Contamination by heavy metals has become a serious environmental pollution issue today due to its potential threat to plant, wildlife, and human health. Photosynthesis, a process in which light energy is used to produce sugar and other organic compounds, is sensitive to heavy metals. In the present study, the response of photosynthetic process and carbon assimilation of Schima superba was investigated under cadmium (Cd) stress. Three Cd concentrations (0, 300, and 600 mg kg) were used designated as control (CK), low Cd (L), and high Cd treatment (L) of plants. Results showed that photosystem II (PSII) acceptor and donor side electron transport were more easily blocked in treatment compared to control, and L have more significant changes than L. A substantial decrease of 820 nm reflection curve absorption was observed both in L and L treatments. Special energy fluxes showed significant difference between the control group and the treated group, which indicated that low concentration Cd stress can cause decrease in quantum yield of PSII in plants studied. Non-stomatal factors resulted in a decrease in net photosynthetic rate and a decrease in photosystem activity. Our results suggested that Cd can damage structure and function of the photosynthesis of S. superba young plants.

The toxic effect of excessive manganese (Mn) on photosystem II (PSII) of woody species remains largely unexplored. In this study, five Mn concentrations (0, 12, 24, 36, and 48 mM) were used, and the toxicity of Mn on PSII behavior in leaves of Ligustrum lucidum was investigated using in vivo chlorophyll fluorescence transients. Results showed that excessive Mn levels induced positive L- and K- bands. Variable fluorescence at 2 ms (V J ) and 30 ms (V I ), absorption flux (ABS/RC), trapped energy flux (TR o /RC), and dissipated energy flux (DI o /RC) increased in Mn-treated leaves, whereas the performance index (PI ABS ), electron transport flux (ET o /RC), maximum quantum yield (φ Po ), quantum yield of electron transport (φ Eo ), and probability that an electron moves further than Q A − (ψ o ) decreased. Also, excessive Mn significantly decreased the net photosynthesis rate and increased intercellular CO 2 concentration. The results indicated that Mn blocked the electron transfer from the donor side to the acceptor side in PSII, which might be associated with the accumulation of Q A − , hence limiting the net photosynthetic rate.