Water-use efficiency of four native trees under CO2enrichment and N addition in subtropical model forest ecosystems

Abstract

We aimed to evaluate the changes in water-use efficiency (WUE) in native tree species in forests of subtropical China, and determine how coexisting species would be responding to increases in atmospheric carbon dioxide (CO2) concentrations and nitrogen (N) deposition. We used model forest ecosystems in open-top chambers to study the effects of elevated CO2 (ca. 700 µmol mol−1) alone and together with N addition (NH4NO3 applied at 100kg N ha−1year−1) on WUE of four native tree species (Schima superba, Ormosia pinnata, Castanopsis hystrix and Acmena acuminatissima) from 2006 to 2010. Our result indicated that all species increased their WUE when they were exposed to elevated CO2. Although higher WUE was shown in faster-growing species (S. superba and O. pinnata) than that of slower-growing species (C. hystrix and Acmena acuminatissima), the increased extent of WUE induced by elevated CO2 was higher in the slower-growing species than that of the faster-growing species (P < 0.01). The N treatment decreased WUE of S. superba, while the effects on other species were not significant. The interactions between elevated CO2 and N addition increased intrinsic WUE of S. superba significantly (P < 0.001), however, it did not affect WUE of the other tree species significantly. We conclude that the responses of native tree species to elevated CO2 and N addition are different in subtropical China. The species-specific effects of elevated CO2 and N addition on WUE would have important implications on species composition in China’s subtropics in response to global change.