Shifting limitation of primary production: experimental support for a new model in lake ecosystems

The limits on primary production vary in complex ways across space and time. Strong tests of clear conceptual models have been instrumental in understanding these patterns in both terrestrial and aquatic ecosystems. Here we present the first experimental test of a new model describing how shifts from nutrient to light limitation control primary productivity in lake ecosystems as hydrologic inputs of nutrients and organic matter vary. We found support for two key predictions of the model: that gross primary production (GPP) follows a hump-shaped relationship with increasing dissolved organic carbon (DOC) concentrations; and that the maximum GPP, and the critical DOC concentration at which the hump occurs, are determined by the stoichiometry and chromophoricity of the hydrologic inputs. Our results advance fundamental understanding of the limits on aquatic primary production, and have important applications given ongoing anthropogenic alterations of the nutrient and organic matter inputs to surface waters.Data and R code have been made available to conduct statistical analyses and generate Figures 2-4. Figures 2 & 4 use the same data file titled 'compiledNutrientLightData.csv'. R code titled 'NutrientLightData_Analyses.R' and 'nutrientLimitationAnalysis.R' generate Figure 2 and Figure 4, respectively. Files for Figure 3 are titled 'gppData.csv' and 'gppAnalyses.R'. Save files and set working directory in R code to where data files are saved.

初级生产力的限制在空间和时间维度上呈现出复杂的差异性。对清晰概念模型进行强有力的验证，对于理解陆地和水生生态系统中这些模式至关重要。在本研究中，我们首次对一种新型模型进行了实验性测试，该模型描述了在营养盐和有机物质的水文输入变化过程中，从营养盐限制向光照限制的转变如何控制湖泊生态系统的初级生产力。我们发现该模型的两个关键预测得到了支持：即总初级生产力（GPP）与溶解有机碳（DOC）浓度的增加呈现出驼峰状的关联；以及最大GPP和驼峰出现的临界DOC浓度由水文输入的化学计量比和色度决定。我们的研究结果深化了对水生初级生产力限制的基本理解，鉴于人类活动对地表水中营养盐和有机物质输入的持续改变，具有重要的应用价值。数据集和R代码已提供，以便进行统计分析并生成图2-4。图2和图4使用了同名的数据文件'titlecompiledNutrientLightData.csv'。R代码'titleNutrientLightData_Analyses.R'和'titlenutrientLimitationAnalysis.R'分别生成了图2和图4。图3的数据文件分别命名为'titlegppData.csv'和'titlegppAnalyses.R'。在R代码中保存文件并设置工作目录，以确保数据文件的位置。