Influence of Short-term Warming on the Composition of Stable Carbon and Nitrogen Isotopes in Cunninghamia lanceolata in Subtropical Region of China

Objective To study the effects of warming on nitrogen cycle and water use efficiency by isotopic method, and to explore the response of the water use efficiency and the nitrogen saturation state of subtropical Cunninghamia lanceolata juveniles grown in subtropical region to global warming.

Method The experimental site is located in the Global Change Experimental Platforms, in Sanming of Fujian Province, China. The heating cables were used to artificially induce the warming. The treatments of control (CT) and warming (W) were set up. The leaves of C. lanceolata and surface soil (0~10 cm depth) were sampled to examine the contents of their stable N and carbon (C) isotopes, i.e., δ¹⁵N and δ¹³C, and the contents of C and N.

Result Compared to the control treatment (-2.79‰), the foliar δ¹⁵N of the warming treatment (0.40‰) significantly increased by 3.19‰; but no significant difference was found in the leaf N contents between the control and the warming treatments. After warming, there was a significant increase in surface soil δ¹⁵N, and leaf ¹⁵N enrichment index was closer to 0 compared to that in the control treatment. The foliar δ¹³C of the warming and control treatments were -29.35‰ and -29.08‰, respectively. There was a significant positive correlation between foliar δ¹⁵N and δ¹³C.

Conclusion These findings suggest that the temperature is an important factor affecting N cycling in subtropical regions. Warming can increase leaf and soil δ¹⁵N significantly, and the metabolism of carbon and nitrogen complement each other.