Effect of simulated SO2 wet deposition on growth and photosystem Ⅱ of mulberry seedlings

In order to reveal effects of SO2 wet deposition on growth and photosystem Ⅱ(PSⅡ)of mulberry seedlings, Na2SO3 and NaHSO3 mixture (molar concentration ratio of 3∶1) were used to simulate SO2 wet deposition for foliage spraying for 28 days. The results showed that significant burns spot appear in leaves in treatments of 50 and 100 mmol·L-1 simulation SO2 wet deposition, meanwhile, photosynthetic ability was significantly lower than control(P<0.05), in addition, the plant height, branch number and leaf number were reduced significantly. However, the photosynthetic capacity of leaves were increased, and then, the plant height, branch number and leaf number were increased significantly, promoted the growth of mulberry. Rapid chlorophyll fluorescence kinetics parameter analysis showed that the absorbed light reaction center (ABS/RC), reaction center of dissipated energy (DIo/RC) and capture reaction center for energy reduction QA (TRo/RC) in treatments of 50 and 100 mmol·L-1 were no significant difference with CK. While, the reaction center capture of the energy for the electron transfer (ETo/RC), active reaction center of the light at 2 ms, open degree of active reaction center (Ψo) and absorb the light energy used for electron transfer quantum yield after QA- (φEo) were decreased. Meanwhile, the maximum amount quantum yield of photochemical quenching (φDo) was rised, which indicated that the light energy absorption of the reaction center were not affect in treatments of 50 and 100 mmol·L-1, while, excess light energy was used in the non-photochemical quenching, photosynthetic performance index (PIABS) were dropped significantly(P<0.05), the reasons of the electron transport in the PSⅡ were suppressed. In this experiment, the PS Ⅱ function and activity of mulberry were improved under ≤20 mmol·L-1 SO2 wet deposition, which could promote the mulberry growth.