Relationships between C3 Plant Foliar Carbon Isotope Composition and Element Contents of Grassland Species at High Altitudes on the Qinghai-Tibet Plateau, China

Relationships of foliar carbon isotope composition (δ 13 C) with foliar C, N, P, K, Ca, Mg contents and their ratios of 219 C 3 species leaf samples, obtained in August in 2004 to 2007 from 82 high altitude grassland sites on the Qinghai-Tibet Plateau China, were examined. This was done with reference to the proposition that foliar δ 13 C increases with altitude and separately for the life-form groups of graminoids, forbs and shrubs and for the genera Stipa and Kobresia . For all samples, foliar δ 13 C was negatively related to foliar K, P and ∑ K+ Ca+ Mg , and positively correlated to foliar C, C/N and C/P. The significance of these correlations differed for the taxonomic and life-form groups. Lack of a relationship of foliar δ 13 C with foliar N was inconsistent with the majority of studies that have shown foliar δ 13 C to be positively related to foliar N due to a decrease of C i /C a (the ratio between intercellular and atmospheric concentration of CO 2 ) and explained as a result of greater photosynthetic capacity at higher foliar N concentration. However this inconsistency relates to other high altitude studies that have found that photosynthetic capacity remains constant as foliar N increases. After accounting for the altitudinal relationship with foliar δ 13 C, of the elements only the K effect was significant and was most strongly expressed for Kobresia . It is concluded that factors critical to plant survival and growth at very high altitudes, such as low atmospheric pressure and low temperatures, may preclude expression of relationships between foliar δ 13 C and foliar elements that have been observed at lower altitudes.