A global synthesis reveals biodiversity loss as a major driver of ecosystem change

Evidence is mounting that extinctions are altering key processes important to the productivity and sustainability of Earth's ecosystems. Further species loss will accelerate change in ecosystem processes, but it is unclear how these effects compare to the direct effects of other forms of environmental change that are both driving diversity loss and altering ecosystem function. Here we use a suite of meta-analyses of published data to show that the effects of species loss on productivity and decomposition--two processes important in all ecosystems--are of comparable magnitude to the effects of many other global environmental changes. In experiments, intermediate levels of species loss (21-40%) reduced plant production by 5-10%, comparable to previously documented effects of ultraviolet radiation and climate warming. Higher levels of extinction (41-60%) had effects rivalling those of ozone, acidification, elevated CO(2) and nutrient pollution. At intermediate levels, species loss generally had equal or greater effects on decomposition than did elevated CO(2) and nitrogen addition. The identity of species lost also had a large effect on changes in productivity and decomposition, generating a wide range of plausible outcomes for extinction. Despite the need for more studies on interactive effects of diversity loss and environmental changes, our analyses clearly show that the ecosystem consequences of local species loss are as quantitatively significant as the direct effects of several global change stressors that have mobilized major international concern and remediation efforts.     

森林土壤温室气体通量对森林管理和全球大气变化的响应

森林土壤是温室气体重要的源和汇。探讨不同森林管理和全球大气变化下土壤温室气体通量特征,为有效减少温室气体排放及森林可持续管理等提供参考。笔者从森林土壤温室气体(forest soil green house gases)、森林管理(forest mangement)和全球大气变化(global atmospheric change)3个关键研究点,查阅近年来相关研究成果,归纳森林管理和全球大气变化下土壤温室气体通量的一般性模式。CO₂、CH₄和N₂O是3种重要温室气体,其通量间存在协同、消长和随机型耦合关系。森林管理如火烧、采伐和造林等显著影响土壤温室气体通量。一般情况下,火烧导致土壤N₂O通量降低,CH₄吸收量增加,CO₂通量因火烧类型、火烧强度、生态系统类型不同出现增加、减低和无影响3种结果; 采伐通常导致土壤CO₂、CH₄和N₂O排放增加; 造林可使土壤CO₂排放减少,对N₂O和CH₄通量的影响随生态系统类型、造林树种等而改变。全球大气变化如CO₂浓度升高、氮沉降和气温升高影响森林土壤温室气体通量。通常,CO₂浓度升高导致土壤CO₂和N₂O排放量增加,CH₄吸收量降低; 氮沉降促进土壤N₂O排放、抑制CH₄吸收。气温升高导致土壤CO₂和N₂O排放增加。森林管理和全球大气变化对土壤温室气体通量的综合影响是非叠加的,有效的森林管理可能改变土壤温室气体通量对全球大气变化的响应。     

Plant diversity enhances ecosystem responses to elevated CO2 and nitrogen deposition

Human actions are causing declines in plant biodiversity, increases in atmospheric CO2 concentrations and increases in nitrogen deposition; however, the interactive effects of these factors on ecosystem processes are unknown. Reduced biodiversity has raised numerous concerns, including the possibility that ecosystem functioning may be affected negatively, which might be particularly important in the face of other global changes. Here we present results of a grassland field experiment in Minnesota, USA, that tests the hypothesis that plant diversity and composition influence the enhancement of biomass and carbon acquisition in ecosystems subjected to elevated atmospheric CO2 concentrations and nitrogen deposition. The study experimentally controlled plant diversity (1, 4, 9 or 16 species), soil nitrogen (unamended versus deposition of 4 g of nitrogen per m2 per yr) and atmospheric CO2 concentrations using free-air CO2 enrichment (ambient, 368 micromol mol-1, versus elevated, 560 micromol mol-1). We found that the enhanced biomass accumulation in response to elevated levels of CO2 or nitrogen, or their combination, is less in species-poor than in species-rich assemblages.     

全球变化研究的新内容与方向

随着对全球变化研究的深入，全球变化已不仅仅局限在全球气候变化上，内容已扩展到全球人口增长、大气成分变化、养分生物地球化学循环变化，土地利用和覆盖的改变及生物多样性的丧失等方面，未来全球变化研究将重点放在全球变化对生物多样性的影响，生态系统中CO2浓度升高，营养、温度、水分变化对生态过程的影响，景观水平上的研究以及人类决定的反馈生态学等方面。     

林业碳汇提升的主要原理和途径

降低大气CO₂含量、缓解气候变暖,已成为当今科学界和国际社会广泛关注的前沿热点问题。林业碳汇作为基于自然解决方案实现“碳达峰、碳中和”的一个重要途径,在应对全球气候变化方面发挥着基础性、战略性、独特的作用。林业碳汇不仅是森林碳汇,林产品碳汇也起着不可忽视的重要作用。林业碳汇潜力提升是一个森林生态系统净碳收支平衡和全产业链林产品碳汇的调控过程,主要包括无机碳的植物固定(光合过程、净生产力等)、土壤有机碳的周转与固定(动植物和微生物残体分解与黏土固定)、林产品碳的固持(林产品产量、木材转换效率、种类和使用寿命等)等3方面的调控原理。笔者从森林碳汇和林产品碳汇两个维度阐述了提升林业碳汇的主要原理、方法或途径。提升林业碳汇潜力的主要途径包括:①通过适地适树、适钙适树人工造林,以增加森林面积;②以完善森林经营措施来增加森林净生产力;③利用矿质黏土对有机碳的保护来增加森林土壤碳汇;④提升林产品产量和改进林产品用途以增加其寿命。在全球尺度上,增加森林面积或提高森林净生产力3.4%,或用可再生能源替换薪炭木材,再将薪炭木材用于制造锯材和人造板,都可以连续30 a每年增加1 Pg的碳汇量。减少全球森林火灾面积1/4或增加森林土壤有机碳含量0.23%,也可以增加碳汇1 Pg。此外,林业固碳还有巨大潜力可以挖掘。     

Increased CO2 uncouples growth from isoprene emission in an agriforest ecosystem

The emission of isoprene from the leaves of forest trees is a fundamental component of biosphere-atmosphere interactions, controlling many aspects of photochemistry in the lower atmosphere. As almost all commercial agriforest species emit high levels of isoprene, proliferation of agriforest plantations has significant potential to increase regional ozone pollution and enhance the lifetime of methane, an important determinant of global climate. Here we show that growth of an intact Populus deltoides plantation under increased CO2 (800 micromol x mol(-1) and 1,200 micromol x mol(-1)) reduced ecosystem isoprene production by 21% and 41%, while above-ground biomass accumulation was enhanced by 60% and 82%, respectively. Exposure to increased CO2 significantly reduced the cellular content of dimethylallyl diphosphate, the substrate for isoprene synthesis, in both leaves and leaf protoplasts. We identify intracellular metabolic competition for phosphoenolpyruvate as a possible control point in explaining the suppression of isoprene emission under increased CO2. Our results highlight the potential for uncoupling isoprene emission from biomass accumulation in an agriforest species, and show that negative air-quality effects of proliferating agriforests may be offset by increases in CO2.     

Nitrogen limitation constrains sustainability of ecosystem response to CO2

Enhanced plant biomass accumulation in response to elevated atmospheric CO2 concentration could dampen the future rate of increase in CO2 levels and associated climate warming. However, it is unknown whether CO2-induced stimulation of plant growth and biomass accumulation will be sustained or whether limited nitrogen (N) availability constrains greater plant growth in a CO2-enriched world. Here we show, after a six-year field study of perennial grassland species grown under ambient and elevated levels of CO2 and N, that low availability of N progressively suppresses the positive response of plant biomass to elevated CO2. Initially, the stimulation of total plant biomass by elevated CO2 was no greater at enriched than at ambient N supply. After four to six years, however, elevated CO2 stimulated plant biomass much less under ambient than enriched N supply. This response was consistent with the temporally divergent effects of elevated CO2 on soil and plant N dynamics at differing levels of N supply. Our results indicate that variability in availability of soil N and deposition of atmospheric N are both likely to influence the response of plant biomass accumulation to elevated atmospheric CO2. Given that limitations to productivity resulting from the insufficient availability of N are widespread in both unmanaged and managed vegetation, soil N supply is probably an important constraint on global terrestrial responses to elevated CO2.     

空气污染现状及咸阳市大气中SO2浓度变化研究

目的研究空气污染所造成严重健康问题以及咸阳市2014-2017年大气中SO_2浓度变化,并对其进行统计分析,为咸阳市能源结构调整和大气污染控制提供参考。方法以全球环境污染对健康影响的最新成果以及历史上SO_2烟雾事件为背景,结合咸阳市2014-2017年大气中SO_2浓度变化,利用Origin9.0软件进行统计分析,总结其变化规律。结果全世界每6个过早死亡者当中就有一个是因为环境污染而导致的,仅2015年约有900万人因为暴露于毒素而导致疾病致死,因为污染年度损失花费约4.6万亿美元,约占全球经济产出的6.2%。咸阳市大气中SO_2浓度变化,每年度的采暖期(11月中旬到来年3月中旬)SO_2浓度要比其它时间段更高一些;2014-2017年9月之间,年度SO_2浓度平均值有逐年下降之势,而且平均值之间存在极其显著性差异(P0.01);SO_2浓度变化与NO_2及CO浓度变化呈现出正线性相关,而与O_3浓度变化呈现出负线性相关。结论面对全球环境污染发展严重之势,咸阳市大气中SO_2浓度变化呈现出逐年下降的发展态势,与咸阳市进行能源结构调整、控制燃煤消费量等环境保护措施有直接关系。但是,同时也应该注意对于其它大气污染物(PM_(2.5),PM_(10),NO_2,CO,O_3)浓度变化的研究,为保护环境、控制污染提供更为全面的参考依据。     

Scaling metabolism from organisms to ecosystems

Understanding energy and material fluxes through ecosystems is central to many questions in global change biology and ecology. Ecosystem respiration is a critical component of the carbon cycle and might be important in regulating biosphere response to global climate change. Here we derive a general model of ecosystem respiration based on the kinetics of metabolic reactions and the scaling of resource use by individual organisms. The model predicts that fluxes of CO2 and energy are invariant of ecosystem biomass, but are strongly influenced by temperature, variation in cellular metabolism and rates of supply of limiting resources (water and/or nutrients). Variation in ecosystem respiration within sites, as calculated from a network of CO2 flux towers, provides robust support for the model's predictions. However, data indicate that variation in annual flux between sites is not strongly dependent on average site temperature or latitude. This presents an interesting paradox with regard to the expected temperature dependence. Nevertheless, our model provides a basis for quantitatively understanding energy and material flux between the atmosphere and biosphere.     

Nitrogen limitation of microbial decomposition in a grassland under elevated CO2

Carbon accumulation in the terrestrial biosphere could partially offset the effects of anthropogenic CO2 emissions on atmospheric CO2. The net impact of increased CO2 on the carbon balance of terrestrial ecosystems is unclear, however, because elevated CO2 effects on carbon input to soils and plant use of water and nutrients often have contrasting effects on microbial processes. Here we show suppression of microbial decomposition in an annual grassland after continuous exposure to increased CO2 for five growing seasons. The increased CO2 enhanced plant nitrogen uptake, microbial biomass carbon, and available carbon for microbes. But it reduced available soil nitrogen, exacerbated nitrogen constraints on microbes, and reduced microbial respiration per unit biomass. These results indicate that increased CO2 can alter the interaction between plants and microbes in favour of plant utilization of nitrogen, thereby slowing microbial decomposition and increasing ecosystem carbon accumulation.     

The Southern Ocean biogeochemical divide

Modelling studies have demonstrated that the nutrient and carbon cycles in the Southern Ocean play a central role in setting the air-sea balance of CO(2) and global biological production. Box model studies first pointed out that an increase in nutrient utilization in the high latitudes results in a strong decrease in the atmospheric carbon dioxide partial pressure (pCO2). This early research led to two important ideas: high latitude regions are more important in determining atmospheric pCO2 than low latitudes, despite their much smaller area, and nutrient utilization and atmospheric pCO2 are tightly linked. Subsequent general circulation model simulations show that the Southern Ocean is the most important high latitude region in controlling pre-industrial atmospheric CO(2) because it serves as a lid to a larger volume of the deep ocean. Other studies point out the crucial role of the Southern Ocean in the uptake and storage of anthropogenic carbon dioxide and in controlling global biological production. Here we probe the system to determine whether certain regions of the Southern Ocean are more critical than others for air-sea CO(2) balance and the biological export production, by increasing surface nutrient drawdown in an ocean general circulation model. We demonstrate that atmospheric CO(2) and global biological export production are controlled by different regions of the Southern Ocean. The air-sea balance of carbon dioxide is controlled mainly by the biological pump and circulation in the Antarctic deep-water formation region, whereas global export production is controlled mainly by the biological pump and circulation in the Subantarctic intermediate and mode water formation region. The existence of this biogeochemical divide separating the Antarctic from the Subantarctic suggests that it may be possible for climate change or human intervention to modify one of these without greatly altering the other.     

Diversity of arbuscular mycorrhizal fungal spore communities and its relations to plants under increased temperature and precipitation in a natural grassland

Arbuscular mycorrhizal fungi(AMF)form mutualisms with most plant species,and therefore,understanding how AMF communities will respond to climate change is essential for predictions of changes in plant communities.To evaluate the impact of global climate change on AMFs and plant-AMF interactions in a natural grassland in Inner Mongolia,both artificial warming and watering treatments were assigned to experimental plots.Our results indicate that(1)warming and precipitation significantly affected the relative spore abundance of abundant sporulating AMF species;(2)the relative abundance of weak sporulating AMF species and AMF diversity decreased under experimental warming;(3)evidence was found that the composition of the AMF community in a given year might be correlated with plant community composition in the following year;and(4)grasses and forbs showing different preferences to Claroideoglomus etunicatum or Ambispora gerdemannii dominated plots.Our results imply that climate change appears to induce changes in AMF assemblages with knock-on effects on grassland plant communities.AMF communities may play a much more important role than we have thought in the responses of ecosystem to global climate changes.     

Reduced calcification of marine plankton in response to increased atmospheric CO2

The formation of calcareous skeletons by marine planktonic organisms and their subsequent sinking to depth generates a continuous rain of calcium carbonate to the deep ocean and underlying sediments. This is important in regulating marine carbon cycling and ocean-atmosphere CO2 exchange. The present rise in atmospheric CO2 levels causes significant changes in surface ocean pH and carbonate chemistry. Such changes have been shown to slow down calcification in corals and coralline macroalgae, but the majority of marine calcification occurs in planktonic organisms. Here we report reduced calcite production at increased CO2 concentrations in monospecific cultures of two dominant marine calcifying phytoplankton species, the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanica. This was accompanied by an increased proportion of malformed coccoliths and incomplete coccospheres. Diminished calcification led to a reduction in the ratio of calcite precipitation to organic matter production. Similar results were obtained in incubations of natural plankton assemblages from the north Pacific ocean when exposed to experimentally elevated CO2 levels. We suggest that the progressive increase in atmospheric CO2 concentrations may therefore slow down the production of calcium carbonate in the surface ocean. As the process of calcification releases CO2 to the atmosphere, the response observed here could potentially act as a negative feedback on atmospheric CO2 levels.     

Interannual variability in the oxygen isotopes of atmospheric CO2 driven by El Niño

The stable isotope ratios of atmospheric CO(2) ((18)O/(16)O and (13)C/(12)C) have been monitored since 1977 to improve our understanding of the global carbon cycle, because biosphere-atmosphere exchange fluxes affect the different atomic masses in a measurable way. Interpreting the (18)O/(16)O variability has proved difficult, however, because oxygen isotopes in CO(2) are influenced by both the carbon cycle and the water cycle. Previous attention focused on the decreasing (18)O/(16)O ratio in the 1990s, observed by the global Cooperative Air Sampling Network of the US National Oceanic and Atmospheric Administration Earth System Research Laboratory. This decrease was attributed variously to a number of processes including an increase in Northern Hemisphere soil respiration; a global increase in C(4) crops at the expense of C(3) forests; and environmental conditions, such as atmospheric turbulence and solar radiation, that affect CO(2) exchange between leaves and the atmosphere. Here we present 30 years' worth of data on (18)O/(16)O in CO(2) from the Scripps Institution of Oceanography global flask network and show that the interannual variability is strongly related to the El Ni?o/Southern Oscillation. We suggest that the redistribution of moisture and rainfall in the tropics during an El Ni?o increases the (18)O/(16)O ratio of precipitation and plant water, and that this signal is then passed on to atmospheric CO(2) by biosphere-atmosphere gas exchange. We show how the decay time of the El Ni?o anomaly in this data set can be useful in constraining global gross primary production. Our analysis shows a rapid recovery from El Ni?o events, implying a shorter cycling time of CO(2) with respect to the terrestrial biosphere and oceans than previously estimated. Our analysis suggests that current estimates of global gross primary production, of 120 petagrams of carbon per year, may be too low, and that a best guess of 150-175 petagrams of carbon per year better reflects the observed rapid cycling of CO(2). Although still tentative, such a revision would present a new benchmark by which to evaluate global biospheric carbon cycling models.     

Volcanic carbon dioxide vents show ecosystem effects of ocean acidification

The atmospheric partial pressure of carbon dioxide (p(CO(2))) will almost certainly be double that of pre-industrial levels by 2100 and will be considerably higher than at any time during the past few million years. The oceans are a principal sink for anthropogenic CO(2) where it is estimated to have caused a 30% increase in the concentration of H(+) in ocean surface waters since the early 1900s and may lead to a drop in seawater pH of up to 0.5 units by 2100 (refs 2, 3). Our understanding of how increased ocean acidity may affect marine ecosystems is at present very limited as almost all studies have been in vitro, short-term, rapid perturbation experiments on isolated elements of the ecosystem. Here we show the effects of acidification on benthic ecosystems at shallow coastal sites where volcanic CO(2) vents lower the pH of the water column. Along gradients of normal pH (8.1-8.2) to lowered pH (mean 7.8-7.9, minimum 7.4-7.5), typical rocky shore communities with abundant calcareous organisms shifted to communities lacking scleractinian corals with significant reductions in sea urchin and coralline algal abundance. To our knowledge, this is the first ecosystem-scale validation of predictions that these important groups of organisms are susceptible to elevated amounts of p(CO(2)). Sea-grass production was highest in an area at mean pH 7.6 (1,827 (mu)atm p(CO(2))) where coralline algal biomass was significantly reduced and gastropod shells were dissolving due to periods of carbonate sub-saturation. The species populating the vent sites comprise a suite of organisms that are resilient to naturally high concentrations of p(CO(2)) and indicate that ocean acidification may benefit highly invasive non-native algal species. Our results provide the first in situ insights into how shallow water marine communities might change when susceptible organisms are removed owing to ocean acidification.     

The effect of millennial-scale changes in Arabian Sea denitrification on atmospheric CO2.

Most global biogeochemical processes are known to respond to climate change, some of which have the capacity to produce feedbacks through the regulation of atmospheric greenhouse gases. Marine denitrification-the reduction of nitrate to gaseous nitrogen-is an important process in this regard, affecting greenhouse gas concentrations directly through the incidental production of nitrous oxide, and indirectly through modification of the marine nitrogen inventory and hence the biological pump for CO2. Although denitrification has been shown to vary with glacial-interglacial cycles, its response to more rapid climate change has not yet been well characterized. Here we present nitrogen isotope ratio, nitrogen content and chlorin abundance data from sediment cores with high accumulation rates on the Oman continental margin that reveal substantial millennial-scale variability in Arabian Sea denitrification and productivity during the last glacial period. The detailed correspondence of these changes with Dansgaard-Oeschger events recorded in Greenland ice cores indicates rapid, century-scale reorganization of the Arabian Sea ecosystem in response to climate excursions, mediated through the intensity of summer monsoonal upwelling. Considering the several-thousand-year residence time of fixed nitrogen in the ocean, the response of global marine productivity to changes in denitrification would have occurred at lower frequency and appears to be related to climatic and atmospheric CO2 oscillations observed in Antarctic ice cores between 20 and 60 kyr ago.     

"植物-土壤"相互反馈的关键生态学问题:格局、过程与机制

植物与土壤之间相互反馈的格局、过程与机制,不但是决定生态系统结构、功能及过程的关键科学问题,而且是陆地生态系统响应全球变化的重要组成部分。基于目前国内外研究现状,从养分循环角度剖析“植物-土壤”间的反馈效应,探明相互反馈在空间尺度(根面、根际、种类、生态系统以及区域等)与时间尺度(秒至千年)上的级联效应及其变化格局;阐明根际、植物种类、生态系统及区域地理等水平上“植物-土壤”的相互反馈机制,重点揭示根系分泌、共生、生长及代谢的根际界面过程对植物水分/养分吸收与土壤物理学修饰的调控机制,剖析“植物种类-凋落物化学-土壤生物-土壤有机质”相互作用对地上-地下养分循环过程的驱动机制,运用“上行-下行控制理论及腐屑食物网模型”揭示地上-地下生物群落交互作用的过程与机制,以及土壤地质演变(岩石风化模式、土壤形成模式及土壤养分格局的变化)与区域植被演替(优势种更替及植被分布模式、地上-地下凋落物输入格局等的变化)相互反馈的过程与机制;从“植物-土壤”相互反馈的理论视角,分析生态退化与恢复、外来物种生态入侵、大气氮沉降、二氧化碳浓度升高以及植物多样性减少等全球生态问题的特征、形成机制以及可能的应对策略,揭示生态系统“地上-地下”相互反馈的生态学过程,以及陆地生态系统对全球生态环境变化的响应特征与机理。     

Effect of iron supply on Southern Ocean CO2 uptake and implications for glacial atmospheric CO2

Photosynthesis by marine phytoplankton in the Southern Ocean, and the associated uptake of carbon, is thought to be currently limited by the availability of iron. One implication of this limitation is that a larger iron supply to the region in glacial times could have stimulated algal photosynthesis, leading to lower concentrations of atmospheric CO2. Similarly, it has been proposed that artificial iron fertilization of the oceans might increase future carbon sequestration. Here we report data from a whole-ecosystem test of the iron-limitation hypothesis in the Southern Ocean, which show that surface uptake of atmospheric CO2 and uptake ratios of silica to carbon by phytoplankton were strongly influenced by nanomolar increases of iron concentration. We use these results to inform a model of global carbon and ocean nutrients, forced with atmospheric iron fluxes to the region derived from the Vostok ice-core dust record. During glacial periods, predicted magnitudes and timings of atmospheric CO2 changes match ice-core records well. At glacial terminations, the model suggests that forcing of Southern Ocean biota by iron caused the initial approximately 40 p.p.m. of glacial-interglacial CO2 change, but other mechanisms must have accounted for the remaining 40 p.p.m. increase. The experiment also confirms that modest sequestration of atmospheric CO2 by artificial additions of iron to the Southern Ocean is in principle possible, although the period and geographical extent over which sequestration would be effective remain poorly known.     

Preliminary regional estimation of carbon sink flux by carbonate rock corrosion: A case study of the Pearl River Basin

The formation of carbonate rocks has had a dramatic sink effect on atmospheric CO2 throughout geological time.The wide global distribution of carbonate rocks and their strong sensitivity to climate change mean that carbonate rock corrosion consuming air/soil CO2 can play an important role in the global carbon cycle.The carbon sink accounts for 12.00%-35.29% of the missing carbon in the global carbon cycle.Using the Pearl River Basin as a case study,we analyzed comprehensively the factors impacting karstific...     

用树轮碳同位素年序列重建大气二氧化碳浓度

大气圈ＣＯ２浓度及其同位素组成是不断变化的。植物在同化大气ＣＯ２过程中产生碳同位素分馏,因此,树轮中稳定碳同位素比值（＾１３Ｃ／＾１２Ｃ）不仅是重建古气候的工具,也是过去大气ＣＯ２浓度变化的敏感指标器。利用采自浙江西天目山的两株柳杉树轮稳定碳同位素（δ＾１３Ｃ）组成年序列,对１９世纪中叶以来大气ＣＯ２浓度变化进行重建,其重建值与大气ＣＯ２浓度的实测值较吻合。