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Relationships of foliar carbon isotope composition (δ13C) with foliar C, N, P, K, Ca, Mg contents and their ratios of 219 C3 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 δ13C 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 δ13C 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 δ13C with foliar N was inconsistent with the majority of studies that have shown foliar δ13C to be positively related to foliar N due to a decrease of Ci/Ca (the ratio between intercellular and atmospheric concentration of CO2) 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 δ13C, 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 δ13C and foliar elements that have been observed at lower altitudes. [ABSTRACT FROM AUTHOR]

Abstract: A digestion trial using six sheep wethers surgically fitted with ruminal cannulae was carried out to evaluate chemical composition and ruminal degradation characteristics of six wildrye (Elymus nutans) populations from Tibet. Nylon bags containing forage were incubated in duplicate for 3, 6, 12, 24, 48 and 72h. Differences were observed in the rapidly soluble fraction, potential degradable fraction, degradation rate and effective degradability between the six populations. The rapidly soluble organic matter (OM), crude protein (CP) and neutral detergent fibre (NDF) fractions ranged from 9.76 to 21.22%, 24.27 to 34.67% and 5.93 to 12.22%, respectively. The potentially degradable OM, CP and NDF fractions ranged from 59.48 to 86.75%, 56.15 to 70.89% and 52.17 to 67.48%, respectively. The effective degradability (ED) of nutrients was also different (P <0.01) among the altitudes. The samples collected from high altitudes had a relatively high content of CP and low content of NDF, and showed a high degradability of nutrients. [Copyright &y& Elsevier]