Abstract
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.
Highlights
In the last 20 years, determination of foliar carbon isotope composition (d13C) has been a powerful tool in plant ecophysiological studies [1]
Foliar d13C is related to the Ci/Ca ratio [2], and Ci/Ca is determined by the balance between stomatal conductance and photosynthetic capacity (A) [3], so environmental factors may cause change of d13C through their effect on A or gs
Correlations between foliar element and ratios Correlations between site leaf elements contents and ratios showed that K, Ca, Mg and their sum were negatively correlated with C and were positively correlated with each other and with N and P
Summary
In the last 20 years, determination of foliar carbon isotope composition (d13C) has been a powerful tool in plant ecophysiological studies [1]. Foliar d13C is related to the Ci/Ca ratio (the ratio between intercellular and atmospheric concentration of CO2) [2], and Ci/Ca is determined by the balance between stomatal conductance (gs) and photosynthetic capacity (A) [3], so environmental factors may cause change of d13C through their effect on A or gs. Nitrogen (N) is an essential nutrient that has important roles related to plant growth, and its positive correlation with photosynthetic rates and chlorophyll pigment content have been reported [9,10,11,12,13,14]. E.g., potassium (K), calcium (Ca), and magnesium (Mg), influence photosynthetic capacity and/or stomatal conductance in several ways, e.g., K is found to play a crucial role in regulation of stomatal function, osmoregulation, enzyme activity and cell expansion [16,17,18]. Carbon (C) content should be positively correlated to d13C [28], because if the leaf ash content is high, the leaf C content is low
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