How long do tree seeds survive in soil seedbanks? A multi-species comparison in an old-growth deciduous temperate forest

We evaluated the performance of tree seeds in the soil seedbank of a temperate deciduous old-growth forest with respect to the total proportion of seeds that emerged as seedlings (<i>P</i>_TOTAL) and the average time seeds were in the soil prior to emergence as seedlings (<i>T</i>_AVERAGE). We analyzed 12 years of data on the seed dispersal and seedling emergence of 16 important tree species collected from more than 100 seed traps and quadrats. Using these estimates, we assessed whether seed banking is an effective regeneration strategy in forests compared to other life-history strategies. Persistence in the soil did not necessarily increase overall seed mortality. Phylogenetic constraints played a limited role in variations in <i>P</i>_TOTAL and <i>T</i>_AVERAGE among species, likely due to pronounced differences between closely related species. Estimated values of <i>T</i>_AVERAGE were mostly less than 1.5 years. Some species had a <i>P</i>_TOTAL greater than 0.20, despite having seeds with no known physical or chemical protection mechanisms. Seed size was not associated with seed performance. By contrast, greater per capita fecundity appeared to compensate for lower performance of banked seeds. Contrary to our expectations, species with longer <i>T</i>_AVERAGE values exhibited higher seedling survivorship, implying an absence of trade-offs between seed banking and seedling banking, and even implying a synergy between these strategies. In old-growth forests, seeds stored in soil seedbanks likely provide a buffer during years with little or no seed production; however, seedbanks may not promote adequate regeneration following natural or artificial large-scale disturbances that remove parent trees.

本研究针对温带落叶原始林的土壤种子库（soil seedbank）中树木种子的性能展开评估，以出苗种子总占比（P_TOTAL）与种子入土至出苗的平均时长（T_AVERAGE）为核心评价指标。研究团队依托100余个种子诱捕器与样方收集得到的16种重要乔木的种子扩散及幼苗出苗数据，开展了为期12年的系统性分析。基于上述估算结果，本研究对比其他生活史策略（life-history strategies），评估了土壤种子库是否为森林生态系统的有效更新策略。种子在土壤中的留存时长未必会提升整体种子死亡率。系统发育限制（phylogenetic constraints）对不同物种间P_TOTAL与T_AVERAGE的变异仅存在有限影响，这大概率源于近缘物种间存在显著的性状差异。T_AVERAGE的估算值大多低于1.5年。部分物种的P_TOTAL高于0.20，尽管其种子未发现已知的物理或化学保护机制。种子大小与种子性能并无显著关联。相较而言，更高的个体繁殖力（per capita fecundity）似乎能够弥补土壤种子库中种子的较低性能表现。与本研究预期相悖的是，T_AVERAGE更长的物种其幼苗存活率更高，这表明种子库策略与幼苗库（seedling banking）之间不存在生活史权衡（trade-offs），甚至二者之间存在协同效应。在原始林中，储存在土壤种子库中的种子或许可在种子产量极低或无种子产出的年份提供缓冲；但在移除母树的自然或人为大规模干扰发生后，种子库或无法支撑足够的森林更新。