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大熊猫(Ailuropoda melanoleuca)是中国的特有濒危物种,是典型的森林土著物种,加上它憨态可掬的外貌特征,受到了世界人民的喜爱。由于道路建设、森林采伐、竹子开花、采药以及放牧等干扰因素的影响,现存的1864只野生个体被分割于中国西南部的秦岭、岷山、邛崃、大相岭、小相岭和凉山等六大山系中[1-5]。竹子作为大熊猫主要的食物来源,是大熊猫保护的关键之一。四川省大熊猫栖息地内大熊猫可采食的竹类有7属32种,其中小相岭山系大熊猫栖息地内大熊猫可采食竹类3属7种,其中面积最大的为峨热竹(Arundinaria spanostachya),占该山系大熊猫栖息地内大熊猫取食竹总面积的38.08%[6]。由于道路建设等因素,该小相岭山系的大熊猫局域种群形成了孤立的小种群,易受到外来因素的干扰而灭绝[6]。
四川栗子坪国家级自然保护区位于小相岭山系,行政区域上位于石棉县南部,地理坐标为北纬28°51'02″—29°08'42″,东经102°10'33″—102°29'07″。整个保护区占地面积为47 885 km2。保护区内最高的海拔为4 551 m,最低的海拔为1 330 m,地势西南高、东北低。区内的年平均温度为11.7 ℃~14.4 ℃,年平均降水量为800~1250 mm。随着海拔的升高,区内植被类型从常绿阔叶林变为针叶林,在高海拔区域分布的植被类型有高山灌丛、草甸、流石滩等[3]。保护区内可供大熊猫取食的竹类有峨热竹、石棉玉山竹(Yushania lineolata)、丰实箭竹(Fargesia ferax)等,除冬季少量采食石棉玉山竹外,该区域的大熊猫全年主要采食峨热竹,该竹类主要分布在区内海拔约2800 m以上的区域[4]。
在植物叶部周围寄生或是附着有大量的微生物,这些微生物有真菌、细菌等[7]。在植物叶围微生物中,细菌的丰富度最高,并与植物叶面形成了一个微生物-植物相互作用的微生态系统[7]。叶面微生物不仅影响植物的生长,还能通过竞争养分和拮抗作用等来抑制植物表面病原菌的生长,对于防治植物病害有极大的作用,然而存在的致病菌也会导致植物患病[7-9]。例如,鞘脂杆菌属(Sphingobium)和鞘氨醇单胞菌(Sphingomonas)的一些物种被证明能降解很多有机污染物[10-11];甲基杆菌属(Methylobacterium)和假单胞杆菌属(Pseudomonas)的物种被报道有植物生长促进剂的潜能[12-14]。影响叶围微生物群落的因素非常多,就生物因素而言,有植物种类、基因型等,例如拟南芥单基因lacs2和pec1突变能改变其叶际微生物的组成[15-16]。就非生物因素而言,紫外压力、空气湿度、地理位置、生长季节等影响叶围微生物组成、多样性等,例如地理位置被证明是大田莴苣微生物的主要驱动因子[17]。因此,叶围微生物的组成、多样性等对于维护植物健康具有十分重要的作用,其影响因素也非常多。
本研究以四川栗子坪国家级自然保护区内峨热竹竹叶为实验材料,通过室内微生物学分析、高通量扩增子测序技术等手段,探讨小相岭山系四川栗子坪国家级自然保护区内野生大熊猫主食竹峨热竹叶围细菌组成、多样性的季节性变化,以期为野生大熊猫食物资源的科学管理提供参考依据。
Seasonal Variation of Bacterial Diversity in Phyllosphere of Giant Pandas’ Staple Food Bamboo
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摘要: 植物与其生长环境中的微生物关系密切,它们彼此相互影响,相互依存。为了探究不同季节竹叶叶围细菌菌群的变化,本文以四川栗子坪国家级自然保护区大熊猫主食竹峨热竹(Arundinaria spanostachya)为研究对象,采用高通量测序技术分析峨热竹不同季节叶围细菌菌群的组成和多样性差异。分析结果发现,峨热竹叶围细菌菌群中变形菌门(Proteobacteria)占优势,春季峨热竹叶围酸菌门(Acidobacteriota)细菌的相对丰度显著大于秋季,而变形菌门细菌(Proteobacteria)则相反。春季1174-901-12、Granulicella等属的细菌相对丰度显著大于秋季,而鞘氨醇单胞菌属(Sphingomonas)、Mucilaginibacter等属细菌相对丰度相反。秋季峨热竹叶围细菌的Sobs 指数和香农指数均显著大于春季。基于加权-UniFrac 距离 和非加权-UniFrac 距离的主坐标分析发现,春季和秋季峨热竹叶围细菌的群落结构具有显著差异。占优势的变形菌门(Proteobacteria)细菌对维系该山系大熊猫肠道健康具有潜在影响;对植物有益的鞘氨醇单胞菌属(Sphingomonas)和假单胞杆菌属(Pseudomonas)细菌有利于该竹种的健康和生长。以上研究结果有助于了解不同季节小相岭山系峨热竹叶围细菌菌群的差异性,可为大熊猫主食竹资源的保护和管理提供参考依据。Abstract: Plants are closely related to the microorganisms in their growing environment, they affect and depend on each other. In order to explore the changes of the bacterial community in the phyllosphere of Arundinaria spanostachya in different seasons, the composition and diversity of phyllosphere bacteria of A. spanostachya in Sichuan Liziping National Nature Reserve were analyzed by high-throughput sequencing technique. The results showed that Proteobacteria phylum was dominant in the phyllosphere of A. spanostachya. The relative abundance of Acidobacteriota bacteria of A. spanostachya in spring was significantly higher than that in autumn, while the opposite trend was found for Proteobacteria bacteria. In spring, the relative abundance of 1174-901-12 and Granulicella was significantly higher than that in autumn, while the opposite trend was found for Sphingomonas and Mucilaginibacter. The Sobs index and Shannon index of phyllosphere bacteria of A. spanostachya in autumn were significantly higher than those in spring. Based on the principal coordinate analysis of weighted-unifrac distance and unweighted-unifrac distance, it was found that there were significant difference in the community structure of phyllosphere bacteria of A. spanostachya in spring and autumn. The dominant Proteobacteria bacteria had a potential impact on maintaining the intestinal health of giant pandas in this mountain range. The plant beneficial Sphingomonas and Pseudomonas bacteria were also beneficial to the health and growth of this bamboo species. The results are helpful to understand the difference of bacteria diversity and community structure of phyllosphere bacteria of A. spanostachya in Xiaoxiangling Mountains, which could provide reference for the management and conservation of giant pandas’ staple food bamboo.
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