| 题名 | 中国北方草地生态系统中丛枝菌根真菌的丰度和多样性对环境因子的响应 |
| 作者 | 胡亚军 |
| 学位类别 | 博士 |
| 答辩日期 | 2014-11 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 陈保冬 |
| 关键词 | 干旱与半干旱草原 气候变化 AM真菌 多样性 微生物群落 碳循环， |
| 其他题名 | Abundance and biodiversity of AM fungi response to environmental factors in the grasslands of northern China |
| 学位专业 | 生态学 |
| 中文摘要 | 我国北方干旱与半干旱草原退化问题一直是环境科学家关注的焦点，在全球气候变暖和人类干扰的影响下，该地区的荒漠化程度日益扩大。目前，针对该地区的生态学研究主要集中在地上生态过程，如：草场退化、植被演替等，鲜有研究关注地下生态过程，尤其缺乏土壤功能微生物分布特征及其生态功能研究。丛枝菌根真菌（arbusuclar mycorrhzial fungi, AMF）能与绝大多数的陆地高等植物形成菌根共生体，对植物适应生物与非生物胁迫有重要积极作用，同时也深刻影响土壤碳氮循环。因此，研究 AM真菌分布特征、多样性及其对环境因子的响应，有助于我们理解脆弱生态系统的地下生态过程。本研究以我国北方干旱与半干旱草原为研究对象，采用宏观与微观相结合的方法，在区域尺度上研究 AM真菌的分布特征、多样性、环境影响因素及稳定土壤碳库的潜在作用。在中观和微观尺度研究菌根真菌群落对气候变化的响应及菌根共生体系调控宿主植物适应气候变化的机制。本研究的主要内容和结果归纳如下： （1）为揭示中国北方干旱与半干旱草原中影响 AM真菌生物量的环境因子，探讨该区域 AM真菌在土壤碳固持方面的生态重要性，通过野外调查取样，结合多元统计与结构方程模型（Structural Equation Modeling, SEM）分析环境因子对 AM真菌生物量的影响，建立 AM真菌相关参数（菌根侵染率、菌丝密度、易提取球囊霉素、总球囊霉素）与土壤碳库的相关关系。研究结果表明，AM真菌菌丝密度与年均温显著正相关，与土壤肥力显著负相关。在有机碳含量较低的土壤中AM真菌生物量较高。基于区域年均温与土壤碳 库间的显著负相关关系，而与菌丝密度呈显著正相关，暗示AM真菌在气候温暖化下情形下有稳定土壤碳库的作用。 （2）我们进一步利用磷脂脂肪酸技术（phospholipid fatty acid, PLFA）定量测定土壤碳库的主要分解者（细菌和腐生真菌）和贡献者（AM真菌），考查环境因子对不同微生物类群的差别影响。研究结果表明，土壤肥力是影响细菌和腐生真菌的主要正驱动因子，这与上述环境因子影响 AM真菌的情况恰恰相反。在相对贫瘠的土壤中，参与土壤碳矿化的细菌和腐生真菌减少，而 AM真菌的生物量增加，表明 AM真菌对土壤碳库相对贡献增大。本研究进一步说明 AM真菌在土壤碳固持中的潜在重要性。 （3）在中国东北样带，沿降雨量梯度（253.4 mm–397.4 mm）采样，利用454高通量测序技术研究AM真菌多样性及生态分布规律。研究结果表明，AM真菌在荒漠草原、典型草原和草甸草原都具有较高的多样性，其Shannon-Wiener多样性指数和丰富度（Richness）并未受到降雨量的影响。Shannon-Wiener多样性指数与年均温和土壤pH值负相关，与植物地下生物量正相关。典范对应分析（Canonical Correspondence Analysis，CCA）结果表明，在测定的环境因子中，年均温、年均降雨量、有机碳和土壤碳氮比对AM真菌群落结构显著影响。在不同种属的 AM真菌中，根内根生囊霉（Glomeraceae Rhizophagus）相对生物量与植物地下生物量显著正相关，而其它 AM真菌种属（如：Gigasporaceae Scutellospora、Diversisporaceae、Diversispora）相对生物量与植物地下生物量关系不显著，表明不同种属的 AM真菌对环境因子的适应性不同。AM真菌多样性与植物多样性关系不显著，说明在大尺度下，AM真菌多样性并未受到植物多样性的影响，至少在区域尺度上挑战了菌根多样性调控植物多样性的假说。 （4）依托内蒙古多伦全球变化多因子试验（GCME）平台，在干旱与半干旱草原生态系统原位模拟增温和增雨情形，采用定量 PCR技术定量分析增温和增雨对 AM真菌及其他真菌类群丰度的差别影响；利用 Miseq高通量测序技术分析增温和增雨对土壤 AM真菌和真菌多样性的影响。研究结果表明：增温对土壤理化因子影响较小，而增雨提高了土壤含水量和碳氮比。增雨降低了真菌生物量，对 AM真菌生物量影响尤为显著，且显著改变AM真菌和真菌群落结构。增温对真菌和 AM真菌生物量影响不显著，对AM真菌和真菌群落结构影响亦不显著，但可通过交互作用影响真菌丰富度和Shannon-Wiener多样性指数。总的来说，在我国干旱与半干旱区，降雨量不仅决定了植物生产力，而且深刻影响到土壤真菌群落结构。 （5）室内模拟晚间增温情形，研究晚间增温对菌根共生体及宿主植物蒺藜苜蓿（Medicago truncatula L.）生理生态的影响。研究结果表明，晚间增温1.53℃显著降低了植物根系生物量、叶片糖含量、地上部和根系 P、Zn浓度，花和籽粒数量。然而，接种 AM真菌能够减缓晚间增温对植物营养和生殖生长、矿质养分吸收的不利影响。晚间增温和接种AM真菌对植物根部的蔗糖浓度和蔗糖合成酶基因（MtSucS1, MtSucS4, MtSucS5）表达的交互作用表明AM真菌与晚间增温共同调节植物的碳代谢过程。晚间增温提高了菌根侵染率，但对丛枝丰度、共生基因表达和根外菌丝密度无显著影响，表明晚间增温总体上对菌根共生体建成和发育无明显消极影响。我们的试验表明植物对气候变暖的响应并不是简单取决于植物种类和环境条件，菌根共生体系在植物应对气候变化的弹性应变方面起到不容忽视的作用。 |
| 英文摘要 | The desertification of the arid and semi-arid grasslands in northern China, as a result of human disturbance and climate changes, has become a threat to the local ecological safety. Previous studies have focused on the above-ground ecological processes (grassland degradation, vegetation succession, etc.) in this region.However, little is known about the impacts of environmental changes on the soil functional microbial communities and their ecological functions. Arbuscular mycorrhizal (AM) fungi are ubiquitous symbionts of higher plants in terrestrial ecosystems. It has been well documented that the symbiotic fungi could protect their host plant against various environmental stresses and it also has profound impact on soil carbon and nitrogen cycles. Therefore, studies on the AM fungal diversity and function were very important for understudying soil ecological processes in fragile ecosystems. In this study, we integrated macroscopic and microscopic analyses to investigate AM fungal diversity, distribution and its potential role in soil carbon stabilization in the arid and semi-arid grasslands across northern China. The main results are as follows: (1) To reveal the regional distribution pattern of AM fungi as driven by multiple environmental factors, and also to understand the ecological importance of AM fungi in natural ecosystems, we carried out a field investigation on AM fungal abundance along environmental gradients in the arid and semi-arid grasslands of northern China. Statistical analyses were performed to reveal the relative contribution of climatic, edaphic and vegetal factors to AM fungal abundance,especially for extraradical hyphal length density (HLD) in the soil. The multiple regressions and structural equation model showed that MAT was the key positive contributor and soil fertility was the key negative contributor to HLD. With regard to the obvious negative correlation between MAT and SOC in the research area, the positive correlation between MAT and HLD implied that AM fungi could potentially mitigate soil carbon losses especially in infertile soils under global warming. (2) Based on the field investigation in the arid and semi-arid grasslands in northern China, we further examined the impact of environmental factors on the major decomposers (bacteria and saprophytic fungi) and contributor (AM fungi), which play key roles in soil carbon cycling. We investigated soil microbial community composition by quantifying the microbial phospholipid fatty acids (PLFAs). The results showed that soil organic carbon (SOC) was the main positive contributor to microbial biomass, while the mean annual temperature (MAT) served as the main negative factor, which was opposite to environmental factor affecting to AM fungi.The lower abundance of saprophytic microorganism, while the higher abundance of AM fungi in the infertile soil could potentially stabilize the soil carbon pool. Therefore, these results further supported the importance of AM fungi in the soil carbon stabilization. (3) The 454 sequencing technology was applied to investigate AM fungi diversity in the Northeast China Transect along precipitation gradient. The results showed that AM fungi exhibited high diversity in the meadow steppe, typical steppe and desert steppe. The Shannon-Wiener diversity indexes of AM fungi were not affected by mean annual precipitation (MAP), but negatively affected by the mean annual temperature (MAT), soil pH, and positively affected by the plant root biomass. Canonical correspondence analysis (CCA) showed that the MAT, MAP, SOC and C/N ratios significantly affected AM fungal community. The relative abundance of Glomeraceae Rhizophagus was significantly positively correlated with belowground plant biomass, while relative abundance of other species showed no significant correlation with the root biomass, indicating that different AM fungal species may respond differently to environmental factors. The fact that AM fungal diversity was not affected by plant diversity at least challenged the hypothesis that mycorrhizal fungal diversity determines plant diversity at regional scale. (4) We simulated scenarios of climate change (warming and precipitation increasing) in situ in the typical steppe in northern China. Real-time PCR and Miseq high-throughput sequencing were performed to reveal the effects of increased temperature and precipitation on the abundance and diversity of fungal taxa including AM fungi. The results showed that warming had no effect on soil physico-chemical properties, while increased precipitation increased soil moisture content and C/N ratio. Furthermore, increased precipitation reduced the AM fungal and total fungal biomass, and changed the fungal community structure. By contrast,warming had no effect on the AM fungal and total fungal biomass, and also the fungal community structure. However, increased temperature could indirectly affect the fungal richness and Shannon-Wiener diversity via interacting with the precipitation. In general, the precipitation not only determined the plant production,but also drived the microbial community in the grassland in northern China. (5) In a pot experiment, we investigated the physiological traits of Medicago truncatula L. in association with AM fungus Rhizophagus intraradices under simulated night warming. The experimental results indicated that a constant 1.53℃ increase of night temperature significantly reduced plant shoot and root biomass,flower and seed number, leaf sugar concentration, and shoot Zn and root P concentrations. However, the AM association increased plant shoot and root biomass, root to shoot ratio, and shoot Zn and root P concentrations under night warming, which essentially mitigated the negative effects of night warming. The significant interaction of AM inoculation with night warming in influencing both root sucrose concentration and the expression of sucrose synthase (SusS) gene suggested that AM fungi and night warming jointly regulated plant sugar metabolisms. Night warming stimulated the AM fungal colonization, but did not influence arbusuclar abundance, expression of symbiosis-related gene and growth of extraradical mycelium (ERM), indicating little effect of night warming on the development of AM symbiosis. Our findings highlighted the importance of mycorrhizal symbiosis in assisting plant resilience to climate changes. |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/34358]  |
| 专题 | 生态环境研究中心_城市与区域生态国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 胡亚军. 中国北方草地生态系统中丛枝菌根真菌的丰度和多样性对环境因子的响应[D]. 北京. 中国科学院研究生院. 2014. |
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