| Arsenic(As),a toxic metalloid,is ubiquitous in soils,which results from various anthropogenic activities.As contamination in soils posed a serious threat to public health.Arsenic is mainly present in soils as inorganic form,namely arsenate(As?)and arsenite(As?).These two have many differences in their behaviors and toxicities,which makes it important to understand the effects of As speciation on As biochemical processes in soils and plants.Pteris vittata(PV),the first As hyperaccumulator,has a great potential to be used for phytoremediation of As-contaminated soil.The key of phytoremediation is the mechanism of heavy metal hyperaccumulation by plants.It is important for a better understanding of the mechanism to investigate the impact of different As species on rhizosphere and As accumulation in PV.In addition,plant-associated microbes also play a significant role in phytoremediation.Particularly,endophytic bacteria,colonizing the internal tissues of plants,is increasingly becoming a research hotspot of phytoremediation enhancement.In this study,a pot experiment was conducted and PV was grown in a soil spiked with 200 mg kg-1 arsenate(As?-soil)or arsenite(As?-soil).Combined with diffusive gradients in thin-films(DGT)technique,we evaluated the effects of soil As species(As? and As?)on biochemical processes in PV rhizosphere and As accumulation by PV.Although As? was gradually oxidized to As? during the experiment,As species impacted PV biomass and As accumulation by PV.More specifically,As?-soil produced the highest PV biomass at 8.6 g plant-1,27%and 46%greater than AsV-soil and control.17.5%more As was accumulated by PV in As?-soil than AsV-soil(36.3 vs.30.9 mg plant-1).Compared to the soil with no plant,pH and DOC concentration were increased in the rhizosphere solution of PV,releasing more As from solid phase into solution in the rhizosphere.Meanwhile,AsCDGT initially decreased and then increased,which suggested PV took up As rapidly at first and subsequently gradual resupply of As from solid phase to solution phase occurred.R value were 0.26-0.41,also indicating As resupply from the solid phase to soil solution.As concentration in PV roots was 30%higher in AsV-soil whereas As concentration in PV fronds was 7.9%greater in As?-soil,suggesting more rapid translocation of As? than AsV.Additionally,As-resistant endophytic bacteria from the tissues of PV were isolated,identified,and characterised.The relationship between their abilities of As resistance and transformation was also evaluated.A total of 43 As-resistant endophytic bacteria were isolated from roots,stems,and leaflets of PV,belonging to 4 phyla and 17 genera.All isolates had plant growth promotion characteristics.Compared to the leaflets isolates,PV roots isolates had higher levels of phosphate solubilization,which was probably associated with the internal colonization by phosphate-solubilizing rhizo-bacteria.All isolates showed resistance to 10 mM As?and AsV.Particularly,in 10 mM AsV,6 isolates had greater growth than control with no As,suggesting As stimulating growth.Furthermore,the root isolates were more resistant to AsV while the leaflet endophytes were higher tolerant to As?,which was probably attributed to the difference of As species in PV tissues.10 endophytes were selected to examine the relationship between their abilities of As resistance and transformation.As resistance of these 10 isolates was positively correlated to their ability in AsV reduction(R2 = 0.68)but irrelevant to As? oxidation.Some of them exhibited a dual function of AsV reduction and As? oxidation. |
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