Phytoremediation assisted by endophytic bacteria is a promising strategy to enhance the remediation efficiency of heavy metals in contaminated soil. In this study, the capacity and role of the endophytic Bacillus sp. D2, previously isolated from Commelina communis growing near a copper (Cu) mine, in assisting the phytoremediation were evaluated. Results showed that inoculation of Bacillus sp. D2 significantly enhanced the biomass production of C. communis by 131.06% under high level of Cu stress. Additionally, the oxidative damages caused by Cu toxicity in C. communis tissues were alleviated as evidenced by significant reductions in malondialdehyde (MDA), superoxide anion (O2 center dot-) and proline content following Bacillus sp. D2 inoculation. Meanwhile, the activities of antioxidant enzymes in plant leaves presented upward trends after Bacillus sp. D2 inoculation. Notably, Bacillus sp. D2 inoculation significantly decreased Cu uptake and translocation by C. communis, while enhancing the Cu stabilization in contaminated soils. Furthermore, soil enzyme activities (acid phosphatase, catalase, and urease), as well as the richness of soil bacterial communities in Cu-contaminated soil increased following Bacillus sp. D2 inoculation. Importantly, the inoculation specifically augmented the relative abundance of key bacterial taxa (including Pseudomonas and Sphingomonadaceae) in the rhizosphere soil, which was positively correlated with soil nutrients cycling and plant growth. Our findings suggest that the endophytic strain Bacillus sp. D2 can strengthen the phytostabilization efficiency of Cu by C. communis through its beneficial effects on plant physio-biochemistry, soil quality and bacterial microecology, which provides a basis for the relative application to Cu-contaminated soils.

Tea gardens are established on acidic soils (pH < 5.5) and undergo extensive fertilization to maximize yield, which inadvertently promotes the proliferation of various weed species. Commelina communis and Tradescantia fluminensis (Commelinaceae) are major threats to tea plantations causing the highest destruction compared to other weed species. This study investigated the mechanisms behind the tolerance exhibited toward elevated aluminum (Al) concentrations in acidic soils and its contribution to these species' invasive behavior and herbicide resistance. Both species displayed only a 17-22% reduction in biomass under 400 M Al, and the Al accumulation remained low, ranging between 100 and 200 mu g g(-1) DW. Interestingly, C. communis responded to low to moderate Al levels (50-150 mu M Al3+) with growth stimulation. Antioxidant enzyme activity and flavonoid and anthocyanin leaf concentrations increased with Al treatment concentrations. Surprisingly, exposure of plants to Al, particularly at the 50 mu M threshold, resulted in a significant reduction in leaf damage inflicted by a spectrum of herbicides (paraquat, glyphosate, clethodim, and 2,4-D), with the effect more pronounced in C. communis. Our results demonstrate that enhancement of antioxidant enzymes and accumulation of detoxifying metabolites, coupled with the accumulation of pivotal intermediates of metabolic pathways under Al treatment collectively contribute to enhanced resistance against an array of herbicides. These findings provide insights into the invasive propensity of C. communis and T. fluminensis, particularly in acidic soil conditions prevalent in tea gardens.