Stable carbon and nitrogen isotope signatures of root-holoparasitic Cynomorium songaricum and its hosts at the Tibetan plateau and the surrounding Gobi desert in China

We first measured the delta C-13 and delta N-15 values of root holoparasite Cynomorium songaricum and its hosts from 19 sites across four provinces in northwest China, in an attempt to investigate their nutritional relationship at the Tibetan plateau and the surrounding Gobi desert. Our study showed that the delta C-13 of C. songaricum closely mirrored the values of its hosts, Nitraria tangutorum and N. sibirica across all sampling sites. C. songaricum was significantly depleted in C-13 compared to host plants at the Tibetan plateau, showing an average parasite/host delta C-13 difference of -0.6 %. In contrast, N-15 of C. songaricum was significantly enriched by +1.3% compared to the hosts, implying that these holoparasites had other nitrogen resources. Although no difference in the delta C-13 and delta N-15 values between holoparasites and hosts was detected, the delta C-13 and delta N-15 values of holoparasites were significantly correlated with those of their hosts at the Gobi desert. The delta C-13 versus delta N-15 values were significantly but negatively correlated for the hosts; however, holoparasite/host variation in delta C-13 was not correlated with the variation in delta N-15. The delta C-13 versus delta N-15 values were negatively correlated in C. songaricum, and this relationship tended to be magnified along the increasing elevations independent of the host plants. C. songaricum at the Tibetan plateau exhibited different delta C-13 and delta N-15 signatures compared with those at the Gobi desert. Furthermore, both delta C-13 and delta N-15 values of C. songaricum and its host plants in salt marshes at the Tibetan plateau were different from those in sand sites at the Tibetan plateau and the Gobi desert. Our results indicate that the isotopic difference depends on the different altitudes and habitats and is host-specific.