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 physicochemical properties of rhizosphere and non-rhizosphere soil under different afforestation modes, then evaluated the structure and diversity of bacterial communities using high-throughput sequencing. Our results showed that: (1) Rhizosphere soil properties of two species responded differently to various afforestation modes, the nutrient status of Sabina chinensis rhizosphere soil was improved after mixing with broadleaved species, but nutrient deficiency appeared in most mixed stands. (2) Bacterial diversities improved in mixed forests, while the composition changed greatly under different afforestation modes. Sabina chinensis exhibited enrichment of Proteobacteria, while Actinobacteria and Gemmatimonadetes had a higher abundance in its pure and mixed forest respectively; In contrast, Armeniaca vulgaris pure forest was characterized by a high frequency of Rokubacteria and Planctomycetes, Acidobacteria were relatively more abundant in mixed forest. Difference between rhizosphere and non-rhizosphere was not obvious. (3) The content 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 modes helped trees to make full use of nutrients while increased soil bacterial diversity, but it also caused insufficient nutrient reserves and restricted trees growth due to interspecific competition. To improve soil quality and ecological value of Xiong’an Millennium Forest, we recommend introducing herbaceous plants as understory vegetation and green manure, which input more nutrients to soil through litter, and further optimize tree growth conditions