Absorption And Transformation Of Sparingly Soluble Phosphorus By Ectomycorrhizal Pinus Massoniana Seedlings Under Acid Aluminum Stress

Phosphorus is an essential element for plant growth and development.Soil acidification results in that aluminium be activated in soil.It not only aggravates the immobilization of phosphorus ion in soil and makes available phosphorus even lower,but also causes original toxicity to root system and severely disrupted the absorption and utilization of phosphorus by plants.Ectomycorrhizal fungi?ECMF?,which is a kind of important microorganism in forest soil,can promote the uptake and utilization of phosphorus in tree and improve the resistance of plants to aluminum toxicity after it establishs symbiotic associations with roots.That is of great significance for the restoration and reconstruction of forest ecosystem.However,it is not clear whether ECMF can promote the transformation of phosphorus forms and facilitate the upstream transport and utilize of phosphorus in plants under acid aluminium stress.Two kinds of ECMF with different aluminium tolerance,Pisolithus tinctorius 715?Pt 715?and Lactarius deliciosus 2?Ld 2?,were selected to infect Pinus massoniana seedlings and then cultured in acidic soil containing aluminum and inorganic sparingly solublephosphorus.The mycorrhizal seedlings of Pinus massoniana were collected after one yearly growth cycles to detect their growth,root morphology,absorption and distribution of phosphorus and aluminum,transformation of phosphorus and absortion kinetics of phosphorus and aluminum.The function of mycorrhization in the uptake and transformation of sparingly solublephosphorus in Pinus massoniana seedlings under acid aluminum stress was explored with non-mycorrhizal seedlings as control.The main results are as follows:?1?Pt 715 and Ld 2 could establish a good symbiotic relationship with Pinus massoniana seedlings,and significantly promote the growth of Pinus massoniana seedlings under acid aluminum stress.The effect of Ld 2 was significantly better than that of Pt 715.Except for Fe-P,Na-P and Al-P significantly increased the biomass of Pinus massoniana seedlings,and Na-P>Al-P>Fe-P?0-P.In the combined treatment of acid aluminum stress and sparingly solublephosphorus?especially Al-P?,both Pt 715 and Ld 2 infection significantly promoted the growth of Pinus massoniana seedlings.And Ld 2 also significantly increased root biomass,root length,root volume,root surface area,root tips and forks of Pinus massoniana seedlings,while Pt715 only significantly increased root biomass,root tips and forks of Pinus massoniana seedlings under Al-P treatment.The effect of Ld 2 on root morphological index was significantly greater than that of Pt 715.Therefore,ECMF infection promotes root growth and elongation of Pinus massoniana seedlings under acid aluminum stress and sparingly solublephosphorus treatment,enlarges root surface area and volume,improves root growth,alleviates original toxicity of active aluminum to roots,and improves tolerance of Pinus massoniana seedlings.The improvement effect of Ld 2 is significantly higher than that of Pt 715.?2?In acid aluminium stress and sparingly solublephosphorus treatment,the inoculation of Pt715 and Ld 2 not only significantly increased the available phosphorus content in rhizosphere soil of Pinus massoniana seedlings,but also significantly promoted the absorption and utilization of sparingly solublephosphorus in soil of Pinus massoniana seedlings in Al-P treatment and promoted the transport of phosphorus in Pinus massoniana seedlings.The utilization of Al-P by Ld 2 was significantly higher than that of Fe-P.Both Pt 715 and Ld 2 infection significantly inhibited the absorption of Al in soil by Pinus massoniana seedlings.They mainly fixed Al in roots and significantly inhibited the upstream transport of Al.?3?The proportion of residual-P was the highest in Pinus massoniana,followed by nucleic-P,ester-P,lipid-P,EDTA-P and inorganic-P.In the combined treatment of acid aluminum stress and sparingly solublephosphorus,inoculation with ECMF significantly increased lipid-P,ester-P,inorganic-P in roots and increased lipid-P,ester-P,inorganic-P and nucleic-P in Pinus massoniana in shoots.And significantly reduced EDTA-P,nucleic-P in roots and residual-P in shoots.It can be indicated that mycorrhizal treatment promoted the transformation of EDTA-P,nucleic-P to lipid-P,ester-P and inorganic-P in the root system of Pinus massoniana.And the transformation of residue-P to lipid-P,ester-P,inorganic-P and nucleic-P in the shoot.It reduced the fixation of EDTA-P and nucleic-P in the root system.It was beneficial to the transport of lipid-P,ester-P,inorganic-P and nucleic-P.?4?The absorption of phosphorus and aluminium by mycorrhizal and non-mycorrhizal seedlings of Pinus massoniana accorded with the rule of active absorption.ECMF inoculation did not significantly change the affinity?K_m?and minimum uptake concentration(C_min)of P in Pinus massoniana seedlings,but significantly affected the maximum uptake rate(I_max).Among them,Ld2 significantly increased I_max,while Pt 715 significantly decreased I_max.In addition,inoculation of Pt 715 and Ld 2 significantly increased the P tolerance of Pinus massoniana seedlings.Ld 2 was more tolerant to low P than Pt 715 mycorrhizal seedlings.The inoculation of two kinds of ECMF significantly decreased the K_m and C_min of Al and increased the I_max.The decrease of K_m and C_minin of Pt 715 was greater than that of Ld 2,while the increase of I_max was less than that of Ld 2.So mycorrhizal treatment can significantly improve the affinity of Pinus massoniana Seedlings to aluminum,reduce the absorption threshold of aluminum,and improve the comprehensive absorption capacity of aluminum.In conclusion,the inoculation of Pt 715 and Ld 2 in acid aluminum stress and sparingly solublephosphorus treatment significantly promoted the growth,root elongation and differentiation of Pinus massoniana seedlings.And it enlarged root surface area and volume,promoted the absorption,utilization and transport of sparingly solublephosphorus.Meanwhile it inhibited the absorption and transportation of aluminum by seedlings.Ectomycorrhizae significantly increased the transformation of residue-P,EDTA-P into lipid-P,ester-P and inorganic-P.And it was beneficial to lipids-P,ester-P,inorganic-P and nucleic-P for transporting upstream.And inoculated with Pt 715 and Ld 2 significantly enhanced the phosphorus tolerance of Pinus massoniana seedlings.Between the two ECMF inoculated,the effect of Ld 2 was better than that of Pt 715.