Effect of afforestation mode on rhizosphere soil physicochemical properties and bacterial community structure of two major tree species in Xiong’an New Area

Two major afforestation species in Xiong’an New Area: Armeniaca vulgaris and Sabina chinensis were selected as research objects. We determined soil physicochemical properties in pure stands of the two species, and mixed stands incorporating study species with other common species, then evaluated the structure and diversity of bacterial communities using high-throughput sequencing. Our results showed that: (1) Rhizosphere soil properties of two afforestation species responded differently to various afforestation modes, the concentration of total nitrogen, total carbon and total phosphorus in S. chinensis rhizosphere soil was improved after mixing with broadleaved species, but available nutrients deficiency appeared in most mixed stands. (2) Bacterial diversity increased in mixed stands, especially for S. chinensis, as indicated by ACE and Chao1. The relative abundances of bacterial taxa varied greatly under different afforestation modes. Some taxa that contributed to organic matter decomposition and nutrient cycling were enriched in S. chinensis mixed stands, for example MND1, uncultured_bacterium_f_Gemmatimonadaceae, and uncultured_bacterium_o_Rokubacteriales. RB41 and Bryobacter with such functions were enriched in A. vulgaris mixed stands. All of them were genera from the common bacterial phylum. (3) The concentration of total carbon, nitrate nitrogen, available phosphorus, pH, soil moisture content and total nitrogen could well explain the variations of soil bacterial community. Our results suggested that, mixing of different species helped trees to make full use of nutrients and increased soil bacterial diversity, but it also caused insufficient available nutrient reserves. To improve soil quality of Xiong’an Millennium Forest, develop its capacity in greening and carbon sequestration, we recommend planting more mixed plantations including both coniferous and broadleaf species, while looking for a suitable method to replenish soil nutrients, further optimizing tree growth conditions.