MAIN CONCLUSION The dead husk is a vital component of the dispersal unit whose biochemical properties can be modified following exposure to drought. This might affect seed performance and fate, soil properties and consequently plant biodiversity. We investigated the effects of extreme drought on the dispersal unit (DU) properties of winter wild oat (Avena sterilis L.) in the Mediterranean ecosystems focusing on a commonly ignored component of the DU, namely the dead floral bracts (husk). DUs were collected from a climate change experimental research station in the Judean Hills, Israel, simulating extreme drought and from two additional sites differing in the rainfall amounts. Our results showed that drought conditions significantly affected A. sterilis reproductive traits displaying reduced DUs and caryopses weights. The husk contributes profoundly to seed performance showing that germination from the intact DUs or the intact florets 1 was higher, faster and more homogenous compared to naked caryopses; no effect of drought on germination properties was observed. The husk stored hundreds of proteins that retain enzymatic activity and multiple metabolites including phytohormones. Changes in rainfall amounts affected the composition and levels of proteins and other metabolites accumulated in the husk, with a notable effect on abscisic acid (ABA). The husk of both control and drought plants released upon hydration substances that selectively inhibited other species seed germination as well as substances that promoted microbial growth. Our data showed that the dead husk represents a functional component of the DU that have been evolved to nurture the embryo and to ensure its success in its unique habitat. Furthermore, drought conditions can modify husk biochemical properties, which in turn might affect seed performance and fate, soil microbiota and soil fertility and consequently plant species diversity.

中文翻译：

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极端干旱改变了冬季野燕麦 (Avena sterilis L.) 的后代传播单位特性

主要结论 死壳是散播单元的重要组成部分，其生化特性可在暴露于干旱后发生改变。这可能会影响种子性能和命运、土壤特性，从而影响植物生物多样性。我们调查了极端干旱对地中海生态系统中冬季野燕麦 (Avena sterilis L.) 的扩散单位 (DU) 特性的影响，重点关注 DU 的一个通常被忽视的组成部分，即死亡的花苞片 (外壳)。DUs 是从以色列 Judean Hills 的一个气候变化实验研究站收集的，模拟极端干旱和另外两个降雨量不同的地点。我们的研究结果表明，干旱条件显着影响了 A. sterilis 的生殖性状，显示出减少的 DU 和颖果重量。外壳对种子性能的贡献很大，表明与裸颖果相比，完整 DU 或完整小花 1 的发芽更高、更快且更均匀；没有观察到干旱对发芽特性的影响。外壳储存了数百种保留酶活性的蛋白质和多种代谢物，包括植物激素。降雨量的变化会影响果壳中积累的蛋白质和其他代谢物的组成和水平，对脱落酸 (ABA) 有显着影响。对照植物和干旱植物的外壳在水合后释放出选择性抑制其他物种种子萌发的物质以及促进微生物生长的物质。我们的数据表明，死壳代表了 DU 的一个功能组成部分，经过进化以培育胚胎并确保其在其独特的栖息地中成功。此外，干旱条件可以改变果壳的生化特性，进而可能影响种子性能和命运、土壤微生物群和土壤肥力，从而影响植物物种多样性。