| Phosphorus deficiency is a common phenomenon in the soil of southern China,which restricts the productivity of forest ecosystems and affects the sustainable development of Cunninghamia lanceolata plantation,that is the main tree species in south China.However,phosphate-solubilizing bacteria have the function of converting the combined phosphorus,which is hardly absorbed and utilized by plants in the soil,into soluble phosphorus that can be absorbed and utilized.In the early period,the researchers screened two strains of high-efficiency inorganic phosphate-solubilizing bacteria WP1 and WP10,and one strain of high-efficiency organic phosphate-solubilizing bacteria YP9.In order to clarify their phosphorus-removing mechanism and evaluate their promoting effect on Cunninghamia lanceolata,this experiment explored the mechanism of phosphorus-removal of the three strains of bacteria obtained,and used annual Cunninghamia lanceolata seedlings as the research object.Three strains of bacteria used as single bacteria,mixed bacteria with different concentrations were returned to the Cunninghamia lanceolata seedlings.The growth indexes,photosynthetic characteristics,physiological characteristics,nutrition indicators of the Cunninghamia lanceolata seedlings,and enzyme activities and nutrient contents of the soil under different treatments were analyzed.The effects of three phosphate-solubilizing bacteria on the growth of Cunninghamia lanceolata seedlings were evaluated.1.Phosphorus removal mechanism of three strains of phosphate-solubilizing bacteriaThe main mechanism of two inorganic phosphate-solubilizing bacteria is acidolysis,which were affected by pH value and acid phosphatase.In the medium of insoluble phosphorus source Ca3(PO4)2,the bacteria concentration OD600 of two strains both reached maximum at 24h,which were 0.980 and 0.915,respectively.The soluble phosphorus content reached a maximum at 24h,which was 237.82 and 224.00 ug/ml,respectively.The organic acids secreted by WP1 strain were mainly oxalic acid,tartaric acid,malic acid,acetic acid,citric acid and succinic acid.The contents of the six acids reached the maximum around 24h,which were 25.42,2.83,6.87,19.29,1.85 and 23.72 mg/mL,respectively.The organic acids secreted by WP10 strain were mainly oxalic acid,succinic acid,malic acid,acetic acid and citric acid.The contents of the five acids reached the maximum around 24h,which were 26.19,12.21,7.13,23.58,and 4.39 mg/mL,respectively.The activity of acid phosphatase of the two strains was higher than that of alkaline phosphatase.The highest acid phosphatase activity of WP1 strain were 493.03 and 499.39 umol·g·h-1 at 24h and 48h,which was same for WP10 strain.The highest values of WP10 were 474.52 and 471.04 umol·g·h-1 at 24h and 48h.The main mechanism of YP9 is enzymolysis.In the lecithin medium,the bacteria concentration OD600 reached maximum at 72h,which was 38.40 ug/ml.The main organic acids secreted were oxalic acid,tartaric acid and acetic acid.The total amount of soluble phosphorus did not change much.The activity of acid phosphatase increased first and then decreased within the first 36h,reaching the highest value at 48h,which was 1144.22 umol·g·h-1.Overall,the activity of acid phosphatase increased with time,and the activity of alkaline phosphatase showed a fluctuating upward trend,reaching two peaks at 36h and 72h,which were 912.45 and 993.66 umol·g·h-1,respectively.There was a negative correlation between acid and alkaline phosphatase activity,but the activities of the 2 phosphatase were all increasing with fluctuation.2.Effects of different strain treatments and different concentration levels on Cunninghamia lanceolata seedlings3 strains of phosphate-solubilizing bacteria and their mixed bacteria(7 treatments)could effectively promote the growth of Cunninghamia lanceolata seedlings under the 3 different concentration levels(low,medium and high).The height and diameter of the seedlings were most increased(21.29%and 29.87%)under the low concentration(1×106cfu/ml)of D treatment;and the biomass was most increased(26.73%)under the medium concentration(0.5×107cfu/ml)of D treatment compared with the contrast.The seedling photosynthesis could be effectively improved by different strains and different concentration levels.The chlorophyll a content,chlorophyll b content and carotenoid content of leaves were most increased(59.03%,57.41%and 43.42%respectively)under the medium concentration of D treatment compared with the contrast;The initial fluorescence was most decreased(30.84%)under the high concentration(1×107cfu/ml)of D treatment;and the maximum fluorescence and variable fluorescence were most increased(33.44%and 33.05%respectively)under the medium concentration of D treatment compared with the contrast.The treatment of different strains and different concentrations could alleviate the lipid peroxidation damage.The content of malondialdehyde was most decreased(46.68%)under the medium concentration of D treatment;and the activity of superoxide dismutase,soluble protein and soluble sugar were most increased(37.75%,55.27%and 34.96%respectively)under the medium concentration compared with the contrast.The nutrient content of seedling leaves could be increased by different strains and different concentration levels.The content of organic carbon,total nitrogen,total phosphorus and total potassium in leaves were most increased(17.18%,20.20%,53.91%and 50.99%respectively)under the low concentration of D treatment compared with the contrast.The results showed that the mixed treatment of 3 strains(D treatment)had the best effection the growth of Cunninghamia lanceolata seedlings,and the medium and low concentration(1×106cfu/ml～0.5×107cfu/ml)was the best.3.Effects of different strain treatments and different concentration levels on soil3 strains of phosphate-solubilizing bacteria and their mixed bacteria(7 treatments)could effectively improve soil enzyme activity under the 3 different concentration levels(low medium high).Cellulase activity,invertase activity,acid phosphatase activity and catalase activity were most increased(29.82%,41.83%,17.10%and 23.87%respectively)under the medium concentration of D treatment;and urease activity was most increased(26.17%)under the high concentration of D treatment compared with the contrast.The soil nutrient content could be increased by different strains and different concentration levels.The contents of organic carbon,total phosphorus,total potassium,total nitrogen,available phosphorus,available potassium and hydrolysable nitrogen were most increased(19.66%,36.21%,16.41%,52.50%,15.52%,5.87%and 15.06%respectively)compared with the contrast under the low concentration of D treatment.The results showed that mixed treatment of 3 strains(D treatment)had significant effects on soil enzyme and nutrient characteristics of Cunninghamia lanceolata,and suitable concentrations are medium and low concentrations.The effects of 3 strains of phosphate-solubilizing bacteria and their mixed bacteria on the growth and soil of Cunninghamia lanceolata seedlings showed that the mixed bacteria D(Three strains of phosphate-solubilizing bacteria mixed in equal amounts)under the medium and low concentrations had the best effect on the growth of Cunninghamia lanceolata,the next is mixed bacteria AC(WP1,YP9 1:1 mixed). |
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