Effects of Multiple Resource Additions on Community and Ecosystem Processes: NutNet Seasonal Biomass and Seasonal and Annual NPP Data at the Sevilleta National Wildlife Refuge, New Mexico

Two of the most pervasive human impacts on ecosystems are alteration of global nutrient budgets and changes in the abundance and identity of consumers. Fossil fuel combustion and agricultural fertilization have doubled and quintupled, respectively, global pools of nitrogen and phosphorus relative to pre-industrial levels. In spite of the global impacts of these human activities, there have been no globally coordinated experiments to quantify the general impacts on ecological systems. This experiment seeks to determine how nutrient availability controls plant biomass, diversity, and species composition in a desert grassland. This has important implications for understanding how future atmospheric deposition of nutrients (N, S, Ca, K) might affect community and ecosystem-level responses. This study is part of a larger coordinated research network that includes more than 40 grassland sites around the world. By using a standardized experimental setup that is consistent across all study sites, we are addressing the questions of whether diversity and productivity are co-limited by multiple nutrients and if so, whether these trends are predictable on a global scale. Above-ground net primary production is the change in plant biomass, represented by stems, flowers, fruit and and foliage, over time and incoporates growth as well as loss to death and decomposition. To measure this change the vegetation variables, including species composition and the cover and height of individuals, are sampled twice yearly (spring and fall) at permanent 1m x 1m plots within each site. Volumetric measurements are made using vegetation data from permanent plots (SEV231, "Effects of Multiple Resource Additions on Community and Ecosystem Processes: NutNet NPP Quadrat Sampling") and regressions correlating species biomass and volume constructed using seasonal harvest weights from SEV157, "Net Primary Productivity (NPP) Weight Data."

对生态系统影响最为广泛的两类人类活动，分别是全球养分收支的改变，以及消费者的丰度与物种组成的变化。化石燃料燃烧与农业施肥分别使全球氮、磷储库相较于工业化前水平增长至原有规模的2倍与5倍。尽管此类人类活动已产生全球尺度的生态影响，但目前尚无全球性协同实验来量化其对生态系统的普遍效应。
本实验旨在探明养分有效性如何调控荒漠草原的植物生物量、多样性与物种组成。这一研究对于理解未来养分（N、S、Ca、K）大气沉降如何影响群落与生态系统尺度的响应具有重要意义。本研究隶属于一个更大规模的协同研究网络，该网络在全球范围内涵盖40余个草原样地。
通过采用所有研究站点统一的标准化实验方案，我们旨在解答两个核心问题：一是生物多样性与生产力是否受到多种养分的共同限制；二是若存在共限制现象，该规律是否可在全球尺度上被预测。
地上净初级生产力（Above-ground net primary production）指的是植物地上部分（茎、花、果实与叶片）的生物量随时间的变化量，既包含植物生长量，也涵盖死亡与分解所导致的生物量损失。为量化这一变化，每个研究站点会在永久性1m×1m样方内，于每年春季与秋季两次采样获取植被变量数据，包括物种组成、植株盖度与高度。
本研究利用来自永久性样地的植被数据（SEV231，《多资源添加对群落与生态系统过程的影响：NutNet净初级生产力样方采样》）以及基于SEV157数据集《净初级生产力（NPP）重量数据》的季节性收获重量构建的物种生物量与体积相关性回归模型，开展体积测量工作。