Excavation and Radiocarbon Dating of Ancient Viable Seeds and Permafrost Soils in Arctic Tundra

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The length of time that seeds remain viable in soils of natural plant communities has long intrigued ecologists and plant physiologists. The proposed project attacks this question directly for tundra soils, which are most likely to contain long-lived seeds. Previous work has demonstrated that isolated viable seeds are found in abundance in solifluction-buried organic soil in alpine tundra environments. Radiocarbon dates of both seeds and soil show that the seeds are on the order of hundreds of years old, at least. Preliminary work also suggests that seeds much older than this are likely to be uncovered by additional fieldwork. The present study will seek still older seeds with extensive excavations of six additional solifluction- buried soil profiles. These extensive excavations are made possible by a grant from Earthwatch, which will support the field research and will supply volunteers. To take maximum advantage of this opportunity both soils and seeds from these profiles will be radiocarbon dated. Radiocarbon dating of the seeds will be accomplished using tandem accelerator mass spectrometry, which allows direct dating of small carbon-containing objects. Through a demonstrated procedure, seed coats will be carefully removed from emerging seedlings and dated, while the seedlings will be transplanted to pots in the greenhouse. Thus, in addition to establishing how long seeds may persist in permafrost soils populations of old and young genotypes of known age classes for future work will be established. Soil will be dated with conventional radiocarbon dating, and rates of solifluction movement will be estimated as a check on the accelerator dates of the seeds themselves. Other checks on the accelerator method of dating will include: (1) measurement of the 14C/13C radio to determine whether isotope discrimination needs to be taken into account in the dating procedure, (2) replication of the dating procedure on several lobes, and (3) dating of seedlings that emerge in the dark, as well as their seed coats.