Data from: Increasing the germination envelope under water stress improves seedling emergence in two dominant grass species across different pulse rainfall events

1. Demographic recruitment processes, such as seed germination and seedling emergence, are critical transitional phases to the re-establishment of degraded plant populations, but often fail due to rainfall not supporting plant requirements. Using species from the widespread arid Australian perennial grass genus Triodia, we investigated the interactions of seeds in different dormancy states and their functional germination envelope in response to water stress after simulated pulse rainfall events. 2. Seed dormancy was alleviated in Triodia species to varying degrees by wet/ dry cycling or by removing floret structures from seeds. The seeds were then exposed to different rainfall frequency and quantity events mimicking the 25th, median, 75th and 95th percentile rainfall events found in natural habitats for the study species in the north-west Australian arid zone. 3. Under 95th percentile rainfall conditions recruitment was highest, but still limited to 35% germination and 10% emergence of cleaned seeds (i.e. the least dormant state evaluated). This was related to the functional germination envelope as indicated by more negative base water potential thresholds (Ψb50) for cleaned seeds (≥ -0.33 MPa) compared to intact florets (≥ -0.26 MPa). As a result the maximum cumulative time where soil water potentials were optimal for germination (Ψsoil ≥ Ψb50) were 1.6–2.6 times longer for cleaned seeds in large frequent rainfall events when compared to intact florets. Furthermore, seed dormancy, that usually prolongs seed survival, was linked to a short-term reduction in seed viability, which may further reduce recruitment rates. 4. Synthesis and applications. Our findings indicate that large frequent rainfall events raised soil water potentials above critical thresholds for germination and are important for successful plant establishment. If recruitment bottlenecks are a result of seed dormancy and variable rainfall for arid grass species, then this study shows benefits for alleviating seed dormancy prior to seeding in restoration sites, as this increases the environmental envelope for germination.1. 种群更新过程（demographic recruitment processes），如种子萌发（seed germination）与幼苗出土（seedling emergence），是退化植物种群重建的关键过渡阶段，但常因降雨量无法满足植物需求而失败。本研究以澳大利亚广泛分布的干旱区多年生禾本科三齿稃属（Triodia）物种为研究材料，探究了不同休眠状态的种子间的互作效应，以及其在模拟脉冲式降雨事件后应对水分胁迫的功能萌发幅（functional germination envelope）。 2. 三齿稃属物种的种子休眠（seed dormancy）可通过干湿循环（wet/dry cycling）或去除种子上的小花结构（floret structures）得到不同程度的缓解。随后将处理后的种子置于不同降雨频率与降雨量的模拟降雨事件中，这些模拟事件对应澳大利亚西北部干旱区研究物种自然栖息地中25分位、中位、75分位及95分位的降雨事件（percentile rainfall events）。 3. 在95分位降雨条件下，种群更新率最高，但经清洁处理的种子（即本研究评估的休眠程度最低的种子状态）的萌发率仅为35%，幼苗出土率仅为10%。这与功能萌发幅相关：与完整小花（基准水势阈值≥-0.26 MPa）相比，清洁种子的50%萌发基准水势（Ψb50）阈值更负（≥-0.33 MPa）。因此，在大规模高频降雨事件中，清洁种子的土壤水势（soil water potentials）处于萌发适宜范围（Ψsoil ≥ Ψb50）的最长累积时长是完整小花的1.6~2.6倍。此外，通常可延长种子存活时间的种子休眠，却与种子活力（seed viability）的短期下降相关，这可能进一步降低种群更新率。 4. 综合与应用。本研究结果表明，大规模高频降雨事件可使土壤水势升至萌发临界阈值以上，这对植株成功建植（plant establishment）至关重要。若干旱区禾本科物种的种群更新瓶颈由种子休眠与降雨变异性共同导致，则本研究表明，在修复生境（restoration sites）播种前缓解种子休眠具有积极意义，因为这可扩大种子萌发的环境适宜范围。