禾本科植硅体电子探针化学组成研究

Phytolith analysis has been widely used to study phytolith formation mechanisms, and archaeological and palaeoenvironmental reconstructions. The research on phytolith morphology, size, and assemblage is intensive. However, few studies have been focused on electron probe microanalysis of chemical elemental composition in different phytolith morphotypes. Phytoliths are morphologically diverse in a single plant species and redundant among different plant taxa. The analysis of elemental composition of phytolith probably provides some information on plant classification that is helpful to improve the accuracy of phytolith used in plant identification. Though the morphology, size, and assemblage of phytolith in plants changes and responds to growth stages and envrionmental factors throughout the growing season, the seasonal variations of mineral composition in phytolith are little understood. The positive silica deposition in some plant species during the early stage of growing season is uncertain. The variations of the chemical elemental composition of phytolith provide opportunities to discern the properties of silica deposited positively in a plant. In this study, by comparing the different methods of electron probe microanalysis of phytolith compositions, the best one will be chosen to investigate the chemical elemental compositions of phytolith in Poaceae plants in the same area in order to reveal its significance on plant classification; and to examine the monthly/seasonal variations of chemical elemental composition of phytolith in mature and newborn leaves in each month of Bambusoideae Dendrocalamus ronganensis; in leaves at different positions in maize in order to explore the evidence of silica deposited positively by plant, and the relationship between phytolith formation and envrionmental factors. This work is useful to provide the theoretical basis for studying the phytolith formation mechanism, and for using phytolith analysis as a tool of archaeological and paleoenvironmental reconstruction.

植硅分析广泛应用于植物分类、植硅体形成机制、考古及古环境重建研究，其中植硅体的形态、大小及组合研究较为深入，然而，不同形态植硅体的电子探针化学组成分析鲜有开展。植硅体形态具有多样性和重复性，其化学组成分析可能提供一些种类信息，提高植硅体鉴定植物的准确性。植物在生长季节内，植硅体形态、大小及组合存在显著变化并响应生长阶段及环境因子，而其化学组成变化尚不清楚；一些植物生长季节初期有主动积硅现象，但有不确定性，植硅体化学组成研究可能识别植物生长季节内主动积硅信号。本研究通过尝试并优选植硅体电子探针化学组成分析方法，调查相同区域不同禾本科植物植硅体化学组成，揭示其化学组成的植物分类意义；监测生长季节内融安黄竹新、老叶片，玉米不同叶位叶片植硅体化学组成月份变化，探究植物主动积硅的证据以及植硅体形成与环境因子之间的关系。此研究可为植硅体形成机制，植硅体分析应用于考古或古环境重建提供理论依据。

尝试了薄片植硅体电子探针分析方法，对中国西南岩溶地区常见禾本科植物，不同生长阶段玉米及融安黄竹叶片植硅体进行了电子探针分析，以探讨植硅体形态、组合及化学组成植物分类意义，植硅体形成机制。同时，对竹林土壤植硅体早期成岩效应及植硅体形态、组合及圈闭碳火灾指示意义进行了初步研究。结果表明：不测碳和校正模式赋碳值电子探针分析方法能够进行薄片植硅体化学组成分析，植硅体主要由SiO2、C、水及多种矿质元素组成，随植硅体形态和微区变化；植硅体化学组成具有一定属级或亚科级植物分类意义，能影响其稳定性；融安黄竹新、老叶片植硅体组合及化学组成不同，月份变化受叶龄及环境因子影响，与玉米前三片真叶一样生长季节早期植硅体SiO2含量较高可能指示主动积硅作用；干旱月份竹叶植硅体及其圈闭碳降低，主要由于有效硅供给不足限制了含碳量高的植硅体形态形成；喀斯特石山旱季土壤系统有效硅旱季显著低于雨季，可能与降水影响生物硅溶解有关。竹林土壤系统植硅体形态、组合能够反映植被，但受不同形态植硅体溶解影响。植硅体形态、组合及圈闭碳对火活动具有指示意义。此研究为解释植硅体形成, 植硅体应用于植物分类、古环境重建及碳硅耦合循环提供依据。