“Puffing” in <i>Sarcoscypha austriaca</i>: Back to Ziegenspeck

Many discomycetes show the phenomenon of “puffing”: the quasi-simultaneous discharge of large numbers of ascospores, rendering them visible to the unaided eye as a whiff of smoke above the fruitbody. Obviously, some kind of synchronization mechanism must be present to make all asci involved burst at about the same time. This mechanism has generally been understood to be of a mechanical nature. For a (small, dung-inhabiting) <i>Ascobolus</i> species, puffing was shown to involve a discharge wave propagating radially outward from a random origin at a speed of about 1.5 cm/s. Using high-speed imaging, we have found no evidence for such a wave in puffing by the (much larger, wood-inhabiting) apothecia of <i>Sarcoscypha austriaca</i>. Rather, extended (but limited) areas seem to become active essentially simultaneously, and within these areas a few percent of the asci discharge their spores randomly. In these large fruitbodies, puffing is found to be preceded by a small but distinct deformation of the apothecium, the geometry of which is such that it increases the lateral compressive stress in the hymenium. The observations suggest that this increase in stress is instrumental in causing many asci to burst quasi-simultaneously in the affected area, a hypothesis essentially already proposed by H. Ziegenspeck, about a century ago.许多盘菌类真菌（discomycetes）会呈现「喷烟」现象：即大量子囊孢子（ascospores）近乎同步释放，使得肉眼可在其子实体（fruitbody）上方观测到类似烟雾的孢子云。显然，必然存在某种同步机制，使得所有参与的子囊（asci）能够在大致同一时刻破裂释放孢子。学界此前普遍认为该同步机制属于机械作用范畴。针对一种（体型微小、栖生于粪便的）粪盘菌属（Ascobolus）物种，已有研究证实其喷烟现象涉及一条从随机起点向外径向传播的释放波，传播速度约为1.5厘米每秒。借助高速成像（high-speed imaging）技术，我们在（体型大得多、栖生于木材的）奥地利肉杯菌（Sarcoscypha austriaca）的子囊盘（apothecium）喷烟过程中，未观测到此类释放波的存在证据。与之相反，似乎是较大但仍有限的区域近乎同时被激活，且在这些区域内仅有百分之几的子囊会随机释放孢子。在这类大型子实体中，喷烟现象发生前，子囊盘会出现微小但清晰可辨的形变，该形变的几何特征能够提升子实层（hymenium）内的侧向压应力。观测结果表明，这种应力升高是促使受影响区域内大量子囊近乎同步破裂的关键因素——这一假说早在约一个世纪前就已由H·齐根施佩克（H. Ziegenspeck）提出。