Responses of carbon isotope ratios of C3 herbs to humidity index in northern China

Abstract

Uncertainties would exist in the relationship between δ13C values and environmental factors such as temperature, resulting in unreliable reconstruction of paleoclimates. It is therefore important to establish a rational relationship between plant δ13C and a proxy for paleoclimate reconstruction that can comprehensively reflect temperature and precipitation. By measuring the δ13C of a large number of C3 herbaceous plants growing in different climate zones in northern China and collecting early reported δ13C values of C3 herbs in this study area, the spatial features of δ13C values of C3 herbs and their relationships with humidity index were analyzed. The δ13C values of C3 herbaceous plants in northern China ranged from-29.9% to-25.4%, with the average value of-27.3%. Te average δ13C value of C3 herbaceous plants increased notably from the semihumid zone to the semiarid zone to the arid zone; the variation ranges of δ13C values of C3 plants in those 3 climatic zones were-29.9% to-26.7% (semihumid area),-28.4% to-25.6% (semiarid area), and-28.0% to-25.4% (arid area). In the semiarid zone, the semihumid zone, and the whole northern area, δ13C values of C3 herbs showed obvious linear negative correlation to humidity indexes (P < 0.05). With the increase of humidity indexes, the average δ13C 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 δ13C value increased significantly by 1.3%. Temperature is the main reason for different 13C fractionation abilities of C3 herbs occurring in different sampling sites. The highly varying response of δ13C of C3 herbaceous plants to humid index reminds us that δ13Cplant-based paleoclimate reconstruction in northern China should be carried out according to the different climatic zones. © TÜBİTAK.