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小熊猫(Ailurus fulgens)属食肉目动物,特化为以竹子为生,其食谱中竹叶占比约为80%~98%[1,5],具有突出的科学研究价值[1]。它们主要分布于我国四川、云南和西藏,少数分布于尼泊尔、不丹、缅甸等国,是我国国家Ⅱ级重点保护野生动物,由于它们分布狭窄,数量日趋减少,因而受到国内外学者的关注[2]。从全球来看,中国是小熊猫的集中分布区,约有6400~7600只[3]。第四次全国大熊猫调查显示,各大熊猫分布山系的小熊猫适宜栖息地和第三次大熊猫调查相比面积普遍增长,其中邛崃山系增加3012.93 km2、大相岭山系增加1291.29 km2、小相岭山系增加502.72 km2、凉山山系增加509.17 km2[4];其中,凉山山系增加面积占凉山山系总面积的10.84%,四川美姑大风顶国家级自然保护区是凉山山系野生小熊猫种群的主要分布区之一[4]。
在不同的地区小熊猫偏爱的竹子种类不同,例如,在卧龙自然保护区,它们主要采食冷箭竹和拐棍竹;在冶勒自然保护区,它们主要采食峨热竹;在马边大风顶自然保护区,它们主要采食大叶筇竹[7]。四川美姑大风顶国家级自然保护区位于四川省凉山彝族自治州美姑县城东北,总面积为50655 hm2,其中核心区31097.5 hm2,缓冲区17185 hm2,实验区2372.5 hm2。保护区属森林生态系统类型自然保护区,主要保护对象为大熊猫、小熊猫等珍稀野生动植物及其栖息环境。保护区属深切割中山地貌类型,地势由西南向东北倾斜,海拔1356~4042 m,垂直高差2686 m[7]。保护区内竹子分布的海拔范围为1356~3770.86 m,该区小熊猫主要采食的竹子有熊竹(Yushania ailuropodina)和冷箭竹(Arundinaria faberi)。其中熊竹分布的面积最大,主要分布于大风顶、维核洛区域,在海拔1356~2820.75 m间生长,面积达16988 hm2[8],是该保护区小熊猫全年采食的竹种。
近年来对小熊猫的研究主要集中在肠道微生物、行为、繁殖生态学等方面[9],前人研究发现,食性对调节肠道微生物群的结构和功能起着很重要的作用,进而影响小熊猫的健康状况[10]。竹叶作为竹林健康状况的重要指示器官,是竹子叶围微生物生存繁衍的重要场所,同时也是小熊猫病原微生物入侵的重要载体[5],进而会影响小熊猫肠道微生物的稳态,甚至是肠道疾病。叶围微生物又可称为叶表微生物、叶面微生物[11]。在全球尺度下,叶围细菌总数多达1026个,其中微生物密度在106至107个·cm−2。叶围微生物是植物微生物组的重要组成部分,其在促进植物生长、保护植物不受外部病原菌侵害及参与植物碳氮循环中起重要作用[12]。影响叶围微生物的因素很多,如CO2含量、大气污染、降雨量等,研究发现CO2对水稻不同生长阶段的叶围细菌群落结构有明显的影响,在灌浆期,群落结构对CO2的反应最为明显[13]。降雨刺激蕨类植物叶围某些细菌种群并改变整个群落结构和活动[14]。海拔、温度和湿度也会对叶围微生物造成影响,在四川栗子坪国家级自然保护区内,随着海拔的升高竹叶叶围细菌多样性和丰富度也在下降,秋季叶围细菌的丰度和多样性高于春季[15]。
因此,本研究以四川美姑大风顶国家级自然保护区的熊竹为研究材料,通过逐月收集竹叶样品和高通量测序技术,探究熊竹叶围细菌的组成、多样性、群落结构的年际变化,揭示叶围微生物年际变化的主要环境影响因素和特点,以期为小熊猫主食竹资源的管理提供参考,为野生小熊猫保护措施的科学制定提供依据。
Interannual Variation of Bacteria Communities in Red Pandas Foraging Bamboos Phyllosphere
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摘要: 竹叶作为竹林健康状况的重要指示器官,是竹子叶围微生物生存繁衍的重要场所,同时也是病原微生物入侵的重要入口,进而会影响野生小熊猫的健康状况。为了探究野生小熊猫主食竹叶围细菌的年际变化,本文以四川美姑大风顶国家级自然保护区的熊竹(Yushania ailuropodina)为研究对象,通过高通量测序技术探究了熊竹叶围细菌组成、多样性、群落结构的年际变化。研究发现,熊竹叶围细菌11月份OTUs最丰富,且OTUs丰富度秋冬季高于春夏季。12个月份的优势门均为变形菌门(Proteobacteria)、拟杆菌门(Bacteroidota)和酸杆菌门(Acidobacteriota),夏季(6月—8月)的变形菌门(Proteobacteria)相对丰度高于其他月份,但拟杆菌门的相对丰度低于其他月份。夏季(6月—8月)假单胞菌属(Pseudomonas)的相对丰度明显高于其他月份,但1174-901-12的相对丰度低于其他月份。秋季 (9月—11月)和冬季 (12月—2月)小熊猫主食竹熊竹叶围细菌的丰富度(Sobs index)和多样性(Shannon index)高于其他季节;群落结构(un)weighted Unifrac distances在不同月份间存在一定的差异,其中夏季(6月—8月)的weighted Unifrac距离显著大于其他月份。本研究表明小熊猫主食竹叶围微生物丰富,其组成、多样性、群落结构具有明显的年际变化规律,且主要受季节的影响。本研究可为小熊猫主食竹资源的科学管理提供支撑,为野生小熊猫保护措施的科学制定提供参考依据。Abstract: As an important indicator organ of bamboo forest health, bamboo leaves are an important place for the survival and reproduction of microorganisms around bamboo leaves, as well as an important entrance for pathogenic microorganisms to invade, which will affect the health of wild red pandas. In order to investigate the interannual variation of bacteria communities in red pandas foraging bamboos phyllosphere, high-throughput sequencing was used to analyze the composition and diversity of phyllosphere bacteria of Yushania ailuropodina in Sichuan Meigu Dafengding National Nature Reserve. The results showed that OTUs was most abundant in November, and the number of OTUs decreased from September 2021 to August 2022. Proteobacteria, Bacteroidota and Acidobacteriota were the predominant phyla in whole 12 months, and the relative abundance of Proteobacteria in June, July and August was higher than that in other months. But the relative abundance of Bacteroidota was lower than that of other months. The relative abundance of Pseudomonas in June, July and August was significantly higher than that in other months, but the relative abundance of Pseudomonas and 1174-901-12 in June, July and August was lower than that in other months. The Sobs and Shannon index of phyllosphere bacteria in September, October and November were higher than those in other months. PCoA analysis based on weighted/unweighted UniFrac distance showed that the bacterial community structure of phyllosphere bacteria varied from different months at OTU level. This study improved our understanding of phyllosphere bacteria in red pandas foraging bamboos, and provided a reference for the protection of bamboo resources.
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