| Arsenic is a ubiquitous metalloid element that widely distributes in soil and water. Arsenic compounds are common toxic materials which can cause many diseases, especially cancers. Arsenic is a priority pollutant in environmental control. Use of micro-phyto combined remediation on polluted soil to enhance phytoremediation efficiency has increasingly drawn academe attention, and some successful achievements have just obtained in labs or small-scale experimental restorations. Many studies have revealed the important roles of micro-phyto combined remediation in nutrients uptake and anti-pollution stress in plants. However, there was no much information available for the function and the mechanism of microbes in enhancing phytoremediation of polluted soil and water. In this study, pot experiments and a field experiment using a hyperaccumulator plant Pteris vittata L., a food crop Triticum aestivum L. and an oil crop Brassica rape were carried out to understand the effects of application different arsenate reducing bacteria and arbuscular mycorrhiza on the growth of plant, the uptake and accumulation of arsenic by the plants as well as the mechanisms. The main results were as follows:1. The effects of arsenate reducing bacteria on plant growth, arsenic uptake and accumulation, and phytoremediation efficiency were studied by an arsenic spiked soil pot experiment. The results showed that application of arsenate reducing bacteria promoted the growth, arsenic uptake of P. vittata L. and the phytoremediation efficiency, with the percentage increased by 93%～290% and 13%～110%, 67%～478%, respectively. Bacterium PSQ was the most effective for P.vittata. Application of arsenate reducing bacteria also promoted the growth of wheat, which the PSQ22 was the most markedly effective, with an increasing percentage of 76% over the control; but Z8 and Ts41 restrained the growth and acculumation of arsenic by wheat, with the decreaing percentage of 24% and 36%, indicating application of arsenate reducing bacteria was an effective measure to decrease asenic accumulation by wheat. The application of arsenate reducing bacteria on rape growth was weak, but promoted its arsenic uptake and accumulation, of which the D5 and Ts41 increased by 42% and 28%, respectively.2. Study on the effects of mycorrhizal fungi on growth, arsenic uptake and accumulation, and phytoremediation efficiency showed that inoculation of AM fungi promoted the growth and arsenic accumulation of P. vittata L., as well as the phtoremediation efficiency, which the increasing percentages were 78%～274%, 39%～337%, 40%～320%, respectively. The improvement effect by XZ03B was the most remarkedly. The inoculation of AM fungi also promoted the growth and arsenic accumulation of wheat. Compared the control, application of SC01A, Gi and SC01A increased by 45%, 96% and 120%, respectively.3. The results on the effect of application of arsenate reducing bacteria and inoculation of AM fungi on soil arsenic availability suggested that arsenate reducing bacteria had no significant effects on soil in wheat soil pot experiment, but promoted soil arsenic availability in rape and P. vittata experiments. Compared with the control, PSQ and Ts41 increased the soil arsenic concentration by 20% and 25%, respectively. Inoculation of AM fungi increased the bioavailability of soil arsenic, with the XZ02B and XZ03B being the most effective, by 30% and 50% compared with the contol, respectively. Further analysis of the effect of arsenate reducing bacteria application on arsenic forms in soil showed that the available fractions of arsenic, including Labile As and Fe-bound As, increased significantly after arsenate reducing bacteria were applied, indicating that application arsenate reducing bacteria promoted the bioavailability of soil arsenic.4. Inoculation of arsenate reducing bacteria and AM fungi affected soil sucrose enzyme activity. The results showed that application of arsenate reducing bacteria obviously decreased the soil rhizosphere sucrose enzyme activity of rape and P. vittata L., with the PSQ22 being the most significant treatment. Compared whith the control, rhizosphere sucrose enzyme activity of rape and P.vittata L. decreased by 26% and 23%, respectively. Application of arsenate reducing bacteria, D5 and Ts41, to wheat increased by and decreased by 30%, respectively. After AM fungi were inoculated, the sucrose enzyme activity of P.vittata L. soil increased by and decreaed by 50% and 20%, for BJ04B and XZ03B, respectively. The sucrose enzyme activity of wheat soil for Gig.m and USA06 increased by and decreaed by 50% and 20%, respectively.5. Study on the effect of arsenate reducing bacteria application and inoculation of AM fungi on soil urease enzyme activity showed that arsenate reducing bacteria application in food crop wheat and oil crop rape enhanced soil urease enzyme activity of wheat, but depressed that of rape; the percentage of increase and decrese was about 30%. The urease enzyme activity in rape soil and the soil available arsenic concentrations by arsenate reducing bacteria was significantly negatively related. Compared with the control, Ts41 and PSQ with obvious effect for P. vittata L. increased by and decreased by 80% and 30%, respectively; USA06 and Gi for wheat increased by and decreased by 25% and 55%, respectively. A negative correlation between wheat rhizosphere urease enzyme activity and plant dry weight was also significant.6. Results on the effect of arsenate reducing bacteria application and inoculation of AM fungi on soil neutral phosphatase activity showed that application arsenate reducing bacteria could promote or restrain neutral phosphatase activity in P. vittata L. and wheat rhizosphere soil. The increase effect by Ts33 on the neutral phosphatase activity was the most significant for P. vittata L. and wheat, with the growth increase were 19% and 43%, respectively; but Ts37 and Ts41 markedly restrained neutral phosphatase activity in P. vittata L. and wheat rhizosphere soil, and the decline were 30% and 40%, respectively. Moreover, arsenate reducing bacteria application significantly decreased neutral phosphatase activity in rape rhizosphere soil, the effect of PSQ22 treatment was the most significant with a decrease by 20%. AM fungi inoculation significantly promoted neutral phosphatase activity in P. vittata L. rhizosphere soil, but restrained neutral phosphatase activity in wheat rhizosphere soil, the rates of increase and reduce were the same, 25%.7. The field study on the effect of arsenate reducing bacteria application on growth, phytoremediation efficiency to arsenic pollution soil by P. vittata L showed that arsenate reducing bacteria improved the growth and promoted arsenic accumulation in P. vittata L., with the plant biomass and arsenic accumulation increased by 50% and 113%, respectively. The phytoremediation efficiency by P. vittata L. increased by 35%～103%. Rhizosphere soil microbial biomass increased by 65%～300% and reached significant levels. In addition, application of arsenate reducing bacteria significantly reduced arsenic leaching, arsenic concentrations in leaching water, with the decrease of 29%～71%. |
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