林复合系统作为一种土地综合利用体系,可以有效吸收和固定CO₂、增加碳储量,在达到收获目的的同时,可有力减轻温室效应.农林复合系统对CO₂的调控作用,使人们认识到农林复合系统较单一作物系统有着明显优势,因此,深入了解不同农林复合系统的碳汇功能及其影响因素,对全球碳循环研究及碳收支准确评估具有重要意义.本文综述了农林复合系统的概念与分类,探讨了农林复合系统不同组分的碳固存潜力及其影响因子,得出不同区域、不同类型农林复合系统内植被的固碳速率相差很大(0.59～11.08 t C·hm^-2·a^-1),其主要受到气候因子和农林复合系统自身特性(物种组成、林木密度和林龄)的影响.农林复合系统内土壤的固碳潜力受到系统内树木和非树木成分输入的生物量多少和质量、土壤质地、土壤结构的影响.不同地区的任何一个农林复合系统的碳储量多少主要依赖于复合系统中各组分的结构和功能.针对目前的研究现状,指出应重点加强农林复合系统优化结构的碳汇功能研究,以及加强农林复合系统碳储量的时空分布格局及其固碳机制的长期研究.     

Carbon isotopes in terrestrial ecosystem pools and CO2 fluxes

Stable carbon isotopes are used extensively to examine physiological, ecological, and biogeochemical processes related to ecosystem, regional, and global carbon cycles and provide information at a variety of temporal and spatial scales. Much is known about the processes that regulate the carbon isotopic composition (delta(13)C) of leaf, plant, and ecosystem carbon pools and of photosynthetic and respiratory carbon dioxide (CO(2)) fluxes. In this review, systematic patterns and mechanisms underlying variation in delta(13)C of plant and ecosystem carbon pools and fluxes are described. We examine the hypothesis that the delta(13)C of leaf biomass can be used as a reference point for other carbon pools and fluxes, which differ from the leaf in delta(13)C in a systematic fashion. Plant organs are typically enriched in (13)C relative to leaves, and most ecosystem pools and respiratory fluxes are enriched relative to sun leaves of dominant plants, with the notable exception of root respiration. Analysis of the chemical and isotopic composition of leaves and leaf respiration suggests that growth respiration has the potential to contribute substantially to the observed offset between the delta(13)C values of ecosystem respiration and the bulk leaf. We discuss the implications of systematic variations in delta(13)C of ecosystem pools and CO(2) fluxes for studies of carbon cycling within ecosystems, as well as for studies that use the delta(13)C of atmospheric CO(2) to diagnose changes in the terrestrial biosphere over annual to millennial time scales.     

杉木人工林不同深度土壤CO2通量

土壤CO₂通量具有明显的时间和空间变异性。土壤温度和含水量是影响土壤CO₂通量的重要因素,同时,不同深度的土壤CO₂通量对温度和含水量变化的响应差异较大,因此,研究土壤CO₂通量和影响因素随土壤深度的变化,对于准确评估土壤碳排放具有重要意义。选择福建三明杉木人工林(Cunninghamia lanceolata)作为研究对象,利用非散射红外CO₂浓度探头和Li-8100开路式土壤碳通量系统,并使用Fick扩散法计算了0-60cm深度土壤CO₂的通量,结果表明:(1)5种扩散模型计算的表层(5cm)CO₂通量与Li-8100测量结果均具有显著相关性(P<0.01),Moldrup气体扩散模型计算结果较好。(2)土壤CO₂浓度随深度的增加而升高,但60cm深度以下土壤CO₂浓度开始降低;不同深度土壤CO₂浓度的日变化均呈现单峰型;0-60cm土壤CO₂通量日通量均值变化范围为0.54-2.17μmol m^-2 s^-1;(3)指数拟合分析显示,5、10cm和60cm深度处土壤CO₂通量与温度具有显著相关性,Q₁₀值分别为1.35、2.01和4.95。不同深度土壤含水量与CO₂通量的相关性不显著。     

海洋生态系统固碳能力估算方法研究进展

气候变化受到全球关注,大气中CO2含量与气候变化息息相关。海洋是地球上最大的活跃碳库,在气候变化中扮演着举足轻重的作用。定量估算海洋中碳元素的吸收、转移、埋藏速率在全球碳循环及全球气候变化研究中有重要意义。目前,海洋固碳能力估算研究包括:利用海-气界面CO2分压差法估算海洋海-气界面CO2交换通量,根据海水中叶绿素含量建立的生态学数理模型法估算真光层浮游生物的初级生产力,234Th—238U不平衡法估算POC输出通量,210Pb定年法估算有机碳沉积通量。但迄今为止的研究工作尚有一定局限性,碳在大气—海水—沉积物3种介质间交换通量间相互影响的研究较少,海洋中碳垂直传输过程的主要影响因素和关键控制因子尚不明确,在海洋生态系统固碳能力估算方法方面国内外还没有统一的规范和标准。为进一步完善海洋生态系统固碳能力的估算方法,今后的工作应注重海洋固碳整套观测技术、分析和估算方法研究,并建立海洋碳汇估算指标体系、指标标准体系、以及评价标准体系,为我国的碳"减排"、"增汇"国家需求提供技术支持。     

海洋微型生物储碳过程与机制概论

在全球气候环境演变的背景下,认识海洋微型生物对碳循环的贡献,需要了解其过程和机制.最近提出的“微型生物碳泵”理论阐释了海洋储碳的一个新机制:微型生物活动把溶解有机碳从活性向惰性转化,从而构成了海洋储碳.这个过程当中,自养与异养细菌、病毒、原生动物等具有不同生理特性微型生物类群扮演着不同的生态角色,本文将围绕微型生物碳泵主线分别论述之.     

Carbon input to soil may decrease soil carbon content

It is commonly predicted that the intensity of primary production and soil carbon (C) content are positively linked. Paradoxically, many long‐term field observations show that although plant litter is incorporated to soil in large quantities, soil C content does not necessarily increase. These results suggest that a negative relationship between C input and soil C conservation exists. Here, we demonstrate in controlled conditions that the supply of fresh C may accelerate the decomposition of soil C and induce a negative C balance. We show that soil C losses increase when soil microbes are nutrient limited. Results highlight the need for a better understanding of microbial mechanisms involved in the complex relationship between C input and soil C sequestration. We conclude that energy available to soil microbes and microbial competition are important determinants of soil C decomposition.     

甘南地区二氧化碳施肥效应对生态系统的影响

陆地生态系统是全球第二大碳库,其碳收支一直是气候变化研究的热点领域,而研究二氧化碳（CO₂）施肥效应又是全球变化碳循环领域较为关注的前沿部分。CO₂与生态系统关系复杂,当前仍无法厘清CO₂对陆地生态系统碳循环的影响作用。基于太阳辐射数据、气温数据及归一化植被指数数据等,利用光能利用率遥感模型,模拟2019年甘南地区的碳循环,选取三个指标,即GPP （陆地生态系统总初级生产力）、NPP （净初级生产力）和NEP （净生态系统生产力）来分析甘南地区植被固碳的时空变化特征及CO₂施肥效应。结果表明：（1）甘南地区2019年植被固碳总量约为2611 tC。甘南地区生态系统GPP、NPP和NEP季节性特征明显,其值均在夏季达到最高;而在空间上,GPP、NPP表现为东高西低的特征,NEP呈现出北高南低的分布特征。（2） CO₂对GPP、NPP存在正向的施肥效应,分别增加了14.4%和14.3%;而对NEP具有负向反馈效应,使其减少了0.3%,并且CO₂对NEP的影响整体也表现为北高南低的特征。研究揭示出：虽然CO₂在提升GPP和NPP时,正向的施肥效应明显,但是对甘南地区的NEP,即固碳量来说,CO₂的影响却很有限。因此在研究CO₂施肥效应时不应一概而论,生态地理环境对其的影响不可忽视。研究可以为揭示陆地生态系统碳循环的动态机制提供一定的理论依据。