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

摘要

Purpose Up to date, most studies about the plant photosyn-thetic 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 sub tropics. 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. Materials and methods 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. 700μmol 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. Results and discussion 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 CO2 concentration than those in the elevated CO2 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 5. 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. Conclusions 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.