植硅体稳定同位素生物地球化学研究进展

植硅体形态鉴定与组合分析广泛应用于古环境重建和农作物起源分析等.鉴于植硅体的抗腐蚀、抗降解,易保存,锢囚的碳不易污染,且保存了植物的原始信息等特性,其有机地球化学研究日益被重视.植硅体稳定同位素分析表明植硅体是植物通过吸收单硅酸,以蒸腾作用为主要动力,在植物的不同部位发生同位素分馏淀积形成,其稳定同位素组成具有丰富的植物生理和环境信息.植物不同部位植硅体稳定同位素组成具有差异,其含量和硅、氧同位素值沿蒸腾流通常有增加的趋势.沉积物植硅体碳同位素分析不仅可以用于恢复草本的C3、C4植物生物量的比例,并且有可能重建古大气的碳同位素构成,是三者中最具有潜力的考古学、古环境研究的指标.植硅体有机化学组成分析,特别是类脂物分析,有利于认识植硅体碳同位素值相对于总有机碳偏负,C3、C4草本植硅体同位素差值范围缩小的原因.

Advances in the Biogeochemical Study of Phytolity Stable Isotope

Phytolith analysis has been widely used to explore paleoenvironment changes and the origin of some crops. Phytolith biogeochemistry has received more and more attention because it resists to chemical erosion and degradation, and in particular the original information of plants are preserved in the occluded carbon in phytolith which is always difficult to be contaminate. Phytolith is produced in living plants and precipitated in the intra-cellular-and extra-cellular structures of their leaf, stem and root systems when monosilicic acid Si(OH)₄]is taken up by root under the driving force of transpiration. Silicon, oxygen and carbon isotopic compositions of phytolith are influenced by environment and regulated by plant physiology, and are different among organs of plant. Moreover, the silicon and oxygen carbon values of phytoltih normally tend to increase with its concentration up the plant in the transpiration stream. Of the three elements investigated, occluded carbon within phytoliths looks the most promising alternative indices for investigating the past environment at the moment. Carbon isotopic compositions of phytolith can be used in reconstructing the proportion of C₃ /C₄ grasses, and be promising for calculating atmospheric carbon isotope. The study of organic chemical components and the lipid in phytoliths may help to explain the reason of which fresh phytoliths extracted directly from grasses exhibit depleted isotopic values relative to the whole plant and a compression of the isotopic range between C³and C₄ phytoliths relative to that for C₃ and C₄ grass.