Data from: Windows of opportunity for germination of riparian species after restoring water level fluctuations: a field experiment with controlled seed banks

1. Restoration activities aiming at increasing vegetation diversity often try to stimulate both dispersal and germination. In wetlands, dispersal and germination are coupled as water and water level fluctuations (WLF) simultaneously influence seed transport and germination conditions (soil moisture). Water regime shifts have been shown to affect vegetation composition. However, the interactions between WLF, dispersal and subsequent germination as drivers of such changes are still poorly understood, especially within the complexity of a field situation. 2. We tested the effect of soil moisture on ten riparian species in the greenhouse and sowed these species on 135 field locations in nine wetlands with recently restored WLF. We used quantile regressions to test the effects of WLF on the window of opportunity for germination from sown seeds and other seeds naturally dispersed to our plots, as well as on community diversity. 3. Soil moisture significantly affected germination both in the greenhouse and in the field. In the complexity of a field situation, a flooding depth just below the soil level, an intermediate flooding duration and a high flooding frequency provided the best opportunities for maximal germination. This was because these conditions enhanced germination from the seed bank as well as increasing germination from dispersed seeds. Seedling diversity showed identical patterns. 4. Other known (i.e., light conditions) and unknown factors played a role as we found low and variable germination, even under optimal conditions. We found evidence that WLF can affect vegetation zonation as flooded seedling communities contained more species with high moisture affinity. 5. Synthesis and applications. Water level fluctuations provide clear windows of opportunity for germination both from the seed bank and from dispersed seeds. Water regime changes are therefore likely to strongly affect recruitment opportunities and subsequent community assembly in riparian ecosystems, for instance through climate change or management. Water level fluctuations can be used as management tool to stimulate plant recruitment and seedling diversity in riparian wetlands.

1. 旨在提升植被多样性的修复活动通常会同时尝试促进种子扩散与萌发。在湿地生态系统中，种子扩散与萌发过程紧密耦合——水体及水位波动（water level fluctuations, WLF）会同时影响种子转运与萌发条件（土壤湿度）。已有研究表明，水文情势变化会改变植被组成。然而，作为此类植被组成变化驱动因子的WLF、种子扩散与后续萌发之间的相互作用机制仍不甚明确，尤其是在复杂的野外实地场景中。
2. 本研究在温室中探究了土壤湿度对10种河岸物种的影响，并在9个近期完成水位波动修复的湿地中的135个野外样地中播种了这些物种。我们采用分位数回归（quantile regressions）方法，分析了WLF对播种种子及自然扩散至样地的天然种子的萌发窗口期，以及群落多样性的影响。
3. 无论是温室还是野外场景，土壤湿度均会显著影响种子萌发。在复杂的野外实地环境中，略低于地表的淹水深度、中等时长的淹水周期与较高的淹水频率，可提供最优的最大化萌发条件。这是因为此类条件既促进了种子库（seed bank）的种子萌发，也提升了扩散种子的萌发率。幼苗多样性也呈现出一致的变化模式。
4. 即便在最优条件下，我们仍观测到萌发率较低且波动较大，这表明其他已知（如光照条件）与未知因子同样会影响萌发过程。研究结果证实，WLF会影响植被分带现象：淹水环境下的幼苗群落中，高湿度亲和性物种的占比更高。
5. 总结与应用。水位波动可为种子库及扩散种子的萌发提供明确的窗口期。因此，诸如气候变化或人为管理引发的水文情势变化，很可能会强烈影响河岸生态系统中的植株定植机会与后续群落组装（community assembly）过程。水位波动可作为一项管理手段，用于提升河岸湿地的植株定植率与幼苗多样性。