Carbon isotope discrimination of C3 vegetation in Central Asian grassland as related to long-term and short-term precipitation patterns

Abstract. The relationship between carbon isotope discrimination (¹³Δ) of C3 vegetation and long-term (30 years) and short-term (growing period) precipitation was investigated. Different species of Stipa, a dominant grass genus in the (semi-)arid Asian steppes, and other C3 species were collected along aridity gradients in Inner Mongolia in 2005 (11 sites, 71 samples) and in the Republic of Mongolia in 2006 (40 sites, 45 samples). The data set was expanded with published and unpublished data of Stipa and other C3 species (11 studies covering 8 years, including 64 observations of Stipa, and 103 observations of other C3 species) and C3 community bulk-samples (11 samples). Weather data were geostatistically interpolated for all sampling sites and years. ¹³Δ of Stipa followed different relationships for the individual years when related to mean annual precipitation due to large anomalies between annual and long-term average precipitation patterns. However, the ¹³Δ response to rainfall converged when the (long-term) mean annual precipitation was replaced by year-specific mean daily precipitation during the growing period (P_G). Remarkably, the ¹³Δ-response to (P_G) for C3 species as a whole (including herbaceous dicots, semi-shrubs and grasses) and also the C3 community-level response were virtually identical to that of Stipa. The relation was also valid outside the geographical and climatic range where it was developed, giving proof of its robustness.