Effect Of Arbuscular Mycorrhizal Fungi(AMF) On Morpho-Physiological And Biochemical Responses Of Maize Under Sub-Optimal Water And Phosphorus Supply

Crop plants generally encounter the wide range of environmental stresses during their growth stages.Among them,Phosphorus（P）deficiency and drought stress are two major constraints for most of the field crops.Maize is major cereal crop which is sensitive to drought and P-deficiency particularly at early growth stage.In natural conditions,maize crop is routinely subjected to a combination of different environmental stresses,therefore,the investigations considering the multiple stress factors are of ecological significance.Response of maize to multiple stress factors is unique and cannot be directly extrapolated by the response to each of the different stresses applied individually.In order to cope with a particular stress condition as drought,plant require energy and sufficient resources,however,nutrient limitations as P-deficiency further hinder the acclimation process of the plants to stress conditions.The application of arbuscular mycorrhizal（AM）fungi to the plants is considered as an effective technique to enhance the plants’growth of many field crops particularly under unfavorable environmental conditions.Despite the dearth of literature on the useful effects of AM fungi under drought and P-deficiency,little work has been done regarding the role of AM fungi in enhancing the tolerance to combine stress factors in maize and to explore the underneath mechanisms.Here,the series of experiments were carried out in green house to unravel the physiological,biochemical,metabolic and mineral nutrient responses in AMF-inoculated and non-occulated maize plants under the interaction of drought and P-deficiency.It was hypothesized that AMF inoculation might have the potential to confer tolerance to drought and P-deficiency by regulating various metabolic processes,modulating the production of osmolytes and secondary metabolites,enhancing the antioxidative defense system,and maintaining the plant-nutrient status.The main findings of the studies are summarized below.First,the effects of different mycorrhizal species were investigated and applied through different methods to maize plants.Four AM fungi species viz.,Claroideoglomus etunicatum（C.E）,Rhizophagus intraradices（R.I）,Funneliformis mosseae（F.M）,and Diversispora versiformis（D.V）were applied to maize through seed coating,soil application,or seed coating+soil application.Application of C.E,R.I,F.M,and D.V through different methods triggered the growth performance of maize by improving morpho-physiological characteristics and root morphology,modulating AM fungi colonization,enhancing the nutrient（N,P,K）uptake,and reducing the root exudates（oxalic,malonic,fumaric,malic,citric,and T-aconitic）compared with control.Among the different mycorrhizal species,F.M applied particularly through seed coating+soil application was more effective in regulating maize growth as compared with C.E,R.I,or D.V species owing to the better root system,higher root colonization,and greater nutrient uptake in this treatment.Interestingly,F.M applied through seed coating+soil application performed better than that of other mycorrhizal species.Second,the physiological and biochemical responses of maize for adaptation to water and P deficiency were investigated.Three levels of water regimes（100%FC,60%FC,and 40%FC）and P,P100:100mg kg^-1soil,P50:50mg kg^-1soil and P0:0mg kg^-1soil were used with two hybrid maize viz ZD958 and XY355.Interaction of water and P-supply levels altered the shoot and root traits,oxidative status,nutrients uptake,and osmolytes accumulation in both hybrid maize cultivars.The plant height,fresh and dry weight of root and shoot,root architecture,and P uptake were significantly（p<0.05）reduced under 60%FC and 40%FC with P50 and P0,as compared with other interactive levels of the water and P-supply.The H₂O₂and MDA contents were increased by decreasing the moisture（60%and40%FC）and P-supply（P50 and P0）.However,SOD,total protein,free proline,and total reducing sugar increased with decreasing the moisture and P-supply but POD and CAT fluctuated.The P0 with 60%FC and 40%FC was noted in the reduction of maize growth traits among P-supply levels but 40%FC was most destructive with different levels of the P-supply.Overall,the trend of interactive levels of water and P on the growth of both cultivars was as follows 40%FC+P0>40%FC+P50>40%FC+P100>60%FC+P0>60%FC+P50>60%FC+P100>100%FC+P0>100%FC+P50>100%FC+P100.These results indicated that the 60%FC and 40%FC were more lethal to maize growth as compared with P levels.Third experiment’s results showed that arbuscular mycorrhizal fungi（AMF）under single and combination of drought and P-deficiency had significant（p<0.05）effects on morpho-physiological and biochemical attributes of maize（Zea Mays L.variety ZD958）.The AMF strain“F.mosseae”was used which was selected from the first study with the seed coating+soil application method.The drought level（40%FC）was selected from the second study with P-deficiency（25mg/kg soil）level.Results showed that drought and P-deficiency and their interaction significantly（p<0.05）affected the maize growth by decreasing the plant height,fresh and dry weight of shoot and root,and root architecture.The trend of stress treatments on maize growth was as follows drought+P-deficiency>drought>P-deficiency.However,inoculation of AMF significantly（p<0.05）increased the plant height,fresh and dry weights,and root architecture,respectively.Compared with non-inoculated plants,AMF inoculation significantly（p<0.05）enhanced the nitrogen,phosphorus,and potassium uptake but AMF colonization was reduced under the individual and concurrent occurrence of drought and P-deficiency.The trend of stress treatments on AMF colonization with maize roots was as follows drought+P-deficiency>drought>P-deficiency.Significant（p<0.05）reduction of AMF colonization was recorded under drought+P-deficiency.Furthermore,H₂O₂and MDA contents were increased under stressful conditions,and plants inoculated with AMF reduced the accumulation of H₂O₂and MDA.Moreover,the activities of SOD,POD,and CAT were significantly（p<0.05）improved in inoculated and uninoculated plants to ameliorate the oxidative effects.Taken together,these lines of evidence could explain,to some extent,the protective role of AMF against the adversities caused by drought stress and P-deprivation in maize seedlings.The results of this study indicated that the inoculation of AMF（Funneliformis mosseae）with maize plants has the potential to confer drought and P-deficiency tolerance by improving below ground growth traits,regulating the production of osmolytes and secondary metabolites,strengthening the antioxidative defense system,and maintaining the plant-nutrient status.