The Influence Of Insoluble Phosphorus On The Growth,Inorganic Phosphorus And Antioxidant Enzymes Activities Of Ectomycorrhizal Fungi Under Acid Aluminum Stress

Phosphorus,an element required in slightly lower quantities than nitrogen,is one of the essential major nutrients in forest ecosystem.The increasing Al3+ leading by soil acidification is one of the reasons the deficiency of phosphorus,which is a serious damage to plant growth.Ectomycorrhizal fungi(ECMF)can form a symbiotic system with lots of trees,and plays an important role of enhancing plants' ability of Al resistance and absorption of nutrients,especially phosphorus.To better understand activation of insoluble inorganic P(including Fe-P and Al-P)by ECMF under acid Al stress and its mechanism,Pt715,Ld2 and Ld3 were used for the study.The effects of insoluble inorganicphosphorus under Al stress on the growth of ECMF,elements absorption,inorganic phosphorus fractions,antioxidant enzyme activity,and the cationic absorption of Al?P were studied to provide a theoretical basis for the restoration of forest causing by the absence of the available P in Southwest Forest.The main conclusions were as follows:(1)The three ECMF all can resistant Al stress and Fe-P promoted the growth best.Among them,Ld2 showed maximum tolerance with aluminum,the mycelia biomass increased significantly under P0 ? Na-P ? Fe-P and Al-P,increased separately Fe-P(22.31%)>P0(15.87%)> Na-P(8.87%)>Al-P(6.91%).Pt715 increased significantly under Na-P ? Fe-P and Al-P,increased separately Fe-P(32.84%)> Na-P(15.35%)>Al-P(7.66%).Ld3 increased significantly under Na-P and Fe-P,increased separately Fe-P(17.19%)> Na-P(14.06%).The mycelia biomass under Na-P?Fe-P and Al-P were higher than P0,the highest was Fe-P,the second was Al-P,the last was Na-P.Compared with the biomass of three ECMF,Ld2>Ld3>Pt715,the result indicated that Ld2 showed the best growth than Ld3 and Pt715 under Al stress.(2)The pH of ending culture medium was lower than the beginning.Compared with no Al,Al stress has enhanced pH of the culture medium.The culture medium pH of Fe-P and Al-P were lower than Na-P under Al stress,this result indicated that ECMF secreted more organic acid or H+ and combined Al to dissolve insoluble P.(3)Both Fe-P and Al-P promoted the absorption of Al?P?Fe-P and Al-P,but the absorption of N had decreased.Al stress had promoted the absorption of N?P?Al and Al-P.Without Al,The content of Fe-P was highest under Fe-P treatment,but it decreased with Al.The content of Al-P was highest under four P treatments,surmised that P combined Al first.Under Al stress,the P content of ECMF ranked as Ld3>Ld2>Pt715,which indicated Ld3 has the stronger ability of dissolving insoluble Pthan Ld2 and Pt715.(4)Al stress had significantly enhanced the SOD and CAT activities of ECMF,but decreased the POD activity.The three antioxidant enzyme activities SOD?POD?CAT under Fe-P and Al-P was higher than Na-P,which indicated insoluble P enhanced the antioxidant enzyme activities.Above all,the increasing magnitude of SOD?CAT inLd2 was higher than Ld3 and Pt715,and the decreasing magnitude of POD inLd2 lower than Ld3 and Pt715,Which indicated that the resisting adversity ability of Ld2 was strongest.(5)Correlation analysis results showed that P content had a positive relationship with Al content(P<0.01),which indicated that there were synergistic effects between P and Al absorption.Al content had a positive relationship with Al-P content,Al-P content increased with the increasing of Al content,surmised that P combined Al in the ECMF.SOD activity had a positive relationship with CAT,both SOD and CAT had a positive relationship with total P,indicated that by enhancing the activities of SOD and CAT,the ability of dissolving insoluble P of ECMF had enhanced.(6)The CEC of three ECMF ranked as Ld3?Ld2>Pt715,surmised that Ld3 and Ld2 absorbed more Al3+ than Pt715.The Km and Imof Ld3 and Ld2 were higher,indicated thatLd3 and Ld2 were more suitable for high Al soil.(7)Both Km and Cm of P absorption in ECMF had decreased,and Imax had increased except the Cmof Ld2 had no obviously change under Al stress.Al stress enhanced the ability of ECMF to absorb P,they can all survive in low phosphorus soil.The Km and Imof Ld2?Ld3 were lower than Pt715,which indicated that Ld2 and Ld3 were more suitable for low phosphorus soil.In summary,the three strains used in the experiment were able to adapt to the high aluminum and low phosphorus environment under the stress of aluminum,and used the insoluble phosphorus.The adaptability and utilization ability of Ld2 and Ld3 were stronger than Pt715.Among them,Ld2 grew fastest,behaved the strongest ability to anti-aluminum,and Ld3 behaved the strongest abilityto absorb phosphorus.ECMF usedthe insoluble phosphorus mainly through the secretion of H+ or organic acids,promote Al-P,Fe-P dissolved,increase the absorption of nutrients phosphorus,increase the adsorption of Al,complex Al3+,and increase SOD,POD,CAT enzyme activityunderaluminum stress.