Seasonal dynamics of foliar δ 13 C and nutrient concentration of Chinese chastetree and spine jujube in foothill rock outcrop habitat of the southern Taihang Mountains, Central China

In this study, in situ investigation was conducted on Chinese chastetree (Vitex negundo var. heterophylla) and spine jujube (Ziziphus jujuba var. spinosa) during early, developed, and closing succession stages. Monthly data were recorded for foliar δ13C values and foliar N, P, and K concentrations from May to October. Foliar δ13C values declined with time and differences by succession stage varied by species. Older spine jujube displayed higher foliar N concentration while foliar P concentration was inversely related with N. Chinese chastetree had lower foliar K concentration than spine jujube. Foliar C/N ratio declined during the dry season and increased in the wet season. Foliar N/P ratio increased during the dry season and declined to its initial level until October, when it increased again. Foliar δ13C value was positively correlated with foliar N concentration. Foliar P and K concentrations were positively correlated to each other. In conclusion, the two shrubs had contrasting strategies of water use efficiency during their succession, but water use efficiency of both species was promoted by N availability and limited by P availability.