Soil microbial community structure in the rhizosphere of Robinia pseudoacacia L. seedlings exposed to elevated air temperature and cadmium-contaminated soils for 4 years

The co-occurrence of heavy metal contamination of soils and increasing air temperature can affect the microbial community in rhizosphere soils by altering the allocation of plant photosynthates to roots. Here, we investigated the community structure of bacteria, fungi, ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) in the rhizosphere of Robinia pseudoacacia L. seedlings exposed to elevated air temperature (+1.99 °C) and cadmium (Cd) for 4 years. Elevated temperature increased the richness of bacterial and AOA communities by 15.1% to 43.8% and by 1.4% to 18.6%, respectively, and decreased fungal and AOB richness by 3.7% to 28.7% and by 2.1% to 30.6%, respectively, under Cd exposure. Elevated temperature combined with Cd exposure decreased fungal diversity by 1.5% to 14.0%. However, elevated temperature decreased the diversity of bacteria, AOB and AOA by 1.4%, 17.4% and 10.1%, respectively, under 1.0 mg Cd kg^-1 dry soil and increased the diversity of these taxa by 1.5%, 15.3% and 9.2%, respectively, under 5.0 mg Cd kg^-1 dry soil relative to Cd exposure alone. Elevated temperature led to increased abundance of genera such as Methylobacterium, Stenotrophomonas, and Archangium and decreased abundance of genera including Ramlibacter, Microascus and Nitrosospira under Cd exposure. Over all, 4 years of exposure to elevated temperature had a greater effect on the community structure of bacteria, fungi, AOB and AOA when combined with Cd pollution.