Code and data for: Nitrogen-induced hysteresis in grassland biodiversity: A theoretical test of litter-mediated mechanisms

The global rise in anthropogenic reactive nitrogen (N) and the negative impacts of N deposition on terrestrial plant diversity are well-documented. The R* theory of resource competition predicts reversible decreases in plant diversity in response to N loading. However, empirical evidence for the reversibility of N-induced biodiversity loss is mixed. In a long-term N-enrichment experiment in Minnesota, a low-diversity state that emerged during N addition has persisted for decades after additions ceased. Hypothesized mechanisms preventing recovery of biodiversity include nutrient recycling, insufficient external seed supply, and litter inhibition of plant growth. Here we present an ODE model that unifies these mechanisms, produces bistability at intermediate N inputs, and qualitatively matches the observed hysteresis at Cedar Creek. Key features of the model, including native species' growth advantage in low-N conditions and limitation by litter accumulation, generalize from Cedar Creek t..., The MATLAB and Mathematica codes used to visualize and simulate the model were developed by Katherine Meyer and James Broda. The data used to estimate parameters come from public datasets obtained from the BioCON experiment (e141) at Cedar Creek Ecosystem Science Reserve and the Total Deposition Maps collection prepared by the National Atmospheric Deposition Program (NADP) and US Environmental Protection Agency. The README.md file provides further details on the sources and processing of data., MATLAB (open-source alternative Octave) Mathematica R/RStudio人为活性氮（anthropogenic reactive nitrogen）在全球范围内的持续攀升，以及氮沉降对陆地植物多样性的负面影响，已有充分的文献记载。资源竞争的R*理论（R* theory）预测，植物多样性会随氮负荷增加出现可逆性下降。然而，关于氮素诱导的生物多样性丧失是否可逆的实证研究结果却莫衷一是。在明尼苏达州开展的一项长期氮富集实验中，施氮阶段形成的低多样性植物群落，在施氮停止后已持续存在数十年之久。被认为会阻碍生物多样性恢复的潜在机制包括养分循环、外源种子供给不足，以及枯落物对植物生长的抑制作用。本研究构建了一个常微分方程（Ordinary Differential Equation, ODE）模型，该模型整合了上述多种机制，在中等氮输入水平下呈现双稳态（bistability），并在定性上匹配了雪松溪（Cedar Creek）生态系统观测到的滞后效应（hysteresis）。该模型的关键特征——包括本土物种在低氮条件下的生长优势，以及受枯落物积累限制的特性——均从雪松溪的相关研究中得到泛化（原文此处存在截断）。用于可视化与模型模拟的MATLAB与Mathematica代码，由Katherine Meyer与James Broda开发。 用于估算模型参数的数据，取自雪松溪生态系统科学保护区（Cedar Creek Ecosystem Science Reserve）BioCON实验（e141）的公开数据集，以及由美国国家大气沉降项目（National Atmospheric Deposition Program, NADP）与美国环境保护署（US Environmental Protection Agency）编制的总沉降地图集。 README.md文件提供了关于数据来源与处理流程的更多细节。MATLAB的开源替代工具为Octave。 Mathematica R/RStudio