Short- and long-term effects of elevated CO<sub>2 </sub>on the growth and nitrogen content of Panax japonicus

<br><i>Panax japonicus</i> (T. Nees) C.A. Mey isarare plant that isused inChinese herbal medicine. Two-year-old <i>Panax japonicus</i> seedlings were grown inopen-top chambers under ambient CO₂ (aCO₂), moderately (e1CO₂:550±15μmol/mol) orsubstantially (e2CO₂: 750 ± 15 μmol/mol) elevated CO₂ tostudy their effects onplant growth and nitrogen (N) content. After 27 days, the net photosynthetic rate (<i>P_n</i>) ofe2CO₂-treated seedlings was significantly higher (20.09%) than that ofseedlings grown under aCO₂. However, byday 51, the Pn ofe1CO₂- and e2CO₂-treated seedlings was 12.87% higher and 9.57% lower, respectively, than that ofseedlings grown under aCO₂. Onday 27, chlorophyll <i>a</i>+ <i>b </i>content, Rubisco activity, soluble protein and starch content ofe1CO₂- and e2CO₂-treated seedlings showed nosignificant change and significant increase compared toaCO₂-treated. Bycontrast, at51days, chlorophyll <i>a</i>content, Rubisco activity, starch and Ncontent of<i>P. japonicus</i> was significantly increased bymoderately eCO₂ condition but was significantly decreased bysubstantially eCO₂ condition. The results suggest that exposure tomoderately eCO₂ was beneficial for <i>P. japonicus</i> growth, whereas under substantially eCO₂, growth were promoted inshort-term but inhibited inlong-term. Owing tothe temporal effect ofeCO₂ on<i>P. japonicus</i> growth, there was nosignificant correlation between Ncontent and <i>P_n</i> of<i>P. japonicus</i> under eCO₂.