祁连山阴阳坡菌根真菌群落分异机理研究

Slope aspect is a significant feature in mountain geography which modifies microclimate and influences ecological processes and spatial distribution of species and their interactions across natural landscape gradient. Landscape topography contributes to habitat heterogeneity by influencing microclimate, ground-water flow, and ecological processes such as biomass decomposition, nutrient cycling, soil formation and production. In the northern hemisphere, north-facing slopes are darker, moister, and colder because they receive less solar radiation than otherwise similar south-facing slopes. However, at local scale, the impact of slope aspect on community assembly of arbuscular mycorrhizal fungi(AMF) and biodiversity and ecosystem multiple functions (ecosystem) are poorly understood. Such insight is necessary to understand landscape community dynamics and multifunctionality. The south- and north-facing slopes in typical subalpine meadow of Qilianshan Moutain were selected and the following three problems were investigated: what are AM fungal species occurring on the two aspects and How distributed in the same environmental conditions; Whether the diversity of AM fungi and host plants are phylogeneticall related across sunny slopes and shading slopes or host phylogeny relatedness drives AM fungal composition; How the soil biodiversity links aboveground plant diversity and influences multiple ecosystem functions, defined as ecosystem multifunctionality. For this purpose, we establish the sample plots along different slopes and aspects. In each plot, the plant diversity and above biomass were counted, and take roots, plant stem and leaves, soil samples for the following parameter analysis: AM fungus community, spore diversity, root colonization, glomain-like enzymes and physical-chemical characteritics. The aims are to accumulate more evidence that the biological diversity is the foundation for the maintenance of ecosystems and sustainability.

生物多样性的形成、维持及群落的构建机制是生态学研究的主流。地下生物多样性与生态系统多功能性之间的关系是近年来关注的焦点和难点，尤其对于阴阳坡梯度上的自然分异机制，研究甚少。诗句“南枝向暖北坡寒，一样春风有两般”是指坡向不同，环境殊异的写照。本项目拟在祁连山自然保护区夏玛保护站，选择典型的阴阳坡，通过测定地表植物群落组成及功能特性，地下土壤及植物根系中AM真菌多样性、土壤AM真菌多态性、根外菌丝长度、球囊霉素以及环境要素，分析阴阳坡AM真菌群落组成和分布规律，阴阳坡AM真菌群落构建机制及其驱动AM真菌群落变化的关键生态学过程，探讨阴阳坡植物群落功能特性与AM真菌多样性的偶联机制，以及地下AM真菌与生态系统多功能性的关系，阐明阴阳坡梯度上AM真菌多样性分异机制，揭示阴阳坡梯度上植物-AM真菌的谱系相关性。为未来全球变化的背景下自然生态系统的有效管理和退化生态系统的重建提供科学依据。

坡向不仅改变微小气候和土壤形成过程，而且影响物种的生物地理格局及生态系统功能。解析阴阳坡地下微生物生物群落特征及其背后的潜在机制将有助于我们在环境变化日益频繁的今天更好地预测生态系统动态及其功能变化，亦将有助于生态系统的科学管理决策。本项目以丛枝菌根真菌（AMF）这一根际共生微生物为对象，选取祁连山高寒生态系统的典型阴阳坡，通过调查与坡向有关的诸多环境要素及地上植物群落的分布，综合地探究了AM真菌群落在阴阳坡上的分布格局及其关键影响因素，并进一步通过分析AM真菌其谱系结构和物种丰度分布，最终揭示了驱动AM真菌群落装配的主要生态学过程。我们的主要结果为如下。（1）阴阳坡微气候和土壤性质均存在显著差异。阳坡具有更高的光强、土壤温度及pH；而阴坡具有更高的土壤湿度及土壤肥力指数。从阴坡到阳坡，植物群落的地上净初级生产力及其物种丰富度均显著降低，且植物群落物种及谱系组成均在不同坡向上差异显著；土壤水分是最关键决定因子。（2）共发现4 科8属32种AM 真菌分子种(VT)，主要从属于球囊霉属(Glomus)。坡向从阳坡向阴坡变化，使得AM真菌物种多样性及其丰度显著下降，且导致了球囊霉属分子种的明显丧失以及根孢囊霉(Rhizophagus)属的优势地位。AM真菌群落的分类学和谱系上的组成在阴阳坡均存在显著的差异，而方差分解显示阴阳坡AM 真菌群落构成的差异主要由环境因素决定，其次为植物群落构成，而地理距离的影响则微乎其微。进一步的Mantel test 及结构方程模型表明AM真菌群落组成主要是由基于微气候、土壤pH和植物物种组成的生态位变化所决定的，而土壤水分则是其最关键的决定因素。（3）AM真菌群落谱系结构分析表明，AM真菌群落在阳坡上谱系聚集，而在阴坡上则谱系随机，表明AM真菌群落构建的首要生态过程结构由生态位主导的过滤向竞争排斥和生态位过滤的组合转变。AM真菌物种丰度分布分析显示，环境过滤是引起AM真菌群落组成与物种多样性变化的主要机制。