Objective  Effects of fertilizer type and application rate on the growth of Kandelia obovate seedlings as well as the microbial community in soil were studied.

  Method   In a field experiment, K. obovate seedlings were planted on lots treated by 3 different organic fertilizers or an inorganic fertilizer at 4 application rates, along with no-fertilizer as control (CK). Plant height and leaf length, width, number, and chlorophyll content of the seedling in the autumn were determined. Composition of the microbial community in soil was detected by high-throughput sequencing based on 16S rRNA gene.

  Result   On the lots applied with Zun Long Fertilizer at the rate of 9.74 g·kg⁻¹, the seedlings, in comparison to those on CK, were 117.50% taller and had 51.15% longer, 63.34% wider, and 178.57% more leaves in 120 d. The microbial compositions in the soil at the lots applied with organic fertilizer, inorganic fertilizer, and CK differed significantly. In addition, there were more distinct species on the organic fertilizers-treated soil than on the others. The plant grew positively with the microbial α-diversity in soil treated with the organic fertilizers, but negatively in soil treated with the inorganic fertilizers. Moreover, the organic fertilization fostered proliferation of beneficial microbes, such as Actinobacteriota and genera Nitrospira, Nocardioides, and Limibaculum, which could synergistically promote the plant growth as well.

  Conclusion  Application of organic fertilizer enhanced the growth of K. obovate as well as the microbial diversity of soil. On the other hand, inorganic fertilizer provided relatively limited benefits on the growth of the plants, yet considerably hindered the development of a healthy soil microbiome.