Ancient DNA sheds light on the historical distribution of the rare and ephemeral plant Coleanthus subtilis in Southern Siberia.

backgroundAncient DNA is a valuable source of information about the distant past of our planet. Reconstructing the past ecosystems is essential for understanding many aspects of life in the steppes of southern Siberia and Central Asia, where numerous human societies representing different archaeological cultures have lived. The remains of their activities, revealed by archaeological excavations, provide a wide range of sources for the cultural and natural/biological history of the region. One of the most enigmatic Iron Age archaeological cultures in southern Siberia is the Tashtyk culture, which dates back to the 1st - 7th centuries AD. The people of this culture inhabited the Minusinsk Basin and practiced different burial rites, including cremation. Thanks to the exceptional preservation of organic remains in individual Tashtyk burials we know of quite an unusual phenomenon: the placement of cremains into the human-like mannequins made from animal skin and filled with herbaceous plants. This study analyses ancient DNA extracted from the grass stuffing of a mannequin found in 2023 at the Oglakhty cemetery, which dates back to 250-300 AD. Our aim is to identify the plant species that were used to stuff the mannequin approximately 1,700 years ago, and to compare their diversity with that of modern-day plant species. This is particularly significant given that the Oglakhty region is part of the Khakassky State Nature Reserve, which was added to the UNESCO Tentative List in 2016 due to its biodiversity and concentration of archaeological sites.

resultsWe sequenced the ancient DNA of a dried historical grass mixture in order to reconstruct the nearly complete chloroplast genomes of several apparent Poaceae species. Our analysis showed that, 1,700 years ago, the diversity of plant species in the Oglakhty area was similar to the modern meadow flora of the Minusinsk Basin. These included typical steppe and forest-steppe zone plant genera of Siberia, such as Holcus, Phleum, Poa, and Stipa. Interestingly, alongside the species commonly found in modern southern Siberian steppes and meadows, we discovered the rare, ephemeral, and protected moss grass, Coleanthus subtilis (Tratt.) Seidel ex Roem. et Schult. whose current distribution range spans highly fragmented areas of northern Eurasia and North America but not the Minusinsk Basin.

conclusionThe herbaceous plant C. subtilis, whose DNA fragments were obtained through the metagenomic profiling of the human-like mannequin's stuffing at the Oglakhty cemetery, provides new insights into the cultural and natural history of Siberia. Firstly, we identified several grass taxa in the mannequin's stuffing. Most of them are characteristic for the steppe zone; the only exception is C. subtilis, which usually inhabits riverbanks. Therefore, we assume that, despite being primarily stuffed with the steppe plants, the Oglakhty mannequin was crafted on a riverbank, where C. subtilis might have got inside likely by chance. It is important to note that the stuffing process apparently took place after the vegetation season of C. subtilis in second half of summer and the beginning of autumn. Secondly, our research suggests that a population of C. subtilis, which is currently absent from the documented flora of southern Siberia, previously grew in the Minusinsk Basin wetlands. Our study highlights the need for field expeditions aimed to identify endemic populations of C. subtilis in the Yenisei River valley.