Data and code for "Resource gradients drive the distribution and photobiont characteristics of two lichen species in a subarctic lava field"

This project described how the distribution and morphology of two species of lichen varied along a transect perpendicular to Lake Myvatn in Iceland. All data were collected in a recent (1729) lava field and we focused on two species Flavocetraria cucullata and Peltigera leucophlebia. Lake Myvatn is famous for large midge (Diptera: Chironomidae) emergences of which many are deposited on land. Thus, the transect reflects variation in midge deposition. P. leucophlebia contains both green algae and cynaobacterial endosymbionts and thus is able to fix atmospheric nitrogen, while F. cucullata contains only green algae and is therefore dependent on environmental nutrients. We suspected that these species differed in their response to the midge-derived nutrient gradient. We measured the distribution of each lichen along a 400 x 15 m transect perpendicular to the lake, characterized their surrounding vegetation, and took thin sections of thalli on which we characterized photobiont thickness and chlorophyll-a concentrations using images taken with a near infrared camera. The data are housed in the Data folder. FLG_Transect_Points.csv contains the location and names of each lichen plot. FLG_Surrounding_Vegetation.csv contains the vegetation inside each plot. Lichen_IR.csv contains the ENDVI, our metric of chlorophyll-a concentration, and photobiont thickness, in units of pixels taken using a standardized zoom. All scripts associated with the project are housed in the Analysis folder. IRProcessing.R contains the code used to calculate the chlorophyll-a concentration and thickness from each of the photographs of the lichen thin sections. Myv_analysis.R contains all the code used for the statistical analyses and to generate figures. GOLichenAnalysis2019.Rproj is the RStudio project, which sets the relative locations of files. See https://support.posit.co/hc/en-us/articles/200526207-Using-RStudio-Projects for more information on .Rproj files.本项目探究了冰岛米湖（Lake Myvatn）垂直样带（transect）上两种地衣（lichen）的分布与形态变化规律。所有数据采集自1729年形成的新近熔岩台地（lava field），研究聚焦于两个物种：星瓣梅衣（Flavocetraria cucullata）与白脉毛瓣衣（Peltigera leucophlebia）。米湖以大规模的蠓（midge，双翅目：摇蚊科（Diptera: Chironomidae））羽化事件闻名，大量蠓尸会沉降至陆地，因此该样带能够反映蠓沉降的空间变异特征。P. leucophlebia同时搭载绿藻与蓝细菌内共生体（endosymbionts），因此可固定大气氮；而F. cucullata仅含有绿藻，依赖环境中的营养物质。我们推测这两种地衣对蠓源性营养梯度的响应存在显著差异。 我们沿垂直于湖面的400×15m样带调查了每种地衣的分布情况，记录了样地周边的植被特征，并制备地衣体（thallus，其复数形式为thalli）的薄切片，借助近红外相机（near infrared camera）拍摄的图像，分析了光合共生体（photobiont）的厚度以及叶绿素a（chlorophyll-a）浓度。 本项目的数据存放于Data文件夹中： - FLG_Transect_Points.csv 记录了每个地衣样点的位置与名称； - FLG_Surrounding_Vegetation.csv 记录了每个样地内的植被信息； - Lichen_IR.csv 记录了以标准化变焦拍摄的像素单位下的光合共生体厚度，以及用于表征叶绿素a浓度的增强型归一化差异植被指数（ENDVI）。 本项目的所有分析脚本存放于Analysis文件夹中： - IRProcessing.R 包含了从地衣薄切片照片中计算叶绿素a浓度与厚度的代码； - Myv_analysis.R 包含了所有统计分析与图表生成的代码； - GOLichenAnalysis2019.Rproj 为RStudio项目文件，用于设定文件的相对路径。如需了解.Rproj文件的更多信息，请参阅https://support.posit.co/hc/en-us/articles/200526207-Using-RStudio-Projects。