| At present,about half of the countries and regions in the world suffer from different degrees of soil desertification damage.A single farming model directly results in a decline in soil fertility.Wind erosion and water erosion exacerbates soil loss,and the soil is desertified.As the time goes by,the problem becomes desertification.Artificial biological crusts are important measures for soil structure change and crop yield increase in desertification areas.In this paper,two strains of high-yield exopolysaccharides(EPS),D3-1 and ZMN-3,and two kinds of EPS-producing desiccants,D3-a and D3-25,were screened out from desertified soil samples.Using the method of multiphase classification and identification,it was determined that ZMN-3 is a new species of the genus Massilia,D3-1 is a strain of the genus Sphingomonas,D3-a is a Chlamydospora genus,D3-25 is a Nasococcus.The exopolysaccharides synthesized by strain ZMN-3 consist of two components with weight average molecular weights(Mw)of 1.91×104 KDa and 947 KDa,respectively;at 30°C for 3days,ZMN-3 fermentation at 6 r/min shear rate.The liquid viscosity was 2150 m Pa·s and it was a viscous pseudoplastic fluid.The polysaccharide product of strain D3-1 contains a number of components of different molecular weights and the highest weight average molecular weight is 2.67×10 4 KDa.At 30°C for 3 days,the viscosity of the fermentation broth reached 9249 m Pa.s at 6 r/min shear rate.These EPS-producing bacteria are sprayed on the surface of the soil and the formed biological crusts have the effect of maintaining water and nutrients and promoting the growth of the crop.The specific findings are as follows:1、The biocrust formed by four kinds of EPS synthesizing bacteria has a water-retaining effect on the soil.The optimal algae-mixed microbial formulation was determined through optimization experiments.The mixed microbial inoculum sprayed in the sand showed a significant water retention effect,and the soil moisture content on the 12 th day was 64 times that of the control group.The experimental results of leaching simulated rainfall showed that the leaching loss of N,P,and K in the soil samples of mixed algae bacteria was reduced by79.8%,37.0% and 63.2%,respectively,compared with the control;the nitrogen,phosphorus and potassium fertilizers were used in the second leaching test.Loss of leaching was reduced by 72.9%,45.2%,and 23.8%,and the mixed bacteria showed a significant fertilizer-preserving effect.2 、 The biological crust formed by the mixed bacteria has a certain influence on themicrobial groups in the soil.After the end of the water and fertilizer maintenance experiment,a large number of D3-1,ZMN-3,D3-a and D3-25 strains can still be isolated in the soil,indicating that these four strains are highly resistant and poor in nutrients.It can survive under drought conditions.The total amount of bacteria,Bacillus,actinomycetes and fungi in the soil was significantly increased due to the addition of the algae mixture,and the number of the four microorganisms in the mixed biological crust was 8.3 times that of the control group.,3.1 times and 1.8 times.3、The biological crust formed by spraying the inoculant also had some influence on the enzyme activity of the soil,and the effect of the mixed agent of algae on soil urease,sucrase and soil catalase was the most significant,and the urease activity was 4.3 times that of the control group.The catalase activity was 1.2 times that of the control group,and the invertase activity was 1.5 times that of the control group.The activity of mixed bacteria and mixed algae bacteria on the three soil enzymes had a certain increase compared with the control group,but there was no significant difference in the algal bacteria mixture.4、Corn and cotton pot experiments showed that the biocrust formed by the bacteria had no effect on the germination of maize and cotton seeds and the emergence of seedlings.Comparing and analyzing the effects of microbial agents,algae agents,and algae-mixtures on crop growth,it can be seen that algae-mixing agents have the most obvious effect on promoting the growth and development of maize and cotton seedlings.After application of algae mixture,the plant height of maize seedlings increased by 19.7% compared with the control group,and the above-ground fresh weight increased by 45.0%;the plant height of cotton seedlings increased by 53.7% compared with the control group,and the aboveground fresh weight increased by 99.6%.It can be seen that algae mixed biological crust has a very obvious effect on the growth of seedlings of corn and cotton. |
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