Interactive Effects And Mechanisms Of Interaction Of P Fertilizer And Amf On Cd Uptake And Accumulation In Maize

In the current study,“Huidan No.4”,a native maize cultivar（Zea mays）in Yunnan province,China,was selected as host plant.Under a series of cadmium（Cd）supplements,we studied the effect of the combined interaction of AMF and organic-inorganic phosphate fertilizer on the absorption and accumulation of Cd in maize.And the mechanisms of the improved Cd resistance of maize by the interaction of AMF and organic-inorganic phosphate fertilizer were also discussed.The main results are the followings:1.The 50-day maize roots were collected,and the colonization intensity of arbuscular mycorrhizal fungi（AMF）was evaluated using the magnified intersections method.We noticed that all root samples of the inoculated maize were colonized by AMF under all 3 Cd supplements surveyed,including diverse AM fungal structures,e.g.arbuscules,vesicles and hyphae.The colonization intensity ranged from 40.62%to80.86%.In contrast,no AMF were observed in the roots of the non-inoculated maize controls.2.After 50-day cultivation,all maize seedlings were collected,and the maize height,the number of grey leaves and fresh leaves,biomass and phosphorus concentrations were measured.The results showed that both AMF inoculation and fertilizer application alone significantly reduced the number of grey leaves,increased the number of fresh leaves,the height,dry weight of maize,promoted the absorption of phosphorus in maize and improved phosphorus utilization efficiency of maize.All these results suggested that AMF inoculation alone or fertilizer application alone significantly alleviated the negative impact on maize growth by the excessive Cd ions.Three-way ANOVA results showed the interaction between inoculation AMF and phosphorus fertilizer application significantly reduced the content of soluble phosphorus in soil,increased the absorption and utilization of phosphorus in maize plants,to promote the growth of the maize.3.The total cadmium concentrations accumulated in the maize shoots and roots were determined using the flame atomic absorption spectrophotometer.The results showed that comparing to the non-inoculated controls,AMF or fertilizer alone have no significant influence on the metal accumulation in the maize shoots at low cadmium concentrations(5 mg kg^-1).At the excessive cadmium concentrations(50 mg kg^-1),compared with their respective controls,AMF significantly reduced cadmium on the shoots of maize under the 0-and 1-time fertilizer application.However,AMF inoculation even slightly increased the cadmium accumulation in the maize shoot under the 5-time fertilizer application.Comparing to their respective no fertilizer application controls,fertilization significantly increased the cadmium concentrations in the maize shoots,regardless of the AMF inoculation.Comparing to their respective controls,AMF alone reduced cadmium in the roots of maize at the same cadmium concentration,but fertilization application showed the opposite trends.Three-way ANOVA results showed that,the interaction of AMF and fertilization significantly influenced the cadmium accumulation in the shoots of maize,but no significant impact on the root cadmium.4.The concentrations of cadmium with different chemical forms accumulated in the maize roots and shoots were determined by Tessier Sequential extraction.Results showed that the percentage of Cd with chemical form extracted by sodium chloride in the shoots and roots of maize was the highest in all treatments.Comparing with their respetive controls,AMF inoculation alone or application phosphorus fertilizer alone increased the percentage of NaCl-extracted cadmium,and reduced the percentage of toxic cadmium in maize shoots.Under the same cadmium levels,and no fertilizer supplements,comparing with their non-inoculation AMF controls,the AMF inoculation significantly increased the percentage of NaCl-extracted cadmium,and significantly reduced the percentage of toxic cadmium in maize roots,but there was a opposite trends in the Cd chemical forms in maize roots when 5-time fertilizer application;While,AMF inoculation had no significant effect on the percentage of NaCl-extracted cadmium and poisonous cadmium in root of maize when 1-time fertilizer application.As for the AMF inoculated maize,fertilization application significantly reduced the percentage of NaCl-extracted cadmium,and markedly increased the proportional of toxic cadmium in maize roots,compared with the non-fertilizer treatments.But,there was no significance on Cd with different chemical forms for the non-inoculated maize between the fertilizer and non-fertilizer treatments.Three-way ANOVA results showed that,the interaction between inoculation AMF and phosphorus fertilizer application significantly affected the percentages of NaCl-extracted cadmium and toxic（including the ethanol and deionized water extracted forms）cadmium in maize shoots and roots.Therefore,preliminary results showed that Cd compartmentation integrated with pectins and proteins might be responsible for the adaptation Cd stress,when maize was inoculated with AMF or supplemented with phosphorus fertilizer.5.The subcellular distribution of cadmium in maize shoots and roots was studied using density gradient centrifugation method.Our results showed that there was a distinct subcellular distribution of Cd among the different treatments.At low cadmium concentration(5 mg kg^-1),the cadmium was mainly distributed in the soluble fractions in maize shoots.In contrast,at high cadmium concentration(50 mg kg^-1),the cadmium was mainly accumulated in cell walls in maize shoots.Under the different treatments,the maize root cadmium mainly accumulated in the cell walls,followed by the soluble fractions,while the percentage of Cd in the organelles was the least.Therefore,our results showed that Cd compartmentation with organo-ligands in vacuoles or integrated with pectins and proteins in cell wall may be an important mechanism for maize plants to tolerant the excessive cadmium ions.The above results revealed that,under 1-time fertilization conditions,mycorrhizal inoculation strengthened the Cd compartmentation with organo-ligands in vacuoles or integrated with pectins and proteins in cell wall to alleviate the toxic stress of maize by the excessive Cd in the substrate.But,the positive effect of mycorrhizal inoculation on maize may be inhibited with the elevated fertilizer application.Conclusively,the combined application including the mycorrhizal technologies and the application of fertilizers with an optimal dose could promote the growth of maize by the alleviating the negative effects from the excessive Cd stress,and enhance the maize tolerance to toxic metal ions.