图2. 本文涉及的主要生物标志物的代表性单体结构示例(用罗马数字指示)。指征植物来源的生物标志物: 植物蜡质脂类, 包括长链的烷烃(I)、脂肪酸(II)等(Otto et al., 2005); 角质单体, 如短链的ω-羟基脂肪酸(III)等; 木质素酚类单体, 如香草醛(IV)、丁香酸(V)等(Thevenot et al., 2010); 软木脂单体, 如长链的α, ω-二元酸(VI)等(Otto et al., 2005)。指征微生物来源的生物标志物: 磷脂脂肪酸(PLFA; Frosteg?rd & B??th, 1996), 如亚油酸(VII)等; 甘油二烷基甘油四醚(GDGT; Schouten et al., 2013), 如GDGT-2 (VIII)等; 氨基糖(Joergensen, 2018), 如α-D-氨基葡萄糖(IX)和α-D-氨基半乳糖(X)等。此外, 中性糖(如α-D-葡萄糖(XI)等)和氨基酸(XII)普遍存在于植物和微生物中。

Fig. 2. Examples of typical monomer structures for the main types of biomarkers introduced in this paper. Plant-derived biomarkers: plant wax lipids including long-chain n-alkanes (I) and fatty acids (II), etc. (Otto et al., 2005); cutin monomers such as short-chain ω-hydroxyalkanoic acid (III); lignin phenols such as vanillin (IV) and syringic acid (V), etc. (Thevenot et al., 2010); suberin monomers such as long-chain α,ω-alkanedioic acid (VI; Otto et al., 2005). Micorbial-derived biomarkers: phospholipid fatty acids (PLFAs) such as linoleic acid (VII; Frosteg?rd & B??th, 1996); glycerol dialkyl glycerol tetraethers (GDGTs) such as GDGT-2 (VIII; Schouten et al., 2013); amino sugars, including α-D-glucosamine (IX) and α-D-galactosamine (X), etc. (Joergensen, 2018). In addition, neutral sugars such as α-D-glucose (XI) and amino acids with side chain (R group; XII) can be synthesized by both plants and microbes.