Tree species composition influenced microbial diversity and nitrogen availability in rhizosphere soil

Abstract

A greenhouse experiment was conducted to evaluate effects of monoculture and mixed planting of three tree species on microbial diversity and nitrogen (N) availability in rhizosphere and bulk soils. Six treatments with poplar, willow, and alder monoor mixed seedlings were grown in the rhizoboxes and both rhizosphere and bulk soils were sampled and analysed after eight-month growth. Microbial diversity in rhizosphere soil was significantly higher than in bulk soils based on denatured gradient gel electrophoresis (DGGE) fingerprinting of 16Sor 18S-rRNA gene fragments of soil microbial community. Tree species composition significantly influenced microbial diversity index and nitrogen contents in the rhizosphere soil, with the highest values of genotypic richness, Shannon diversity index and inorganic nitrogen contents were observed in rhizosphere soils of poplar-alder mixture. Shannon diversity indices of bacteria and fungi in the rhizosphere soils were positively and significantly correlated with nitrogen contents. Alder addition significantly improved genotypic richness, microbial diversity index and nitrogen availability in the rhizosphere soils, suggesting that adding N-fixing alder into poplar plantations is a good option in the practice.