Biodiversity effects on seasonality, trends, and events in highly resolved long-term time series of the N and P cycles: a synthesis

植物多样性影响着许多生态系统变量，如生产力和养分循环。然而，只有少数研究区分了植物多样性的初始（短期）和长期影响。在现有的包括耶拿实验在内的少数长期研究中，植物多样性与生态系统变量（主要是生产力）之间的关系随着时间的推移而增强，这表明短期实验低估了生物多样性的影响。植物多样性对生产力的影响可以预期反馈元素循环，甚至随着实验持续时间的延长而更加明显。这可能导致沿着植物多样性梯度的不同显著的时间趋势，也可能改变（季节）变异的大小和极端事件对生态系统功能的影响。我们的目标是测试(i)植物多样性的强度是否对元素浓度、通量和（化学计量）比率的影响随季节而变化；（二）如果植物多样性控制着元素浓度、通量和比率的可变性；（三）月分解元素浓度、通量和比率（反映在线性和非线性趋势、季节振幅和断点上）的时间过程是否取决于植物群落组成。此外，我们还评估了其他样地属性和环境条件的作用，包括特别的干湿阶段、极端温度和植被期关键时期的降水总和或温度等累积气象指标；（iv）在三角洲- bef试验中，特定样地的土壤或植物历史是否影响生物多样性-养分循环关系。我们的分析将依赖于自2003年以来每两周分辨率的水通量和元素浓度、通量和比率的时间序列。为了处理测量间隙，我们将使用贝叶斯建模来填充间隙。完成的数据集将用数学时间序列分析的方法进行处理。

Plant diversity influences many ecosystem variables, such as productivity and nutrient cycling. However, only a few studies differentiated between initial (short-term) and longer-term effects of plant diversity. In the few existing longer-term studies including the Jena Experiment, the relationship between plant diversity and ecosystem variables, mostly productivity, became stronger with time suggesting that short-term experiments underestimated biodiversity effects. Plant diversity effects on productivity can be expected to feed back on element cycling, and even more so with ongoing experimental duration. This may cause differently pronounced temporal trends along the plant diversity gradient and also may modify the size of (seasonal) variability and the effects of extreme events on ecosystem functioning. Our objectives are to test (i) whether the strength of plant diversity effects on element concentrations, fluxes, and (stoichiometric) ratios changes with season; (ii) if plant diversity controls variability in element concentrations, fluxes and ratios; (iii) whether the temporal course of monthly-resolved element concentrations, fluxes and ratios (as reflected by linear and non-linear trends, seasonal amplitudes, and breaking points) depend on plant community composition. Furthermore, we assess which role other plot properties and environmental conditions including particularly wet and dry phases, extreme temperatures, and cumulative meteorological indicators such as sum of precipitation or temperature during key periods in the vegetation period play; (iv) whether the plot-specific soil or plant histories in the delta-BEF experiment influence the biodiversity-nutrient cycling relationship. Our analyses will rely on time series of water fluxes and element concentrations, fluxes, and ratios in fortnightly resolution since 2003. To cope with measurement gaps, we will use Bayesian modeling for gap filling. The completed data sets will then be treated with methods of the mathematical time series analysis.