第四纪异常气候环境与地质微生物2013年度报告

第四纪异常气候下微生物的响应和反馈的研究不但对了解现代全球变暖背景下微生物与气候变化之间的关系具有启示作用,同时对也为地质历史时期微生物和环境之间的协同演化的假设提供验证的案例。因而,第四纪异常环境下地质微生物的研究是联系微生物作用的现代过程与地质过程的桥梁。该研究借助于洞穴沉积物、泥炭沉积物和长江中游的湖泊沉积等地质载体,建立评估不同环境典型微生物地质过程的分子和原子(同位素)水平的示踪技术方法,查明微生物通过影响碳循环等地质地球化学过程对地质环境的作用。在前期的研究基础上,2013年的研究取得以下重要进展:(1)利用石笋碳酸盐热释光对土壤生物过程进行了示踪,获得土壤有机质分解与微生物降解过程的信息,发现了温度对土壤呼吸的影响,为未来全球变暖下土壤碳库大小的评估提供依据;(2)对发生在全新世的一次气候异常事件进行了解剖,发现东亚季风区8.2 ka BP气候事件的石笋记录与著名的格陵兰冰芯氧同位素记录具有高度相似性,说明在北大西洋降温和东亚季风减弱之间存在密切气候耦合;(3)开发了GDGTs和霍类化合物两个表征古水文的指标,并成功地用于古环境的重建,有望为预测全球变暖过程中不断出现严重的洪灾和旱灾的预测和防范发挥作用;(4)建立了微生物脂类定量重建古温度的新方法,探索地球表层长期温度的波动,为评估自然条件下地球环境变化的频率和强度提供基础资料(;5)第四纪动物演化及其对环境变化的响应的研究,对当今全球变暖的适应性具有启示作用。     

长期野外增温对不同草原土壤有机碳分解过程的影响

土壤异养呼吸/有机碳分解的温度敏感性是理解和预测全球气候变化下土壤有机碳库动态的关键基础之一,田间实验增温是当前模拟气候变化影响的一个重要手段.本研究通过室内土壤培养,测定了在长期田间实验增温下内蒙古温带草原和美国俄克拉荷马高草草原土壤异养呼吸的变化.结果显示,在多年的连续增温下,温带草原土壤有机碳的含量没有明显降低(P0.05),以有机碳的可分解性表征的土壤有机碳质量也没有下降,土壤有机碳分解对温度变化的响应(Q10)未受到增温的影响(P0.05).全球气候变化下的土壤碳循环和动态是一个复杂的多情景现象,需要进一步的深入研究.     

土壤有机碳分解温度敏感性及其形成机理研究

土壤有机碳分解的温度敏感性(Q_(10))对预测生态系统碳循环对全球气候变化的响应具有重要意义.科学研究已证实有机碳质量和土壤微生物对有机碳分解的温度敏感性都有一定的影响,但目前的分歧仍然很大.本研究以灭菌后的土壤作为碳源,用少量未灭活的鲜土作为微生物源,采用变温培养方法,在受控条件下对比不同碳源+微生物源组合中土壤有机碳分解的温度敏感性,解析土壤底物和微生物对土壤呼吸和温度敏感性的贡献.结果表明:(1)接种后的土壤呼吸随微生物源发生相应变化;未灭菌土壤的呼吸速率低于灭菌后接种自身土壤的呼吸值;土壤可溶性有机碳含量越高呼吸越强.(2)与未灭菌土壤相比,灭菌后接种本源微生物的Q_(10)显著降低;土壤灭菌后接种比自身Q_(10)高的异源微生物,Q_(10)会随之升高,接种比自身Q_(10)低的异源微生物则Q_(10)随之降低.表明微生物源和有机碳质量对碳分解的温度敏感性都起重要影响.在酸性土壤中,微生物对碳分解Q_(10)值的影响要大于碳源,微生物的贡献约为63.2%,碳源贡献为36.8%.在碱性土壤中,碳源的贡献则更为重要,微生物的相对贡献约为41.8%,碳源相对贡献为58.2%.     

崇明东滩围垦区不同土地利用类型对土壤呼吸及其组分的影响

在崇明东滩围垦区,采用Licor-8100A土壤碳通量观测系统及分层去根法,连续测定5种土地利用类型(芦苇湿地、白茅湿地、幼龄林、中龄林和农田)的土壤呼吸、异养呼吸和自养呼吸,以及0～10 cm表层土壤温度、体积含水率和电导率等环境因子,系统地比较了崇明东滩围垦区不同用地类型土壤呼吸及其组分的差异.结果表明:(1)幼龄林、中龄林和农田样地的土壤呼吸显著低于芦苇湿地和白茅湿地样地;(2)幼林龄、中林龄和农田样地的异养呼吸占比显著高于芦苇湿地和白茅湿地样地;(3)土壤呼吸及其组分与土壤温度呈显著的指数关系,但与土壤含水率和电导率的相关性较弱.与残存湿地相比,不同的农林利用方式显著降低了围垦区土壤呼吸,但大幅增加了异养呼吸,这可能说明土壤有机碳库在围垦20年后仍处于净损失状态.因此,需要采取有效措施进一步提升该区域土壤的碳固持能力.     

陆地生态系统土壤有机碳分解温度敏感性研究进展

在全球变化背景下,土壤有机碳的分解及其温度敏感性在陆地生态系统碳循环中的重要性备受关注。温度敏感性指数(Q₁₀)微小的变化都可能导致未来土壤碳库大小评估的巨大偏差,充分了解土壤有机碳分解温度敏感性的调控机理对预测未来土壤碳变化具有重要意义。笔者对国内外已有研究进行分析,比较培养温度模式、底物质量、物理化学保护和微生物属性对土壤有机碳分解温度敏感性的影响。结果发现:(1)与传统的恒温模式相比,变温培养模式更好地克服了土壤微生物对恒定培养温度的适应性以及不同培养温度下底物消耗不均的缺点,能够更加准确地估算Q₁₀。(2)较多的研究发现难分解有机碳的Q₁₀大于易分解有机碳的Q₁₀,但也有研究发现难分解有机碳的Q₁₀并不比易分解有机碳的Q₁₀高,这主要是由于土壤有机碳库的异质性造成的。(3)团聚体和矿物吸附保护通过改变底物有效性或者反应位点的底物浓度来影响土壤有机碳分解的温度敏感性。(4)微生物的生理特性、群落组成和结构也会对温度敏感性造成影响,温度变化会造成土壤微生物群落组成及其相关生理特征的变化,进一步引起相关功能基因丰度的改变,从而改变有机碳分解的温度敏感性。土壤有机碳分解及其温度敏感性是全球气候变化对碳循环影响研究中很重要的一部分,对它的精确估算有利于完善全球气候变化模型,对准确预测未来全球气候变化具有重要意义。     

陆地生态系统土壤有机碳分解温度敏感性研究进展

在全球变化背景下,土壤有机碳的分解及其温度敏感性在陆地生态系统碳循环中的重要性备受关注。温度敏感性指数(Q₁₀)微小的变化都可能导致未来土壤碳库大小评估的巨大偏差,充分了解土壤有机碳分解温度敏感性的调控机理对预测未来土壤碳变化具有重要意义。笔者对国内外已有研究进行分析,比较培养温度模式、底物质量、物理化学保护和微生物属性对土壤有机碳分解温度敏感性的影响。结果发现:(1)与传统的恒温模式相比,变温培养模式更好地克服了土壤微生物对恒定培养温度的适应性以及不同培养温度下底物消耗不均的缺点,能够更加准确地估算Q₁₀。(2)较多的研究发现难分解有机碳的Q₁₀大于易分解有机碳的Q₁₀,但也有研究发现难分解有机碳的Q₁₀并不比易分解有机碳的Q₁₀高,这主要是由于土壤有机碳库的异质性造成的。(3)团聚体和矿物吸附保护通过改变底物有效性或者反应位点的底物浓度来影响土壤有机碳分解的温度敏感性。(4)微生物的生理特性、群落组成和结构也会对温度敏感性造成影响,温度变化会造成土壤微生物群落组成及其相关生理特征的变化,进一步引起相关功能基因丰度的改变,从而改变有机碳分解的温度敏感性。土壤有机碳分解及其温度敏感性是全球气候变化对碳循环影响研究中很重要的一部分,对它的精确估算有利于完善全球气候变化模型,对准确预测未来全球气候变化具有重要意义。     

脉冲降雨对土壤异养呼吸影响机制的模拟研究

为研究脉冲降雨对土壤异养呼吸的影响机制,通过设置土壤+凋落物+降雨(A)、土壤+降雨(B)、土壤+凋落物+灭菌+降雨(C)、土壤+灭菌+降雨(D)和土壤+凋落物+无降雨(CK)共5组处理,采用室内培养法分析了脉冲降雨对中亚热带湿地松林下凋落物土壤异养呼吸的影响.结果表明:模拟降雨不同程度地激发了凋落物呼吸和矿质土壤呼吸,两者在0.25~1 h达到峰值,后逐渐恢复到降雨前水平,模拟降雨引起的物理排气过程持续时间较短.凋落物呼吸对降雨激发的土壤异养呼吸的平均贡献率为93.1%,而矿质土壤呼吸仅为6.9%.由此可知,降雨不同程度地激发了凋落物呼吸和矿质土壤呼吸,物理排气过程对土壤呼吸贡献有限,而凋落物呼吸对激发土壤异养呼吸贡献很大,且作用时间较长(48 h),是主导土壤异养呼吸对降雨响应的关键.     

中国典型森林生态系统土壤呼吸差异性分析

通过总结中国近年来发表文献中的土壤呼吸数据,分析研究了中国典型森林生态系统的土壤呼吸特征与规律.结果表明,中国5种典型森林生态系统的土壤平均呼吸速率依次为:针阔混交林(3.04μmol·m-2·s-1)落叶阔叶林(2.74μmol·m-2·s-1)常绿阔叶林(2.65μmol·m-2·s-1)常绿针叶林(2.60μmol·m-2·s-1)落叶针叶林(2.04μmol·m-2·s-1).落叶针叶林的土壤呼吸温度敏感性(Q10)最高(3.35),常绿阔叶林最低(2.35).总体来看,阔叶林土壤呼吸速率(2.69μmol·m-2·s-1)高于针叶林(2.32μmol·m-2·s-1);然而,阔叶林土壤呼吸温度敏感性(2.30)却低于针叶林(2.68).土壤自养呼吸贡献率因森林类型而异,针阔混交林比例最低(30.3%),而落叶针叶林最高(41.2%).土壤呼吸的森林类型间差异是气候因素和土壤碳输入模式共同调控的结果.本研究表明,在预测未来陆地碳循环及其对气候变化反馈效应时,不同森林生态系统间的土壤呼吸及其温度敏感性的差异性应给予充分的考虑.     

木麻黄人工林土壤异养呼吸及其季节动态

为了探讨不同林龄木麻黄防护林异养呼吸在土壤呼吸中所占的比例,本研究用挖壕沟法对异养呼吸和自养呼吸进行了分离,并采用LICOR-8100 Automated Soil CO2 Flux System法测定木麻黄纯林的土壤自养呼吸和异养呼吸.结果表明:土壤异养呼吸在总呼吸中所占比例的季节动态变化较小,变化幅度为68.59%～76.87%,基本稳定在72.73%左右:异养呼吸在各林龄间差异不明显,季节动态也没有一致的规律.     

水盐变化对滨海湿地土壤有机碳累积与碳排放的影响综述

滨海湿地作为海岸带蓝碳生态系统的重要组分,具有巨大的碳捕获和碳封存潜力,在减缓气候变暖方面具有重要意义．水盐变化通过影响滨海湿地土壤有机碳的累积和排放过程实现对滨海湿地生态系统碳收支的调控．本文综述了水盐变化对滨海湿地土壤有机碳累积和碳排放过程的影响,以及滨海湿地土壤碳排放研究方法等方面的研究进展,分析了水盐驱动下滨海湿地土壤有机碳分解的微生物作用机制．针对当前研究存在的不足,提出今后应重点关注滨海湿地土壤有机碳分解的温度、湿度和盐度敏感性及其水盐-温度的协同作用机制,氮磷输入和多重污染胁迫对滨海湿地土壤有机碳排放的作用机制,以及滨海湿地土壤微生物碳代谢过程与氮磷硫代谢过程的耦合作用及其水盐驱动机制等方面的研究,以期揭示水盐变化对滨海湿地土壤碳循环的作用机制,为气候变化背景下滨海湿地的碳汇功能提升与管理提供科学依据．      

Acclimatization of soil respiration to warming in a tall grass prairie.

The latest report by the Intergovernmental Panel on Climate Change (IPCC) predicts a 1.4-5.8 degrees C average increase in the global surface temperature over the period 1990 to 2100 (ref. 1). These estimates of future warming are greater than earlier projections, which is partly due to incorporation of a positive feedback. This feedback results from further release of greenhouse gases from terrestrial ecosystems in response to climatic warming. The feedback mechanism is usually based on the assumption that observed sensitivity of soil respiration to temperature under current climate conditions would hold in a warmer climate. However, this assumption has not been carefully examined. We have therefore conducted an experiment in a tall grass prairie ecosystem in the US Great Plains to study the response of soil respiration (the sum of root and heterotrophic respiration) to artificial warming of about 2 degrees C. Our observations indicate that the temperature sensitivity of soil respiration decreases--or acclimatizes--under warming and that the acclimatization is greater at high temperatures. This acclimatization of soil respiration to warming may therefore weaken the positive feedback between the terrestrial carbon cycle and climate.     

Long-term sensitivity of soil carbon turnover to warming

The sensitivity of soil carbon to warming is a major uncertainty in projections of carbon dioxide concentration and climate. Experimental studies overwhelmingly indicate increased soil organic carbon (SOC) decomposition at higher temperatures, resulting in increased carbon dioxide emissions from soils. However, recent findings have been cited as evidence against increased soil carbon emissions in a warmer world. In soil warming experiments, the initially increased carbon dioxide efflux returns to pre-warming rates within one to three years, and apparent carbon pool turnover times are insensitive to temperature. It has already been suggested that the apparent lack of temperature dependence could be an artefact due to neglecting the extreme heterogeneity of soil carbon, but no explicit model has yet been presented that can reconcile all the above findings. Here we present a simple three-pool model that partitions SOC into components with different intrinsic turnover rates. Using this model, we show that the results of all the soil-warming experiments are compatible with long-term temperature sensitivity of SOC turnover: they can be explained by rapid depletion of labile SOC combined with the negligible response of non-labile SOC on experimental timescales. Furthermore, we present evidence that non-labile SOC is more sensitive to temperature than labile SOC, implying that the long-term positive feedback of soil decomposition in a warming world may be even stronger than predicted by global models.     

Temperature sensitivity of soil carbon decomposition and feedbacks to climate change

Significantly more carbon is stored in the world's soils--including peatlands, wetlands and permafrost--than is present in the atmosphere. Disagreement exists, however, regarding the effects of climate change on global soil carbon stocks. If carbon stored belowground is transferred to the atmosphere by a warming-induced acceleration of its decomposition, a positive feedback to climate change would occur. Conversely, if increases of plant-derived carbon inputs to soils exceed increases in decomposition, the feedback would be negative. Despite much research, a consensus has not yet emerged on the temperature sensitivity of soil carbon decomposition. Unravelling the feedback effect is particularly difficult, because the diverse soil organic compounds exhibit a wide range of kinetic properties, which determine the intrinsic temperature sensitivity of their decomposition. Moreover, several environmental constraints obscure the intrinsic temperature sensitivity of substrate decomposition, causing lower observed 'apparent' temperature sensitivity, and these constraints may, themselves, be sensitive to climate.     

Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization

Global warming is predicted to be most pronounced at high latitudes, and observational evidence over the past 25 years suggests that this warming is already under way. One-third of the global soil carbon pool is stored in northern latitudes, so there is considerable interest in understanding how the carbon balance of northern ecosystems will respond to climate warming. Observations of controls over plant productivity in tundra and boreal ecosystems have been used to build a conceptual model of response to warming, where warmer soils and increased decomposition of plant litter increase nutrient availability, which, in turn, stimulates plant production and increases ecosystem carbon storage. Here we present the results of a long-term fertilization experiment in Alaskan tundra, in which increased nutrient availability caused a net ecosystem loss of almost 2,000 grams of carbon per square meter over 20 years. We found that annual aboveground plant production doubled during the experiment. Losses of carbon and nitrogen from deep soil layers, however, were substantial and more than offset the increased carbon and nitrogen storage in plant biomass and litter. Our study suggests that projected release of soil nutrients associated with high-latitude warming may further amplify carbon release from soils, causing a net loss of ecosystem carbon and a positive feedback to climate warming.     

温暖化加剧青藏高原高寒草甸土非生长季冻融循环

在2013年10月至次年4月,首次利用微根管直接观测和土壤温度间接观测相结合的方法,研究增温对青藏高原高寒草甸土壤冻融循环过程的影响。结果显示:1)全年增温和冬季增温均显著增加非生长季5,10,20 cm的土壤温度,而且冬季增温处理下的5~20 cm土壤非生长季月平均温度比全年增温处理下的高0.01~0.18oC;2)全年增温和冬季增温显著降低了完全冻结期和冬春解冻期的冻土层厚度,而对秋冬始冻期的冻土层厚度没有影响;3)全年增温和冬季增温显著减少了完全冻结期的持续天数和增加冬春解冻期的持续天数,而对秋冬始冻期的持续天数没有影响;4)冬季增温比全年增温对冻土层厚度和冻融循环持续天数的影响更加显著。研究表明,在青藏高原高寒草甸气候温暖化的趋势下,非生长季土壤冻融交替天数的增加,可能会进一步对高寒地区的地下碳氮循环产生重要的影响。     

从MWP看20世纪全球变暖

气候变暖已引起全球的广泛关注,正确的认识当前的气候变化已成为亟待解决的问题．目前的主流观点虽然认为近几十年的升温是由人类活动导致的,但许多学者发现MWP时期的气温与现代相当甚至更暖．结合国内外学者对MWP的研究,对比了MWP与现代暖期的温暖程度,指出20世纪暖期并不是过去千年最暖的世纪,现代升温可能只是气候冷暖波动中的一次自然现象,是uA过后的正常回暖．因此对MWP的认识对于人们深入认识当前全球变暖的性质和原因,具有十分重要的意义．     

Similar response of labile and resistant soil organic matter pools to changes in temperature

Our understanding of the relationship between the decomposition of soil organic matter (SOM) and soil temperature affects our predictions of the impact of climate change on soil-stored carbon. One current opinion is that the decomposition of soil labile carbon is sensitive to temperature variation whereas resistant components are insensitive. The resistant carbon or organic matter in mineral soil is then assumed to be unresponsive to global warming. But the global pattern and magnitude of the predicted future soil carbon stock will mainly rely on the temperature sensitivity of these resistant carbon pools. To investigate this sensitivity, we have incubated soils under changing temperature. Here we report that SOM decomposition or soil basal respiration rate was significantly affected by changes in SOM components associated with soil depth, sampling method and incubation time. We find, however, that the temperature sensitivity for SOM decomposition was not affected, suggesting that the temperature sensitivity for resistant organic matter pools does not differ significantly from that of labile pools, and that both types of SOM will therefore respond similarly to global warming.     

Decadal co-variability of the summer surface air temperature and soil moisture in China under global warming

The self-calibrating Palmer Drought Severity Index (PDSI) is calculated using newly updated ground observations of monthly surface air temperature (SAT) and precipitation in China. The co-variabilities of PDSI and SAT are examined for summer for the period 1961-2004. The results show that there exist decadal climate co-variabilities and strong nonlinear interactions between SAT and soil moisture in many regions of China. Some of the co-variabilities can be linked to global warming. In summer,sig-nificant decadal co-variabilities from cool-wet to warm-dry conditions are found in the east region of Northwest China,North China,and Northeast China. An important finding is that in the west region of Northwest China and Southeast China,pronounced decadal co-variabilities take place from warm-dry to cool-wet conditions. Because significant warming was observed over most areas of the global land surface during the past 20-30 years,the shift to cool-wet conditions is a unique phenomenon which may deserve much scientific attention. The nonlinear interactions between SAT and soil moisture may partly account for the observed decadal co-variabilities. It is shown that anomalies of SAT will greatly affect the climatic co-variabilities,and changes of SAT may bring notable influence on the PDSI in China. These results provide observational evidence for increasing risks of decadal drought and wet-ness as anthropogenic global warming progresses.     

内蒙古草原区土壤碳密度(SOCD)和氮密度(TND)的影响因素分析

在内蒙古草原区选取94个样点, 涵盖耕地、退耕地、人工林和草原4种土地利用类型, 根据土壤质地将草原细分为沙质草原和非沙质草原。 通过对这些样点土壤有机碳密度(SOCD)和全氮密度(TND)的研究, 发现在内蒙古草原区, SOCD主要受到土壤质地的影响, 黏粒(<2m)、粉砂(2~16m)和细粉砂(16~63 m)的含量越高, SOCD越高。而TND同时受到土壤质地和土地利用类型的影响, 分布在非沙质土壤的草原具有最高的TND。耕作不会导致SOCD显著降低, 但是会造成TND降低。人工林不能显著提高土壤养分含量, 相反, 由于人工林对养分和水分的需求很大, 可能导致土壤肥力的降低。此外, 草原区温度越高, 土壤养分越低, 这预示着在全球变暖的背景下, 这一地区的土壤可能成为重要的碳源。植被退化越严重, 土壤养分越低, 因此保护草原区的植被免受过度放牧的影响非常重要。     

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.