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

种子在自然植物群落的土壤中存活的时间长短一直是生态学家和植物生理学家感兴趣的问题。拟议中的项目直接针对冻土带土壤解决这个问题，冻土带土壤最有可能含有长寿种子。以前的工作已经证明，在高山冻土带环境中埋藏的有机土壤中，存在大量孤立的可存活种子。种子和土壤的放射性碳测年表明，这些种子至少有数百年的历史。初步工作还表明，比这更古老的种子很可能会通过额外的田野调查而被发现。目前的研究将通过广泛挖掘另外六个埋藏的土壤剖面来寻找更古老的种子。这些大规模的挖掘是由地球观察提供的赠款实现的，该基金将支持实地研究并提供志愿者。为了最大限度地利用这一机会，来自这些剖面的土壤和种子都将进行放射性碳年代测定。种子的放射性碳测年将使用串联加速器质谱仪完成，这使得可以直接对含碳小物体进行测年。通过一个示范程序，种皮将被小心地从出苗的幼苗上移除并标明日期，而幼苗将被移植到温室的花盆中。因此，除了确定种子可以在永久冻土中保存多长时间外，还将为今后的工作建立已知年龄段的老年和年轻基因类型的种群。土壤将用传统的放射性碳测年进行测年，土壤吸收移动的速度将被估计为对种子本身的加速器日期的检查。对加速器测年方法的其他检查将包括：(1)测量14C/13C无线电，以确定测年过程中是否需要考虑同位素歧视，(2)在几个叶上重复测年程序，以及(3)对在黑暗中出现的幼苗及其种皮进行测年。

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.