陆地生态系统碳-氮-水循环的关键耦合过程及其生物调控机制探讨

陆地生态系统碳循环、氮循环和水循环是全球变化科学研究的三大主题,而陆地生态系统碳氮水耦合循环过程及其生物调控机制则是全球变化生态学研究的前沿性科学问题。目前,对陆地生态系统碳氮水耦合循环过程及其调控机制认识的不足是制约评估陆地增汇/减排效果,预测分析全球变化对生态系统生产力和固碳功能影响的瓶颈性问题。本文在综合分析陆地生态系统碳氮水循环的耦合过程基础上,论述了制约生态系统碳氮水循环空间格局耦联关系的生物地理学机制,制约典型生态系统碳氮水循环耦合关系的生物生理生态学机制,以及典型生态系统碳氮水耦合循环的关键生物物理和生物化学过程。重点评述了生态系统碳氮水耦合循环的主要过程及其生物调控机制研究进展,包括:(1)植物叶片冠层生物学过程和根系冠层生物学过程及其对生态系统碳氮水耦合循环控制机制,以及二者之间的关联与互作关系;(2)土壤微生物功能群网络及其对碳氮循环过程的影响;(3)生态系统碳氮水交换通量的时空变化规律,以及生态系统的生态化学计量学理论与实践。本文最后还简要介绍了国家基金委重大研究项目"森林生态系统碳氮水耦合循环的生物控制机制"的研究思路及其主要研究内容。期望能够通过这些探讨对推动我国该研究领域的基础理论建设和新技术发展有所贡献。     

气候变暖对陆地生态系统的影响

人类活动引起的温室效应导致全球气候变暖,气候变暖对全球生态环境的影响越来越受到人们的关注.作为人类赖以生存的环境主体,陆地生态系统对气候变暖将做出何种响应,更是人们关注的重点.植物物候的变化可以直观地反映某些气候变化,尤其是气候变暖.气候变暖影响植物的生长节律,进而引起植物与环境关系的改变及生态系统物质循环(如水和碳的循环)的改变.不同种类植物对气候变化的差异响应,会使植物间和动植物间的竞争与依赖关系发生深刻的变化,如北半球中高纬度地区植被生长季延长、植物提早开花、昆虫提早出现、鸟类提早产蛋以及冰川退缩、永冻土带融化、江河湖泊结冰推迟而融化提早等.本文主要从陆地生态系统的分布和演替两方面着眼,以植物和动物作为考察对象,系统论述了森林、草原、荒漠、湿地及农田等陆地生态系统在气候变暖背景下产生的变化,并从微观和宏观尺度上提出陆地生态系统变化的生态学机制,最后在技术和政策层面给出若干对策.     

陆地生态系统碳循环对土地利用变化的响应

陆地生态系统碳循环在全球碳循环中占有重要地位,而土地利用变化是估测陆地生态系统碳储存与释放的最大不确定性因素。植被和土壤是陆地生态系统的两大碳库,是碳循环中的两个重要纽带,土地利用变化影响陆地生态系统土壤和植被碳的固定、积累与释放,从而影响整个碳循环过程。本文主要从土壤和植被碳库的角度出发,综述了近年来土地利用变化对陆地生态系统碳循环的影响及其机理,以及研究方法进展,着重分析了模型在此方面的应用;并提出了未来研究方向的展望。     

大气CO_2升高与农田土壤碳循环研究

大气CO2浓度的升高通过植物-土壤-微生物的相互作用对陆地生态系统中最大碳库土壤的稳定性产生重要影响。大气CO2浓度升高,影响许多植物生长发育过程,进而影响土壤有机碳输入量。与此同时,土壤微生物的群落与功能也会随之发生变化,参与土壤碳的转化,深刻影响陆地生态系统的碳循环。文章分析了大气CO2浓度升高影响农田土壤碳循的有关过程,包括高CO2浓度条件下,作物地下部分的生长响应,以及向土壤中输入作物光合有机物量和质的变化,探讨了土壤碳库对大气CO2浓度升高反馈的土壤微生物作用机制,进一步解析了土壤微生物群落结构在土壤碳与大气CO2浓度之间的相互作用,提出研究土壤有机碳转化的土壤微生物作用机制是预测全球气候变化条件下的农田土壤碳循环规律的关键。图1,参79。     

冻融作用对植物生理生态的影响

土壤冻融作用是指由于土壤温度变化而出现的反复冻结和解冻过程,是季节性冻土区和多年冻土区常见的自然现象。冻融作用不仅会影响土壤理化性质、生物地球化学循环,而且还会通过生境胁迫或土壤环境改变影响植物的生理生态过程,从而可能对冻土广泛分布地区的植被生态系统生产力产生重要影响。本文分别论述了土壤冻融作用对植物生理生态的直接和间接影响,总结了不同气候环境条件下植物物候、光合作用、细胞膜和渗透调节物质、生产力和和群落组成、根系生长等的生理生态表现,并对目前土壤冻融与植物生理生态领域存在的不足进行了分析。提出应加强冻融作用对植物生理生态的长期影响研究,并从分子生物学角度探讨其机理等研究冻融胁迫对植物影响的建议。     

丛枝菌根真菌介导的土壤有机碳稳定机制研究进展

土壤有机碳(SOC)的稳定是陆地生态系统碳循环的关键过程之一,对维持土壤肥力和减少温室气体排放具有重要意义。以往认为植物残体中难降解性物质的物理保护和腐殖质影响土壤中有机碳库的稳定性。最近的研究结果表明,微生物介导的碳循环过程在土壤有机碳稳定中发挥着重要作用。丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)作为土壤中一类重要的共生微生物,参与植物光合碳向土壤的转运和分配,是陆地生态系统碳循环的重要一环,但其在土壤有机碳稳定中的作用潜力还未得到充分挖掘。基于此,本文估算了植物光合碳在AMF根外菌丝的分配量;总结了AMF介导的土壤有机碳稳定机制,主要包括AMF活体菌丝对碳的截留,分泌物及残体的分子结构抗性和土壤矿物吸附,提高植物源碳的质量和数量,菌丝分泌物及残体的激发效应和稳定土壤团聚体;探讨了影响AMF介导的稳定性有机碳形成的非生物(气候因子、土壤养分和土壤矿物)和生物因子(植物和AMF种类);提出了AMF与土壤有机碳周转互作机理进一步的研究方向,包括探究菌根植物光合碳转化为稳定性SOC的机制,解析不同生态系统中AMF对稳定性SOC的贡献及影响因素,并厘清...     

生物地球化学循环模型DNDC及其应用

生物地球化学模型是模拟研究化学元素动态的新兴领域,可用于陆地生态系统内植物、有机物和无机营养元素动态变化和循环。DNDC模型(DeNitrification-DeComposition Model)是美国新罕布什尔州大学陆地海洋空间研究中心开发研制的,最初是为了模拟农田生态系统固碳、氮流失和水平衡而创建,目前该模型可以模拟草地、湿地、林地等陆地生态系统碳氮动态过程。DNDC模型已经在美洲、欧洲、澳洲以及亚洲的一些地区得到了验证和运用。DNDC模型可用来分析陆地植物生长规律、土壤硝化和反硝化作用、温室气体和痕量气体排放预测研究、不同土壤类型及气候条件对森林生态系统碳氮通量变化的影响以及气候变化对生物地球化学循环的影响预测等。     

土壤侵蚀对陆地碳源汇的作用机制研究进展

土壤碳库是全球碳循环的重要组成部分,土壤侵蚀作为重要的地表过程,每年导致大量陆地生态系统内碳发生迁移,显著改变碳在地表的空间分布格局,影响植物初级生产力与土壤呼吸。然而,因欠缺对侵蚀与碳循环过程的了解、被侵蚀碳去向的不确定性以及研究手段与所关注侵蚀过程的差异,目前土壤侵蚀对陆地生态系统碳源汇的贡献仍存在较大争议。本文从侵蚀过程、迁移过程与沉积过程的角度分别探讨了土壤侵蚀过程中影响碳动态的主要机制及影响碳收支的主要环境因素,总结当前研究的主要问题与发展方向。分析认为,在全球变化背景下,深入研究侵蚀过程中的碳动态,探讨多因素交互作用过程,明确合理的时间和空间研究尺度,对认识土壤侵蚀在碳源汇及其在全球变化中的作用具有重要意义。     

森林植被不同尺度的碳水过程及耦合机制研究进展

[目的]陆地生态系统中的碳循环和水循环是陆地生态系统物质和能量循环的核心,也是连接地圈、生物圈和大气层的纽带。森林植被是陆地生态系统的重要组成部分,是表征陆地碳-水循环的重要变量,在维持生物圈和大气圈的动态平衡中发挥着重要作用。目前,对陆地生态系统中碳-水循环的耦合关系和机制缺乏系统的分析和总结。[方法]从森林植被碳与水过程及其相互作用、植被水分利用和耦合机制的角度,综述了森林植被碳与水循环过程及其相互作用的研究与进展,以及不同空间尺度(叶片到区域/全球尺度)碳-水耦合的定义、方法、进展和展望。[结果]新兴的技术和方法实现了不同尺度碳水过程的高频观测,WUE等耦合指标体系推动了碳水耦合机制的研究和发展。[结论]通过系统阐述植被碳水耦合关系的多尺度整合和碳水耦合机理,为系统认识森林碳水耦合机理和水资源管理提供了理论基础,对未来植被经营管理决策具有重要的科学支撑意义。     

陆地生态系统碳收支及其主要影响因素分析

CO2的增加是导致全球气温增加的主要因素之一。本文针对陆地生态系统是全球的3大碳库之一,分析了碳在森林、草地、湿地以及农田等陆地生态系统中的收支,并重点评价了碳在不同陆地生态系统中的积累部位和积累量;同时详细分析了影响不同陆地生态系统释放碳的因素,最后提出了增加陆地生态系统对CO2截存和减少CO2排放的措施。     

酸雨对土壤呼吸的影响机制研究进展与展望

土壤呼吸是陆地生态系统与大气之间进行碳交换的主要途径,其动态变化直接影响着全球碳平衡。由于人类活动的影响,酸雨成为人类当前面临的最严重的生态环境问题之一,但其对土壤呼吸的影响及其机理尚无定论。本文综述了不同生态系统土壤呼吸对酸雨的响应特征,多数文献表明,高强度的酸雨抑制土壤呼吸,而在低强度的酸雨作用下土壤呼吸的响应存在差异。从影响土壤呼吸的4个关键生物因子,即光合作用、微生物、凋落物和根系生物量,重点讨论了酸雨对土壤呼吸的影响机制。在此基础上,提出了以下研究展望:①开展土壤呼吸对不同组成类型酸雨的响应研究;②开展与土壤碳排放相关的功能微生物对酸雨的响应研究;③开展不同物候期土壤呼吸对酸雨的响应研究;④开展土壤呼吸各过程对酸雨的响应研究;⑤建立全球酸雨地区土壤碳排放监测研究网络。     

氮输入对陆地生态系统碳库的影响研究进展

碳氮循环是生物地球化学的重要过程。陆地生态系统碳循环在全球碳收支中占有重要的地位,人类活动导致生态系统中氮含量增加,影响土壤和植物体中碳的积累与重新分配,对陆地生态系统不同的碳过程产生不同的影响。本文综述了近年来氮输入的研究现状,并对未来的研究方向做了展望,提出今后重点研究的方向。     

The use of integrated soil microcosms to predict effects of pesticides on soil ecosystems

Most studies that aim at assessing the effects of pesticides on soil organisms or soil ecosystem processes are related to a single species of organism or soil process. Such individual studies are usually performed according to standard test guidelines, prepared by national or international authorities or approved test organizations and used in risk assessment. Over the last four years, with scientists from Germany and Russia, we have tested integrated soil microcosms, as model terrestrial ecosystems, to assess simultaneously the overall effects of a single pesticide, on a range of representative soil organisms, ecosystem processes, and environmental fate. This integrated approach takes account of interactions between organisms and processes which may influence the overall environmental impact and fate of a pesticide. Results from a detailed study of the environmental impact of the fungicide carbendazim are presented and some results on the impact of copper on soil systems are also reviewed. Some ecosystem structural parameters that were affected include: microbial activity, nematode communities, earthworm numbers and masses and plant growth. Some of the ecosystem processes affected include: nitrogen mineralization, and nutrient transformations.     

外来植物水花生和苏门白酒草入侵对土壤碳氮过程的影响

外来入侵植物对土壤生态系统的影响已成为入侵生态学研究的热点问题。以我国典型入侵植物水花生（Alternanthera philoxeroides,Ap）和苏门白酒草（Conyza sumatrensis,Cs）为对象,选取撂荒的稻田为试验样地,以土著优势物种马唐（Digitaria sanguinalis,Ds）为参照,通过对入侵植物和土著植物的根际土壤进行采样分析,研究了入侵植物对入侵地土壤特性及土壤碳氮过程的影响。结果表明,与土著物种Ds相比,Ap和Cs入侵分别使土壤有机质含量增加106和27,全氮量增加63和97,铵态氮含量增加97和94,硝态氮含量增加71和243,微生物量碳增加123和225,微生物量氮增加225和399,氮净矿化速率增加2.1倍和3.8倍,反硝化速率增加1.0倍和0.8倍,酶的活性和硝化速率亦显著增加;矿化过程中Cs和Ap的CO2平均排放速率分别增加2.3倍和2.6倍,土壤N2O的平均排放速率分别增加1.9倍和2.2倍。由此可见,入侵植物显著地改变了入侵地土壤的理化特性,加速了土壤碳氮转化过程,呈现正反馈效应。     

The effects of simulated nitrogen deposition on plant root traits: A meta-analysis

Global atmospheric nitrogen deposition has increased steadily since the 20th century, and has complex effects on terrestrial ecosystems. This work synthesized results from 54 papers and conducted a meta-analysis to evaluate the general response of 15 variables related to plant root traits to simulated nitrogen deposition. Simulated nitrogen deposition resulted in significantly decreasing fine root biomass (<2 mm diameter; −12.8%), while significantly increasing coarse root (≥2 mm diameter; +56.5%) and total root (+20.2%) biomass, but had no remarkable effect on root morphology. This suggests that simulated nitrogen deposition could stimulate carbon accumulation in root biomass. The root: shoot ratio decreased (−10.7%) suggests that aboveground biomass was more sensitive to simulated nitrogen deposition than root biomass. In addition, simulated nitrogen deposition increased the fine root nitrogen content (+17.6%), but did not affect carbon content, and thus decreased the fine root C:N ratio (−13.5%). These changes delayed the decomposition of roots, combined with increasing of the fine root turnover rate (+21.4%), which suggests that simulated nitrogen deposition could increase carbon and nutrient retention in the soil. Simulated nitrogen deposition also strongly affected the functional traits of roots, which increased root respiration (+20.7%), but decreased fungal colonization (−17.0%). The effects of simulated nitrogen deposition on the plant root systems were dependent on ecosystem and climate zone types, because soil nutrient conditions and other biotic and abiotic factors vary widely. Long-term simulated experiments, in which the experimental N-addition levels were less than twofold of the average of atmospheric nitrogen deposition, would better reflect the response of ecosystems under atmospheric nitrogen deposition. These results provide a synthetic understanding of the effects of simulated nitrogen deposition on plant root systems, as well as the mechanisms underlying the effects of simulated nitrogen deposition on plants and the terrestrial ecosystem carbon cycle.     

Drought and ecosystem carbon cycling

Drought as an intermittent disturbance of the water cycle interacts with the carbon cycle differently than the ‘gradual’ climate change. During drought plants respond physiologically and structurally to prevent excessive water loss according to species-specific water use strategies. This has consequences for carbon uptake by photosynthesis and release by total ecosystem respiration. After a drought the disturbances in the reservoirs of moisture, organic matter and nutrients in the soil and carbohydrates in plants lead to longer-term effects in plant carbon cycling, and potentially mortality. Direct and carry-over effects, mortality and consequently species competition in response to drought are strongly related to the survival strategies of species. Here we review the state of the art of the understanding of the relation between soil moisture drought and the interactions with the carbon cycle of the terrestrial ecosystems. We argue that plant strategies must be given an adequate role in global vegetation models if the effects of drought on the carbon cycle are to be described in a way that justifies the interacting processes.     

Climate change goes underground: effects of elevated atmospheric CO<Subscript>2</Subscript> on microbial community structure and activities in the rhizosphere

General concern about climate change has led to growing interest in the responses of terrestrial ecosystems to elevated concentrations of CO₂ in the atmosphere. Experimentation during the last two to three decades using a large variety of approaches has provided sufficient information to conclude that enrichment of atmospheric CO₂ may have severe impact on terrestrial ecosystems. This impact is mainly due to the changes in the organic C dynamics as a result of the effects of elevated CO₂ on the primary source of organic C in soil, i.e., plant photosynthesis. As the majority of life in soil is heterotrophic and dependent on the input of plant-derived organic C, the activity and functioning of soil organisms will greatly be influenced by changes in the atmospheric CO₂ concentration. In this review, we examine the current state of the art with respect to effects of elevated atmospheric CO₂ on soil microbial communities, with a focus on microbial community structure. On the basis of the existing information, we conclude that the main effects of elevated atmospheric CO₂ on soil microbiota occur via plant metabolism and root secretion, especially in C3 plants, thereby directly affecting the mycorrhizal, bacterial, and fungal communities in the close vicinity of the root. There is little or no direct effect on the microbial community of the bulk soil. In particular, we have explored the impact of these changes on rhizosphere interactions and ecosystem processes, including food web interactions.