Assessment of Changes on Rhizospheric Soil Microbial Biomass, Enzymes Activities and Bacterial Functional Diversity under Nickel Stress in Presence of Alfafa Plants

Abstract

ABSTRACT Anthropic activities and agricultural practices have increased the rate of pollutants in ecosystems. Consequently, this can alter soil chemical properties, biological functioning, and fertility. Our work aimed to evaluate the impact of nickel (Ni) contamination on rhizospheric soil’s physico-chemical properties and microbiological activities in the presence of alfalfa plants. For this purpose, five concentrations of Ni (0, 50, 150, 250, and 500 mg.kg−1) were applied to Tunisian agricultural soils cultured with Medicago sativa. At the end of the experiment, the physico-chemical properties of these soils and the Ni uptake by alfalfa plants were analyzed. Additionally, soil enzyme activities were assessed. Finally, the microbial biomass and functional diversity of microbial communities were determined using SIR (Substrate-induced respiration) and Biolog Ecoplates™ techniques, respectively. The results revealed that Ni accumulation was dose-dependent, with a significant amount of Ni being translocated from the roots to the shoots. With respect to the physico-chemical properties of soil, the most important Ni concentration led to the lowest organic matter content and cation-exchange capacity (CEC). Our data also showed a decrease in soil enzyme activities following Ni contamination. However, a crucial increase on microbial biomass of soils was revealed with the high Ni contamination. Moreover, the microbial functional diversity index and substrate utilization pattern were observed to increase in soils exposed to the most potent Ni concentrations. Our data provided evidence regarding the apparent toxicity of Ni and the fact that enzymatic activities and microbial biomass could be exploited as Ni-stress bioindicators.