Effect Of Calcium On Root Morphology And Physio-biochemical Characteristics In Malus Hupehensis Var. Pingyiensis Roots Under Acid Treatment

In China, due to the unreasonable fertilization, environmental pollution and acidprecipitation and so on, a large-scale soil have already acidized that were over20%of landarea. And with the development of industrial and agricultural production, the situation furtherdeteriorated. Calcium is not only the necessary macroelement for plants, but the secondmessenger for coupling extracellular signals and physiological reaction inside the cells. And itplayed a role in controlling the cells’ reaction and adaptability in adversities. In this paper,Malus hupehensis var. pingyiensis was taken as experiment material to explore the effects ofacid treatment and additional calcium under acid treatment on root morphology andarchitecture, the functions of antioxidant systems and mitochondria through controlling thepH of nutrient solutions. The aim is to discuss the damage mechanism of acid treatment, theadditional calcium’s physiological function and mechanism under acid treatment to base forfurther study on mechanism of acidized soil how to damage the plants.The Malus hupehensis var. pingyiensis rootstock seedlings were cultured in1/2Hoagland nutrient solutions of different pH （pH4, pH4.5, pH5and pH6） and different Ca²⁺concentrations (10,20and30mmol·L^-1) in pH4, pH4.5and pH5, respectively. And theparameters of root architecture were measured in the day4,8and12with the professionalWinRHIZO2007. And the rootstock seedlings were cultured in1/2Hoagland nutrientsolutions of different pH （pH3, pH4, pH5and pH6） and different Ca²⁺concentrations (10,20and30mmol·L^-1) in pH3, pH4and pH5, respectively. And the antioxidant enzymeactivities and mitochondria characteristics were measured in the day0,2,3and4. The resultsare as follows:（1） Compared with the control （pH6）, the treatments significantly decreased the totalroot length, main root length, and lateral root length. With the increasing of the acidity and thetime, the growth of lateral roots was more susceptible to acid treatment than taproots. Thetreatments significantly decreased the fractal dimension, length, diameter, surface area andvolume of roots, and they kept decreasing followed the increase of the acidity and treatmenttime which showed the significant logarithmic dose-effect relationship. The composition ofroots significant changed, the proportion of roots （0＜D≤0.5mm） decreased and the proportion of roots （0.5＜D≤1.5mm） increased that the acid treatment mainly inhibited thegrowth of rootlets, significantly decreased the proportion of rootlets that changed thecomposition of roots, and then simplified the space structure of roots.（2） Compared with the control （pH6）, the activities of superoxide dismutase （SOD）,peroxidase （POD） and catalase （CAT） in the treatments were all increased firstly and thendecreased. The maximum activity of SOD, CAT in the treatments occurred in day2, and thechange of POD activity was different, the maximum of POD in pH3and pH4occurred inday2and pH5in day3.（3） The mitochondrial membrane absorbance （MPTP）, Δψm and cytochrome c/adecreased with the increasing of the acidity and the time and the content of H₂O₂wasdecreased at first and then increased, the stage3of mitochondrial respiration significantlydecreased and stage4significantly increased, respiration control rate and rate of phosphorusand oxygen significantly decreased. The damage seriously increased followed the increasingacidity.（4） The exogenous application of calcium (10and20mmol·L^-1) in nutrient solutionunder acid treatment relieved the damage of root morphology and architecture but notsignificantly; the30mmol·L^-1Ca²⁺increased the damage.（5） The exogenous application of calcium (10and20mmol·L^-1) in nutrient solutionunder acid treatment relieved the damage had better results while the30mmol·L^-1Ca²⁺increased the damage of the activities of SOD, POD and CAT.（6） The low concentration of Ca²⁺(10mmol·L^-1and20mmol·L^-1) could inhibit theopenness of MPTP, the decreased of Δψm and Cyt c/a, the accumulation of H₂O₂contents andweaken of mitochondrial respiration while the high concentration promotes it.