Knowledge Resource Center for Ecological Environment in Arid Area
| 土壤真菌在区域尺度下的多样性及其群落构建 | |
| 其他题名 | Regional diversity and community assemblages of soil fungi in natural ecosystems |
| 杨腾 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 褚海燕 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 真菌多样性是地球生物资源的重要组成。据估计，真菌的物种数介于150万到510万种之间。土壤是各类群真菌的大本营，其中，腐生真菌分解土壤有机质，推动土壤圈的养分循环与能量流动；菌根真菌与宿主植物共生，在不大量施用化肥的同时亦可保证作物的优质和高产；此外，某些土传病原真菌常蛰伏于土壤中，伺机侵染植物体，危害作物生长。因此，对土壤真菌的多样性及其群落构建的认识不仅关乎生物多样性的保护、生态系统多功能性的维持，更与我们的粮食生产、日常生活以及生态环境息息相关。先前，由于技术手段的限制，详尽的区域尺度下的真菌生物地理研究在我国还很缺乏。目前，国外的相关研究主要发现了气候、空间和土壤因素对真菌多样性和群落组成的显著影响，然而，就地上植物是如何制约土壤真菌在区域尺度下的多样性和群落构建，以及随机过程在极端环境下对真菌群落构建的可能影响等问题还未有明确的答案。我国幅员辽阔，生态系统类型多样，从西到东，降雨量逐增，植被类型也从西部的荒漠草地，过度到高寒草原，再转变为东部的山地森林。在不同的生态系统下，生物多样性资源和群落构建的特点是不同的。本论文基于长期的野外采样工作，共收集三种不同生态系统下的土壤样品，包括了青藏高原西部的荒漠草地、青藏高原东中部的高寒草原、以及我国东部的五座山地森林（长白山、东灵山、神农架、天目山和古田山），共计549份土壤样品。利用Illumina Miseq PE250测序平台，我们靶标真菌的ITS区段，并结合土壤理化性质、气候、地上植被、空间与地形数据对土壤真菌在区域尺度下（跨度在1000 km左右）的多样性及其群落构建过程加以研究，找寻驱动真菌多样性及其群落分布的关键因素。具体的：（1）青藏高原西部的荒漠草地，平均海拔4500米以上，年降雨量约100毫米，八级以上年大风日数149天，对大部分动植物而言，堪称“生命之禁区”。在本研究中，我们采用高通量测序，靶标真菌的ITS2区段，研究了该区表层（0-15cm）和亚表层（15-30cm）土壤的真菌多样性及其群落分布，并对随机过程和确定性过程在不同土层的真菌群落构建过程中的相对影响加以探究。研究表明：i）表层土壤真菌的多样性极显著大于亚表层土壤真菌的多样性；ii）真菌的群落组成在上下层显著分异，其中，表层土壤与亚表层土壤之间（厘米尺度）的真菌群落的差异性显著地大于样地之间（公里尺度）的表层土壤的真菌群落差异；iii）随机过程主导了表层土壤真菌的群落构建，伴随高度的扩散，形成了样地间物种库随机的高度重合。如，在表层土壤中，132个真菌OTUs出现在所有表层样品中，占总序列数的60%，并且气候和空间对表层土壤真菌的群落变异的解释率只有6%。综上，研究结果表明了土壤深度对真菌的多样性、群落组成和群落构建过程的显著影响，暗示了在极端环境下，高度进化的真菌孢子可能打破动植物地域性分布的常见规律。（2）高寒草原是生物响应气候变化的敏感区域，然而，其地上植物群落与地下真菌群落的关系如何，还未见报道。在此，我们发现土壤碳氮比、总磷、溶解性有机碳和植物物种多样性是真菌alpha多样性的最强预测因子，而年降雨和植物生产力是植物多样性的最强预测因子。土壤真菌多样性，包括alpha多样性（指每个样地内的真菌物种多样性）和beta多样性（指两两样地间的群落组成差异），与相对应的植物alpha多样性和beta多样性呈极显著的正相关。当我们用偏分析控制了真菌和植物多样性共同的环境驱动因子，以及地理距离的影响后，这种显著的正相关性仍然存在。结构等式模型和多元回归模型一致地表明植物多样性直接地影响真菌多样性，暗示资源的多样性（如宿主植物的多样性和营养底物的多样性）可能是植物多样性直接影响真菌多样性的主要原因。然而，植物生产力对真菌多样性的影响主要是通过增加的植物多样性来间接完成的。综上，本研究反映了极强的单向的植物多样性对土壤真菌多样性的影响，对我们合理保护地下生物资源，特别是保护土壤真菌资源有一定的参考价值。（3）相较荒漠和草原，森林拥有更为复杂的层级系统、多样的生境和更多的生物资源。其中，不乏高大的乔木和低矮的灌木，还包括了种类与功能都高度多样化的真菌类群。尽管在森林中，树木个体间通过菌根网络维持密切的联系，然而就具体的树木种属对其邻近土壤真菌群落的影响还未有详尽报道。在此，我们首次收集了343份对应不同树木个体的邻近土壤样品（以树木胸径为范围），包括了我国东部的五座山地森林共22个不同的植物属。结合土壤性质、地理地形信息、气候数据、树木功能性状以及植物种属信息，我们研究了森林土壤真菌多样性的分布规律及其制约因子，特别是树木种属对邻近土壤真菌群落构建的可能影响。结果表明：i）海拔、pH和总碳是土壤真菌多样性的最佳预测因子，但只累积解释了12%的多样性的变化；ii）年降雨、年均温和pH是驱动土壤真菌群落分布的三个最强因子；iii）在区域尺度以及五个森林内部，随空间距离的增加，土壤真菌的群落相似性显著下降。然而，相比于空间距离对真菌群落的影响，当代环境因子才是真菌群落分布的最主要因素；iv）植物种属对真菌多样性以及群落组成也有显著影响，且这种影响随着植物分类程度的提高而显著上升，暗示了树木与其邻近土壤真菌间的基因兼容性。 |
| 英文摘要 | Fungal diversity is an essential component of Earth bio-resources. It is estimated that species diversity of environmental fungi is between 1.5 million and 5.1 million. Especially in natural ecosystem, such as forest, grassland and desert, there are hyper-diverse fungal species. Among these, saprotrophs account for an abusulute number of percentages of functional guilds, which strongly promote carbon-nitrogen cycling and energy flow in pedosphere by degrading organic matters. There are still various kinds of symbiotic fungi, such as arbuscular mycorrhizal fungi, ectomycorrhizal fungi, dark septate endophytes, foliar endophytes and ericoid mycorrhizal fungi. During some parts of their life stage, they live with host plants, helping plants absorb water and nutrients, as well as adapt to the variable soil and climatic conditions. Some symbionts can also modify the diversity and community assembly of plants. Likewise, some of soil-borne pathogenic fungi often remain dormant or inactive in soils. Once the opportunity ripes, they will infect plants. A few members of pathogens can cause serious plant diseases, impairing agricultural production as well as forest resources. Therefore, the understanding on diversity and distribution of soil fungi is not only related to the biological diversity conservation and manitance of ecosystem multifunctionality, but also directly affect our agricultural production, ecological environment and daily life. Currently, the studies have shown the significant effects of soil, climate and space on fungal communities, however, the roles of floristic factors and stochastic dispersal in structuring fungal communities are still limited.China has various ecosystem types. From west to east, with increasing precipitation, the vegetation types include desert steppe, alpine grasslands and mountain forests. Biodiversity resources and community assemablages are different with repect to ecosystems. Based on the long field work, we collected 549 soil samples and measured the edaphic, climatic, geographic and floristic data, which included Ngari drylands in Tibet, natural grasslands in the Tibetan Plateau and five mountain forests in Eastern China. We addressed the fungal diversity, community composition and the associated drivers at the regional scale (here we defined the transcect range about 1000 km) by using Illumina sequencing of the ITS region for fungal identification. Specifically:(1) Recent studies have showed patterns in the surface-soil fungal diversity and biogeography over the broad spatial scales around the world. However, less is known about variation in the subsurface-soil (15–30 cm of depth) fungal communities, especially under the extreme soil conditions of cold, infertile and water-deficient. Here we studied depth profiles of fungal assemblages in Ngari drylands, Tibet. The relative abundance of Basidiomycota and Zygomycota was higher in surface layers, while that of Ascomycota was higher in subsurface layers. The alpha diversity (including observed OTUs and predicted Chao1) in surface layers was extremely higher than that in subsurface layers (P<0.001). Fungal communities significantly differed between the two layers, strongly correlating with the variation in soil C:N ratio and precipitation seasonality. Likewise, fungal community dissimilarity between the surface and subsurface soil in each single site was significantly larger than that between different surface-soil samples that are separated hundreds of kilometers apart. Both dispersal limitation and environmental selection had weaker effects on communities in surface layers as reflected by negative deviations from the null model expectations, which was also corroborated by Mantel test and multivariate analysis. 132 cosmopolitans were observed in all the surface-soil samples accounting for 60% of total sequences, while only 4 OTUs were shared among all the subsurface-soil samples, which substantiated high dispersal in surface soil layers on this extreme environment. Taken together, these results reveal the random distribution of surface-soil fungal communities due to high dispersal and the absence of edaphic effects. Oppositely, the deterministic process with respect to soil, climate and space play more important roles in subsurface soil layers.(2) Previous studies have revealed that correlations exist between soil fungal richness and plant richness from local to global scales, but there is limited information about the direct causal effects and the role of productivity. Here we addressed the direct and indirect effects of plant diversity and productivity on soil fungi across 60 grassland sites on the Tibetan Plateau by using Illumina sequencing of the ITS2 region for fungal identification. Fungal alpha and beta diversity were best explained by plant alpha and beta diversity, respectively, when accounting for environmental drivers and geographic distance. Multiple regression and structural equation modeling collectively indicated that plant richness had a direct positive effect on fungal richness, and plant productivity affected fungal richness indirectly through enhanced plant richness. However, the effects of plant richness on fungal richness were not evident for fungal functional guilds. AM plant coverage and site productivity enhanced arbuscular mycorrhizal and ectomycorrhizal fungal richness, respectively. Our study points to the strong unidirectional effect of plant diversity on the soil fungal richness. Path analyses are required to disentangle the directionality and internal relationships of complex environmental predictors for addressing richness-to-richness effects.(3) Compared with desert and grassland, forest owns highly hierarchical structure and various habitats, as such there are more diverse biological resources, such as gaint trees, low shrubs and hyper-diverse fungal speices. Some studies reported that fungal community composition was significantly affected by plant diversity and vegetation types, yet there is lack of the reports about neighboring effects of tree species on soil fungal community assemblages. Here, we sampled 343 soils near the tree individuals (the range of diameter at breast height), which covered five mountain forests (From north to south: Changbai Mountain, Dongling Mountain, Shengnongjia Mountain, Tianmu Mountain and Gutian Mountain) and twenty-two different plant genera. Based on soil properties, geographic and terrain information, climatic variables, tree’s functional traits and plant species identity, we explored fungal diversity pattern and its drivers, especially for the neighboring effects of tree species on soil fungal community assemblages. The results showed: i) Elevation, pH and soil carbon were the strongest predictors of soil fungal alpha diversity in the best OLS multiple regression models; ii) Mean annual precipitation, mean annual temperature and soil pH are the strongest predictors of fungal community composition; iii) Within the different scales of five mountains and across the whole regional scale, fungal community dissimilarity all increased with the increasing geographic distance, however, the spatial effect was mainly resulted from the variation of current environment, which was supported by partial Mantel tests and multivariate analyses; iv) the plant speices identity also significantly affected the richness and community composition of neighboring soil fungi. As the taxonomic resolution of plants increased, this plant effect increased accordingly, which indicated genetic compatibility between trees and soil fungi in forests. |
| 中文关键词 | 荒漠草地 ; 高寒草原 ; 山地森林 ; 土壤真菌 ; 多样性和群落构建 |
| 英文关键词 | desert steppe alpine grasslands mountain forests soil fungi diversity and community assemblages |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 环境科学 |
| 来源机构 | 中国科学院南京土壤研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287894 |
| 推荐引用方式 GB/T 7714 | 杨腾. 土壤真菌在区域尺度下的多样性及其群落构建[D]. 中国科学院大学,2017. |
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