The Response Of Plant Root Morphology And The Accumulation Of As And Fe Under As-Fe Interaction:

Arsenic(As)is a typical heavy metal contaminant that requires to be controlled primarily.The activation and release of arsenic pose a serious threat to ecological environment and human health.It is of great significance to explore the mechanism of arsenic migration and transformation in the environment.The root system is an important organ for plants to absorb water and nutrients,and has a relatively sensitive response to soil pollutants.However,there are few reports on the response of roots to aquatic plants under arsenic pollution.In this study,the common pioneering mangrove plant,Avicennia marina(Forssk.)Vierh.,and the rice(Oryza saliva L.),which have been studied in China,were used as experimental materials to study systematically under As(0,10μmol·L-1,30μmol·L-1)and Fe(0,100μmol·L-1)interaction.In order to clarify the stress effect of high As pollution on roots of aquatic plants and the alleviation effect of Fe on this stress effect,the similarities and differences of root morphology responses of two aquatic plants under arsenic stress were compared.The main findings are as follows:(1)The effect of arsenic on the morphological changes of rice and Avicennia marina has obvious dose effect,and the response of different root morphological indicators to arsenic pollution stress is different.Long-time high arsenic stress significantly inhibited the root formation of the two plants.The root volume and average diameter decreased significantly with the increase of arsenic treatment concentration,which showed As0μmol·L-1>As10μmol·L-1>As30μmol·l-1.The addition of iron significantly slowed the inhibition of arsenic treatment on the above indicators;correlation analysis showed that there was a significant positive correlation between root length,surface area and volume of the two plants(p<0.001).The response of root length and root surface area of two plants under arsenic stress was different.The root length of A.marina decreased with the increase of arsenic treatment concentration,and the root surface area increased first and then decreased with the increase of arsenic concentration.The length and root surface area are irregularly changed.(2)Anatomical analysis showed that the aerenchyma tissue of both plants changed significantly under As stress.After 30 days of As-Fe treatment,the proportion of O.sativa root aerenchyma tissue increased significantly(up to 46.32%),and typical radial radiation aeration tissue appeared.Moreover,under the highly arsenic concentration without iron treatment,the aerenchyma tissue was destroyed obviously,and the iron treatment did not have this phenomenon.It indicates that iron addition is beneficial to reduce the damage of arsenic to aerenchyma tissue.After 90 days of As-Fe treatment,the root of Avicennia marina appered many air cavities in the root cortex,including the endothelium,the middle cortex and the outer cortex.And the air cavity gradually increases with the increase of arsenic treatment concentration(3)Under arsenic treatment,the radical oxygen loss of the two species is quite different.The ROL of O.sativa was inhibited significantly with the increase of As concentration,presenting the trend of As0μmol·L-1>As10μmol·L-1>AS30μmol·L-1.The ROL of A.marina was increased first and then decreased.Under the treatment of As10μmol·L-1,the highest ROL of roots was 732.38 mmol O2·day-1·g-1 DW.The addition of iron increased the ROL of O.sativa and A.marina and alleviated the inhibitory effect of arsenic effectively(p<0.05).Correlation analysis showed that there was a significant positive correlation between ROL and root morphology,root porosity,proportion of aerated tissue and total biomass in O.sativa(p<0.05).However,the ROL of A marina was significantly positively correlated with root length,root surface,root weight and biomass(p<0.05).(4)A.marina has greater radical oxygen loss and iron plaque content than O sativa,indicating that species with larger ROL have more iron plaque.The results showed that there was a significant positive correlation between ROL and DCB-Fe both in O.sativa and a.marina(p<0.05).(5)The content of As(DCB-As)in the iron plaque of O.sativa roots was significantly positively correlated with the concentration of iron plaque on the root surface(DCB-Fe)(p<0.001,n=54).Under short-term treatment conditions(1d,7 d),the addition of iron promoted the transport of arsenic to the aerial part,but the longer-term treatment(30d)significantly inhibited the transport of arsenic to the aerial part.However,There was no significant positive correlation between the content of As in the iron plaque of the root surface(DCB-As)and the concentration of iron in the iron plaque of the root surface(DCB-Fe).The application of Fe2+ treatment would reduce the content of DCB-As.(6)Under the conditions of this experiment,the accumulation of As in different organs of two plants increased with the concentration of As.The roots were the main enrichment organs of arsenic in the two plants,which showed:root>stem>leaf.The cumulative distribution of Fe also shows a similar pattern.