Study On The Effect Of Arbuscular Mycorrhizal Fungi On Acquiring Insoluble Phosphate In Trifoliate Orange

Arbuscular mycorrhizas are mutualistic symbiosis between arbuscular mycorrhizal (AM) fungi in the soil and the roots of host plants.This study is to evaluate the effects of AM fungi on acquiring insoluble phosphate in citrus.The main results in the study are as follows:(1) The effect of arbuscular mycorrhizal fungus on excreting phosphatase in trifoliate orange[Poncirus trifoliata(L.)]seedlings under low P stress:The effect of arbuscular mycorrhizal fungus(Glomus mosseae,Glomus versiforme,Glomus mosseae and Glomus versiforme) on excreting phosphatase in trifoliate orange[Poncirus trifoliata (L.)]seedlings under low P stress was studied in greenhouse.All seedlings were cultivated in sand culture.The results obtained from the present study indicated that inoculation significantly increased the phosphatase of root and hyphae,especially the acid phosphatase and litmusless phosphatase,but both of them decreased with the increase of Al-P.The primary phosphatase in the sand are acid phosphatase and litmusless phosphatase,while alkaline phosphatase is very little.Acid phosphatase is in the range of 1.010-3.558 mg phenol/g sand,of the total phosphatase 47.1%-61.0%,litmusless phosphatase phenol contains 0.558-2.118 mg/g sand,of the total phosphatase 29.1% -43.9%,while the alkaline phosphatase in the proportion of only 4.8%-12.1%.Three kinds of phosphatase and total phosphatase in the sand inoculated with AMF are expressed as Gm＞G.m+Gv＞Gv.The contribution of fungus in P uptake was significantly positively correlated with acid phosphatase,litmusless phosphatase,alkaline phosphatase and total phosphatase.(2) The effect of arbuscular mycorrhizal fungus on the organic acids in the exudates of mycorrhizal Poncirus trifoliata(L.) Raf.Seedlings under low P stress:The effect of arbuscular mycorrhizal fungus(Glomus mosseae.Glomus versiforme,Glomus mosseae and Glomus versiforme) on the components and concentrations of organic acids in the exudates of mycorrhizal Poncirus trifoliata(L.) Raf.Seedlings under low P stress was studied in greenhouse.The results show that inoculation increased the trifoliate orange root of the components of organic acid secretion,it detected only six acid(oxalic acid, malic acid,lactic acid,acetic acid,maleic acid and citric acid),while G.m treatment detected 7 acid(oxalic acid,tartaric acid,malic acid,lactic acid,acetic acid,citric acid. succinate),and G.v treatment detected tartaric acid,not detected succinate;Inoculation also increased the contents of organic acid secretion(than uninoculation treament increased by 19.80 mg/g-56.87 mg/g)of trifoliate orange root,and the application of AlPO₄ greatly increased organic acid content(an increase of 20.06 mg/g-21.84 mg/g); uninoculated root plants secreted a small amount of organic acids;Mycorrhizal Poncirus trifoliata(L.) Raf.Seedlings excreted organic acid by malic acid(42.87%),citric acid(39.22%) and oxalic acid(12.06%) primarily. (3) The effect of arbuscular mycorrhizal fungi on the growth and mineral nutriention in Poncirus trifoliata(L.) Raf.seedlings under low P stress:The effect of arbuscular mycorrhizal fungi on the growth and mineral nutriention in Poncirus trifoliata(L.) Raf.seedlings under low P stress was studied in greenhouse.The seedlings were grown in sterilized sand amended with Al-P or Fe-P,inoculated with Glomus mosseae.The results showed that:fungi inoculation significantly increased the dry weight of the trifoliate orange(an increase of 12.30%-53.04%),phosphorus concentration (4.81%-30.41%) and phosphorus uptake(15.78%-64.84%);Plant can use a certain amount of Al-P and Fe-P on uninoculation conditions,but more Fe-P easily;After inoculation,the use of Al-P were significantly higher than those not inoculated.With the application rate of Al-P increasing,mycorrhizal effect,phosphorus uptake by AM fungus and the contribution of phosphorus uptake were greatly increased,mycorrhizal fungi increased 34.31 percent,phosphorus uptake increased by 2.27 mg/pot,the contribution of phosphorus uptake increased 13.48 percent;There was no great increase in P uptake of Fe-P compared with control,but P uptake of Fe-P was lower than that of Al-P;Inoculated with Glomus mosseae,sand available P concentration was significantly higher than that of control with 2.35 mg/kg-52.98mg/kg,which was increased with the rise of P level; Inoculation of AM fungi increased plant nitrogen,potassium,calcium,copper and manganese concentration,It reduced the concentration of magnesium,iron and zinc,, while there was no significant difference of iron concentration betweenFe-P treament and control.AM fungi inoculation significantly or very significantly increased the plants Poncirus nitrogen,potassium,calcium,magnesium,iron,copper,zinc and manganese absorption.