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内生真菌是一类生活在植物组织内,但不会引起任何外在疾病迹象的真菌[1]。它能促进植物生长、提高植物抗病防御[2-4],对农业及自然生态系统的可持续管理有重要意义[5]。植物的根与叶均是内生真菌生活的热点场所。热带森林中几乎所有的叶都受到内生真菌侵染[6],单株植物的叶内生真菌达30多种[7],而单片叶的内生真菌甚至达20种以上[2]。除叶内生真菌外,植物的根普遍与真菌形成菌根,能提高养分的有效性和促进植物的耐胁迫能力。外生菌根与丛枝菌根是自然界最常见的菌根类型,外生菌根主要长生在壳斗科、松科植物上,真菌主要为担子菌和少量子囊菌;而丛枝菌根涉及80%以上的陆生植物,真菌主要为球囊菌门[8]。在功能上,外生菌根真菌促进植物吸收氮,而丛枝菌根真菌促进植物吸收磷。不同菌根类型在生态生理上的差异,会改变植物营养和土壤过程[9]。植物的菌根类型会影响叶内生真菌群落,如丛枝菌根真菌影响叶内养分的有效性,进而影响叶内生真菌群落组成[10];菌根真菌与叶内生真菌的互作影响植物抗虫性[11]。比较同一片森林中外生菌根植物和丛枝菌根植物的叶内生真菌群落可以更好地理解2种类型植物与真菌之间的相互作用和生态功能。海南岛位于我国南部,地处热带北缘,同时具有热带和亚热带的气候特征,物种丰富,被誉为“热带北缘生物物种基因库”。海南岛的热带山地雨林是当前保存最完整、面积最大的热带森林,具有面积广、物种多样性高、层次结构复杂等特点,是具有国家和国际意义的生物多样性保护的热点地区的代表性植被类型[12-13]。在海南岛尖峰岭的热带山地雨林中,樟科植物重要值最高,其次是壳斗科植物[13],二者的根部真菌群落分别以丛枝菌根真菌和外生菌根真菌为主[14]。目前,基于微生物DNA条形码(如真菌ITS、细菌16S rRNA基因)的高通量测序技术,相对于依赖培养的一代测序技术,具有检测更全面、通量更高的特点,能在短期内高效地获得海量的微生物DNA序列,越来越多地被应用于揭示环境微生物群落的多样性和复杂性[15]。本研究拟采用高通量测序技术检测尖峰岭热带山地雨林樟科和壳斗科植物的叶内生真菌群落的物种组成,旨在揭示植物身份与叶性状在叶内生真菌群落构建中的作用。
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对热带山地雨林中的樟科(26株)和壳斗科(22株)2科植物进行了叶内生真菌ITS2区的高通量测序,共获得叶内生真菌序列数1 557 620 ,经过序列分析被划分为6 805个OTUs。去除仅序列数为1的OTUs后,叶内生真菌序列数仍有1 539 567,5 471个OTUs,每株达( 690 ± 31)个OTUs。这些叶内生真菌隶属于8门、30纲、108目、281科、892属。樟科与壳斗科植物获得叶内生真菌序列数分别为991 193和548 374,平均每株分别为38122 ± 1785和24926 ± 3250 。在樟科与壳斗科中,序列数占比例最高的均是子囊菌门Ascomycota,分别达95.7%和92.4%,其次是担子菌门Basidiomycota,分别占2.5%和3.9%,尚有其他类群的真菌分别占1.8%和3.7%。在纲级分类单元,樟科与壳斗科植物的叶内生真菌序列数占比较高的前四类真菌分别为Dothideomycetes(56.4%和49.5%)、Eurotiomycetes(22.5%和19.3%)、Sordariomycetes (10.4%和11.0%)、Lecanoromycetes (3.2%和8.8%)。此外,Leotiomycetes在樟科植物中占比较高(2.3%),而Agaricomycetes在壳斗科植物中较多(2.2%)。在樟科植物中,序列数占比最高的前5种真菌是Asperisporium caricae(5.4%)、Mycosphaerella quasiparkii(2.4%)、Gonatophragmium triuniae (2.2%)、Zasmidium dalbergiae(1.8%)、Zasmidium lonicericola和Sporidesmium sp.(1.5%),而壳斗科植物中Mycosphaerellaceae sp2(3.0%)、Dothideomycetes sp1(2.8%)、Xylographa trunciseda和Asperisporium caricae(2.1%)、Zasmidium lonicericola (1.9%)较多(图1)。
稀释曲线显示,随着测序深度的增加,真菌物种数增加的趋势变平缓(图2-a),表明当前测序深度能够较为全面地反映热带山地雨林壳斗科、樟科的叶内真菌多样性。整体上单株植物的叶内生真菌达(690 ± 31)个 OTUs,并且樟科植物单株叶内生真菌物种丰富度达(805 ± 32 )个OTUs,显著高于壳斗科植物的(554 ± 41)个 OTUs(Kruskal-Wallis test: χ2 = 16.283,P = 0.000)(图2-b);而Shannon-Wiener多样性指数和Simpson多样性指数在两科植物间均无显著差异(χ2 = 1.028,P = 0.311;χ2 = 0.035,P = 0.852)。
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在群落水平,非度量多维尺度分析(NMDS)的结果(图3)显示壳斗科和樟科的叶内生真菌群落组成显著不同(stress = 0.188)。偏冗余分析(RDA)结果表明,宿主科、属、种身份对叶内生真菌群落组成有显著的影响(P = 0.001),去除植物性状的效应后,宿主科、属、种身份能独立解释叶内生真菌群落物种组成的变异量分别达2.9%、15.7%、33.7%。取样高度对叶内生真菌群落组成没有影响(R2 = 0.026,P = 0.081)。
偏冗余分析结果表明,叶性状对叶内生真菌群落结构也有显著影响(R2 = 0.213,P = 0.003)。各性状拟合排序轴的结果表明,对叶内生真菌群落影响程度由高到低依次为:叶钙含量(R2 = 0.572,P = 0.001),比叶面积(R2 = 0.413,P = 0.001),叶氮含量(R2 = 0.181,P = 0.008)和叶钾含量(R2 = 0.137,P = 0.031)(表1)。
表 1 叶性状解释叶内生真菌群落组成的变异量
RDA1 RDA2 R2 P 叶钙含量(LCaC) 0.748 −0.664 0.572 0.001*** 比叶面积(SLA) −0.747 −0.665 0.413 0.001*** 叶氮含量(LNC) −0.763 −0.646 0.181 0.008 ** 叶钾含量(LKC) −0.198 −0.980 0.137 0.031 * 叶磷含量(LPC) −0.724 −0.690 0.0912 0.122 叶面积(LA) −0.472 −0.882 0.060 0.237 鲜质量(FW) −0.196 −0.981 0.012 0.780 叶含水量(LWC) 0.673 −0.740 0.0002 0.995 干质量(DW) 0.315 −0.949 0.018 0.663 叶干物质含量(LDMC) 0.186 0.983 0.009 0.836 注:*:P<0.05,**:P<0.01,***:P<0.001。
Effects of host identity and leaf traits on foliar endophytic fungal communities in Lauraceae and Fagaceae plants of tropical montane rainforest of Hainan Island
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摘要: 为了揭示植物身份与叶性状在叶内生真菌群落构建中的作用,笔者使用Illumina Miseq测序平台检测海南尖峰岭热带山地雨林中优势植物叶内生真菌群落的物种组成,并探讨宿主身份和叶性状对叶内生真菌群落物种组成的影响。本研究共检测到来自8种樟科和7种壳斗科植物的叶内共生真菌的1539567条真菌的ITS2序列,并将它们划分为5471个真菌分类单元(Operational Taxonomic Units,OTUs),隶属于8个门、30个纲、108个目、281个科、892个属。其中,子囊菌是叶内生真菌的最大类群,占所测真菌序列数的94.5%。单株樟科植物叶内生真菌物种数805 ± 32OTUs显著高于壳斗科植物554 ± 41 OTUs。相比之下,Shannon-Wiener、Simpson多样性指数在两科植物的叶内生真菌间均无显著差异。偏冗余分析(partial redundancy analysis)结果表明,宿主科、属、种身份对叶内生真菌群落组成有显著的影响。去除植物性状的效应后,宿主科、属、种身份能够独立解释叶内生真菌群落物种组成的变异量分别达到2.9%、15.7%、33.7%。去除宿主植物身份的影响后,叶性状在总体上能够解释叶内生真菌群落物种组成的变异量达到21.3%(P = 0.003),其中,叶钙含量、比叶面积、叶氮含量和叶钾含量对叶内生真菌群落物种组成有显著影响。上述结果表明,宿主身份和叶性状是热带山地雨林叶内生真菌群落构建的重要驱动因子。Abstract: To investigate the effects of plant identity and leaf traits on foliar endophytic fungal community assembly, the species composition of foliar endophytic fungi in dominant plants in the tropical mountain rainforest in Jianfengling, Hainan Island were determined by using the Illumina Miseq sequencing method, based on which the effects of host identity and leaf traits on the species composition of foliar endophytic fungi were explored. A total of 1,539,567 fungal ITS2 sequences were obtained from the leaves of 8 species of Lauraceae plants and 7 species of Fagaceae plants, which were classified into 5,471 Operational Taxonomic Units (OTUs) belonging to 8 phyla, 30 classes, 108 orders, 281 families, and 892 genera. Ascomycota was the largest group of the foliar endophytic fungi, accounting for 94.5% of all the fungal sequences. The number of endophytic fungal species in the leaves of individual Lauraceae plants (805 ± 32) OTUs was significantly higher than that of Fagaceae plants (554 ± 41) OTUs. However, there was no significant difference in Shannon-Wiener and Simpson diversity indices between the endophytic fungi in the leaves of the plants of these two families. Partial redundancy analysis showed that the host plant identities of family, genus and species significantly affected the composition of endophytic fungal communities. After removing the effect of plant traits, the host plant identities of family, genus, and species could independently explain 2.9%, 15.7%, and 33.7% of the variation in endophytic fungal species composition, respectively. After removing the effect of host plant identity, leaf traits could explain 21.3% of the variation in endophytic fungal species composition (P =0.003), of which leaf calcium content, specific leaf area, leaf nitrogen content, and leaf potassium content had significant effects on the composition of endophytic fungal communities. These findings suggest that host identity and leaf traits are important factors driving the assembly of endophytic fungal communities in the tropical mountain rainforest.
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Key words:
- foliar endophytic fungi /
- tropical montane rainforest /
- diversity /
- host identity /
- leaf traits
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表 1 叶性状解释叶内生真菌群落组成的变异量
RDA1 RDA2 R2 P 叶钙含量(LCaC) 0.748 −0.664 0.572 0.001*** 比叶面积(SLA) −0.747 −0.665 0.413 0.001*** 叶氮含量(LNC) −0.763 −0.646 0.181 0.008 ** 叶钾含量(LKC) −0.198 −0.980 0.137 0.031 * 叶磷含量(LPC) −0.724 −0.690 0.0912 0.122 叶面积(LA) −0.472 −0.882 0.060 0.237 鲜质量(FW) −0.196 −0.981 0.012 0.780 叶含水量(LWC) 0.673 −0.740 0.0002 0.995 干质量(DW) 0.315 −0.949 0.018 0.663 叶干物质含量(LDMC) 0.186 0.983 0.009 0.836 注:*:P<0.05,**:P<0.01,***:P<0.001。 -
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