Conifer water use patterns in the East River Watershed, Colorado US, based on stable water isotopes and cellulose isotopes

This data package contains a series of datasets aimed at understanding the seasonal origins of water used by the dominant conifer species, Abies lasiocarpa and Picea engelmannii, in the East River Watershed. There is a distinct difference in the stable isotopic ratio of summer rain and snowpack and thus by tracking the isotopic ratio of the xylem water in trees, it is possible to separate when a tree is using snow vs. summer rain. Following typical protocols, we sampled and extracted water from soils in the "Research Meadow" near Gothic, CO within the East River Watershed through the 2016 growing season. The stable isotopic ratio of these waters were then measured. Using values of the isotopic ratio of precipitation and snowpack from that season, we develop a mixing model to show how the trees transitioned from use of snowpack to summer in late July. We extended the information on the seasonal origins of water from 2016 back until 1980 by using measurements of the isotopic ratio of cellulose from trees in the Research Meadow. The isotopic ratio of tree ring cellulose records a signal both of the Vapor Pressure Deficit at the leaf-atmosphere boundary and also the source water for the trees. We concluded from this extended analysis that the trees underwent transitions between periods where snow was the dominant water source and summer rain was the dominant water source. More details on this analysis can be found in the publication: Persistence and Plasticity in Conifer Water Use Strategies. JGR Biogeoscience. DOI 10.1029/2018JG004845. The dataset specifically includes stable isotope measurements of xylem and soil water for Spruce and Fir trees at the Rocky Mountain Biological Lab's Research Meadow as well as snowpack and precipitation stable isotopes from nearby National Atmospheric Deposition Program sites. The dataset also includes intra-ring measurements of the d18O of cellulose from these trees at this site as well as at the Ziegler Reservoir site in Snowmass, CO. Associated meteorological data is included, which is needed to understand the source water for the trees based on the cellulose measurements.

本数据包包含一系列数据集，旨在解析东河流域（East River Watershed）内优势针叶树种——亚高山冷杉（Abies lasiocarpa）与恩格尔曼云杉（Picea engelmannii）所利用水分的季节来源。夏季降雨与积雪（snowpack）的稳定同位素比率（stable isotopic ratio）存在显著差异，因此通过追踪树木木质部水（xylem water）的同位素比率，即可区分树木利用积雪与夏季降雨的时段。遵循通用实验规程，我们在2016年生长季全程，于东河流域内科罗拉多州哥特镇附近的“研究草甸（Research Meadow）”中采集并提取了土壤水，随后测定了这些水体的稳定同位素比率。利用该季降水与积雪的同位素比率数据，我们构建了混合模型，用以揭示树木在7月下旬如何从利用积雪转为依赖夏季降雨。我们通过分析研究草甸内树木纤维素（cellulose）的同位素比率测量数据，将2016年的水分季节来源信息回溯至1980年。树木年轮纤维素（tree ring cellulose）的同位素比率同时记录了叶-气界面处的蒸汽压亏缺（Vapor Pressure Deficit）信号与树木的水源信号。通过此次回溯分析，我们得出结论：树木会在以积雪为主要水源与以夏季降雨为主要水源的时段之间发生转换。有关本次分析的更多细节可参阅以下发表文献：《针叶树水分利用策略的持续性与可塑性》（Persistence and Plasticity in Conifer Water Use Strategies），发表于《JGR生物地球科学》（JGR Biogeoscience），DOI：10.1029/2018JG004845。本数据集具体包含落基山生物实验室（Rocky Mountain Biological Lab）研究草甸内云杉与冷杉树木的木质部水及土壤水稳定同位素测量数据，同时包含邻近区域国家大气沉积计划（National Atmospheric Deposition Program）站点的积雪与降水稳定同位素数据。本数据集还包含该研究草甸与科罗拉多州斯诺马斯镇齐格勒水库（Ziegler Reservoir）站点处上述树木纤维素的氧18同位素（d18O）环内（intra-ring）测量数据。数据集同时附带相关气象数据（meteorological data），该数据是基于纤维素测量结果解析树木水源所必需的资料。