Different Mechanisms Of Two Indica-Japonica Rice Cultivars Responses To Cadmium Stress Under Elevated Carbon Dioxide

The increase in global atmospheric carbon dioxide(CO2)concentration has been widely concerned.And the elevated atmospheric CO2 concentration will certainly affect the ecological environment and agricultural production.Rice(Oryza sativa L.)as the main grain crops,because of the increasing pollution of soil cadmium(Cd)in agricultural production,agricultural production and food security are seriously challenged.This study attempts to artificially simulate the elevated CO2 concentration and Cd stress in the growth environment of rice,to study the combined effects of Cd stress and elevated CO2 concentration on Cd absorption,transport,accumulation and antioxidant capacity of rice.It provides a theoretical basis for predicting the impact of heavy metal pollution on crops and food security in an environment with elevated atmospheric CO2 concentrations and forward-looking measures.In this study,test materials are the Ningjing 7(Oryza sativa L.subsp.Japonica)and Yangdao 6(Oryza sativa L.subsp.Indica),which are popularized rice cultivars.Liquid culture in CO2 artificial climate chamber,study the effects of elevated CO2 on rice growth,Cd absorption and transport,and antioxidant capacity under Cd stress.The main findings are as follows:1.After the Ninggeng 7 and Yangdao 6 are exposed to 0,1,2,5,10 μmol L-1 CdCl2 for 9 days,when the Cd concentration was 5 μmol L-1,the relative elongation inhibition rate of Cd on the shoots and roots of the two rice varieties reaches 50%,and the biomass decreased significantly,and the biomass of Indica Yangdao 6 decreased more than the control.The root of Yangdao 6 has a lower Cd concentration than Japonica Ninggeng 7,but the increase of its transport factors and stem Cd concentration is significantly higher than Ninggeng 7.There suggested that compared with Japonica Ninggeng 7,the growth of Indica Yangdao 6 is more easily inhibited by Cd stress.2.After the treatment of 1200 ppm CO2 and 5μmol L-1 Cd,it was found that the elevated CO2 significantly promoted the growth of rice,and had a greater effect on the growth of Japonica Ninggeng 7,and the shoots dry weight,roots dry weight and the growth rate of the whole plant increased by 65.9%,101.2%and 30.5%,respectively.Cd stress significantly inhibited the promoting effect of elevated CO2 on the two rice cultivars,and it inhibited Ningjing 7 more significantly.Under Cd stress,the shoots dry weight,roots dry weight and the growth rate of the whole plant increased only by 48.7%,67.3%and 21.5%,after the CO2 concentration increased.Elevated CO2 increased the total root length,total root surface area and root vitality of the two rice cultivars,which in turn increased the absorption of magnesium(Mg)by the rice roots,increased the content of chlorophyll,and enhanced photosynthesis.However,Cd stress significantly inhibited the promotion of CO2 on the appeal index of Ningjing 7,but the increase of Indica Yangdao 6 under the condition of elevated CO2 did not decrease significantly.The effect of short-term elevated CO2(EC1)and continuous elevated CO2(EC2)on the two rice cultivars was not significantly different.After the increase of CO2 concentration,the increase in Mg absorption by the roots of the two rice varieties did not decrease significantly under Cd stress,but the root Cd content of Ninggeng 7 and Yangdao 6 decreased by 21.5%and 11.4%,respectively.After the increase of CO2 concentration,the instantaneous water use efficiency of Japonica Ninggeng 7 increased more significantly than that of Yangdao 6,and the Cd concentration and Cd transport factors of Ninggeng 7 increased significantly,but Indica Yangdao 6 did not change significantly.3.Elevated CO2 reduced the H2O2,and O2-content of the two rice cultivars under Cd stress,alleviated the degree of membrane lipid peroxidation,and improved the integrity of the root cell plasma membrane.By increasing the activity of ascorbate peroxidase and glutathione reductase,the content of glutathione is increased,and the content of antioxidants such as ascorbic acid,total polyphenols,and non-protein sulfhydryl groups in the ground is also increased,which relieves the peroxidation stress caused by Cd,improved the antioxidant capacity of the two rice cultivar.And under the Cd stress,the elevated CO2 had a more obvious mitigation effect on Indica Yangdao 6.In summary,the Indica Yangdao 6 is more sensitive to Cd stress.But,under Cd stress,the elevated CO2 alleviated the Cd stress on the rice,and the alleviation effect on Yangdao 6 was stronger.Elevated CO2 has a greater growth promotion effect on the Ningjing 7 of japonica rice,but compared to Yangdao 6,the promotion effect of Ningjing 7 is more easily inhibited by Cd.This difference between indica-japonica inter-subspecific rice provides a theoretical basis for dealing with heavy metal pollution and elevated CO2 in rice production.