The significance of ericoid mycorrhizal mycelium for carbon turnover in heathland

杜鹃花菌根菌丝体对石南地碳周转的意义

• 批准号: NE/F013760/1
• 金额: $ 8.56万
• 依托单位: University of Aberdeen
• 依托单位国家: 英国
• 项目类别: Training Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF013760%2F1
• 关键词: significance; ericoid; mycorrhizal; mycelium; carbon

Ericaceous plants (Calluna, Vaccinium etc) are major components of boreal forest, heathlands and peatlands. These biomes contain enormous quantities of carbon and so play a key role in global biogeochemical cycles. In nature, most plants are mycorrhizal and the autotrophs allocate large amounts of photosynthate very rapidly to their fungal partners, and in return the fungi provide host plants with increased quantities of nutrients. Ericaceous plant roots associate with ericoid mycorrhizal fungi but, unlike other mycorrhizal types, virtually nothing is known of their functional importance in the carbon cycle. Because ericaceous plants have low primary productivity, it has been suggested that their fine 'hair' roots and the external mycelium of the ericoid mycorrhizal fungi that colonise them are one of the most important inputs of relatively labile carbon to heathland soils, although this hypothesis remains to be tested. This lack of knowledge represents a major gap in our understanding of soil biodiversity and ecosystem functioning; these are two priority areas of NERC's research strategy. In addition to its likely role as an important carbon source to heathland soils, external ericoid mycorrhizal mycelium also has an active role in regulating nutrient cycles. The nature of litter produced by ericaceous plants is highly recalcitrant and comprises large quantities of phenolic compounds. The fungi forming ericoid mycorrhizas (e.g. Hymenoscyphus ericae) have adapted to these oligotrophic conditions and it is thought that they are crucial components of the microbial biomass for regulating decomposition rates. Simplified laboratory experiments have demonstrated that the breakdown of complex phenolic compounds by H. ericae is facilitated by production of extracellular enzymes, such as laccases, by the external mycelium. While direct evidence for laccase production by ericoid mycorrhizal fungi when grown in symbiosis with a host plant still remains to be obtained, it is thought that such enzymes are released to facilitate nutrient acquisition by the fungal partner from soil organic matter. There is some evidence for considerable diversity in laccases among potentially ericoid mycorrhizal ascomycetes, yet little is known about the genetic diversity, mode of action, and modulation of laccases and other phenol oxidases in such systems. This project will test the hypothesis that ericoid mycorrhizal mycelium has a key role in carbon turnover in heathlands. We will 1) determine rates of turnover of ericoid mycorrhizal mycelium in a range of field conditions, 2) determine the rates of photosynthate transfer from host plant to hair roots and external mycelium in microcosm systems and in the field, 3) determine the potential for different ericoid mycorrhizal fungi to produce laccases and determine how the production of laccases is regulated, and 4) establish if there is a link between carbon supply to ericoid mycorrhizal fungi, laccase gene expression and resource transfer to the host plant. This project will use a range of techniques in routine use in our laboratories including stable and radioisotopes, molecular biology and synthesis of microcosm systems to manipulate combinations of plant and ericoid mycorrhizal fungi. Mycelial turnover will be studied using 13C labelled mycelial material from ericoid mycorrhizal fungi. This will be introduced into microcosms containing plants grown in the mycorrhizal and non-mycorrhizal condition, and into the field in litterbags. The fungal assemblages colonising decomposing carbon sources in the field will be characterised using molecular fingerprinting techniques targeting the ribosomal internal transcribed spacer (ITS) region. The genetic diversity and activity of polyphenol oxidase (PPO) enzymes involved in the degradation of litter will be studied using PPO enzyme activity assays and molecular fingerprinting techniques.

杜鹃花植物（Calluna、越橘等）是北方森林、荒地和泥炭地的主要组成部分。这些生物群落含有大量的碳，因此在全球生物地球化学循环中发挥着关键作用。在自然界中，大多数植物都是菌根，自养生物非常迅速地将大量光合产物分配给它们的真菌伙伴，作为回报，真菌为宿主植物提供更多的营养。杜鹃花植物根与杜鹃花菌根真菌相关，但与其他菌根类型不同，实际上对其在碳循环中的功能重要性一无所知。由于杜鹃花植物的初级生产力较低，因此有人认为，它们的细“毛”根和寄生在其上的杜鹃花菌根真菌的外部菌丝体是向石南地土壤输入相对不稳定的碳的最重要输入之一，尽管这一假设仍有待检验。这种知识的缺乏表明我们对土壤生物多样性和生态系统功能的理解存在重大差距；这是 NERC 研究战略的两个优先领域。除了可能作为石南地土壤的重要碳源外，外部环状菌根菌丝体在调节养分循环方面也发挥着积极作用。杜鹃花植物产生的垃圾性质非常顽固，并且含有大量酚类化合物。形成杜鹃花菌根的真菌（例如杜鹃花膜囊菌）已经适应了这些寡营养条件，并且认为它们是调节分解速率的微生物量的关键组成部分。简化的实验室实验表明，外部菌丝体产生胞外酶（例如漆酶）促进了埃里克斯菌对复杂酚类化合物的分解。虽然仍然没有获得与寄主植物共生生长时杜鹃花菌根真菌产生漆酶的直接证据，但人们认为释放此类酶是为了促进真菌伙伴从土壤有机物中获取养分。有一些证据表明，潜在的杜鹃花菌根子囊菌中的漆酶具有相当大的多样性，但对于此类系统中漆酶和其他酚氧化酶的遗传多样性、作用方式以及调节知之甚少。该项目将检验杜鹃花菌根菌丝体在荒地碳周转中发挥关键作用的假设。我们将 1) 确定各种田间条件下蓟马菌根菌丝体的周转率，2) 确定微观系统和田间中从宿主植物到毛根和外部菌丝体的光合产物转移率，3) 确定不同杜鹃花菌根真菌产生漆酶的潜力并确定如何调节漆酶的产生，4) 确定碳供应与碳供应之间是否存在联系。杜鹃花科 菌根真菌、漆酶基因表达和资源转移到宿主植物。该项目将使用我们实验室常规使用的一系列技术，包括稳定同位素和放射性同位素、分子生物学和微观系统合成，以操纵植物和杜鹃花菌根真菌的组合。将使用来自杜鹃花菌根真菌的 13C 标记的菌丝体材料来研究菌丝体周转。这将被引入含有在菌根和非菌根条件下生长的植物的微观世界，并通过垃圾袋引入田间。将使用针对核糖体内部转录间隔区（ITS）区域的分子指纹技术来表征田间定殖分解碳源的真菌组合。将使用 PPO 酶活性测定和分子指纹技术来研究参与凋落物降解的多酚氧化酶 (PPO) 的遗传多样性和活性。