Responses of carbon isotope ratios of C_3 herbs to humidity index in northern China

Authors: XIANZHAO LIU, QING SU, CHAOKUI LI, Yong ZHANG, Qing WANG

Abstract: Uncertainties would exist in the relationship between delta^{13}C values and environmental factors such as temperature, resulting in unreliable reconstruction of paleoclimates. It is therefore important to establish a rational relationship between plant delta^{13}C and a proxy for paleoclimate reconstruction that can comprehensively reflect temperature and precipitation. By measuring the delta^{13}C of a large number of C_3 herbaceous plants growing in different climate zones in northern China and collecting early reported delta^{13}C values of C_3 herbs in this study area, the spatial features of delta^{13}C values of C_3 herbs and their relationships with humidity index were analyzed. The delta^{13}C values of C_3 herbaceous plants in northern China ranged from -29.9%o to -25.4%o, with the average value of -27.3%o. The average delta^{13}C value of C_3 herbaceous plants increased notably from the semihumid zone to the semiarid zone to the arid zone; the variation ranges of delta^{13}C values of C_3 plants in those 3 climatic zones were -29.9%o to -26.7%o (semihumid area), -28.4%o to -25.6%o (semiarid area), and -28.0%o to -25.4%o (arid area). In the semiarid zone, the semihumid zone, and the whole northern area, delta^{13}C values of C_3 herbs showed obvious linear negative correlation to humidity indexes (P < 0.05). With the increase of humidity indexes, the average delta^{13}C value of C3 herbaceous plants tended to decrease to different extents. In the arid zone, however, a linear positive correlation was found between them (P < 0.05). With every 0.1 increase in humidity index, the average delta^{13}C value increased significantly by 1.3%o. Temperature is the main reason for different ^{13}C fractionation abilities of C_3 herbs occurring in different sampling sites. The highly varying response of delta^{13}C of C_3 herbaceous plants to humid index reminds us that delta^{13}C_{plant}-based paleoclimate reconstruction in northern China should be carried out according to the different climatic zones.

Keywords: Arid and humid climate zones, C_3 herbaceous plants, carbon isotope, humidity index, northern China

Full Text: PDF