Effects of proline on microbial carbon source utilization and enzyme activity in cotton rhizosphere microorganisms
[Objective]The objective of this study is to study the effects of exogenous application of proline on carbon source utilization by soil microorganisms in the cotton rhizosphere and soil enzyme activities,and deeply understand the ecological mechanism of proline in disease prevention and cotton growth promotion.[Methods]In this study,the application of different proline concentrations(0,50,100,200 and 400 mmol-L1)were set,with a cotton Verticillium wilt-susceptible variety Ejing 1 as the experimental material,and the Biolog-ECO plate method was used to evaluate the functional diversity and carbon source utilization of rhizosphere soil microbial communities under different treatments.Principal component analysis was used to compare the carbon source utilization characteristics of rhizosphere soil microorganisms under different treatments.The activities of neutral phosphatase(NP),arylsulfatase(ASF),urease(UE),and β-glucosidase(β-GC)in cotton rhizosphere soil of different treatments were determined,respectively.Redundancy analysis was used to analyze the correlation between soil enzyme activities and the utilization ability of soil microorganisms for different types of carbon sources.[Results]The McIntosh index of soil microorganisms treated with 400 mmol L-1 proline increased significantly,while there were no significant differences in the Simpson index,Shannon-Wiener index,Richness index,and Pielou index of soil microorganisms treated with proline compared with control.The soil microbial metabolic activities treated with 50-200 mmol·L-1 proline were all lower than that of the blank control after incubating for 6 to 20 days,while the soil microbial metabolic activity treated with 400 mmol·L-1 proline was significantly higher than that of the blank control.Soil microorganisms treated with proline have higher utilization ability for amino acids,carboxylic acids,and carbohydrates.The utilization ability of soil microorganisms treated with 50-400 mmol·L-1 proline was significantly enhanced for L-phenylalanine,D-galactonolactone,β-methyl-D-glucoside,and glycogen;while the utilization ability for L-arginine,D-galacturonic acid,D-xylose,and i-erythritol was significantly reduced.Compared with the blank control,proline treatments significantly reduced the activities of soil β-GC and UE,and had no significant effect on the activity of NP.The activity of ASF showed a trend of first decreasing and then increasing with the increase of proline concentration.Redundancy analysis shows that UE activity was positively correlated with the utilization ability of soil microorganisms for L-arginine,D-galacturonic acid,γ-hydroxybutyric acid,D-xylose,and i-erythritol;β-GC activity was positively correlated with the utilization ability of soil microorganisms for L-arginine,pyruvic acid methyl ester,D-xylose,and i-erythritol;NP activity was positively correlated with the utilization ability of soil microorganisms for L-asparagine,D-galacturonic acid,γ-hydroxybutyric acid,glycogen,and β-methyl-D-glucoside;ASF activity was positively correlated with the utilization ability of soil microorganisms for L-phenylalanine,L-serine,L-threonine,glycyl-L-glutamic acid,D-glucosaminic acid,D-galactonolactone,itaconic acid,and D-mannitol,respectively.With carbohydrates as carbon source,the activities ofβ-GC and UE are negatively correlated with the utilization ability of soil microorganisms for glycogen.[Conclusion]The proline treatments can change the soil microbial metabolic activities,leading to a significant decrease in the activities of soilβ-GC and UE.With carbohydrates as carbon source,the activities of β-GC and UE are positively correlated with the utilization ability of soil microorganisms for D-xylose and i-erythritol,but negatively correlated with the utilization ability of soil microorganisms for glycogen.
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