Responses of the natural abundance of carbon and nitrogen isotopes of Quercus mongolica leaf and soil to elevated CO2

Abstract

The rising atmospheric CO2 concentration significantly changed soil nitrogen (N) cycling which is important for us to predict the carbon (C) sequestration potential of terrestrial ecosystems. The natural abundance of N isotope as an integrative indicator of ecosystem N cycling processes can effectively indicate the effect of elevated CO2 on soil N cycling processes. Here, we used an open top chamber experiment to examine the effects of elevated CO2for ten years on the natural abundance of Quercus mongolica, soil and microbial biomass C and N isotopes in northeastern China. Our results showed that elevated CO2 significantly changed soil N cycling processes, resulting in the increase of microbial and leaf δ15N; stimulated the decomposition of 13C-enriched soil organic C, and offset the effect of more 13C-depleted plant photosynthetic C inputs, resulting in unchanged δ13C of soil dissolved organic C and microbes under elevated CO2. These results indicated that elevated CO2 likely increased the mineralization of soil organic matter, and the system is getting more N-limited.