Objectives This study aimed to study effects of different dosages of biological carbon and carbon based slow release fertilizers on fluorescence dynamics of functional leaves of peanut at the key growth stages in a field location experiment, investigate variation of the blade light system under different conditions, and provide a theoretical basis for the development of new fertilizer production.

Methods The location experiment started in 2011. There were 5 treatments, no fertilization (CK), single apply biological carbon (C15 and C50), combined application of N, P and K (NPK), and biochar-based slow-release fertilizer(TJHS). The C15 and TJHS had equivalent carbon content, and the NPK and TJHS had equal nitrogen, phosphorus and potassium nutrients. In 2013 the peanut leaves were collected at the function period of flowering, fluorescence kinetics curves, performance of optical systemⅠand optical system Ⅱ were measured using an MPEA-2 type plant efficiency instrument.

Results The results showed that the application of the biochar-based slow-release fertilizer can reduce the K, J and I points of OJIP fluorescence induction curves. The probability of a trapped exciton move from the electron transport chain beyond Q_A (Ψ_o) to the Q_B under the biochar-based slow-release fertilizer was significantly higher than that under the same level of carbon input, and the Ψ_o was increased by 6.56%, which equaled to the same level of nutrient treatment effect. The performance index of absorption basis (PI_ABS) under the biochar-based slow-release fertilizer was also significantly higher than those under the same level of carbon input or the same level of nutrient treatment effect, and the PI_ABS values were increased by 12.27% and 17.62%, respectively. The leaf chlorophyll variable fluorescence F_j accounted for F_o-F_p amplitude ratio (V_j) under the biochar-based slow-release fertilizer was better than those of the same level of carbon input or the same level of nutrient treatment effect, and the V_j values were decreased by 10.26% and 5.41%, respectively. The leaf chlorophyll variable fluorescence F_k accounted for F_o-F_p amplitude ratio (W_k) under the biochar-based slow-release fertilizer was same as those of the same level of carbon input or the same level of nutrient treatment effect. Under the biochar-based slow-release fertilizer the index of leaf photosynthesis system had obvious influence, the relative absorption value of 820nm in peanut leaves was "V" type, and ΔI_t value change was relatively stable, in a gradual upward trend. The maximum redox activity of PSⅠunder the biochar-based slow-release fertilizer was higher than the same level of nutrient treatment effect, and ΔI/I_o was increased by 4.30%.

Conclusions Application of biochar-based slow-release fertilizer could cause significant changes in the fluorescence induction curve of peanut leaves in vegetative growth stage, and improve the photosynthetic performance of leaves, especially in the electron transfer and energy absorption, which was better than those of biological carbon or combined application of nitrogen, phosphorus and potassium fertilizer.