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Abstract The reliability of Cassiope tetragona as temperature proxy might be restricted by influence on growth of precipitation and amount of Photosynthetically Active Radiation (PAR). Carbon-13 discrimination (Δ) in C3-plants is generally influenced by temperature and precipitation and can therefore potentially record important additional climatic information. We doubled precipitation and reduced PAR ( -43%), during four and two growing seasons, respectively, at a high arctic site in Svalbard. Differences in discrimination in leaves from separate light, and thus temperature, regimes (sun-facing and soil-facing leaves) were also assessed. A Δ-chronology (1975–2008) in annual shoot length increments was developed. C . tetragona growth did not respond to enhanced precipitation and only slightly to PAR-reduction. Discrimination against carbon-13 was stronger in leaves and shoots receiving extra precipitation and weaker in sun-exposed leaves compared to soil-facing leaves. The annual climate signal in the Δ-chronology was strongly smoothed by secondary radial growth. Our results show that the temperature signal in C . tetragona is hardly disturbed by changes in summer precipitation or PAR, which confirms its suitability as temperature proxy. The experimental evidence for the sensitivity of carbon-13 discrimination in C. tetragona to precipitation and temperature changes shows its potential as proxy for hydrological changes in the polar semi-desert.
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