稳定碳同位素技术在土壤-植物系统碳循环中的应用

碳作为重要的生命元素,在土壤-植物系统物质循环中发挥重要作用.作为一种天然的示踪物,稳定碳同位素（13C）较放射性同位素具有安全、无污染、易控制的优点,在土壤-植物生态系统碳循环研究中得到广泛应用.通过检测土壤-植物体系中稳定碳同位素的自然丰度或采用稳定碳同位素标记有机材料,能够较真实地了解植物的光合特性、光合产物在土壤-植物体系中的运转及其在土壤中的分解、转化等过程.本文概述了稳定碳同位素技术在植物光合作用及光合产物运转、古气候重建、土壤有机质周转以及植物-根际微生物相互作用等方面的研究进展,并针对当前研究中存在的问题提出了今后的研究展望.     

植物根际微生物群落构建的研究进展

植物根际是指植物根系与土壤的交界面,是根系自身生命活动和代谢对土壤影响最直接、最强烈的区域,其物理、化学和生物性质不同于土体土壤。在这个区域里,与植物发生相互作用的大量微生物,被称为根际微生物。根际微生物在植物的生长发育和植物病虫害的生物防治等方面都具有十分重要的意义。本文总结了根际微生物群落构建的研究现状,介绍了根际微生物的经典和最新的研究方法,包括根箱法、同位素技术以及高通量测序、菌群定量分析、高通量分离培养等方法在根际微生物研究中的应用,讨论了植物根系分泌物(碳水化物、氨基酸、黄酮类、酚类、激素及其信号物质)和土壤物理化学性质对根际微生物群落的影响,概述了根际微生物-植物的互作机制,以及根际微生物群落对植物的促生作用、提高植物抗逆性和抑制作用,并对根际微生物群落研究中存在的问题和未来发展方向进行了展望。     

稳定碳同位素技术在土壤-植物系统碳循环中的应用

碳作为重要的生命元素,在土壤 植物系统物质循环中发挥重要作用.作为一种天然的示踪物,稳定碳同位素（¹³C）较放射性同位素具有安全、无污染、易控制的优点,在土壤 植物生态系统碳循环研究中得到广泛应用.通过检测土壤 植物体系中稳定碳同位素的自然丰度或采用稳定碳同位素标记有机材料,能够较真实地了解植物的光合特性、光合产物在土壤 植物体系中的运转及其在土壤中的分解、转化等过程.本文概述了稳定碳同位素技术在植物光合作用及光合产物运转、古气候重建、土壤有机质周转以及植物 根际微生物相互作用等方面的研究进展,并针对当前研究中存在的问题提出了今后的研究展望.     

农田作物同化碳输入与周转的生物地球化学过程

作物同化碳在“大气-植物-土壤”系统中流通的生物地球化学过程,显著影响全球陆地生态系统碳循环过程。作物同化碳是土壤有机碳的重要来源,与根际环境及作物生长发育有密切联系,但由于其复杂性和多变性,作物生长期内同化碳在土壤中的分配、转化与稳定的机理尚不十分清楚。因此,综述了作物同化碳向土壤碳库输入及其对土壤有机碳库的贡献,在土壤碳库中的分配与转化特征,在土壤中流通的微生物机制以及同化碳在土壤-微生物系统分配、稳定的微观机制。探讨同化碳在地上部-根际-土壤系统中的分配及调节机制,土壤界面同化碳流动过程与土壤微生物多样性形成的关系;提出了在不同生态系统尺度上加强作物同化碳在土壤-作物系统中分配过程的定量研究对于明确陆地生态碳循环过程的重要意义;指出了研究作物同化碳向土壤碳库迁移、分配定量过程与机制的重要性,以及应用显微镜成像技术与同位素示踪技术相结合的纳米二次离子质谱技术、和微生物分子与群落生态相偶联的技术是未来研究作物同化碳生物地球化学特性的有效手段。     

根际土壤动物及其对植物生长的影响

土壤动物是根际土壤生物的重要组成部分,对于营养物质的转化、储存和释放,土壤微生物的调节及土壤理化性质的改变都发挥着积极作用,最终影响地上植物生长及其生产力。本文综述了土壤动物在根际土壤生态系统中的作用、根际土壤动物与土壤微生物之间的关系、根际土壤动物对植物生长的影响等。就目前根际土壤动物及其对植物生长的影响研究中亟待解决的一些问题进行了探讨,并提出今后应加强研究的方向。     

黄土高原典型植物根际对土壤微生物生物量碳、氮、磷和基础呼吸的影响

选择黄土高原7种典型植物的根际与非根际土壤为研究对象,对土壤的养分含量、微生物生物量碳、氮、磷和基础呼吸的影响进行了初步研究。结果表明,7种不同植物根际土壤与非根际土壤的养分含量、微生物生物量和基础呼吸均存在显著差异;除冷蒿的土壤微生物生物量磷以外,其他各种植物的根际土壤的养分含量、微生物生物量和基础呼吸均比非根际土壤的高;土壤有机碳、全氮与土壤微生物生物量碳、氮及基础呼吸之间均具有极显著或显著相关关系,表明了土壤微生物生物量碳、氮可以作为判断土壤肥力状况的生物学指标,同时也可为提高土壤肥力水平和土壤培肥效果提供依据。     

宁南山区典型植物根际与非根际土壤碳、氮形态

以宁南山区典型植物冰草、冷蒿、长芒草、百里香和铁杆蒿为对象,研究不同植物根际土壤和非根际土壤碳、氮形态的变化.结果表明:5种植物对根际土壤和非根际土壤碳、氮含量的影响不同.其中,铁杆蒿的根际土壤碳含量最高,总有机碳、轻组有机碳和重组有机碳含量分别为22.94、1.95和20.88g·kg-1,长芒草的根际土壤氮含量最高,总氮、可矿化氮和速效氮含量分别为2.05g·kg-1、23.73mg·kg-1和11.99mg·kg-1.冷蒿的根际土壤中活性有机碳/总有机碳、可矿化氮/总氮最高,有利于土壤中碳素和氮素向活性态转变.轻组有机碳、可矿化氮可作为植物生境改变的敏感指标.5种植物根际土壤各形态碳、氮含量总体上高于非根际土壤.     

樟子松林根际与非根际土壤碳氮磷化学计量特征

为揭示呼伦贝尔沙地樟子松根际与非根际土壤碳氮磷化学计量特征,以不同林龄(28、37、46年生)樟子松人工林为研究对象,以樟子松天然林为对照,研究根际与非根际土壤有机碳、全氮和全磷含量及其化学计量比,分析土壤性质与土壤化学计量特征间的相关性。结果表明：在樟子松人工林中,根际效应显著影响土壤N∶P,林龄显著影响土壤有机碳含量;各林龄人工林的土壤有机碳含量均显著低于天然林。人工林的根际与非根际土壤有机碳、全氮含量均随林龄增加先降低再升高;全磷含量在根际土壤中先升高再降低,在非根际土壤中先降低再升高。C∶N与C∶P在根际土壤中呈显著正相关,但在非根际土壤中不存在显著相关关系,说明根际土壤氮磷限制具有更高的协同性。根际与非根际土壤N∶P均值分别为4.98与8.40,表明樟子松人工林的生长受土壤N限制,且根际土壤受N限制程度更高。根际与非根际土壤碳氮磷化学计量特征受土壤性质的显著影响,其中,速效磷是最主要的驱动因子。呼伦贝尔沙地樟子松生长受N限制,其植物根系对土壤养分的富集与维持有明显作用,建议在樟子松生长阶段适当补充土壤氮素,并根据根际土壤氮磷限制的协同性适当补充磷素。     

干旱荒漠区不同灌木根际与非根际土壤氮素的含量特征

选取广泛分布于阿拉善干旱荒漠区的白刺、霸王、红砂、沙冬青、沙木蓼、梭梭和驼绒藜7种不同的旱生灌木,研究其根际与非根际土壤各种形态氮素、有机碳的含量特征及土壤pH的变化.结果表明,相对于非根际土壤,根际土壤全氮、铵态氮、硝态氮分别平均高24.9%、24.5%和65.1%,土壤有机碳平均高出18.5%,土壤pH值平均低0.14个单位.根际与非根际土壤的全氮、铵态氮、硝态氮、有机碳和pH之间都呈现出了极显著差异(p<0.01).7种灌木根际土壤全氮、硝态氮和有机碳含量均比非根际土壤含量高.除沙冬青根际铵态氮含量较非根际低以外,其余6种灌木根际土壤铵态氮含量均高于非根际土壤.梭梭的根际土壤pH高于非根际,其它6种灌木均是根际pH低于非根际土壤.在根际与非根际,土壤有机碳与土壤全氮之间均呈显著相关,二者表现为线性关系.而土壤全氮与铵态氮在根际与非根际则均无相关性,全氮与硝态氮在根际和非根际土壤均显著相关,且二者也呈线性相关.     

基于菌植互作的植物根际细菌钝化镉作用和机制研究进展

土壤重金属镉(Cd)污染严重危害农产品安全生产,植物根际细菌在钝化土壤Cd和帮助作物抵御Cd胁迫方面发挥重要作用。本文首先概括在修复Cd污染土壤中得到广泛应用的植物根际细菌种类,并从根际细菌直接吸附Cd、调整土壤理化特性、调控土壤微生物群落和其他作用4方面阐述了植物根际细菌对Cd的钝化作用,其次从菌植互作角度阐述植物根系分泌物与根际细菌群落相互影响对土壤Cd的钝化作用。最后展望重金属胁迫下植物根际钝化Cd核心菌群的构建,以在新兴学科与技术的快速发展中探明植物根系-微生物互作体系的分子机制,深入开展植物根际细菌钝化修复重金属污染土壤的理论研究和实践。     

Spatially explicit patterns in a dryland's soil respiration and relationships with climate,whole plant photosynthesis and soil fertility

Arid and semiarid ecosystems play a significant role in regulating global carbon cycling, yet our understanding of the controls over the dominant pathways of dryland CO₂ exchange remains poor. Substantial amounts of dryland soil are not covered by vascular plants and this patchiness in cover has important implications for spatial patterns and controls of carbon cycling. Spatial variation in soil respiration has been attributed to variation in soil moisture, temperature, nutrients and rhizodeposition, while seasonal patterns have been attributed to changes in moisture, temperature and photosynthetic inputs belowground. To characterize how controls over respiration vary spatially and temporally in a dryland ecosystem and to concurrently explore multiple potential controls, we estimated whole plant net photosynthesis (A_net) and soil respiration at four distances from the plant base, as well as corresponding fine root biomass and soil carbon and nitrogen pools, four times during a growing season. To determine if the controls vary between different plant functional types for Colorado Plateau species, measurements were made on the C₄ shrub, Atriplex confertifolia, and C₃ grass, Achnatherum hymenoides. Soil respiration declined throughout the growing season and diminished with distance from the plant base, though variations in both were much smaller than expected. The strongest relationship was between soil respiration and soil moisture. Soil respiration was correlated with whole plant A_net, although the relationship varied between species and distance from plant base. In the especially dry year of this study we did not observe any consistent correlations between soil respiration and soil carbon or nitrogen pools. Our findings suggest that abiotic factors, especially soil moisture, strongly regulate the response of soil respiration to biotic factors and soil carbon and nitrogen pools in dryland communities and, at least in dry years, may override expected spatial and seasonal patterns.     

Modelling the impact of microbial grazers on soluble rhizodeposit turnover

Rhizodeposition represents a relatively large carbon flow from a plant’s root into the surrounding soil. This carbon flow may have important implications for nitrogen mineralisation and carbon sequestration, but is still poorly understood. In this paper we use a simple compartment model of carbon flow in the rhizosphere to investigate the proposed benefits of rhizodeposition and the effect of microbial grazers. Model parameters were fitted to published, experimental data. Analysis of the model showed that dead organic matter (necromass) had a much longer time-scale than the other carbon pools (soluble, microbial and grazer carbon), which allowed an approximate, mathematical solution of the model to be derived. This solution shows that the level of necromass in the soil is an important factor in many processes of interest. The short-term carbon and nitrogen turnover increases with the level of necromass. Microbial grazers decrease carbon turnover at high levels of necromass, whilst at lower, and possibly more realistic, levels of necromass grazers increase turnover. However, the largest effect of grazers was to increase carbon turnover by 10%, suggesting that grazers are relatively unimportant in larger scale models of soil organic matter turnover. The marginal benefits of rhizodeposition increase with the level of necromass. The model suggests that the short-term benefits of rhizodeposition to a plant are marginal, but long-term benefits may still occur.     

亚热带山区红壤地碳平衡研究进展

碳平衡研究日益成为全球变化与地球科学研究领域的热点问题.亚热带红壤区是我国发展粮食作物和各种热带、亚热带经济作物与林木的重要基地,因该区特殊的生态地理位置,在我国碳平衡研究中占有重要地位.本文论述了亚热带山区红壤地碳平衡研究的重要性,对碳平衡研究中植被、凋落物、土壤碳库和土壤呼吸的研究现状和主要结论等进行阐述,总结了碳平衡的综合研究方法,并对亚热带山区红壤地碳平衡研究中存在的问题和今后的发展方向进行探讨.     

Phylogenetically structured traits in root systems influence arbuscular mycorrhizal colonization in woody angiosperms

Background

Rhizodeposition is the release of organic compounds from plant roots into soil. Positive relationships between rhizodeposition and soil microbial biomass are commonly observed. Rhizodeposition may be disrupted by increasing drought however the effects of water stress on this process are not sufficiently understood.

Scope

We aimed to provide a synthesis of the current knowledge of drought impacts on rhizodeposition. The current scarcity of well-defined studies hinders a quantitative meta-analysis, but we are able to identify the main effects of water stress on this process and how changes in the severity of drought may produce different responses. We then give an overview of the links between rhizodeposition and microbial communities, and describe how drought may disrupt these interactions.

Conclusions

Overall, moderate drought appears to increase rhizodeposition per gram of plant, but under extreme drought rhizodeposition is more variable. Concurrent decreases in plant biomass may lessen the total amount of rhizodeposits entering the soil. Effects on rhizodeposition may be strongly species-dependant therefore impacts on soil communities may also vary, either driving subsequent changes or conferring resilience in the plant community. Advances in the study of rhizodeposition are needed to allow a deeper understanding of this plant-soil interaction and how it will respond to drought.

     

暖温带落叶阔叶林碳循环的初步估算

 森林生态系统碳循环过程与大气中二氧化碳含量有密切的关系,直接影响着大气成分的组成,进而对全球气候变化有重要影响。以我国暖温带落叶阔叶林生态系统近10年的定位研究为基础,初步建立了该类生态系统碳循环数值模式。结果表明：暖温带落叶阔叶林典型生态系统每年从外界主要是大气中吸收的碳是10.3 t·hm-2·a-1,植物呼吸释放到大气中的碳通量为5.5 t·hm-2·a-1。森林植物干物质积存的碳量为4.8 t·hm-2·a-1,通过凋落物分解释放到大气中的碳通量为2.46 t·hm-2·a-1。森林同化的碳绝大部分以活生物呼吸和凋落物分解的形式释放到大气中去了,存留在活生物体和凋落物中的很少。通过对碳现存量的研究发现,所研究的森林生态系统碳现存量为165.05 t·hm-2,其中活生物体碳现存量为61.2 t·hm-2,死生物体碳现存量为104.05 t·hm-2 (包括土壤中碳),土壤碳现存量为96 t·hm-2。土壤碳储量占总碳储量的58%,土壤是该地区森林生态系统主要的碳库,森林生态系统土壤中碳储量的变化必然引起整个区域碳储量整体动态的变化。     

陆地土壤碳循环的研究动态

１　引　言陆地碳循环不仅关系到陆地生态系统生产力的形成，同时也影响到整个地球系统的能量平衡，是陆地生态系统结构和功能的综合体现。近几十年来，由于人类活动引起大气ＣＯ２浓度的急剧上升，并可能导致全球气候变化，而且这种变化与陆地碳循环之间存在复杂的相互反馈机制，陆地碳循环已成为生态学、气候学、土壤学、生理学及地质学等众多学科研究的共同目标。在国际地圈生物圈研究计划（ＩＧＢＰ）中，碳循环也是全球尺度模型化工作最初集中的主要目标［１３］。然而由于陆地生态系统的多样性和复杂性，目前在陆地碳循环研究中仍存…     

The effects of tree rhizodeposition on soil exoenzyme activity, dissolved organic carbon, and nutrient availability in a subalpine forest ecosystem

Previous studies have found that root carbon inputs to the soil can stimulate the mineralization of existing soil carbon (C) pools. It is still uncertain, however, whether this “primed” C is derived from elevated rates of soil organic matter (SOM) decomposition, greater C release from microbial pools, or both. The goal of this research was to determine how the activities of the microbial exoenzymes that control SOM decomposition are affected by root C inputs. This was done by manipulating rhizodeposition with tree girdling in a coniferous subalpine forest in the Rocky Mountains of Colorado, USA, and following changes in the activities of nine exoenzymes involved in decomposition, as well as soil dissolved organic C, dissolved organic and inorganic nitrogen (N), and microbial biomass C and N. We found that rhizodeposition is high in the spring, when the soils are still snow-covered, and that there are large ephemeral populations of microorganisms dependent upon this C. Microbial N acquisition from peptide degradation increased with increases in microbial biomass when rhizodeposition was highest. However, our data indicate that the breakdown of cellulose, lignin, chitin, and organic phosphorus are not affected by springtime increases in soil microbial biomass associated with increases in rhizodeposition. We conclude that the priming of soil C mineralization by rhizodeposition is due to growth of the microbial biomass and an increase in the breakdown of N-rich proteins, but not due to increases in the degradation of plant litter constituents such as cellulose and lignin.     

Decomposer biomass in the rhizosphere to assess rhizodeposition

Quantification of the organic carbon released from plant roots is a challenge. These compounds of rhizodeposition are quickly transformed into CO₂ and eventually bacterial biomass to be consumed by bacterivores (protozoa and nematodes). Microbes stimulate rhizodeposition several-fold so assays under sterile conditions give an unrealistic value. Quantifying bacterial production from ³H-thymidine incorporation falls short in the rhizosphere and the use of isotopes does not allow clear distinction between labeled CO₂ released from roots or microbes. We reduced rhizodeposition in 3–5 week old barley with a 2 week leaf aphid attack and found that biomass of bacterivores but not bacteria in the rhizosphere correlated with plant–induced respiration activity belowground. This indicated top-down control of the bacteria. Moreover, at increasing density of aphids, bacterivore biomass in the rhizosphere decreased to the level in soil unaffected by roots. This suggests that difference in bacterivore biomass directly reflects variations in rhizodeposition. Rhizodeposition is estimated from plant-induced increases in bacterial and bacterivore biomass, and yield factors, maintenance requirements, and turnover rates from the literature. We use literature values that maximize requirements for organic carbon and still estimate the total organic rhizodeposition to be as little as 4–6% of the plant-induced respiration belowground.     

Microbial community dynamics associated with rhizosphere carbon flow

Root-deposited photosynthate (rhizodeposition) is an important source of readily available carbon (C) for microbes in the vicinity of growing roots. Plant nutrient availability is controlled, to a large extent, by the cycling of this and other organic materials through the soil microbial community. Currently, our understanding of microbial community dynamics associated with rhizodeposition is limited. We used a (13)C pulse-chase labeling procedure to examine the incorporation of rhizodeposition into individual phospholipid fatty acids (PLFAs) in the bulk and rhizosphere soils of greenhouse-grown annual ryegrass (Lolium multiflorum Lam. var. Gulf). Labeling took place during a growth stage in transition between active root growth and rapid shoot growth on one set of plants (labeling period 1) and 9 days later during the rapid shoot growth stage on another set of plants (labeling period 2). Temporal differences in microbial community composition were more apparent than spatial differences, with a greater relative abundance of PLFAs from gram-positive organisms (i15:0 and a15:0) in the second labeling period. Although more abundant, gram-positive organisms appeared to be less actively utilizing rhizodeposited C in labeling period 2 than in labeling period 1. Gram-negative bacteria associated with the 16:1omega5 PLFA were more active in utilizing (13)C-labeled rhizodeposits in the second labeling period than in the first labeling period. In both labeling periods, however, the fungal PLFA 18:2omega6,9 was the most highly labeled. These results demonstrate the effectiveness of using (13)C labeling and PLFA analysis to examine the microbial dynamics associated with rhizosphere C cycling by focusing on the members actively involved.     

冬季升温对高山生态系统碳氮循环过程的影响

全球温度升高是目前面临的重要环境问题,但存在明显的季节差异性,即冬季升温幅度显著高于夏季的季节非对称性趋势,这在高纬度和高海拔地区更加显著。冬季升温会直接影响积雪覆盖与冰冻层厚度,并引起冻融交替循环的增加,而冬季植物处于休眠状态,这会直接影响土壤中有效氮的吸收与损失,引起土壤有效氮可利用性的变化。然而,关于冬季增温对后续生长季节植物活动、土壤碳氮循环过程的影响等方面的研究仍存在诸多不确定。综述了冬季升温对积雪覆盖与冻融交替循环改变对高山生态系统物质循环的影响,以及冬季升温对土壤碳氮循环、微生物与酶活性的影响,并由此引起的植物物候期、群落结构、生产与养分循环与凋落物分解等生理、生态过程方面的研究进展。在未来的研究中,应针对不同生态系统特点选择合适的冬季增温方式,加强非极地苔原地区关于冬季升温的研究,注重关注冬季升温对植物-土壤微生物之间反馈作用的影响,重点关注冬季升温对生态系统的延滞效应。