The importance of intra- and interspecific diversity of ectomycorrhizal fungi on ecosystem functioning

生物多样性包含许多不同的“层面”，包括物种和基因型（即属于同一物种的不同个体）。物种之间的功能、分散、竞争和其他特征和过程的变化支持了生态系统受到现存物种数量的极大影响的观点。然而，在物种内部也可以看到类似的变异，但实际上对这种基因型变异对生态系统功能的作用一无所知。此外，支持物种和基因型多样性作用的生态学理论很少在土壤微生物方面得到检验。事实上，目前的生物多样性理论主要是从植物和动物发展起来的，由于土壤微生物的生理、形态、多样性和丰度都大不相同，因此对土壤微生物的适用性可能有限。这是一个重要的遗漏，因为土壤微生物在调节分解速率、植物生长、碳循环和其他重要过程中发挥着重要作用。因此，本项目测试土壤微生物的种间和种内多样性（种内或基因型多样性）对生态系统功能的作用。所使用的生物群是所谓的“外生菌根”真菌。这些真菌与植物根系形成非常密切的联系，并依赖于它们的寄主植物提供碳。寄主植物依赖真菌提供氮等矿质养分，因此，这种共生关系在调节植物生长和养分循环的速度方面起着核心作用。正在测试的中心思想是种间和种内多样性可以对生态系统产生i)直接影响，例如通过生态位互补过程（不同个体利用总资源库不同组成部分的能力），或ii)间接影响，即种内多样性可以影响物种多样性，反之亦然。此外，这些过程和相互作用可能受到环境异质性等外部驱动因素的调节。实验将验证4个特定假设：1)ECM真菌的种内和种间多样性增加了植物和真菌的生产力；2)由于生态位互补性，当土壤养分资源化学组成复杂时，种内和种间ECM多样性对生产力的影响最大；3)种内物种多样性和种间物种多样性对生态系统过程（DOC和无机氮渗滤液造成的资源损失、土壤呼吸）都有可量化的影响。4)ECM种内多样性有助于维持ECM物种丰富度，反之亦然。这些将通过构建包含微型“森林”的实验室微观环境和室外中生态环境进行测试，其中标准数量的桦树宿主树每棵都支持一种外生菌根真菌的个体基因型。将建立一系列实验来操纵物种和基因型多样性。进一步的处理将使我们能够测试资源异质性对模型生态系统性能的影响。我们将结合真菌的分子分析来确定种群如何随时间变化，并结合生态生理学测量来确定群落在植物生产力、土壤二氧化碳外排、真菌生物量以及氮和碳淋滤方面的差异。该项目将确定在高等生物中看到的生态学理论在多大程度上可以转化为土壤真菌，并将增加我们对北方和北温带森林土壤生物多样性功能意义的理解。此外，它将帮助保护主义者和土地所有者制定有效的政策，以更好地管理土壤的生物多样性。

Biodiversity encompasses many different 'levels', including species and genotypes (i.e. different individuals belonging to the same species). Variation in function, dispersal, competition and other traits and processes between species supports the idea that ecosystems are greatly affected by the number of species present. Yet similar variation is also seen within species but virtually nothing is known about the role of this genotypic variation for ecosystem functioning. Moreover, the ecological theory underpinning the role of both species and genotypic diversity has rarely been tested in relation to soil microorganisms. Indeed, current biodiversity theory developed largely from plants and animals is likely to have limited applicability to soil microorganisms because of their vastly different physiology, morphology, diversity, and abundance. This is a crucial omission because soil microorganisms have major roles in regulating rates of decomposition, plant growth, carbon cycling and other important processes. This project therefore tests the role of both between (interspecific) and within species diversity (intraspecific or genotypic diversity) of soil microorganisms on the functioning of ecosystems. The group of organisms used are so called 'ectomycorrhizal' fungi. These fungi form very close associations with plant roots and are dependent on their host plant for carbon. The host plant is dependent on the fungi for mineral nutrients like nitrogen, and so together, the symbiosis has a central role in regulating the rates at which plants grow and nutrients are recycled. The central ideas being tested are that inter and intraspecific diversity can have i) direct effects on ecosystems, for example through the process of niche complementarity (the ability of different individuals to exploit different components of the total resource pool), or ii) indirect effects, whereby intraspecific diversity can affect species diversity and visa versa. Further, these processes and interactions may be regulated by external drivers like environmental heterogeneity. The experiments will test 4 specific hypotheses: 1) Plant and fungal productivity increase in response to both intra- and interspecific diversity of ECM fungi; 2) The effects of intra- and interspecific ECM diversity on productivity are greatest when the chemical composition of nutrient resources in soil are complex, due to niche complementarity; 3) Both intra- and interspecific species diversity have quantifiable effects on ecosystem processes (Loss of resources via DOC and inorganic N leachate, soil respiration) 4) ECM intraspecific diversity helps maintain ECM species richness and vice versa. These will be tested by constructing laboratory microcosms and outdoor mesocosms containing miniature 'forests', in which a standard number of birch host trees each support an individual genotype of an ectomycorrhizal fungus. A range of experiments will be constructed to manipulate both species and genotypic diversity. Further treatments will enable us to test the effects of resource heterogeneity on the performance of the model ecosystems. We will combine molecular analyses of the fungi to determine how the populations change with time and ecosphysiological measurements to determine how the communities differ in plant productivity, soil CO2 efflux, fungal biomass and nitrogen and carbon leaching. This project will establish the extent to which ecological theory seen in higher organisms can be translated into soil fungi, and will increase our understanding of the functional significance of soil biodiversity in boreal and northern temperate forests. Moreover, it will help conservationists and land-ownder formulate effective policies to better manage the biodiversity of soil.