[Effects of NO2 on Cinnamomum camphora seedlings growth and photosynthesis]

A 2-month fumigation experiment was conducted with opened top chambers to study the effects of different concentration (0.1, 0.5, and 4.0 microl x L(-1)) NO2 on the growth and photosynthesis of 1-year Cinnamomum camphora seedlings. Fumigation with 0.1 and 0.5 microl NO2 x L(-1) promoted the growth of the seedlings, while with 4.0 microl NO2 x L(-1) was in adverse. The diurnal variation of net photosynthetic rate (P(n)) presented two-peaks, with an obvious depression in midday. 0.5 microl NO2 x L(-1) increased the P(n), the maximum of P(n) reached 8.542 micromol CO2 x m(-2) s(-1); 4.0 microl NO2 x L(-1) decreased the P(n) in most period of time; while the effect of 0.1 microl NO2 x L(-1) varied with time period. Fumigation with 0.5 and 4.0 microl NO2 x L(-1) increased the maximal and minimal values of stomatal conductance (G(s)) and intercellular CO2 concentration (C( i)), while 0.1 microl NO2 x L(-1) increased the maximal and minimal values of C(i) but decreased the maximal and minimal values of G(s). At the middle and late stages of fumigation, the mean P(n) of the seedlings treated with 0.5 microl NO2 x L(-1) was significantly higher than that treated with 0.1 and 4 microl NO2 x L(-1). At the early stage of fumigation, 0.5 and 4.0 micro NO2 x L(-1) significantly decreased the maximal PS II efficiency (F(v)/F(m)); and at the late stage, 4.0 microl NO2 x L(-1) still decreased the F(v)/F(m) significantly.