PREMISE Adaptive seed dispersal mechanisms are fundamental to plant fitness, but dispersal advantage is scale-dependent. We tested the hypothesis that informed dispersal in response to an environmental cue enables dispersal by wind on a local scale for Astragalus holmgreniorum, a desert species restricted to swales and wash skirts with overland flow, but prevents longer-distance dispersal by water into unfavorable wash habitats. METHODS Pod biomechanics in A. holmgreniorum lead to major shape modifications with changes in moisture content. We performed laboratory experiments to examine the interaction of pod shape with wind and water, and conducted field experiments in A. holmgreniorum habitat evaluating the roles of wind, water, and seed predators on dispersal. RESULTS Dry pods exhibit a flattened crescent shape with partial dehiscence that facilitated wind dispersal by ground tumbling and seed scattering in laboratory experiments. Rain simulation experiments showed that even small precipitation events returned wetted pods to their cylindrical shape and opened the dorsal suture, exposing the seeds. In the field experiments, dry pods were moved locally by wind, whereas rain caused pod opening and washing out of seeds in place. Seed predators had minimal effect on pod movement. CONCLUSIONS Astragalus holmgreniorum exhibits pod structural remodeling in response to environmental change in a striking and novel demonstration of informed dispersal. Wind-driven movement of dry pods facilitates local seed dispersal, but rain causes pods to open and release seeds, ensuring that they are not transported out of suitable habitats and into active washes where they would be lost from the seed bank.

中文翻译：

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豆荚是帆而不是船：栖息地受限的沙漠紫云英的扩散生态学

前提 适应性种子传播机制是植物适应性的基础，但传播优势取决于规模。我们测试了这样一种假设，即根据环境线索进行知情传播可以使黄芪在当地范围内通过风传播，黄芪是一种沙漠物种，仅限于具有陆上流动的洼地和冲洗裙部，但可以防止通过水进行更远距离的扩散进入不利的冲洗栖息地. 方法 A. holmgreniorum 中的豆荚生物力学会随着水分含量的变化而导致主要的形状改变。我们进行了实验室实验以检查豆荚形状与风和水的相互作用，并在 A. holmgreniorum 栖息地进行了现场实验，以评估风、水和种子捕食者对传播的作用。结果 干燥的豆荚呈现扁平的新月形，部分开裂，在实验室实验中通过地面翻滚和种子散布促进了风的传播。降雨模拟实验表明，即使是很小的降水事件也会使湿润的豆荚恢复到圆柱形并打开背缝，露出种子。在田间试验中，干燥的豆荚被风局部移动，而雨导致豆荚打开并在原地洗掉种子。种子捕食者对豆荚运动的影响很小。结论 Astragalus holmgreniorum 表现出豆荚结构重塑以响应环境变化，这是一项引人注目的新颖的知情传播示范。干豆荚的风驱动运动促进了当地的种子传播，但雨水会导致豆荚打开并释放种子，