Periphyton plays an indispensable role in coastal saline-alkali land, but its function is poorly understood. Soil physical and chemical properties (pH value, salinity, soil organic matter), enzyme activity and microbial diversity (based on 16s rDNA, ITS and functional genes) were measured in periphyton formed on rice-growing coastal saline-alkali soil modified by a new type of soil conditioner. The results showed that the content of organic matter and catalase activity in periphyton were significantly higher than in the unplanted control soil. Soil pH and salinity were decreased in periphyton compared to the unplanted control soil. Based on the relative abundance, bacterial genera Desulfomicrobium, Rhodobacter, cyanobacterium_scsio_T−2, Gemmatimonas, and Salinarimonas as well as fungal genus Fusarium were more abundant in periphyton than the unplanted control soil. In terms of functional genes, the cbbM and cbbL sequencing showed higher abundance of Hydrogenophaga, Rhodovulum, Magnetospira, Leptothrix, and Thiohalorhabdus, whereas the nifH sequencing indicated higher abundance of Cyanobacteria in the periphyton compared to the unplanted soil. The relative abundance and community structure of soil microorganisms were improved by periphyton, thus reducing soil salinity and pH, increasing soil organic matter and enzyme activity. This indicated that the periphyton can improve the conditions and offer a suitable environment for plant growth in coastal saline-alkali soil.

Saline-alkali soils are widely distributed in China, affecting plant growth and sustainable development of ecosystems. This study characterized the effects of planting Melia azedarach L. on chemical properties and microbial communities in saline-alkali soils [bare (CK), bulk (BS) and rhizosphere soil (RS)]. Compared with the bare soil, planting Melia azedarach L. lowered salt content and concentrations of extractable Na, K, Ca, Mg and Cl-, but significantly increased organic matter, total nitrogen, total phosphorus, available phosphorus, soil urease activity and alkaline phosphatase activity in the rhizosphere soil. High-throughput sequencing results indicated that bacterial richness and diversity decreased in the order RS>BS>CK. The richness of fungi was ranked RS>CK>BS, and their diversity decreased in the order CK>RS>BS. The three dominant bacterial phyla were Proteobacteria, Actinobacteria and Bacteroidetes, and the three dominant fungal phyla were Ascomycota, Basidiomycota and Glomeromycota. Redundancy analysis indicated that total phosphorus concentration and alkaline phosphatase activity significantly influenced bacterial diversity, whereas soil Ca and Mg concentrations were closely related to the fungal community diversity. In conclusion, planting Melia azedarach L. improved soil properties, increased the diversity and richness of soil microbial communities, and thus ameliorated the saline-alkali soil.