| In this study,two indigenous bacteria-feeding nematodes and PSB strains were screened from the wheat rhizosphere as test nematodes and strains.Phosphorus-solubilizing bacteria were labeled with green fluorescent protein(GFP).The gnotobiotic microcosm culture system was conducted to explore the interaction between bacteria-feeding nematodes and PSB on soil available phosphorus,microbial biomass phosphorus(MBP),oxalic acid,phosphatase activity,changes of phosphorus fractions,wheat growth and the response of wheat phosphate transporter genes to reveal the mechanism of phosphorus activation of wheat growth promoted by soil bacteria-feeding nematodes from molecular biology perspective.The results of the study are as follows:1.Two test indigenous bacteria-feeding nematodes Mesorhabditis sp.(N1,c-p =1)and Acrobeloides sp.(N2,c-p =2),and two PSB strains Bacillus safensis(B1,Gram-positive)and Pseudomonas chlororaphis(B2,Gram-negative)were screened from the wheat rhizosphere.The test strains were labeled by green fluorescent protein(GFP).2.The result of the interaction between soil bacteria-feeding nematodes and phosphatesolubilizing bacteria through microcosm culture system suggested that: During all the incubation,the number of nematodes increased first then decreased with the maximum at 20 days,which increased by 33.8%-89.7% compared with 0d.Inoculation of bacteria-feeding nematode could increase the number and activity of PSB,and there is a difference on the number of bacteria-feeding nematode and PSB due to the species difference of both nematode and bacteria.As the consequence,B2N1 was higher than other treatments;the trend of the number of nematodes was same to bacteria,with a "positive feedback effect" between them.3.The result of the colonization status on wheat root of PSB at the presence of bacteria-feeding nematode observed by laser confocal microscopy showed that: Phosphorus-solubilizing bacteria were able to colonize in the elongation zone,root hair zone,and secondary root formation point of the wheat root;The fluorescence brightness of nematode inoculated was greater than uninoculated,indicating that bacteria-feeding nematodes could promote the colonization ability of phosphorussolubilizing bacteria in wheat roots.4.Bacteria-nematodes can effectively increase soil available phosphorus,microbial biomass phosphorus,oxalic acid content and phosphatase activity.There were also differences between different bacteria-feeding nematodes and phosphorus-solubilizing bacteria.During10-40 days,the contents of available phosphorus and microbial biomass of B2N1 were higher than other treatments.The content of oxalic acid decreased with the increase of incubation time then stabilized.The content of oxalic acid of B2N1 treatment was higher than others at 40 days,but the difference was not significant.At 40 days,the content of acid phosphatase under B2N1 treatment was significantly higher than other nematode inoculated treatments with the order of B2N1> B1N2> B1N1> B2N2,and which increased by 15.37%,28.42%,and 34.26%,respectively,compared with CK treatment;Soil alkaline phosphatase activity showed an overall increasing trend.The alkaline phosphatase activity of inoculation with B2 strain was significantly greater than that of the inoculation with strain B1.At 40 days,the nematode grazing could increase soil alkaline phosphatase activity compared to the treatment inoculated with B2.Principal components analysis(PCA)of environmental factors found that and phosphate-solubilizing bacteria grazed by nematodes could increase the quantity and activity of soil phosphorus-solubilizing bacteria,the content of available phosphorus and microbiomass P,oxalic acid content,and phosphatase activity.5.Bacterial-feeding nematodes could promote the transformation of soil phosphorus from nonabsorbed phosphate(NAP)to available phosphorus(AP)form and improve the bioavailability of soil phosphorus.The proportion of soluble phosphorus with nematodes inoculated was higher than uninoculated treatment.B2N1 performed best compared to others with a 45% of the proportion of AP content,accompanied with 25% of the increase,compared with CK,while the NAP content was reduced by 27%.6.The inoculation of bacteria-feeding nematode could promote the above-ground and underground biomass and phosphorus accumulation of wheat compared with inoculation.The dry matter accumulation of above/underground inoculated with N1 was better than N2 nematode.After 30 days of incubation,the accumulation of phosphorus in shoots of B2N1 was higher than other treatments,while the accumulation of underground of B1N1 was higher than B2N1.7.Inoculation with bacteria-feeding nematodes could effectively increase root indices such as RL,RV and RSA of wheat with more of wheat root tips,root length,and surface area and more branches.The development of root morphology of B2N1 become well-distributed.The morphology of wheat roots was mainly related to the inorganic phosphorus fractions,and there was a significant positive correlation between Resin-P,Na HCO3-Pi and all root morphology parameters;The content of Na OH-Pi was significantly related to RL,RF,RV and RSA;HCl-Pi and conc.HClPi were significantly negatively correlated with all root indices,indicating that the wheat root morphology was affected by soluble phosphorus8.Inoculation with bacteria-feeding nematode could up-regulate the relative expression of the low-affinity phosphate transporter genes Ta PHT1;1 and Ta PHT2;1,and down-regulate the relative expression of the high-affinity gene Ta PTH1;2.Available phosphorus(AP)was positively correlation with the expression of Ta PHT1;1 and Ta PHT2;1 but negatively correlated with Ta PTH1;2.A significant positive correlation between available phosphorus content and the relative expression of Ta PHT2;1 was found with the correlation coefficient 0.929.The content of Resin-P showed a significant positive correlation with the relative expression of Ta PHT1;1 while as the Na OH-Po was negatively correlated with it.The content of HCl-Pi,one of the non-absorbed phosphorus(NAP),was significantly positively correlated with Ta PHT1;2 with a correlation coefficient of 0.821.And There was a negatively correlation between the content of concentrated HCl-Pi and the relative expression of Ta PHT2;1with the correlation coefficient of 0.857.The results indicated that the change of available phosphorus content could affect the expression of the phosphorus response gene,which further confirmed the response mechanism of wheat from the perspective of the molecular biology of phosphorus protein transport under the flounce of bacteriafeeding nematode. |
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