Study On Mercury Volatilization From Rice And The Affecting Factors

Wetland is an important sink for mercury,and the reductive substrate favors the production of gaseous elemental mercury.Rice seedlings were studied as a typical wetland plants to understand the role of roots in transporting gaseous mercury to atmosphere.In this study,roots of rice seedlings were separated from the aerial parts by an air-tighten culture chamber,and exposed to mercury vapor.The gaseous mercury volatilized from the leaves was collected by gas absorbents.Additionally,the effects of root iron plaque and nutrient starvation on mercury volatilization were studied by hydroponic experiments.The results are as followings.(1)Gaseous elemental mercury could be uptake by rice seedlings from root system and then transported to the aboveground tissue.The root mercury content was negatively correlated with root porosity(R = 0.8309,P<0.01).There was a linear positive correlation between the aboveground mercury mass and root surface area and root volume(R = 0.896,P<0.01;R = 0.871,P<0.01).The results showed that the mercury absorbed by the roots could be volatilized into the atmosphere through the leaves.The volatilization of the mercury from the leaves was increased linearly with the leaf area(R = 0.897,P<0.01),and the evapotranspiration(R = 0.73,P<0.01).(2)There were significant differences in the amount of iron palque produced between different genotypes(P<0.05).The amount of iron palque produced in indica rice was significantly higher than that in japonica rice,and the mercury adsorption capacity was positively correlated with the amount of iron in the root surface(R= 0.701,P<0.01).The iron plaque of rice root can significantly reduce the absorption of gaseous elemental mercury on roots,inhibiting the Hg transportation and Hg volatilization from rice leaves.(3)Under nitrogen and phosphorus stress,rice growth was affected by different effects.The nitrogen deficiency treatment inhibited the growth of rice roots and leaves.Compared with the normal group,we found that the root surface area,root length,root volume and root dry weight of the three rice varieties under nitrogen stress were significantly decreased,while the root porosity of the rice increased significantly(P<0.05)And the leaf area and dry weight of the shoots decreased as the nitrogen concentration decreased.We found that nitrogen stress reduced the uptake,transport and volatilization of gaseous elemental mercury in rice.In contrast,phosphorus deficiency promoted the growth of rice roots and leaves,and the phosphorus stress decreased the mercury of roots and reduced the mercury transported to shoots.Under the phosphorus stress,the volatilization of mercury in leaves of three genotypes was slightly different.the volatilization of mercury in the rice leaves of Tu267 was only slightly decreased,and it was not significantly lower than that of the control(P>0.05),and the volatiles of rice ?you1259 and wuyunjing21 decreased with the decrease of phosphorus concentration Group was significantly different(P<0.05).The results demonstrated that the rice root can not only absorb gaseous elemental mercury,but also can transfer mercury from the root to the aboveground,and then released to the air through the leaf stomata.The results provide a scientific basis for further revealing the mechanism of mercury migration and regulation in wetland ecosystems.