A consecutive 4-year elevated air temperature shaped soil bacterial community structure and metabolic functional groups in the rhizosphere of black locust seedlings exposed to lead pollution

Abstract

Global warming may influence the bioavailability and mobility of heavy metals by stimulating or inhibiting plant growth, thereby influencing rhizosphere soil chemistry and microbial characteristics. Black locust has been widely planted in China as a promising species for afforestation programs, farmland shelterbelt projects, and soil restoration in mined areas because of its rapid growth and adaptability to environmental stressors. Here, we examined soil bacterial community structure and predicted bacterial metabolic function in the rhizosphere of black locust exposed to elevated temperature (+1.99 °C) and Pb for 4 years. Elevated temperature significantly (p < 0.05) reduced total carbon (TC), total nitrogen (TN), and total sulfur (TS) contents in above-ground parts but increased TC and TN contents in roots and seedling height under Pb exposure. Elevated temperature significantly (p < 0.05) increased Pb availability and raised pH, TC, TN, TS and water-soluble organic carbon (WSOC) contents, and the C:H ratio in rhizosphere soils under Pb exposure. The interactive effects between Pb and temperature on pH, TC, TH, TS, WSOC, and the C:H ratio were significant (p < 0.05). Elevated temperature significantly (p < 0.05) reduced the diversity and the richness of bacterial community, altered genus-level bacterial community composition, and improved (p < 0.05) the relative abundances of some bacteria involving in terpenoids and polyketides and xenobiotics biodegradation metabolism under Pb exposure. Canonical correspondence analysis indicated that pH, WSOC, C:N ratio, and soluble Pb were significant (p < 0.05) factors on the relative abundance of bacterial genera, such as Ochrobactrum and Sphingomnas. Overall, long-term elevated temperature resulted in changes in rhizosphere soil characteristics and Pb availability, thus affecting the bacterial community structure and metabolic functional groups. The conclusion helps us understand the response mechanism of soil bacteria in the rhizosphere to heavy metals under global warming scenarios.