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

北极苔原古代活种子和永久冻土的挖掘和放射性碳测年

• 批准号: 8906004
• 负责人: James McGraw
• 金额: $ 2.59万
• 依托单位: West Virginia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1989
• 资助国家: 美国
• 起止时间: 1989-06-15 至 1991-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8906004&HistoricalAwards=false
• 关键词: Excavation; Radiocarbon; Dating; Ancient; Viable

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.

种子在天然植物群落土壤中保持活力的时间长度一直引起生态学家和植物生理学家的兴趣。拟议中的项目直接针对冻土带土壤解决了这个问题，冻土带土壤最有可能含有寿命较长的种子。以前的工作已经证明，在高山冻土带环境中，在日蚀埋藏的有机土壤中发现了大量分离的有活力的种子。种子和土壤的放射性碳年代测定表明，这些种子至少有几百年的历史。初步工作还表明，通过额外的田野调查，可能会发现比这更古老的种子。目前的研究将通过对另外六个溶蚀埋土剖面的广泛挖掘来寻找更古老的种子。这些广泛的挖掘工作是由“地球观察”资助的，该组织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，将对来自这些剖面的土壤和种子进行放射性碳定年。种子的放射性碳定年将使用串联加速器质谱法完成，这允许对含碳小物体进行直接定年。通过演示程序，将小心地从正在发芽的幼苗上除去种皮并进行标记，同时将幼苗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存在多长时间之外，还将确定已知年龄类别的老基因型和年轻基因型的种群，以供未来的工作使用。土壤将用传统的放射性碳测年法测定年代，并通过检查种子本身的加速日期来估计溶蚀运动的速度。对加速器测年方法的其他检查将包括：(1)测量14C/13C无线电，以确定在测年过程中是否需要考虑同位素区分，(2)在几个叶片上复制测年过程，以及(3)在黑暗中发芽的幼苗及其种皮的测年。