不同积雪覆盖期荒漠齿肋赤藓结皮层丛枝菌根真菌多样性变化

Variation of arbuscular mycorrhizal fungi(AMF)biological diversity in the mosses crust layer of desert during snow cover season

【背景】温带荒漠有积雪背景条件下的荒漠苔藓植物与丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)共生关系的研究非常有限。【目的】揭示不同积雪覆盖期(降雪前、雪盖期、融雪期)齿肋赤藓结皮层中AMF多样性的差异,为正确认识荒漠特色植物与微生物在冬季积雪期互利的重要生存策略提供数据支撑。【方法】利用高通量测序技术,分析稳定积雪期的古尔班通古特沙漠优势苔藓齿肋赤藓结皮AMF群落组成与多样性状况,尤其是降雪前和融雪期AMF群落结构差异。【结果】降雪前、雪盖期及融雪期检测到的OTU分属于球囊菌门(Glomeromycota)的5目9科11属,其中,近明球囊霉属(Claroideoglomus)、原囊霉属(Archaeospora)、类球囊霉属(Paraglomus)和球囊霉属(Glomus)为优势类群;降雪前和融雪期齿肋赤藓结皮层中绝对优势属(>50%)均为近明球囊霉属。群落丰富度Chao1指数和ACE指数均表现为雪盖前>积雪期>融雪期,表明降雪减少了AMF群落丰富度。近明球囊霉属融雪期比例大幅增加,而类球囊霉属、球囊霉属则较降雪前比例下降。基于MEGAN的分类学组成信息可视化分析表明,低丰度AMF类群更容易受到影响,无梗囊霉属(Acaulospora)主要集中在降雪前采集的样品中,而多样孢囊霉属(Diversispora)主要集中在融雪期样品中。结合聚类分析的属水平群落组成热图发现,高丰度分类单元的类别由降雪前的5种集中为2种。主成分分析结果表明,主成分1能够区分降雪前后的AMF群落结构特征,进一步验证降雪缺失对藓类结皮层AMF群落组成有筛选作用。高丰度优势属近明球囊霉属和球囊霉属之间、类球囊霉属和原囊霉属之间均呈现负相关,可能存在竞争关系;低丰度属巨孢囊霉属(Gigaspora)、隔球囊霉属(Septoglomus)、双型囊霉属(Ambispora)、盾巨孢囊霉属(Scutellospora)呈现正相关,可能存在协作关系以适应降雪。【结论】古尔班通古特沙漠的冬季降雪对苔藓结皮层AMF类群中的优势属和低丰度属有不同的选择策略。融雪期绝对优势属会降低存在竞争关系优势属的比例,进一步巩固优势地位,而存在正相关的低丰度属会同步降低比例,而且苔藓结皮层AMF优势属在该沙漠为近明球囊霉属。

[Background]Up to now,there was very limited research exploring the symbiotic relationship between bryophytes and arbuscular mycorrhizal fungi(AMF)in temperate desert with the context of snow.[Objective]To reveal the difference of AMF biological diversity in mosses crust layer of desert during the period of early winter(before snowfall),mid-winter(snow-accumulation)and snow melt,we further understand the crucial win-win survival strategy between desert characteristic plants and microorganisms in winter snow accumulation.[Methods]High-throughput sequencing technique was used to study the community composition and diversity of AMF in the dominant bryophyte crusts growing in Gurbantonggut Desert under stable snowfall period,and the difference of AMF community structure before and after snowfall is analyzed.[Results]All operational taxonomic units(OTUs)belonged to 5 orders,9 families and 11 genera.Of these,these species assigned to the taxonomy of Claroideoglomus,Archaeospora,Paraglomus and Glomus were the dominant groups.There was no significant difference among the dominant genus of AMF in the mosses crust layer between early winter(December)and snow melt(March),and the absolutely dominant genus(>50%)was Claroideoglomus.However,the relative abundance of different AMF groups have different trends between early winter and snow melt.The proportion of Claroideoglomus increased significantly during snow melt period.Compared with early winter,the abundance of AMF assigned to the level of Paraglomus and Glomus decreased.The value of Chao1 index and ACE index used to measure the community richness were in the following order:before snowfall>snow-accumulation>snow melt.It showed that the abundance of AMF community decreased due to snowfall.The visual analysis of taxonomic composition information based on MEGAN software suggested that low abundance AMF groups were more easily affected.Acaulospora was mainly from the samples collected before snowfall,while Diversispora was mainly from the samples collected during the snow melt period.Based on the cluster analysis of genus level communities,it was found that the types of high abundance taxons decreased from 5 before snowfall to 2 after snowfall,which indicated that snowfall had a certain selectivity to AMF groups in bryophyte crusts.The results of principal component analysis(PCA)showed that the characteristics of AMF community structure,including early winter and snow melt,could be effectively distinguished by PCA1.This further verified that the snowfall factors have a significant screening effect on AMF community in the moss crusts.A competitive relationship may exist between the high abundance genus,Claroideoglomus and Glomus,Paraglomus and Archaeospora,due to the negative correlation among them.But because of positively correlated,a cooperative relationship may exist to survive in environment of snowfall between low abundance genus:Gigaspora,Septoglomus,Ambispora and Scutellospora.[Conclusion]The winter snowfall in Gurbantonggut Desert has different selection strategies for the dominant genera and low abundance genera for the AMF group of moss crusts.During the snow melt period,the absolute dominant genus will reduce the proportion of competitive dominant genus,thus further consolidate the dominant position.While the existence of positive correlation of low abundance will synchronously reduce the proportion.Unlike the Tengger Desert,the dominant genus of AMF in the moss crusts is Claroideoglomus but not Glomus in this desert.