Abstract: With the extensive implementation of mangrove afforestation and restoration projects in China, the problem of insufficient suitable land for mangrove planting has become increasingly prominent. Afforestation in currently unsuitable sites is one effective way to break through bottleneck and expand mangrove area. In this study, field experiments on planting Rhizophora stylosa seedlings and related indicator measurements were conducted in poor-fertility tidal flats. Tidal flat soil was improved by adding biochar and slow-release fertilizer. Four treatments were set up, including blank control group (CK), single biochar application group (Bc), single slow-release fertilizer application group (Cf), and combined biochar+slow-release fertilizer application group (Bc+Cf). The survival rate, growth indicators (height and basal diameter increment), and physiological and biochemical indicators (chlorophyll content, photosynthetic factors, soluble sugar content, and malondialdehyde content) of R. stylosa under different treatments were compared to screen out the optimal combined application scheme. The results showed that the Bc+Cf group exhibited the strongest positive effects on height and basal diameter of R. stylosa seedlings, along with good photosynthetic characteristics in summer and autumn (July-September) and good stress resistance in winter and spring (December-February). Overall, the combined application of biochar and slow-release fertilizer had the best promoting effect on the growth of R. stylosa seedlings, which was superior to the single application of biochar or slowrelease fertilizer. In afforestation activities, auxiliary materials can be scientifically applied according to actual needs to improve the fertility of tidal flat soil, so as to promote the growth of R. stylosa under difficult site conditions.

Key words: Rhizophora stylosa, mangrove, biochar, slow-release fertilizer, seedling, growth