表土δ^(13)C揭示C4植物比C3植物更易分解和消化

Surface soilδ^(13)C reveals C_(4) plants decompose and digest more easily than C_(3) plants

表层土壤中总有机碳(TOC)与相应上覆植物/植被之间的正/负δ^(13)C偏移量已被广泛报道,并被认为可能是由多种因素(如大气、气候和土壤因素)变化引起的。开展更大空间尺度的研究,可以更好地揭示其主导因素。本文对中国内陆空间跨度数千公里的107个样点的表土和食草动物粪便样品进行了采集,对表土TOC、表土中分离出来的植物残体全样(PL)、食草动物粪便全样(HF)、表土植物残体和食草动物粪便中提取的α纤维素(α-cellulose)开展了δ^(13)C分析测试。数据分析显示,表土TOC与表土中植物残体全样之间的δ^(13)C偏移量(Δ^(13)C_(TOC-PL))和食草动物粪便全样与表土中植物残体全样之间的δ^(13)C偏移量(Δ^(13)C_(HF-PL))均与δ^(13)C_(PL)呈负相关关系。同样,食草动物粪便α纤维素与表土中植物残体α纤维素之间的δ^(13)偏移量(Δ^(13)C_(HF-PL-cell))也与δ^(13)C_(PL-cell)呈负相关关系。对这些负相关关系最合理的解释是,在表土中的分解过程和食草动物体内的消化过程中,C_(4)植物的分解/消化速度比C_(3)植物更快。研究结果表明,基于现代表土、沉积物和动物残骸δ^(13)C数据估算的C_(4)植物相对丰度,可能被普遍低估,在以后的相关研究当中应当予以适当考虑和评估。

The positive or negativeδ^(13)C shifts between total organic carbon(TOC)in surface soils and the corresponding overlying plants/vegetation have been widely reported and are thought to result from various factors,such as atmospheric,climatic,and soil changes.Conducting studies on a larger spatial scale can better reveal the dominant factors.In this study,107 surface soil and herbivore fecal samples were collected across several thousand kilometers of inland China.δ^(13)C analyses were performed on surface soil TOC,bulk plant litter separated from surface soil(PL),bulk herbivore feces(HF),andα-cellulose extracted from both surface soil plant litter and herbivore feces.Data analysis showed that theδ^(13)C shift between surface soil TOC and bulk plant litter(Δ^(13)C_(TOC-PL))and theδ^(13)C shift between bulk herbivore feces and bulk plant litter in surface soils(Δ^(13)C_(HF-PL))both exhibited a negative correlation withδ^(13)C_(PL).Similarly,theδ^(13)C shift between herbivore fecesα-cellulose and surface soil plantα-cellulose(Δ^(13)C_(HF-PL-cell))also showed a negative correlation withδ^(13)C_(PL-cell).The most reasonable explanation for these negative correlations is that during decomposition in surface soils and digestion within herbivores,C_(4) plants decompose/digest faster than C_(3) plants.The findings suggest that the relative abundance of C_(4) plants,estimated based on modern surface soils,sediments,and animal remainsδ^(13)C data,may have been commonly underestimated,and this should be appropriately considered and evaluated in future studies.