土壤有机碳含量与同位素特征

根据长江口崇明东滩典型高程部位柱状样与鼎湖山不同海拔土壤剖面土壤有机碳(SOC)含量与SOC同位素资料(δ13C、Δ14C),研究了土壤有机质更新的元素与同位素特征。结果表明,土壤剖面δ13C最大值(δ13Cmax)深度以上土层的SOC含量与δ13C值呈负相关,该深度以下呈正相关。土壤SOC含量与δ13C呈负相关,说明有机质分解程度低,有机质中快循环组分的比例较高,为土壤表层新鲜有机质,有机质14C表观年龄不足200年;二者呈正相关指示有机质分解程度较高,为中、下部土层较稳定的有机质组分,成土年龄在300年以上。土壤SOC含量随时间下降的速率与成土时间呈负相关,δ13Cmax深度以下土层的下降速率明显低于该深度以上土层,且年代越老,SOC含量下降速率越慢,表明其有机质主要为慢循环组分。不同土壤剖面δ13C的时间趋势基本一致,在δ13Cmax深度以上土层,δ13C随时间延长而增大,该深度以下δ13C随时间延长而降低。土壤有机碳δ13C与SOC含量随时间的变化具有明显对应关系,表明二者的变化机制存在内在关联。     

14C示踪技术在土壤有机质周转研究中的应用

采用碳同位素标记有机材料能够较真实地反映其在土壤中的分解和转化过程,是研究土壤有机质周转动力学的必要方法。本文介绍了^14C示踪技术在土壤腐殖质的形成与分解过程、有机底物在土壤中的分解和转化及其对原有土壤有机质分解的影响、土壤微生物生物量碳及其周转以及温室气体排放等方面研究中的应用进展。     

土壤剖面碳氮稳定同位素自然丰度的垂直分布模式及其影响机制

土壤碳、氮稳定同位素自然丰度(δ¹³C和δ¹⁵N)随土壤深度变化的研究,对揭示碳、氮元素生物地球化学循环机制具有重要意义。本文在概述土壤剖面δ¹³C和δ¹⁵N垂直分布特征的基础上,重点介绍了土壤δ¹³C和δ¹⁵N垂直分布模式的影响机制。土壤剖面δ¹³C垂直分布模式的影响机制主要有3种: 1)植被δ¹³C值的历史变化;2)植物群落C3-C4植物优势度变化;3)分解过程中¹³C富集的微生物源碳的积累。此外,讨论了¹³C休斯效应对土壤剖面δ¹³C垂直分布模式的影响。土壤剖面δ¹⁵N垂直分布模式的影响机制主要有4种: 1)反硝化过程产生的¹⁵N贫化气体的损失;2)分解过程中¹⁵N富集的微生物源氮的积累;3)菌根将¹⁵N贫化的含氮化合物转移到植物而在深层土壤积累¹⁵N富集的菌根真菌残留物;4)土壤有机质-矿物相互作用。最后提出了未来土壤剖面碳、氮稳定同位素自然丰度的垂直分布模式研究应该关注的重点。     

典型滨岸草地生态系统碳稳定同位素组成及分布特征

通过测定上海市青浦区东风港百慕大、白花三叶草、高羊茅和白茅等4种典型滨岸草本植物各组织以及不同垂直深度土壤有机质δ¹³C值,对滨岸草地生态系统的植物-土壤碳稳定同位素特征进行了分析.结果表明: 白花三叶草、高羊茅属于C3植物,百慕大、白茅属于C4植物,其茎叶、凋落物和根系各组织间δ¹³C值无显著差异.C3和C4植物样带表层土壤有机质δ¹³C值随着土壤深度递增而呈现截然不同的变化特征,这与样带本底δ¹³C值以及碳稳定同位素分馏效应有关,同时还受植物根系分布深度的影响.植物输入是土壤有机碳(SOC)的最主要来源,植物有机体δ¹³C组成对土壤有机质δ¹³C值有直接影响,植物各组分δ¹³C值与土壤有机质δ¹³C值均存在极显著相关.4种草本植物样带SOC含量与δ¹³C值均呈极显著相关,其中,C3植物样带SOC含量与δ¹³C值呈线性负相关,C4植物样带SOC含量与δ¹³C值呈线性正相关.     

碳同位素在湿地碳循环研究中的应用及进展

湿地碳库是区域生态系统中最重要的碳库之一,湿地碳循环是全球碳循环的重要环节。在湿地碳循环研究中,传统方法越来越不能满足人们对湿地中碳循环微观机理的了解,而碳同位素方法因其特殊的物源和过程示踪价值成为湿地碳循环研究的重要手段。本文从湿地碳循环的主要研究对象和基本研究方法出发,讨论了碳同位素方法的基本原理及其在碳循环研究中的优势,分析了碳同位素方法在湿地生物过程、水体、沉积物和土壤以及温室气体排放等方面的应用,归纳总结了碳同位素在我国湿地生态系统碳循环研究中的不足及未来发展方向。     

若尔盖草甸退化对土壤碳、氮和碳稳定同位素的影响

为了解不同退化阶段高寒草甸土壤碳、氮和碳稳定同位素的差异,对若尔盖湿地内沼泽草甸、草原化草甸、退化草甸3个阶段土壤的碳、氮和碳稳定同位素进行了分析.结果表明:若尔盖湿地草甸土壤δ¹³C 值介于-26.21‰～-24.72‰之间,土壤δ¹³C 值随土层加深而增大.土壤δ¹³C 值与有机碳含量对数值呈线性负相关.表层土壤(0～10 cm)δ¹³C值大小顺序为草原化草甸>退化草甸>沼泽草甸,β值大小顺序为草原化草甸>沼泽草甸>退化草甸.沼泽草甸、草原化草甸、退化草甸0～30 cm 土壤碳含量分别为105.32、42.11和31.12 g·kg^-1,氮含量分别为8.74、3.41和2.81 g·kg^-1,C/N分别为11.26、11.23和10.89.随着草甸的退化,土壤碳、氮呈降低趋势,退化草甸C/N值低于沼泽草甸和草原化草甸.随着土层深度加深,碳、氮含量呈现降低趋势.草甸退化导致的土壤δ¹³C 值差异主要发生在表层0～10 cm.3个退化阶段中,退化草甸土壤的β值和C/N最低,表明退化草甸土壤矿化作用较强.     

黄土地区不同覆被下土壤无机碳分布及同位素组成特征

土壤无机碳在剖面上的分布在评估区域碳库储量、陆地碳循环以及全球变化的研究中具有重要作用.本文通过测定黄土地区不同植被类型覆盖下土壤pH值、碳酸盐含量、δ13C和δ18O值,探讨了黄土地区植被类型对碳酸盐在土壤剖面中分布和同位素组成特征的影响.结果表明:各剖面碳酸盐含量为5.7％ ～ 14.1％,其均值大小为荒地＞草地＞林地;林地中,阔叶林＞灌木林＞针叶林,针叶林变化最明显;受成土母质影响,各剖面土壤pH值在7～8,呈弱碱性;土壤碳酸盐δ13C值分布为-6.2‰～-1.8‰,各剖面δ13C均值大小为荒地＞灌木林＞针叶林＞草地＞阔叶林;植被类型主要是通过向土壤输入有机质来影响土壤无机碳同位素组成;不同覆被下土壤剖面碳酸盐δ18O值差异明显,其可能受土壤物理性质如孔隙度、湿度等影响;黄土地区不同覆被下土壤无机碳含量和δ13C、δ18O值明显不同,因此,在植被演替过程中,植被类型的改变会影响到土壤无机碳库的储量和区域碳循环过程.     

海北高寒草甸土壤有机碳同位素组成及C3/C4碳源的变化

通过对高寒嵩草草甸土壤剖面不同深度(0～5cm,5～15cm,15～25cm,25～35cm,35～50cm,50～65cm)有机碳稳定性碳同位素的测定发现,土壤有机碳稳定性同位素(δ^13C)随土壤深度的增加而变大。表层土壤(0～5cm,定义为现代土壤)的δ^13C值最小,基本上接近现代植被的碳同位素特征。在土层5～10cm深度以下(粗略地定为古土壤),土壤有机碳稳定性同位素骤然上升,与表层土壤的同位素特征明显不同。考虑到影响土壤碳同位素的诸多因素,通过稳定性碳同位素的质量平衡模型计算,得出初步结果：来自C4(或CAM)植物的碳源随土壤深度的增加而增大。进一步推测,该地区植被可能经历由C4植物占优势的群落向C3植物占优势的群溶演化的过程。在这个过程中,大气碳同位素的变化和土壤有机质的形成过程(有机质淋溶过程)等也会引起土壤碳同位素的升高,因此质量平衡模型可能会过多地估算C4组分,而低估C3组分。     

蒙古栎叶片及其土壤碳、氮同位素自然丰度对大气CO2浓度升高的响应

大气CO₂浓度升高对土壤氮素转化过程产生重要影响,研究其变化有助于更好地预测陆地生态系统的固碳潜力.氮同位素自然丰度作为生态系统氮素循环过程的综合指标能够有效地指示CO₂浓度升高对土壤氮素转化过程的影响.本研究采用开顶箱CO₂ 熏蒸法研究连续10年的大气CO₂ 浓度升高对我国东北地区蒙古栎及其土壤和微生物生物量碳、氮同位素自然丰度的影响.结果表明: 大气CO₂浓度升高改变了土壤氮循环过程,增加了土壤微生物和植物叶片δ¹⁵N;促进了富¹³C土壤有机碳分解,中和了贫¹³C植物光合碳输入的效果,导致土壤可溶性有机碳和微生物碳δ¹³C在CO₂升高条件下没有发生显著变化.这些结果表明,CO₂浓度升高很可能促进了土壤有机质矿化过程,并加剧了系统氮限制的状态.     

蒙古栎叶片及其土壤碳、氮同位素自然丰度对大气CO2浓度升高的响应

大气CO₂浓度升高对土壤氮素转化过程产生重要影响,研究其变化有助于更好地预测陆地生态系统的固碳潜力.氮同位素自然丰度作为生态系统氮素循环过程的综合指标能够有效地指示CO₂浓度升高对土壤氮素转化过程的影响.本研究采用开顶箱CO₂ 熏蒸法研究连续10年的大气CO₂ 浓度升高对我国东北地区蒙古栎及其土壤和微生物生物量碳、氮同位素自然丰度的影响.结果表明: 大气CO₂浓度升高改变了土壤氮循环过程,增加了土壤微生物和植物叶片δ¹⁵N;促进了富¹³C土壤有机碳分解,中和了贫¹³C植物光合碳输入的效果,导致土壤可溶性有机碳和微生物碳δ¹³C在CO₂升高条件下没有发生显著变化.这些结果表明,CO₂浓度升高很可能促进了土壤有机质矿化过程,并加剧了系统氮限制的状态.     

Terrestrial fluxes of carbon in GCP carbon budgets

The Global Carbon Project (GCP) has published global carbon budgets annually since 2007 (Canadell et al. [2007], Proc Natl Acad Sci USA, 104, 18866–18870; Raupach et al. [2007], Proc Natl Acad Sci USA, 104, 10288–10293). There are many scientists involved, but the terrestrial fluxes that appear in the budgets are not well understood by ecologists and biogeochemists outside of that community. The purpose of this paper is to make the terrestrial fluxes of carbon in those budgets more accessible to a broader community. The GCP budget is composed of annual perturbations from pre‐industrial conditions, driven by addition of carbon to the system from combustion of fossil fuels and by transfers of carbon from land to the atmosphere as a result of land use. The budget includes a term for each of the major fluxes of carbon (fossil fuels, oceans, land) as well as the rate of carbon accumulation in the atmosphere. Land is represented by two terms: one resulting from direct anthropogenic effects (Land Use, Land‐Use Change, and Forestry or land management) and one resulting from indirect anthropogenic (e.g., CO₂, climate change) and natural effects. Each of these two net terrestrial fluxes of carbon, in turn, is composed of opposing gross emissions and removals (e.g., deforestation and forest regrowth). Although the GCP budgets have focused on the two net terrestrial fluxes, they have paid little attention to the gross components, which are important for a number of reasons, including understanding the potential for land management to remove CO₂ from the atmosphere and understanding the processes responsible for the sink for carbon on land. In contrast to the net fluxes of carbon, which are constrained by the global carbon budget, the gross fluxes are largely unconstrained, suggesting that there is more uncertainty than commonly believed about how terrestrial carbon emissions will respond to future fossil fuel emissions and a changing climate.     

碳输入方式对森林土壤碳库和碳循环的影响研究进展

凋落物和植物根系是森林土壤有机碳的主要来源.综述了不同碳输入方式对土壤全碳、微生物生物量碳和可溶性有机碳等碳库组分及土壤呼吸影响的研究进展.不同地区、不同森林土壤有机碳对碳输入的响应程度不同,且采用添加和去除凋落物,以及去除根系方法(DIRT)对土壤碳的影响具有树种差异和区域差异.目前主要侧重于土壤呼吸和碳库组分的研究,亟需开展对土壤碳的结构类型和稳定性,以及土壤生物尤其是土壤动物的响应机制的相关研究.     

Channeling of carbon monoxide during anaerobic carbon dioxide fixation

Carbon monoxide is an intermediate in carbon dioxide fixation by diverse microbes that inhabit anaerobic environments including the human colon. These organisms fix CO(2) by the Wood-Ljungdahl pathway of acetyl-CoA biosynthesis. The bifunctional CO dehydrogenase/acetyl-CoA synthase (CODH/ACS) catalyzes several key steps in this pathway. CO(2) is reduced to CO at a nickel iron-sulfur cluster called cluster C located in the CODH subunit. Then, CO is condensed with a methyl group and coenzyme A at cluster A, another nickel iron-sulfur cluster in the ACS subunit. Spectroscopic studies indicate that clusters A and C are at least 10-15 A apart. To gain a better understanding of how CO production and utilization are coordinated, we have studied an isotopic exchange reaction between labeled CO(2) and the carbonyl group of acetyl-CoA with the CODH/ACS from Clostridium thermoaceticum. When solution CO is provided at saturating levels, only CO(2)-derived CO is incorporated into the carbonyl group of acetyl-CoA. Furthermore, when high levels of hemoglobin or myoglobin are added to remove CO from solution, there is only partial inhibition of the incorporation of CO(2)-derived CO into acetyl-CoA. These results provide strong evidence for the existence of a CO channel between cluster C in the CODH subunit and cluster A in the ACS subunit. The existence of such a channel would tightly couple CO production and utilization and help explain why high levels of this toxic gas do not escape into the environment. Instead, microbes sequester this energy-rich carbon source for metabolic reactions.     

Elevated atmospheric carbon dioxide increases soil carbon

The general lack of significant changes in mineral soil C stocks during CO₂‐enrichment experiments has cast doubt on predictions that increased soil C can partially offset rising atmospheric CO₂ concentrations. Here, we show, through meta‐analysis techniques, that these experiments collectively exhibited a 5.6% increase in soil C over 2–9 years, at a median rate of 19 g C m^?2 yr^?1. We also measured C accrual in deciduous forest and grassland soils, at rates exceeding 40 g C m^?2 yr^?1 for 5–8 years, because both systems responded to CO₂ enrichment with large increases in root production. Even though native C stocks were relatively large, over half of the accrued C at both sites was incorporated into microaggregates, which protect C and increase its longevity. Our data, in combination with the meta‐analysis, demonstrate the potential for mineral soils in diverse temperate ecosystems to store additional C in response to CO₂ enrichment.     

Improving the carbon balance of fermentations by total carbon analyses

Carbon balancing of microbial fermentations is a valuable tool for the evaluation of the process performance and to identify the presence of undesired by-products. In this study, we demonstrate the relevance of total carbon (TC) analysis for carbon balancing in fermentations with the wild-type of Corynebacterium glutamicum by (i) quantifying significant amounts of dissolved inorganic carbonic species (TIC) in the culture medium and (ii) determining the effective (mass) carbon content of the biomass fraction (M_C,X). In principle, TC based carbon balancing yielded at fully matching carbon balances. Thus, the application of our TC approach for the accurate detection of TIC and M_C,X increased the total carbon recovery in standard batch fermentations with C. glutamicum on glucose from about 76% to carbon closures of 94–100% in contrast to conventional approaches. Besides, the origin of the missing 6%-gap could be attributed to incomplete quantification of all carbon sources in the liquid phase. To conclude this study, the concept of TC-based balancing was transferred to an l-lysine production process, successfully quantifying relevant system carbon fractions, which resulted in matched carbon recoveries.     

Effect of carbon source on compost nitrogen and carbon losses

The effect of C source on N losses by volatilization during composting was measured using four bulking agents, each at three humidity levels and composted in duplicate under passive and active aeration. The bulking agents were pine shavings alone and corrected with soybean, chopped grass hay alone and corrected with urea, long (unchopped) wheat straw and chopped oat straw. The readily available C of each bulking agent was determined by analyzing for BOD5. In 105 l laboratory vessels, the bulking agents were mixed with liquid swine manure and tap water for a C/N of 20 and three humidity levels of 60%, 65% and 70%. While being aerated actively or passively, the mixtures were composted for 21 days. Their initial and final C and N contents were measured to conduct a mass balance analysis and calculate C and N losses. C and N losses were compared to bulking agent BOD5. N losses were compared to C losses. The humidity level and aeration regime had no effect on C and N losses but the N losses were correlated to C losses and only the C losses could be correlated to the BOD5 of the bulking agent. Thus, the N losses are related not only to the availability of C but also to the extent of composting. A relationship established between N and C losses indicated that 85% of the initial total N of the compost was available for microbial degradation and that 70% of the available C was lost as CO2 during the immobilization process.