RESUMO
With Indocalamus barbatus as test material, the effects of silicon on the relative content of chlorophyll, diurnal variations of photosynthesis, and chlorophyll fluorescence were examined under simulated acid rain (pH 3.0) stress. The results showed that under acid rain stress, 20 and 500 mg x L(-1) of Na2SiO3 could prohibit the decrease of the relative content of chlorophyll to some extent; 100 mg x L(-1) of Na2SiO3 could get best effect, with the relative chlorophyll content being 22.7% higher than the control; while 500 mg x L(-1) of Na2SiO3 didn't have any effect. Under the stress, the midday depression of photosynthesis became more serious. The average daily net photosynthetic rate (Pn), stomatal limitation value (Ls), and stomata conductance (Gs) were all decreased significantly, while the intercellular CO2 concentration (Ci) increased. After treated with 20-100 mg x L(-1) of Na2SiO3, the Pn, Ls, and Gs increased to some extent while Ci decreased, and 100 mg x L(-1) of Na2SiO3 was most effective, with the average daily Pn increased by 39.2%. The maximum fluorescence of dark adaptation (Fm), maximal photochemical efficiency (Fv/Fm), potential activity (Fv/Fo), effective photochemical efficiency (Fv'/Fm'), maximum fluorescence of light adaptation (Fm') of PSII, photochemical quenching (qp), non-photochemical quenching (qN), and actual photochemical efficiency of PSII (PhiPSII) were all decreased obviously under simulated acid rain stress, but the minimum fluorescence of dark adaptation (Fo) and the minimum fluorescence of light adaptation (Fo') increased. 100 mg x L(-1) of Na2SiO3 could restrain the changes of fluorescence parameters obviously, with the Fv/Fm, Fv/Fo, Fv'/Fm' and PhiPSII increased by 35.2%, 146.2%, 55.0% and 24.3%, respectively, compared with the control. It was suggested that applying appropriate concentration of exogenous silicon to I. barbatus could efficiently relieve the decrease of its photosynthetic activity and the damage of its photosynthetic system caused by acid rain, and thus, improve its photosynthetic ability under the stress.
