Impacts of Global Warming on the Radial Growth and Long-Term Intrinsic Water-Use Efficiency (iWUE) of Schrenk Spruce (Picea schrenkiana Fisch. et Mey) in the Sayram Lake Basin, Northwest China

Abstract

Global warming and the sharp rise in atmospheric CO2 concentrations have a profound impact on forest ecosystems. To better manage these changes, a comprehensive understanding of forest ecosystem responses to global change is essential. There is a lack of knowledge about the growth response of Schrenk spruce (Picea schrenkiana Fisch. et Mey)—an endemic tree species found in the arid Central Asian region—to climate change and rising atmospheric CO2 concentrations. In this study, core samples of Schrenk spruce were collected in the Sayram Lake Basin, Xinjiang. Tree-ring radial growth and long-term intrinsic water-use efficiency (iWUE) chronologies were established based on standard tree-ring width and stable carbon isotope methods. The relationships between atmospheric CO2 concentrations, climate, radial growth, and iWUE were analyzed. Our results indicate that the iWUE of trees in this region has continued to rise rapidly but that radial growth has not increased over the past 160 years. The main factor affecting iWUE is atmospheric CO2 concentrations (Ca), whereas the radial growth is much more sensitive to water availability. This may explain why the increase Ca has not had a fertilizer effect on the radial growth of trees.