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植物硅酸体,简称植硅体,是植物内的含水非晶态二氧化硅(SiO2)颗粒,存在于植物不同部位的细胞内[1-2]。植硅体碳因具有很强的抗腐蚀、抗分解、抗氧化等特性[2-3],可在土壤中保存数千年乃至万年之久[4],是陆地生态系统长期固碳的主要机制之一[5-6],对调节全球碳平衡和应对气候变化意义重大。当前对植硅体的研究主要集中于古环境与古气候重现、农业与环境考古、古生态以及植物分类学等方面,基于宏观估测和默认植硅体恒久稳定的前提进行,因此学界对土壤中植硅体的稳定性存在很大争议。PARR等[7-8]发现:经过2 000 a的分解,土壤中植硅体碳质量分数从仅占表层土壤有机碳不到10%的比例,上升到82%,表明土壤中植硅体碳的封存是一个长期积累的过程[9]。WILDING等[4]发现:植硅体中碳的放射性年龄约为1.33万a。因此,植硅体具有长期稳定性。也有研究认为植硅体是不稳定的。如FRAYSSE等[10]发现竹林土壤中的植硅体的溶解度等同于玻璃质硅石,是石英的17倍;BARTOLI等[11]认为植硅体的溶解速率比硅酸盐矿物高一个数量级[11];CONLEY等[12]发现:保存死亡植物的地方,水溶性硅的输出明显增加。竹类作为禾本科Poaceae中典型的硅富集植物,植硅体碳含量高,提取、纯化相对方便[13-14]。其次,竹类植物分布广泛,种类丰富[15],不同生境竹种差异大[16],为比较不同竹种植硅体碳稳定性差异和微观形态特征提供了理想的材料。选择竹类植物为研究对象,对揭示植硅体碳稳定性机理和准确估测竹类植硅体碳封存潜力具有双重意义。扫描电子显微镜(scanning electron microscope,SEM)是由电子光学技术、真空技术、精细机械结构以及现代计算机控制技术等共同组成的电子光学仪器[17],在植物研究工作中主要被应用于植物来源和种类鉴定、植物微形态学研究以及植物生长的优劣与环境污染等质量控制[18-19]。近年来,随着植物和土壤植硅体碳研究的深入,扫描电子显微镜等先进仪器也被应用到植硅体碳测定上[20-21]。本研究以毛竹Phyllostachys edulis叶片为材料,利用扫描电子显微镜的高清成像功能检测植硅体微观形态特征,从微观形态上研究毛竹植硅体的稳定性,建立植硅体稳定性微观表征方法,为深入开展植硅体碳研究提供依据。
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