Bippus Alexander C, Escapa Ignacio H, Wilf Peter, Tomescu Alexandru M F
Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, United States of America.
Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Museo Paleontológico Egidio Feruglio, Trelew, Argentina.
PeerJ. 2019 Dec 12;7:e8244. doi: 10.7717/peerj.8244. eCollection 2019.
In extant ecosystems, complex networks of ecological interactions between organisms can be readily studied. In contrast, understanding of such interactions in ecosystems of the geologic past is incomplete. Specifically, in past terrestrial ecosystems we know comparatively little about plant biotic interactions besides saprotrophy, herbivory, mycorrhizal associations, and oviposition. Due to taphonomic biases, epiphyte communities are particularly rare in the plant-fossil record, despite their prominence in modern ecosystems. Accordingly, little is known about how terrestrial epiphyte communities have changed across geologic time. Here, we describe a tiny fossil epiphyte community that sheds light on plant-animal and plant-plant interactions more than 50 million years ago.
A single silicified (Osmundaceae) rhizome from a new locality of the early Eocene (ca. 52 Ma) Tufolitas Laguna del Hunco (Patagonia, Argentina) was studied in serial thin sections using light microscopy. The community of organisms colonizing the tissues of the rhizome was characterized by identifying the organisms and mapping and quantifying their distribution. A 200 × 200 µm grid was superimposed onto the rhizome cross section, and the colonizers present at each node of the grid were tallied.
Preserved , this community offers a rare window onto aspects of ancient ecosystems usually lost to time and taphonomic processes. The community is surprisingly diverse and includes the first fossilized leafy liverworts in South America, also marking the only fossil record of leafy bryophyte epiphytes outside of amber deposits; as well as several types of fungal hyphae and spores; microsclerotia with possible affinities in several ascomycete families; and evidence for oribatid mites.
The community associated with the Patagonian rhizome enriches our understanding of terrestrial epiphyte communities in the distant past and adds to a growing body of literature on osmundaceous rhizomes as important hosts for component communities in ancient ecosystems, just as they are today. Because osmundaceous rhizomes represent an ecological niche that has remained virtually unchanged over time and space and are abundant in the fossil record, they provide a paleoecological model system that could be used to explore epiphyte community structure through time.
在现存生态系统中，生物之间复杂的生态相互作用网络易于研究。相比之下，对地质历史时期生态系统中此类相互作用的了解并不完整。具体而言，在过去的陆地生态系统中，除了腐生、食草、菌根共生和产卵外，我们对植物生物相互作用的了解相对较少。由于埋藏学偏差，附生植物群落尽管在现代生态系统中很突出，但在植物化石记录中却极为罕见。因此，对于陆地附生植物群落在地质时期的变化情况知之甚少。在此，我们描述了一个微小的化石附生植物群落，它揭示了5000多万年前的植物 - 动物和植物 - 植物相互作用。
对来自始新世早期（约5200万年前）图福利塔斯拉古纳德洪科（阿根廷巴塔哥尼亚）一个新地点的一块硅化（紫萁科）根茎进行了研究，使用光学显微镜制作连续薄片。通过识别生物并绘制和量化它们的分布，对定殖在根茎组织上的生物群落进行了表征。在根茎横截面上叠加一个200×200微米的网格，并统计网格每个节点上的定殖者。
这个保存下来的群落为通常因时间和埋藏过程而消失的古代生态系统的各个方面提供了一个难得的窗口。该群落令人惊讶地多样化，包括南美洲最早的叶状苔类化石，这也标志着除琥珀矿床外叶状苔藓附生植物的唯一化石记录；以及几种类型的真菌菌丝和孢子；与几个子囊菌科可能有亲缘关系的微菌核；还有甲螨的证据。
与巴塔哥尼亚根茎相关的群落丰富了我们对遥远过去陆地附生植物群落的理解，并为关于紫萁根茎作为古代生态系统中组成群落的重要宿主的文献增添了内容，就像它们在今天一样。由于紫萁根茎代表了一个在时间和空间上几乎保持不变的生态位，并且在化石记录中很丰富，它们提供了一个古生态模型系统，可用于探索附生植物群落随时间的结构。
