Photosynthesis acclimation, leaf nitrogen concentration, and growth of four tree species over 3 years in response to elevated carbon dioxide and nitrogen treatment in subtropical China

Up to date, most studies about the plant photosynthetic acclimation responses to elevated carbon dioxide (CO(2)) concentration have been performed in temperate areas, which are often N limited under natural conditions and with low ambient N deposition. It is unclear whether photosynthetic downregulation is alleviated with increased N availability, for example, from increased N deposition due to fossil fuel combustion in the tropics and subtropics. Awareness of plant photosynthetic responses to elevated CO(2) concentration will contribute to the better understanding and prediction of future forest productivity under global change. Four tree species, Schima superba Gardn. et Champ., Ormosia pinnata (Lour.) Merr, Castanopsis hystrix AC. DC., and Acmena acuminatissima (Blume) Merr. et Perry were exposed to a factorial combination of atmospheric CO(2) concentration (ambient and elevated CO(2) concentration at ca. 700 mu mol CO(2) mol(-1)) and N deposition (ambient and ambient + 100 kg N ha(-1) year(-1)) in open-top chambers in southern China for 3 years since March 2005. Light-saturated net photosynthetic rate, leaf N concentration, and tree growth of all species were measured. The CO(2) treatments did not affect light-saturated net photosynthetic rate of all species grown with the high N treatment. However, S. superba grown with the low N treatment (ambient) had 23% and 47% greater net photosynthesis in the ambient CO(2) concentration than those in the elevated CO(2) concentration for December 2006 and November 2007 (20 and 31 months after the treatments were applied), respectively, and A. acuminatissima grown with the low N treatment had 173%, 26%, and 121% greater net photosynthesis in trees grown in the ambient CO(2) concentration than those in the elevated CO(2) concentration for July 2006 (16 months after the treatments), December 2006 (20 months), and November 2007 (31 months), respectively, whereas, photosynthetic acclimation was not found for C. hystrix and O. pinnata. With the photosynthetic acclimation of S. superba and A. acuminatissima, we also found that the elevated CO(2) concentration decreased significantly leaf N concentration in trees of S. superba and A. acuminatissima grown with the low N treatment, respectively. C. hystrix seems to be a good species for C fixation under global climate change, particularly with the rising CO(2) concentration. We demonstrated that the relative responses to elevated CO(2) concentration and N treatment differ among tree species and functional types in the tropical and subtropical areas.