Vital effects of K isotope fractionation in organisms: observations and a hypothesis

• 作者: Weiqiang Li
• 来源期刊: 地球化学学报(英文）
• 关键词: K isotopes Isotope fractionation Vital effects
• 年，卷（期）: 2017,（3）
• 页码范围: 374-378
• 页数: 4页
• 语种: 英文
• DOI: 10.1007/s11631-017-0167-1

摘要

Compared with the measureable but limited K isotope variation in geological samples, biological samples have much larger variations in δ41K values: from -1.3‰ to +1.1‰ relative to the international K standard NIST SRM 3141a. Notably, higher plants generally have δ41K values that are lower than igneous rocks, whereas sea plants (algae) have δ41K values that are higher than seawater; the range in δ41K values of plants encompasses the δ41K values of both igneous rocks and seawater. Plant cells utilize different K uptake mechanisms in response to high-and low-K conditions. In a low-K environment, plant cells use energy-consuming ion pumps for active uptake of K; plant cells in high-K environments use non-energy-con-suming ion channels. Based on these facts and on K isotope data from sea and land plants, it is hypothesized that the different K uptake mechanisms are accompanied by distinct K isotope fractionation behaviors or vital effects. The enrichment of light K isotopes in terrestrial plants could be attributed to preferential transport of isotopically light K in the energy-consuming active uptake process by K ion pumps in the membranes of plant root cells. On the other hand, the enrichment of heavy K isotopes in algae may be caused by a combination of the lack of K isotope fractionation during K uptake from seawater via ion channels and the preferential efflux of light K isotopes across the cell membrane back to the seawater. The large variation of K isotope compositions in biological samples therefore may reflect the diversity of isotopic vital effects for K in organisms, which implies the great potential of K isotopes in biogeochemical studies.