| Helianthus tuberosus L.is a perennial herbaceous plant belonging to the sunflower family Compositae.It has been planted in many places in my country because of its strong stress resistance and high nutritional value.In recent decades,with the frequent precipitation of acid rain,soil acidification has intensified,and aluminum toxicity has become the main factor restricting the growth of crops in southern acidic soils.Organic acid secretion is one of the main mechanisms for plants to adapt to aluminum toxicity stress and external rejection of aluminum.Its type and quantity are closely related to the degree of aluminum toxicity mitigation.Malic acid,citric acid and oxalic acid are the main organic acids that most plants respond to aluminum toxicity and they are also excellent chelators agents for plants to adapt to aluminum toxicity.In this study,Jiangsu Xuzhou H.tuberosus and Sichuan Ziyang H.tuberosus were used as materials,and the soil culture method was used to determine the optimal concentration of malic acid,citric acid and oxalic acid（OA）to alleviate the aluminum toxicity of H.tuberosus and from the aspects of photosynthetic characteristics,antioxidant capacity,etc.Clarify the effect and mechanism of compound organic acid to relieve aluminum toxicity.The results are as follows:（1）Taking Ziyang H.tuberosus as material,the soil culture method was used for 21days,and the L9（34）Orthogonal experiment showed that the root relative elongation of 300μmol/L malic acid,700μmol/L citric acid and 1000μmol/L oxalic acid combined spraying treatment was the highest,which increased by 103.26%compared with that of single Al group,indicating that the three organic acids combined spraying concentration had the best alleviating effect on aluminum toxicity of H.tuberosus,which was used as the exogenous organic acid compound spraying concentration in subsequent experiments.（2）The effects of malic acid,citric acid and oxalic acid compound organic acids on growth and photosynthetic damage of H.tuberosus under aluminum stress were investigate by soil culture experiments with Xuzhou H.tuberosus（aluminum-resistant variety）and Ziyang H.tuberosus（aluminum-sensitive variety）.The results showed that the relative elongation of root system and plant height,and the dry matter accumulation of root system and above-ground part of Xuzhou H.tuberosus and Ziyang H.tuberosus were significantly reduced compared with the control on 7,14,and 21 days of Al treatment.Chlorophyll a,chlorophyll b,chlorophyll fluorescence parameters,leaf stomatal conductance（Gs）,net photosynthetic rate（Pn）,and transpiration rate（Tr）all decreased to varying degrees.After exogenous spraying of compound organic acids（OA）,the relative elongation of roots and shoots of Xuzhou H.tuberosus and Ziyang H.tuberosus increased significantly compared with Al treatment,and the shoots and root dry weight increased by 89.69%,68.42%,148.39%,97.95%,Leaf area increased by 16.86%and 25.52%,Gs increased by 193.22%and 195.45%,chlorophyll content increased,Pn and Tr both rebounded.It shows that the treatment of exogenous compound organic acid retard the damage of aluminum toxicity to PSII reaction center,weakens photosynthetic inhibition and photosynthetic structure damage caused by aluminum toxicity to a certain extent,increases leaf transpiration rate and net photosynthetic rate,and reduces aluminum stress on H.tuberosus leaves The interference of the photosynthetic system allows photosynthesis to proceed normally.（3）Using soil culture experiments,foliar sprays of three organic acids in equal proportions were used to explore the effects of compound organic acids on the physiological response and antioxidant capacity of H.tuberosus under aluminum stress.The results showed that compared with the control,the root activity of Xuzhou H.tuberosus and Ziyang H.tuberosus decreased by 37.25%and 57.96%on the 21st day of Al treatment and the leaf proline content increased by 155.56%and 94.83%.The SOD activity increased,the largest decrease in CAT activity was 24.69%and 24.74%,and the MDA content increased significantly by 92.61%and 131.96%.After foliar spraying with compound organic acids,the root activity of the Xuzhou H.tuberosus and Ziyang H.tuberosus Al+OA treatment groups had the largest growth rates of 43.14%and 74.36%compared with the single Al group.The increase in Al-induced proline content was effectively alleviated,and the antioxidant enzymes The activity increased,the antioxidant substances ascorbic acid（As A）and glutathione（GSH）increased by 22.00%and 25.00%,51.96%and 81.01%,and MDA decreased by 25.51%and 30.44%.It shows that the exogenous application of organic acids can enhance the protective enzyme activity of H.tuberosus and increase the content of antioxidant substances,improve the antioxidant capacity,and reduce the degree of membrane lipid peroxidation of H.tuberosus in the aluminum-toxic habitat.（4）Through exogenous application of compound organic acids,the effects of organic acids on the accumulation of aluminum in the root tip of H.tuberosus and the secretion of organic acids and soluble sugars in the roots of H.tuberosus under aluminum stress were studied.The Al content of Xuzhou H.tuberosus and Ziyang H.tuberosus under Al stress increased by 32.21 and 36.13 times compared with the control.The secretion of citric acid and oxalic acid from roots increased by 43.94%and 32.63%,120.63%and 38.91%respectively compared with the control.After spraying with exogenous organic acid,the root tip Al content of Xuzhou H.tuberosus and Ziyang H.tuberosus was reduced by17.26%and 27.66%compared with the single Al treatment,and the secretion of citric acid,malic acid and oxalic acid in the roots increased by 22.38%and 40.24%,86.11%and44.18%,52.31%and 59.69%,the soluble sugar content of roots increased significantly.It shows that the exogenous compound organic acid can improve the growth of H.tuberosus,reduce the aluminum content of the root tip,and increase the root secretion capacity of citric acid,oxalic acid,malic acid,and soluble sugar of H.tuberosus,so as to cope with the adverse effects of aluminum toxicity on the growth of H.tuberosus. |
