Changes in the integrated functional stability of microbial community under chemical stresses and the impacting factors in field soils.

• The loss of biodiversity caused by heavy metals did not affect microbial functional stability. • The decrease of the GP/GN ratio trigged by heavy metals increased microbial functional stability. • Soil organic matter, Cd, C/N were crucial factors governing microbial functional stability. • Microbial functional stability can be a feasible indicator in ecological risk assessment. The functional stability (FS) of soil microbial communities contributes in a fundamental way to maintaining soil ecosystem functioning and services, when environmental disturbances, e.g. contamination arise. While, the mechanisms enabling soil microbial communities to remain stable under stresses are not clear. Thus, this work aims at investigating changes in integrated microbial FS under long-term stress of heavy metals (FS HM) and subsequent herbicide siduron (FS sid). A second objective is to determine which factors affect the FS of microbial communities. The results show that the overall function, alpha diversity, and composition of microbial communities are affected significantly by the presence of heavy metals and herbicide siduron. The loss of biodiversity induced by heavy metal does not appear to impair the functions of microbial communities or their functional stability in response to the additional stress of siduron. Whereas, the change of microbial community composition, e.g., the decrease of the gram positive/gram negative ratio triggered by the adaption and tolerance process to the pre-disturbance of heavy metals, is the central factor governing FS. Soil organic matter content, the concentration of heavy metals and the C/N value are the dominant abiotic factors affecting FS through direct effect on microbial activities involved in functional processes and indirect effect on microbial community composition. Our study highlights that the structural composition of soil microbial community is more important than the diversity of microbial species to explain the functional stability of microbial communities under chemical stresses, and that a number of soil properties and the disturbance history also play a decisive role. Thus, the functional stability of soil microbial community can be used as a feasible and pragmatic indicator to assess the overarching responses to environmental stresses at ecological system level. [ABSTRACT FROM AUTHOR]