Plant and microbial impacts of an invasive species vary across an environmental gradient

Invasive plants often successfully occupy large areas encompassing broad environmental gradients in their invaded range, yet how invader dominance and effects on ecological communities vary across the landscape has rarely been explored. Furthermore, while the impacts of invasion on plant communities are well studied, it is not well understood whether responses of aboveground (plant) and belowground (microbial) communities are coupled.
Here we test patterns in Phragmites australis (common reed) invasion in a field survey of eight sites situated across a salinity gradient, ranging from freshwater to saline marsh, in Southeast Louisiana. At each site, we surveyed plant composition and used metabarcoding methods to assess soil fungal and bacterial composition in plots within the dense Phragmites stand, in a transition zone of ~50:50 Phragmites:native plants, and in native-only areas. We hypothesized that Phragmites’ abundance and impact on above and belowground communities would vary across..., Eight field sites across SE Louisiana were surveyed, ranging from freshwater to saline marsh. We classified sites based on dominant vegetation. Freshwater marshes were Barataria Preserve and Turtle Cove Research Station. Intermediate/Brackish mashes were Pearl River WMA, Fontainebleau State Park, Big Branch NWR, and Bayou Sauvage NWR. Saline marshes were two sites at the Louisiana Universities Marine Consortium, LUMCON.
In 2017 at each site, 21 permanent 1 m2 plots were established in three transects based on vegetation type: Phragmites stand, transition, and native, each with 7 plots. The Phragmites stand transect plots were located entirely within an area where Phragmites was highly dominant. The native plots ran parallel to, but outside of, the Phragmites stand and contained only native plants representing the native marsh community. The transition plots ran along the edge of the Phragmites stand, capturing the interface of the native community and the invading Phragmites front. Plot..., Phragmites haplotyping was performed at each site, and we found that the Phragmites at our freshwater and brackish sites was haplotype I, and the Phragmites at our saline sites was haplotype M1.
Some ITS and 16S samples did not sequence well and thus are NAs in this dataset.
One 16S sample had an extraordinarily high number of reads and a very high richness and Chao1. Thus we added a separate column omitting this sample from the column (the value is NA).
The Plant Pathogen relative abundance also contained two outliers, thus we added a separate column omitting these samples from the column (the value is NA).

入侵植物在其入侵范围内常可成功占据大范围区域，且覆盖跨度广泛的环境梯度，但目前极少有研究探讨入侵植物的优势度及其对生态群落的影响如何随景观异质性发生变化。此外，尽管生物入侵对植物群落的影响已得到充分研究，但地上（植物）与地下（微生物）群落的响应是否存在耦合关联，目前仍未明确。

本研究针对路易斯安那州东南部沿盐度梯度（从淡水沼泽到咸水沼泽）布设的8个样地开展野外调查，以检验普通芦苇（Phragmites australis, common reed）的入侵格局。在每个样地内，我们分别在茂密的普通芦苇群落、约50:50比例的普通芦苇与本土植物混合的过渡带，以及纯本土植物区域的样方中开展植物群落组成调查，并采用元条形码测序（metabarcoding）技术分析土壤真菌与细菌群落组成。我们提出假设：普通芦苇的丰度及其对地上、地下群落的影响将随[原文本省略部分]发生变化。本研究共对路易斯安那州东南部的8个样地开展调查，样地盐度梯度覆盖淡水沼泽至咸水沼泽。

本研究依据优势植被类型对样地进行分类：淡水沼泽样地为巴拉塔里亚保护区（Barataria Preserve）与海龟湾研究站（Turtle Cove Research Station）；中度咸水/咸淡水沼泽样地包括珍珠河野生动物管理区（Pearl River WMA）、芳特尼博勒州立公园（Fontainebleau State Park）、大分支国家野生动物保护区（Big Branch NWR）与索瓦奇湾国家野生动物保护区（Bayou Sauvage NWR）；咸水沼泽样地为路易斯安那大学海洋联盟（Louisiana Universities Marine Consortium, LUMCON）的2个样地。

2017年，我们在每个样地内依据植被类型设置3条样带，每条样带内布设7个永久样方（共21个1 m²样方）：普通芦苇群落样带、过渡带样带与本土群落样带。其中，普通芦苇群落样带的样方完全位于普通芦苇占绝对优势的区域内；本土群落样带与普通芦苇群落带平行且位于其外侧，仅包含代表本土沼泽群落的本土植物；过渡带样带沿普通芦苇群落带的边缘布设，以捕捉本土群落与入侵的普通芦苇前沿的交界区域。[原文本此处省略]

我们在每个样地开展了普通芦苇单倍型分型，结果显示：淡水与咸淡水样地的普通芦苇为单倍型I，咸水样地的普通芦苇为单倍型M1。

部分ITS与16S样本的测序质量不佳，因此本数据集中将其标记为NA（缺失值）。有1个16S样本的测序读长数极高，其群落丰富度与Chao1指数也显著偏高。因此我们新增了一列数据，将该样本从该列中移除（对应值标记为NA）。植物病原菌相对丰度数据中也存在2个异常值，因此我们新增了一列数据，将这些样本从该列中移除（对应值标记为NA）。