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。在包括耶拿实验在内的少数几项现有的较长期研究中，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变得更加紧密，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通过元素循环来反馈，随着正在进行的实验持续时间更是如此。这可能会导致沿植物多样性梯度的不同显着的时间趋势，也可能改变(季节)变异性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)植物多样性对元素浓度、通量和(化学计量比)比率的影响强度是否随季节变化；(Ii)植物多样性是否控制元素浓度、通量和比率的变异性；(Iii)月分辨元素浓度、通量和比率(由线性和非线性趋势、季节幅度和突变点反映)的时间进程是否取决于植物群落组成。此外，我们评估了其他地块属性和环境条件，包括特别是干湿相、极端温度和植被时期关键时期的降水量或温度总和等累积气象指标，在植被周期中所起的作用；(Iv)Delta-BEF实验中特定地块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。为了应对度量缺口，我们将使用贝叶斯建模来填补缺口。然后，将用数学时间序列分析的方法处理完成的数据集。

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.