Laforest-Lapointe Isabelle, Messier Christian, Kembel Steven W
Centre d'étude de la forêt, Montreal, Canada; Sciences Biologiques, Université du Québec à Montréal, Montreal, Quebec, Canada.
Centre d'étude de la forêt, Montreal, Canada; Sciences Biologiques, Université du Québec à Montréal, Montreal, Quebec, Canada; ISFORT - Institut des Sciences de la Forêt Tempérée, Université du Québec en Outaouais, Ripon, Quebec, Canada.
PeerJ. 2016 Aug 24;4:e2367. doi: 10.7717/peerj.2367. eCollection 2016.
The diversity and composition of the microbial community of tree leaves (the phyllosphere) varies among trees and host species and along spatial, temporal, and environmental gradients. Phyllosphere community variation within the canopy of an individual tree exists but the importance of this variation relative to among-tree and among-species variation is poorly understood. Sampling techniques employed for phyllosphere studies include picking leaves from one canopy location to mixing randomly selected leaves from throughout the canopy. In this context, our goal was to characterize the relative importance of intra-individual variation in phyllosphere communities across multiple species, and compare this variation to inter-individual and interspecific variation of phyllosphere epiphytic bacterial communities in a natural temperate forest in Quebec, Canada.
We targeted five dominant temperate forest tree species including angiosperms and gymnosperms: Acer saccharum, Acer rubrum, Betula papyrifera, Abies balsamea and Picea glauca. For one randomly selected tree of each species, we sampled microbial communities at six distinct canopy locations: bottom-canopy (1-2 m height), the four cardinal points of mid-canopy (2-4 m height), and the top-canopy (4-6 m height). We also collected bottom-canopy leaves from five additional trees from each species.
Based on an analysis of bacterial community structure measured via Illumina sequencing of the bacterial 16S gene, we demonstrate that 65% of the intra-individual variation in leaf bacterial community structure could be attributed to the effect of inter-individual and inter-specific differences while the effect of canopy location was not significant. In comparison, host species identity explains 47% of inter-individual and inter-specific variation in leaf bacterial community structure followed by individual identity (32%) and canopy location (6%).
Our results suggest that individual samples from consistent positions within the tree canopy from multiple individuals per species can be used to accurately quantify variation in phyllosphere bacterial community structure. However, the considerable amount of intra-individual variation within a tree canopy ask for a better understanding of how changes in leaf characteristics and local abiotic conditions drive spatial variation in the phyllosphere microbiome.
树叶（叶际）微生物群落的多样性和组成在不同树木和宿主物种之间以及沿着空间、时间和环境梯度存在差异。个体树冠内叶际群落的变化是存在的，但相对于树木间和物种间的变化，这种变化的重要性却知之甚少。用于叶际研究的采样技术包括从树冠的一个位置采摘树叶到混合从整个树冠随机选择的树叶。在此背景下，我们的目标是描述多个物种中叶际群落个体内变异的相对重要性，并将这种变异与加拿大魁北克一个天然温带森林中叶际附生细菌群落的个体间和种间变异进行比较。
我们选取了包括被子植物和裸子植物在内的五种优势温带森林树种：糖枫、红枫、纸皮桦、香脂冷杉和白云杉。对于每个物种随机选择的一棵树，我们在六个不同的树冠位置采集微生物群落样本：树冠下层（1 - 2米高）、树冠中层的四个方位（2 - 4米高）和树冠上层（4 - 6米高）。我们还从每个物种的另外五棵树上采集了树冠下层的树叶。
基于通过对细菌16S基因进行Illumina测序测量的细菌群落结构分析，我们证明叶细菌群落结构中65%的个体内变异可归因于个体间和种间差异的影响，而树冠位置的影响不显著。相比之下，宿主物种身份解释了叶细菌群落结构中47%的个体间和种间变异，其次是个体身份（32%）和树冠位置（6%）。
我们的结果表明，从每个物种的多个个体的树冠内一致位置采集的个体样本可用于准确量化叶际细菌群落结构的变异。然而，树冠内相当数量的个体内变异要求我们更好地理解叶片特征和局部非生物条件的变化如何驱动叶际微生物组的空间变异。
