Modeling the interactions between inter-correlated variables of plant and soil micro-ecology responses under simultaneous cadmium stress and drought

Cadmium and water stress are considered two important prevalent abiotic stresses which may occur simultaneously in many parts of the world. The occurrence of different stress factors in nature is often simultaneous and the effect of multiple stress factors on living organisms cannot be investigated separately. Although it is essential to evaluate plant and microbial community responses to the combination of different abiotic stresses simultaneously, many scientists have used a single evaluative approach to study the effect of cadmium and/or water stress on the response of plant and/or soil microorganisms. The purpose of this study is to assess the effects of water stress and cadmium together on the development and growth of Medicago scutellata L. and soil biological activity. To investigate potential relationships among inter-correlated variables and comprehend potential mechanisms, predictive regression modeling, principal component analysis, and path analysis were implemented. Considering the outcomes, cadmium at low concentrations stimulates nodule growth and the fungi population. Moderate water stress (50%) decreased the bacteria population while it did not affect the fungi population. The obtained results of this study suggest that soil microsymbiont such as fungi might have a significant role in maintaining (as well as increasing) the nitrogen fixation ability of Medicago under low cadmium stress. Except for the removal rate (0.683), all predictive equation models showed strong linear fitness of the regression models, with adjusted R2 values ranging from 0.838 to 0.987. Based on the path analysis, urease has a significant positive direct effect on phosphatase activity. Due to the high removal rate and bioconcentration factor, M. scutellata can be considered as a potential cadmium hyperaccumulator.