Increased drought and atmospheric CO2 positively impact intrinsic water use efficiency but do not promote tree growth in semi-arid areas of northwestern China

Abstract

This work studied the response of tree growth to the increased drought and carbon dioxide in semi-arid areas of northwestern China. Forests ecosystems play a key role in the global carbon cycle. However, effects of increased drought and rising atmospheric carbon dioxide (Ca) on it are complex and there are many uncertainties. In this study, we evaluated this issue through dendroecology in semi-arid regions of northwest China. Results found the basal area increment of trees decreased by 28% (from 7.59 to 5.43 cm2 year−1) as the intrinsic water use efficiency increased 32% (from 98.61 to 130.28 µmol mol−1). Despite both Ca and drought positively affected intrinsic water use efficiency, they did not promote tree growth. Meanwhile, values of intercellular [CO2] increased 14% (from 158.83 to 180.89 ppm) while the ratio of intercellular [CO2] to Ca decreased 7% (from 0.50 to 0.46). Our study advances understanding of the variability of the global carbon cycle under climate change.