Correlations between net primary productivity and foliar carbon isotope ratio across a Tibetan ecosystem transect
Warming climate could affect leaf-level carbon isotope composition (13C) through variations in photosynthetic gas exchange. However, it is still unclear to what extent variations in foliar 13C can be used to detect changes in net primary productivity (NPP) because leaf physiology is only one of many determinants of stand productivity. We aim to examine how well site-mean foliar 13C and stand NPP co-vary across large resource gradients using data obtained from the Tibetan Alpine Vegetation Transects (1900–4900 m, TAVT). The TAVT data indicated a robust negative correlation between foliar 13C and NPP across ecosystems (NPP=−2.722413C-67.738, r2=0.60, p<0.001). The mean foliar 13C decreased with increasing annual precipitation and its covariation with mean temperature and soil organic carbon and nitrogen contents. The results were further confirmed by global literature data. Pooled 13C data from global literature and this study explained 60% of variations in annual NPP both from TAVT-measures and MODIS-estimates across 67 sites. Our results appear to support a conceptual model relating foliar 13C and nitrogen concentration (Nmass) to NPP, suggesting that: 1) there is a general (negative) relationship between 13C and NPP across different water availability conditions; 2) in water-limited conditions, water availability has greater effects on NPP than Nmass; 3) when water is not limiting, NPP increases with increasing Nmass.
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Document Type: Research Article
Publication date: June 1, 2009